ffiCAL BOTANY GIFT OF PRACTICAL BOTANY BY JOSEPH Y. BERGEN, A.M. AUTHOR OF "ELEMENTS OF BOTANY," "FOUNDATIONS OF BOTANY" " PRIMER OF DARWINISM," ETC. OTIS W. CALDWELL,'PH,IX '"" V- ,'*? AUTHOR OF "PLANT MORPHOLOGY" AND LABORATORY M?AM?Ai, ojfBT ) AV$ ASSOCIATE PROFESSOR OF BOTANY IN THE SCHOOL OF EDUCATION UNIVERSITY OF CHICAGO GINN AND COMPANY BOSTON NEW YORK CHICAGO LONDON ATLANTA - DALLAS COLUMBUS SAN FRANCISCO ',,' ', ', ENTERED AT STATIONERS' HALL r COPYRIGHT, 1911, BY : BERGEN AND OTIS W. CALDWELL ALL RIGHTS RESERVED 021.10 gftc fltftenaeum GINN AND COMPANY PRO- PRIETORS BOSTON U.S.A. PREFACE There are already so many books embodying elementary courses in botany that whoever offers another should give reasons for so doing. As here set forth, the study of plants is related to everyday life more closely than is usually done. Those aspects of plant life are presented which have the largest significance to the public in general, and which are of interest and educative value to beginning students. The book includes the principles of plant nutrition, the relation of plant nutrition to soils and climate and to the food of animals and men ; it discusses some of those diseases of plants, ani- mals, and men, which are produced by parasitic plants ; the propagation of plants, plant breeding, forestry, and the main uses of plants and plant products are given in an elementary way. The elements of plant life and structure are presented synthetically rather than by use of the special divisions of botanical study, which are more helpful to advanced students than to beginners. It is believed that this mode of treatment stimulates and develops a scientific method of thinking by directing attention to the plant as a living unit and a citizen of the plant world. No attempt is made to include references to such recent discoveries in the field of botany as are botani- cally significant but not important for elementary instruction. Chapters I and II are so arranged that a student may secure a general introductory appreciation of the significance of plant structure and work. It is intended that Chapter I should be used as a means of raising questions concerning the place of plants in nature. Chapter II presents an outline of the five dominant structures of seed plants, and the kind of work that is done by each. It is intended that this chapter shall enable the student to see the plant as a working unit, while the chapters iii iv PRACTICAL BOTANY following it give a more detailed treatment of each of the dominant structures, and the outline sketch of the whole plant now serves as the basis of interpretation of this more special study. Then follow rather brief though adequate chapters dealing with the great groups in the order of their increasing complexity, and these are followed by chapters which treat of broad aspects of plants and their relation to plant industries. The material in the book, which is sufficient for a year's course, is so arranged that it can be adjusted to a half-year course when local needs make this desirable. When seasons are favorable it is thought best to follow the order of chapters as given, but seasonal conditions are so diverse in different parts of the country that the teacher is urged to rearrange chapters whenever necessary for adequate illustration of such topics as flowers, seeds, and weeds. If this is done, Chapters I and II may be studied briefly, and then followed by chapters dealing with special topics. When the book is used in a half-year course, Chapters I and II should constitute an introduction, and it will usually be found advisable to follow these with Chapters III-XI and XXI-XXV. In some cases, however, it will be found advis- able to follow Chapters I and II with Chapters X~XX. In any event, in a half-year course, Chapters XXI-XXV, be- cause of their practical significance, should be assigned for collateral reading if they are not used as the basis of regular class work. Not infrequently facts are restated in connection with topics other than those with which they first appear. This seems un- avoidable unless other important considerations are sacrificed, such as securing plasticity in the order of use of the various chapters and avoiding excessive cross reference. The number of botanical terms used is as small as is con- sistent with a clear presentation of the facts. The order of the great groups of plants agrees with the most recent usage of the best botanists. In accordance with this usage the bac- teria and the blue-green algae are presented first in the studies PREFACE V of the great groups. The relatively large importance to general students of a knowledge of bacteria justifies the considerable amount of space that is given to this group. The course outlined in this book will meet the needs of students who wish to present botany for college entrance. While the point of view is somewhat different from that which is usual in elementary textbooks of botany, the topics treated are those outlined for secondary schools by the Botanical Soci- ety of America and the North Central Association of Colleges and Secondary Schools. These units are the ones generally recognized throughout the United States. The authors wish heartily to recognize the valuable assist- ance that has been rendered them by the following authori- ties : Professor Henry C. Cowles, Mr. George D. Fuller, and Professor Edwin O. Jordan, of The University of Chicago; Professor Benjamin M. Davis, of Miami University ; Professor William F. Ganong, of Smith College; Director Charles E. Thorne, Botanist Augustine D. Selby, and Agronomist C. G. Williams, of the Ohio Agricultural Experiment Station ; Act- ing Director Herbert J. Webber and Professor C. G. Warren, of the New York State College of Agriculture ; and Professor Edgar N.Transeau, of the Eastern Illinois State Normal School. A large number of high-school teachers of botany have given suggestions and criticisms, and we desire to express our appreciation of this assistance from those who are in direct contact with the problems of teaching botany in sec- oiidary schools. Mr. William L. Eikenberry, of the University High School, Chicago, has given abundantly of his experience and his time in making suggestions and reading manuscript and proof. Mr. Paul T. Sargent, Mr. E. N. Fischer, and Mr. F. Schuyler Mathews, the illustrators, have added to their artistic ability a genuine interest in the presentation of plant life to beginning students, for which we wish to express our appreciation. JOSEPH Y. BERGEN OTIS W. CALDWELL CONTENTS CHAPTER PAGE I. INTRODUCTORY PLANTS IN NATURE 1 II. GENERAL STRUCTURE AND WORK OF PLANTS .... 5 III. ROOTS , . . . 24 IV. THE STEM AND THE LEAF 39 V. UNDERGROUND STEMS; STORAGE IN STEMS AND LEAVES; REPRODUCTION 72 VI. BUDS AND BRANCHES 90 VII. FLOWERS 104 VIII. POLLINATION AND FERTILIZATION 115 IX. SEEDS AND SEEDLINGS; SEED DISTRIBUTION .... 136 X. THE GREAT GROUPS OF PLANTS 156 XL THE BACTERIA (SCHIZOMYCETES) 161 XII. THE BLUE-GREEN ALG^E (CYANOPHYCE*:) 180 XIII. THE GREEN ALG^E (CHLOROPHYCE*:) AND OTHER ALG^C 188 XIV. THE ALG^-FUNGI (PHYCOMYCETES) 213 XV. THE SAC FUNGI (ASCOMYCETES) ; THE LICHENS; THE BASIDIUM FUNGI (BASIDIOMYCETES) 226 XVI. MOSSES AND LIVERWORTS (BRYOPHYTES) 257 XVII. THE PTERIDOPHYTES 274 XVIII. GYMNOSPERMS 299 XIX. ANGIOSPERMS 321 XX. SOME LEADING FAMILIES OF FLOWERING PLANTS AND v THEIR USES 335 XXI. FURTHER DISCUSSION OF DEPENDENT PLANTS . . . 371 XXII. TIMBER: FORESTRY 390 XXIII. PLANT BREEDING . . ... . 412 XXIV. FURTHER DISCUSSION OF PLANT INDUSTRIES .... 434 XXV. WEEDS 465 XXVI. ECOLOGICAL GROUPS ; REGIONAL DISTRIBUTION OF PLANTS 477 APPENDIX 515 GLOSSARY 520 533 vii PRACTICAL BOTANY CHAPTER I INTRODUCTORY PLANTS IN NATURE 1. Abundance and distribution of plants. We are so accus- tomed to the presence of plant life almost everywhere on the earth that an extreme scarcity of plants over any considerable area seems more remarkable than does their abundance. The complete absence of living plants from any large part of the land surface or the shallower waters is a condition which prob- ably seldom occurs. It may occur in regions where there are poisonous salt deposits, or in times of extreme dryness, or when the temperature is too high or too low for plants to live. Some of the simplest plants can for long periods withstand the most intense cold ever encountered upon the earth, and a few of these plants can withstand high temperatures for a brief time. Ordinarily volcanoes or bodies of hot lava, and some hot springs and alkali deposits are therefore the chief visible portions of the earth which are quite lifeless. It is a matter of familiar knowledge that the lands and the waters differ greatly in the density of their plant population. Some areas of the barest Nebraska sand hills do not on the average contain more than one flowering plant to every three thousand square feet, while a weedy garden has been found to contain as many as 75,000 plants in a similar area. If the barest portions of the Sahara were compared with a good lawn or meadow, the disproportion would be far greater. The purest natural waters contain no organisms visible to the eye, while stagnant pools are often so filled with pond scums and other simple and minute plants that each cubic inch contains many 1 2 PRACTICAL BOTAXY thousands of individuals. We cannot enumerate all the kinds 'of /peaces', 'hi ;whif,h plants find lodgment and grow. They occur in all the seas, as well as in the fresh waters, on every kind of soil from the wettest swamps to arid deserts, on rocky cliffs and the bark and leaves of trees. Microscopic forms sometimes occur in myriads in the blood of animals, and most soils teem with them to the depth of several inches below the surface. It is a notable fact that some plants are the smallest and others the largest of living beings, and it is evident that plants are on the whole by far the most conspicuous of living things. 2. Plants and animals. A little thought about the things upon which common animals feed will show that plants directly or indirectly supply food for animals. Many animals get their food directly from living plants, in the form of roots, leaves, seeds, fruits, etc., and these are called herbivores (plant eaters). Those animals called carnivores, which eat the flesh of other animals, are dependent upon plants, since their prey are plant feeders or may live upon those that are plant feeders. In one way or another all animals are dependent upon plants for food. 3. Plants and the industries. Man is also directly or in- directly dependent upon plants for his food. His animal food is indirectly derived from plants, his bread is made from the seeds of plants, and there is a constantly growing list of foods, spices, and flavors that are prepared from roots, stems, leaves, seeds, and fruits. Much of the work in which men are engaged is performed by domesticated animals as beasts of burden, or is concerned with rearing domesticated animals or growing plants for the market. These animals could not be cared for were it not pos- sible to feed them with the products of domesticated plants, and many of the kinds of work for which beasts of burden are used would not exist were it not for the need of growing plants for the world's uses. INTRODUCTORY PLANTS IN NATURE 3 The domestication and improvement of plants has been an essential part of the development of many industries, and has advanced until at the present time the greater part of the food of the world is secured from certain kinds of plants which once grew wild and produced little that was of value to men. The plant producing the biggest crop in the world is the potato, which in 1906 produced 284,000,000,000 pounds of potatoes. But the most important crop in the world from the point of view of the market value of its product is wheat. In each of three great agricultural regions of the United States one plant is dominant in its value. In the central corn belt there are seven states that produce nearly one half the corn used in the whole world, an amount which in 1909 was worth nearly $3,000,000,000. The Southern States produce over three fifths of the cotton of the world, an amount worth nearly $1,000,000,000. The Northwestern States produce wheat, which, while not so large a proportion of the world's crop, is of tremendous importance to the welfare of the nation. Plant fibers are extensively used in the manufacture of clothing. Timber is used in the construction of buildings, furniture, vehicles, and implements for use in the industries. Plant extracts compose the most of our medicines. The paper upon which our ideas are recorded is made chiefly from wood pulp, though it is now proposed to make it from cornstalks. The processes by means of which green plants live, as will be shown later, contribute to the purification of the atmosphere that we breathe. The farmers' barns, the city feed stores, warehouses, cold- storage establishments, almost every manufactory and sales- room, and many of the railway and steamship transportation lines in some way are illustrations of the important relations which plant life bears to the fundamental industries. 4. How plants live: the most important phase of botany. In connection with the preceding discussion regarding the place of plants in nature, it must be clearly understood that 4 PRACTICAL BOTANY plant structures and processes are of importance primarily for their function in maintaining the life of plants themselves, and that their use in the industries is a by-product of plant life. The body of a tree is produced in the tree's ordinary processes of growth, and thereafter it chances to be useful to men for timber. Though corn and wheat have been improved artifi- cially until now they supply much of the food of mankind, in nature as wild plants they produced seeds which were small but sufficed to give rise to new plants. The possibilities of utility result from the ordinary activities and structures of plants, and the study of these possibilities must be made accessory to the consideration of the general principles of plant life. What plants are and how and where they live are the most fundamental questions, and are the ones which we shall first consider in the following chapters. CHAPTER II GENERAL STRUCTURE AND WORK OF PLANTS l 5. Introductory. Any one of our most familiar plants con- sists of roots, stem, leaves, flowers, and fruits containing seeds. Each of these parts is usually distinct (Fig. 1). Each does one or more particular kinds of work, and together they do the work of the whole plant. The plant, therefore, is a complex structure, whose life is depend- ent upon the work of its different parts. 6. Roots and their work: anchor- age. The most obvious work of roots is done in holding plants in place, or in giving them an- chorage. On steep hillsides, on banks of streams, and in shal- low soil which lies upon stone, the amount of anchorage which roots afford is often so small FIG. 1. A buttercup (Ranun- culus acris) The plant consists of roots, stem, leaves, flowers, and seeds. A, the plant, shown about one eighth natu- ral size ; B, cluster of ripened seeds, shown almost natural size; (7, a section through one seed, shown almost three times natural size 1 This chapter presents an outline of a plant as a working machine. It does not include details but gives a general view of the plant and the kind of work that it does. If this outline chapter is studied briefly, later discussions will be more easily understood and more profitable than if numerous details are pre- sented first. The chapter should be read carefully by each member of the class and discussed in one or two recitations, or it may be read and discussed by pupils and teacher together. 6 PRACTICAL BOTANY that trees are uprooted (Fig. 4) in times of heavy wind. In other cases the anchorage may be so great that during a heavy wind the plant will be broken off instead of having its roots upturned. A study of such situations as those just mentioned will give some idea of the distance to which the larger roots spread and of the amount of soil that lies as weight upon them. A FIG. 2. Tips of two cornstalks A is in normal growing condition, while B, through excessive loss of water, has wilted and its leaves are contracted into tube-like rolls 7. Roots and their work: water supply. Water is essential to the growth of plants. Plants of the farm, garden, lawn, and those commonly grown in our homes have their roots in the soil and their stems and leaves in the air, and therefore, if they secure water at all, must get it from the soil or air, or both. When roots are deprived of water the plants soon wilt (Fig. 2) and eventually die. If one should pour water upon the stems and leaves, but deprive the roots of it, the plants would not thrive. Ordinarily roots secure water for the entire plant. 8. Roots and their work: root hairs. Most root systems branch near the base of the stem and continue to subdivide (Fig. 3) FIG. 3. The root system of the corn plant The soil has been washed away so as to show the quantity and spread of the roots, and, to some extent, the positions that they assume in the soil. Photograph by the United States Department of Agriculture FIG. 4. Two upturned spruce trees which grew upon a stony surface The entire root system spread over the rock did not provide sufficient anchorage to hold the tree in place in time of a very heavy wind 7 8 PRACTICAL BOTANY until the roots are extremely small. During periods of active growth root hairs appear upon the smaller rootlets (Fig. 5). These rootlets, like the other parts of the plant, are made up of many cells (Fig. 6). Each cell has a wall, the cell wall, which incloses the living mate- rial, called the protoplasm. In the root hairs, as in Fig. 6, two parts of the protoplasm are shown, the nucleus and the granular cytoplasm. Cells con- tain other protoplasmic bodies, which need not be discussed at this time. The root hairs are extensions of the surface or epidermal cells of the rootlet and are parts of those cells. They grow a little way back from the tip of the rootlet and new ones appear as the root tip pushes for ward in the soil, so that with the dying of older root hairs and the de- Note the diff erence in length and velopment of newer condition of the root hairs on the ones on new growth different parts of the root of the rootlet, the actual number of root hairs n on a rootlet during the growing season may remain practi- cally constant. It is evident that the area of root hairs on a rootlet advances, al- though the single root hairs do not move f OI'- FIG. 5. A mustard seedling grown in a band of filter paper inside a drinking glass so as to show the root hairs w FIG. 6. Cells from the surface of a young rootlet Showing epidermal cells (e), and one young and two older root hairs (A). In the root hairs the nucleus (n) and granular cytoplasm of the cells are shown. Greatly magnified laterally from the rootlet, growing through the soft particles of the soil and around the harder ones, thus constituting a The root hairs extend STRUCTURE AND WORK OF PLANTS 9 network in the region about the tip of the rootlet. If the seedlings are grown in sawdust, on damp blotting paper, or within earthen pots that are kept moist by covering or by being inverted upon a damp surface, they will afford interest- ing demonstrations of how rootlets and root hairs grow under different conditions. 9. Roots and their work : water-lifting power. If the top of a vigorously growing potted plant is cut off and an upright glass tube is attached to the plant stump by means of a rubber tube, water may be forced upward in the latter, thus showing that roots can lift water from the soil. Actively growing trees and shrubs, when cut, often show this same phenomenon by forcing out through the cut surface some of the water that is brought up from the soil. This is sometimes incorrectly spoken of as " bleeding " of the stump. The roots, however, are not the only parts of the plant that may lift water. That the leaves and stem may also do this work may be shown by cutting off the top of a plant under water, and, while still under water, attaching the stem to a water-filled U-shaped tube. The top of a plant that has been so treated may continue to lift water for several days. In plants that are growing normally, the roots, by means of the root hairs, take up water from the soil. It passes into the interior of the rootlet, then into the larger roots, into the stem, and finally into the leaves. Some of this water is carried from the leaves into the air, and that process will be discussed under the topic transpiration. 10. Roots and their work : turgidity. Root hairs and other cells of plants usually take up water until the cell walls are distended with water and protoplasm. The outward pressure which distends and stretches the walls is called turgor, and the resulting condition is called turgidity. Turgor doubtless helps to force water upward through the stem. The distention of cells due to turgor also accounts for the rigid or erect position of most leaves, growing shoots, and succulent stems. Each distended cell, like an inflated balloon, assumes a semi-rigid 10 PRACTICAL BOTANY position, and a mass of distended cells pressing against one another makes the whole structure rigid. But as when the air FIG. 7. A photograph of a cottonwood leaf from which the green tissue has been removed so as to show the network of veins through which the food material is carried throughout the leaf and to the stem Natural size. Leaf prepared by Ellsworth Bethel escapes from a balloon its wall collapses of its own weight, so do the cells of the leaves and shoots when, through loss of water, they lose their turgidity. When soil water is not STRUCTURE AND WORK OF PLANTS 11 available to the plant, the outgo from the leaves is often greater than .the income from the roots, and in such cases wilting follows. If water does not again become available, the plant will die, but with a renewed supply turgidity and the resulting rigidity soon return. 11. Stems and their work: water passes through the stem. The stem is a means of connection between the roots and the leaves. It also serves to support the leaves in the air. Ascend- ing water passes mainly through special regions of the stem and the leaf. When a fresh leaf of celery or leafy stem of hydrangea is placed for a few minutes in one of the ani- line dyes, and then removed and examined by sectioning, defi- nitely stained regions appear, which show not only that the staining liquid passed upward into the stalk, but that it passed through only certain tissues of the stalk. These special tissues through which the liquids pass are composed of bundles of very small tubular cells which are many times as long as they are thick. The bundles are known as fibrovascular bundles, which term simply means " collections of thread-like tubes." The different cells of these bundles overlap one another in such a way that they are continuous from roots, through stem and branches, into the leaves. In the leaves the bundles are the so-called veins (Fig- 7). 12. Stems and their work: kinds of stems. There is a striking and im- portant difference in the arrange- ment of fibrovas- F IG. 8 - A cornstalk broken so as to show the number la b die ' anc * ^ istribution of tlie vascular bundles the stems of different kinds of plants. If a stem of corn or a plantain leafstalk is broken, whitish strings are pulled from the pith (Fig. 8). These are vascular bundles. They are somewhat irregularly distributed throughout the stem, and 12 PKACTICAL BOTANY -,-6 '-P FIG. 9. Diagram of a cross section of a geranium stem The regions are the outer bark (6) , the cortex (c), the woody tissue (w), and the pith (p) are intermingled with the soft pith tissue. There is a large group of plants, the monocotyledons, which have the irregular distribution of bundles just described. In such stems there is usually, around the outside, a much harder tissue, which is extremely strong, and which .. c serves to strengthen the stem. In other kinds of plants a cylinder of bundles is defi- nitely arranged about the pith (Fig. 9), and this arrangement is also characteristic of a great group, the dicotyledons. Other features of these groups are discussed in later chapters, and in this connection it is important only to note some general characters of the stem. 13. Stems and their work : annual growth. In many of our common annual plants (those that live for but one year) the arrangement of the bundles or woody tissue in the form of a cylinder about the pith is readily seen. In such plants the pitli usually occupies more of the stem than does the wood. The proportion of pith to wood is much less in the perennial plants (those that live for two or more years). In a cross section of one of the common trees, unless the specimen be quite young, it will be difficult or impossible to discover any pith region. The greater part of the section is made up of wood. Each year there is formed a layer of this woody tissue from the inner, heavy-walled cells of the bundles, which persist and give strength and support to the whole tree. The great size of our forest trees is made possible by this arrangement of bundle tissues. The record of growth may be .read by stud}; - ing the rings of wood. The amount of a year's growth and the total time that a tree has lived can be reckoned. You will also find it interesting to study the top of your desk or th STEUCTUEE AND WOEK OF PLANTS 13 furniture in the room to see if you can recognize the partial rings of wood or can tell the way in which the timber was sawed. In later chapters there will be a more extensive study of stems and the ways in which they grow. 14. Leaves, general form : the epidermis. Most leaves con- sist of two parts, the leafstalk or the petiole, and the blade, which is the expanded portion. In some leaves the petiole is absent, and in others the blade is subdivided into several parts, in which case the leaf is said to be compound. To most observers leaves appear to be a uniformly green mass of mate- rial. More careful observation discloses the fact that many leaves are not .equally green on both surfaces, and that running throughout the leaf there are more or less regularly arranged veins or fibrovas- cular bundles which are not green. From the upper and lower surfaces of leaves such as those of live-forever, Wan- dering Jew, Easter lily, and epiderwort one may peel a thin, almost colorless layer, which is known as the epider- mis (Fig. 10). The epidermis is composed of cells more or less compactly arranged. In the epidermis from one and sometimes from both sur- faces there are special struc- tures known as stomata (Fig. 10). From a surface view a stoma (plural, stomata) presents two more or less crescentic or kidney-shaped cells, the guard cells, between which is an elliptical opening, the stomatal opening. Unlike other epidermal cells, the guard cells are greenish. The opening serves as a place of entrance for FIG. 10. A surface view of leaf epider- mis from the geranium (Pelargonium) Among the ordinary epidermal cells (c) are four stomata, each with two guard cells (gc) and the mouth of an air cavity (p). Con- siderably magnified 14 PRACTICAL BOTANY most of the carbon dioxide used by the plant. The guard cells press closely together, or they may separate until a cir- cular opening is formed, and in thus closing and opening they influence the interchange of air between the interior and the exterior of the leaf. This obviously affects the interchange of such gases as carbon dioxide and oxygen, as well as the outgo of moisture from the leaf. 15. Leaves : internal structure. The interior cells of the leaf, except those of the veins, are colored green by chlorophyll, FIG. 11. Cross section of a geranium leaf a, air space; a.c, air chamber; e, upper epidermis; e', lower epidermis; p, pali- sade cells; s, stoma; sp, spongy parenchyma (usually spongy parenchyma has fewer chloroplasts than the palisade tissue) ; v, vein. Magnified 150 times. After drawing by Mrs. F. E. Clements which means " leaf green." The cells are not uniformly green, but the chlorophyll is contained in special small bodies, known as chloroplasts or chlorophyll bodies (Fig. 11), which are within the cells. It must be clearly understood that the chloroplast and the chlorophyll are not the same. Plastids (plasts) may or may not contain chlorophyll, just as a sponge may or may not contain water. It is evident, therefore, that a plastid can properly be called a chloroplast only when it contains chlorophyll. STRUCTURE AND WORK OF PLANTS 15 In summing up the structures of the leaf we may say that it usually consists of a petiole and a blade. The outer portions of the blade both above and below are the epidermis ; in ad- dition to the ordinary epidermal cells the epidermis contains special structures, the stomata ; within the epidermis are the veins and masses of green tissue ; the green tissues are made up of more or less compact cells in which, in addition to other cell contents, are plastids, which contain the green coloring matter, chlorophyll. 16. Leaves: material for leaf work. In connection with the discussion of roots and stems it was found that water is carried into the leaves. In the soil are many substances which are dissolved by the water, just as common salt or sugar would be. When water is taken up into the plant some of these sub- stances that are in solution also enter. In this way there may be carried into the plant compounds containing such things as nitrogen, potassium, phosphorus, sulphur, and iron. Through the surface of the leaf, chiefly through the stomata, the plant secures carbon dioxide. This is a gaseous substance which exists in the atmosphere in the ratio of about .3 parts in 10,000 of air. Inside the leaf, therefore, there is a supply of the so- called raw materials for food, as water, carbon dioxide, and substances that were in solution in soil water. 17. Leaves: food manufacture. Carbon dioxide and water must undergo change before they can be used in nourishing and building up the plant. The sun shines upon the leaf and the chlorophyll absorbs some of the energy from the sun's rays. This energy serves in some way as yet unknown to break up the compounds water and carbon dioxide into the carbon, hydrogen, and oxygen of which they are made. The carbon, hydrogen, and some of the oxygen immediately unite again ; not, however, into the compounds carbon dioxide and water, but into new compounds. These rapidly pass through several changes and may finally become sugar and starch. At present the changes before starch and sugar are formed are not all known. Some of the oxygen resulting from the breaking up 16 PKACTICAL BOTANY of carbon dioxide and water is used in making starch and sugar, but much of it is set free and may pass out into the air. The oxygen thus set free by plants may be collected as shown in Fig. 12 and then tested. This process that is carried on by green plants is a principal factor in maintaining the oxygen supply that is so necessary to the life of animals. Plants also use some free oxygen in some of their later food-making proc- esses. This series of occurrences by means of which green plants under the influence of sunlight make foods, such as starch and sugar, from carbon dioxide and water, is known as photosynthesis. The word photosynthesis means " putting together by means of light." 1 1 The chemistry of photosynthesis is not completely known, but some of the simpler aspects of it may prove valuable at this point. Water is usually expressed by the chemist by the formula H 2 O, in which H stands for hydro- gen and O for oxygen, and the figure 2 indicates that two parts of hydrogen are united with one part of oxygen. Similarly CO 2 indicates that one pait of carbon is united with two parts of oxygen to form carbon dioxide. When these compounds are broken up, there is, for a very brief time at least 1 ,, free C, H, and O. If one unit of each compound (H 2 and CO 2 ) is thus broken up, there will be two H, one 0, one C, and two (or in all three 0). After photosynthesis has been going on for some time, starch is usually formed. Starch consists of (C 6 H 10 O 5 ) "n". This means that six parts of carbon, ten parts of hydrogen, and five parts of oxygen unite to form stare and the ft n" means that the unit C 6 H 10 O 5 does not appear singly, but that an unknown number of them are united. Disregarding the fact that sev- eral of the starch units are held together, and considering the single unit C 6 H 10 O 5 , we may be able to see what happens in the work of photosynthesis. To secure the amount of carbon necessary to form starch, six times the unit CO 2 must be taken, since there are to be used six units of carbon. To secure the needed amount of hydrogen, five times the unit H 2 must be used, since there must be ten units of hydrogen and two are secured with each unit of water. We have, therefore, 6 C0 2 and 5H 2 O. When the energy of the sun has broken these things into their constituent parts there are 6C, 12 O, 10 H, and 5O, or 17 O in all. But starch consists of C 6 H 10 5 , and in making this unit of starch there has been used all of the carbon, all of the hydrogen, and five units of the oxygen, thus leaving twelve units of oxygen to be set free or to be used by the plant in some other way. Some of this free oxygen passes into the air, though some of it is used by the plant in a later process. The compounds thus constructed, as starch and sugar, are called carbo- hydrates, the name indicating that they are compounds of carbon and water. STEUCTUEE AND WOEK OF PLANTS 17 Sugar and starch may be used as food by the plant, being transported to and made into the living parts of the plant. Or these things may be made [^ into more complex foods, (Vpt known as the proteins, by Irhf the addition of some of the compounds of nitrogen, potassium, phosphorus, or other substances, and then digested and used by the plant. Replenishment and growth of new parts can take place only by means of foods, and since the plant makes its own supply, the importance of the process is very great. Manufactured foods are carried to all the living parts of the plant. They may also be stored in almost any plant structure. When in proc- ess of moving through the plant, these foods are believed to pass through the soft portions of the fibrovascular bundles. Furthermore, often more food is made by green plants than they FIG. 12. Apparatus for collect- need at the time, or even, in case ing oxygen from working plants of some plants, than they ever use, "SSSSSSlSSffSt and this is Stored most Commonly uate. Bubbles of oxygen pass in the form of starch, though some- u P ward f 5 Qm th f cu * ends of f e & stems and crowd out some water times in Other forms. This Stored from the previously filled grad- food may be USed later by the uate. The ordinary test for oxy- J J gen with a burning stick will plant, Or as food for men and Other determine whether it is present. animals. It may also be moved by In such an experiment care must _ . * , J be taken to see that there is the plant and stored in a different plenty of space about the collect- structure from that in which it was in s tube to 5f it * re * pass f ge of the gases that are m the water, first located. After Ganong 18 PRACTICAL BOTANY 18. The work of the leaf : transpiration. When a potted plant, so covered that no moisture can escape from the pot or earth, is placed under a dry bell jar, within a few hours moisture is seen to collect upon the inner surface of the jar. After a longer time the amount of moisture may cause streams or large drops of water to run down the inner wall of the jar. If a plant that wi]l thrive with its roots in water is planted in a jar of water and carefully sealed around the stem, and the whole apparatus weighed from day to day, a constant loss of water may be demonstrated. Water is ordinarily taken up by the plant in much larger quantities than are used for the work of photosynthesis. Large amounts of water are carried into the air through the leaves. By making careful demon- strations of the weight and volume of this water loss and the area of the leaf surface that is exposed, it is possible to deter- mine the 'amount of water which, on an average, passes through each square inch of leaf surface in a given time. This evapo- ration or loss of water from the plant is known as transpira- tion, and the current of water thus passing through the plant is called the transpiration current. Water evaporates from the stomatal openings or from other parts of the leaf surface. As superficial evaporation occurs, water from the moister portions of the plant must take the place of that evaporated, or there is danger of injury to the plant. Such danger and resulting death often occur, due to great or sudden loss of water. The quantity of water loss in transpiration is often surpris- ingly great. It has been estimated in one case that a beech tree 110 years old, in one summer transpired approximately 2250 gallons of water ; that an oak tree with 700,000 leaves tran- spired about 180 gallons of water daily ; and that an acre of cabbages in their growing season (about four months) tran- spired 500,000 gallons of water. One can scarcely picture in his mind the immense quantity of water that is constantly transpiring from all the vast stretches of forests, grasslands, farm crops, roadside weeds, and swamp plants. STRUCTURE AND WORK OF PLANTS 19 19. The work of the leaf : temporary responses. On exces- sively dry days plants such as wheat and com sometimes wilt, since they are transpiring more water than they are securing. If the soil becomes very hard, the water passes into the air quite readily ; but if the soil is kept well pulver- ized upon the surface, more soil water is held and a larger supply is available. Observations made upon a garden that is constantly cultivated during hot, dry weather, and upon one that is not so cultivated, show a great difference in ability of the plants to withstand drought. In a cornfield on a dry, hot day the leaves of the corn often roll into rather tight tubes. This form of leaf exposes less surface to evaporation and consequently loses less water than would the fully ex- panded leaves. This habit is doubtless of advantage in main- taining a balance in water supply. In setting out young orchard or shade trees, nurserymen recommend that the branches be well pruned ; otherwise the leaves may soon grow in such numbers that they will tran- spire more water than comes into the newly transplanted trees, which do not have their ordinary amount of absorbing root surface. Obviously newly transplanted trees and garden plants should be kept especially well watered until their root systems are well formed. 20. Respiration. The work of respiration in both plants and animals is commonly associated with the interchange of gases between the exterior and interior of the living body. In plants the interchange of gases may take place through the leaf or through other parts of the plant. This interchange, however, is no longer regarded as the ' fundamental thing in respiration, since respiration takes place in active, living pro- toplasm in all parts of the plant. It consists in decomposition of protoplasm or of some of its parts, or, as is supposed by some physiologists, it may consist in decomposition of food materials that have not yet become protoplasm. Through respiration complex plant substances are broken down, and the energy released by this decomposition is the energy by 20 PRACTICAL BOTANY means of which plants carry on their work. Energy in the form of heat is also one of the results of respiration. Respira- tion may occur in the absence of free oxygen, but is more complete, and thus releases more energy, when oxygen is present. When respiration is complete, it results in the forma- tion of various compounds, chief of which are carbon dioxide and water. Carbon dioxide and water may be carried from the plant through the leaf, or other parts of the plant, and the oxygen supply may enter in the same way. It is evident, how- ever, that the transfer of these gases is an incident associ- ated with the real respiration, which consists in decomposition of complex substances and the release of energy therefrom. Also it is evident that, so far as respiration is concerned, plants and animals behave in the same way. It should be noted that in photosynthesis green plants utilize carbon dioxide, though they, like other plants and animals, may produce carbon dioxide as one of the products of respiration. 21. Flowers and seeds : the parts of the flower. The flower is the part of the plant by means of which seeds are produced. Flowers differ ^Corolla ^W\ widely, but an examination of any such sim- ple flower as that of the gera- nium or the ox- alis shows that there are four kinds of floral parts in it (Fig. FIG. 13. Drawings of two flowers 13).Outermost A, entire flower ; B, part of the floral structures removed -j i owps f j a set of greenish leaves known collectively as the calyx, the sep- arate leaves being known as the sepals. Just above the calyx, and usually larger and more conspicuous, is the corolla, each leaf of which is a petal. Above the corolla is the group of STRUCTURE AND WORK OF PLANTS 21 stamens, easily recognized by their slender stalks and the en- larged tips which are known as the anthers. Within the anther is the pollen or pollen grains. At the tip of the flower, within the group of stamens, is the pis- til, consisting of one or more units or carpels. Often the tip of the pistil is expanded, and some- times divided into two or more short branches, this portion being called the stigma; the elongated part of the pistil is the style, and the swollen base is the ovary, so called because it contains the ovule or ovules. The ovules are the developing seeds. 22. Flowers and seeds: seed formation. The ovules begin their development within the ovary, but cannot alone form mature seeds which will grow into new plants. Some of the .pollen from the anther of the same or an- other flower falls upon the stigma (Figs. 13, 14, and 15). From one or more of these pollen grains there grows down through the style into the ovule an extremely small tube. Inside this tube are carried some of the cellular con- tents of the pollen grain, which meantime have divided into three cells. One of these cells thus carried into the ovule by the pollen tube unites with a special egg cell that is formed within the ovule (Fig. 14). The cell that is made by the union of the one from the ovule and the one from the pollen tube grows into the new plant within FIG. 14. A diagram of a pistil (carpel) Within the cavity of the ovary is an ovule (n), and within the ovule is an embryo sac. At the free end of the ovule is the micropyle (ra). In the end of the embryo sac near the micropyle is the egg (egg) with two other nuclei lying close to it ; in the center of the sac is the endosperm nucleus (en) ; and at the other end are the antipodal nuclei (a) . Pollen grains (p) are on the stigma, and from one is shown a pollen tube which has grown down to the egg A B FIG. 15. Stages in the development of the bean pod A, pistil of a bean flower, showing the ovary (o), style (sty), and stigma (sti) ; also the calyx at the base of the pistil. B, a pistil a few days older, in which the ovary has grown, and from which the style and stigma have disappeared. C, a pistil which has grown into the ripe bean pod. D, a ripe pod opened so as to show the arrangement of the seeds (beans) in the pod ; each seed (s) is attached to a region along the wall of the ovary, known as the placenta (pi), by means of the base of the old ovule. All two thirds natural size FIG. 16. Seedling of the peanut Below the seed leaves or cotyledons (c) is the hypocotyl (K), from the lower end of which the roots (r) have grown ; from the main stem (s) branches (br) and leaves (I) have grown ; at the base of the leaves are stipules (st), and at the tip is the bud (6) STRUCTURE AND WORK OF PLANTS 23 the ovule. While still within the ovule wall, the root, stem, and leaves of the new plant are formed. The ovule wall be- comes hard, and, with the new plant within it and with more or less stored food, constitutes the seed. During the time when the seeds are developing the ovary also may grow (Fig. 15), FIG. 17. Growth of new plants from seeds of the beech tree At the left are very young seedlings, one of which shows only the seed leaves (cotyledons) , the other showing between the seed leaves a slender stalk which is the beginning of the stem. In the plants 'at the right the seed leaves still are present, but other leaves and the stems have grown considerably 23. Flowers and seeds: the fruit, and seed germination. When the seeds are ripe they may fall from the ovary, or with one or more of the structures about them they may com- pose the so-called fruit. Under favorable conditions the young plant within the seed bursts the seed coat and begins its growth. It pushes out its roots, stem, and leaves, and soon assumes the ap- pearance of the kind of plant that formed it (Figs. 16 and 17). Details regarding the parts of the plant and the work they do will be treated in later chapters. CHAPTER III ROOTS 24. Structure of roots. A very young root is often translu- cent enough to be examined directly with a low power of the compound microscope. It is then seen to be composed of an exterior hollow cortex, nearly cylindrical in form, and a central cylinder within the cortex. The outermost por- tion of the cortex is a layer of somewhat brick-shaped cells constituting the epider- mis, and from some of the cells of the epidermis root hairs often spring (Fig. 6). The growing tip of the root is covered with several layers of cells, most of them dead or dying, constituting the root cap. A moderately magnified cross section of a very young dicotyledonous root shows c, epidermis; c, cellular layer of cortex; the epidermis as a narrow cyl, central cylinder ; w, woody strands of ring, Surrounding a much fibrovascular bundles of central cylinder. j / fi j Alternating with these are much smaller broader ring O the Unde strands of bast fibers, not shown in the dia- lying COrtex, and within this gram. Modified after Bonnier and Sablon _f , , . , . the central cylinder, contain- ing a fixed number of radially arranged fibrovascular bundles. The relative proportions of the several regions can be under- stood from Fig. 18. 24 . : ~~ ^ FIG. 18. Diagrammatic cross section of a very young dicotyledonous root KOOTS 25 25. Uses of roots. It was explained in Sects. 9 and 10 that tvater is absorbed by roots and forced up into the stem of a plant under considerable pressure. All plants must have water, at any rate during the part of their lives when they are actively manufacturing plant food, and it is by means of their roots that most familiar plants absorb water and the substances that are dissolved in it. Yet absorp- tion of water is not the only function of roots. They often ab- sorb oxygen ; they commonly serve to anchor the plant ; they may aid it to climb ; they frequently store food, water, or both ; and in or on them there are sometimes carried on important chemical operations which result in gaining material for the production of plant food (Sect. 17). Many kinds of roots repro- duce the plant ; that is, a root or part of one may grow into a new individual plant like the one to which the root belonged. The great importance of roots to life and growth is well shown by the results which follow from any severe injury to the root system. Cut off most of the roots of a tree and it will die for lack of water. On the other hand, many (though not all) kinds of trees may be cut down nearly level with the ground and still sur- vive, the stump throwing up a vigorous crop of sprouts which grow into saplings that eventually replace the fallen trunk. The necessity of roots for anchorage is well shown by Fig. 4. In many cases the power of the roots to hold trees upright is greatly increased by the formation of buttresses of wood, which extend some distance up the trunk from the origins of the larger roots (Figs. 259 and 260). In some great tropical trees these buttresses attain enormous dimensions. 26. Earth roots. The roots of most of the higher plants with which we have practical dealings, such as forest trees and the plants of the orchard, farm, and garden, are earth roots; that is, they are formed, grow, and live at a moderate distance under ground. Plants with roots suited to life in the earth usually cannot grow as well in water as in soil, and they cannot grow at all upon a bare rock, though sometimes they grow 26 PRACTICAL BOTANY with their roots in the crevices of rocks. It makes a great difference to the plant in what sort of soil it grows. Every good farmer knows that beans will thrive well in a light sandy soil in which corn or broom corn would starve. All who are familiar with the distribution of our forest trees and shrubs have noticed that some kinds, such as the spruces, most pines, the chestnut, and the jack oak, do well in sandy or other poor soils. On the other hand, the black walnut, the tulip tree, the mulberry, the Osage orange, and the papaw usually nourish only in a deep rich soil. 27. Direction and extent of the root system. In sand or porous loam the root system of the plant is usually much more extensively developed than in clay. If there is a shallow layer of loam overlying a shaly or clayey subsoil, the roots spread out horizontally but do not go far down in the earth. In sand, roots are usually long and branch but little, while in rich soil they branch so freely as to form a close network. If nutrient materials are irregularly distributed in the earth in which a plant is growing, rootlets are so much more exten- sively developed in the richer portions of the soil that, as the great agricultural chemist Liebig forcibly said, " Roots search for food as if they had eyes." The various kinds of plants differ .greatly in the general direction taken by their roots, those of asparagus, for example, forming a sort of shallow mat, and those of many hardwood trees, the radish, and the sugar beet beginning with a single taproot which descends for a considerable distance nearly or quite vertically. It is impossible to get an accurate idea of the root system of a very large plant, since its length usually consists mainly of slender fibers which are inextricably interwoven with each other and penetrate the soil in every direction. The root system even of an oat plant, all contained in a cubic yard or two of soil, has in one instance been found to measure altogether over 450 feet in length. Many plants which ordinarily have their roots near the surface, when grown in dry soils send their roots to great depths to secure the needed water supply. In ROOTS 27 some of the drier parts of California wheat roots have been known to grow to a depth of 15 feet and the roots of the California poppy to a depth of 13 feet. Roots may penetrate to much greater depths, those of the mesquite of the South- western States and Mexico sometimes descending to reach water as much as 60 feet. It is not difficult to get an idea of the extent of the root system of such a plant as Indian corn. Carefully dig away the earth from one side of the plant at a distance of about two feet, keeping a constant lookout for smaller rootlets. If none are found, extend a trench com- pletely about the plant at the distance already used as a radius. Make the trench about two feet deep and stand a piece of poultry netting in it, so as to make a circular fence about the roots of the plant. Run some wire stakes crosswise through the mass of roots, so as to reach across its entire diameter. With a stream of water from a garden hose or with numerous pails of water wash away the earth as completely as possible from the mass of roots and remove the root system entire. It may then be used for illustration in the schoolroom. 28. Pull exerted by roots. After root fibers or the taproots of herbaceous plants have attained their full length, in many kinds of plants a decided shortening of the root takes place. This shortening originates in the cellular portion of the cor- tex, between its outer layers and the central cylinder of the root, and it may amount to from 10 to 25 per cent of the length of the root before contraction. Because the epidermis does not contract, its outer surface often becomes much wrin- kled, especially in the roots of bulbous plants. The shorten- ing of the fibrous roots which spring from a taproot holds it firmly in place, as a derrick is held upright by guy ropes. Sometimes, as in the dandelion, the taproot shortens about as fast as the short stems which crown the root grow upward. In this way the rosette of leaves is kept firmly pressed against the ground, or it may even be drawn slightly into the e.arth. Grass jolants on a lawn are injured or destroyed by being de- prived of light by the rosette of dandelion or fall dandelion. 28 PEACTICAL BOTANY 29. Effects of roots on the soil. If we dig up a spadeful of earth from a well-grassed meadow, or from a little inside the circumference of the circle formed by the roots of a tree, we shall find the soil bound together by the living roots or full of little, crooked, tubular channels left by the decay of dead ones. Thus the soil is in the one case, held together so as to pre- vent its becoming gullied and washed away by rains, and in the other case made more porous and easily penetrated by air and water. The latter effect is a very important one in the case of stiff clay soils, which when closely packed are almost waterproof. The extensive washing away of soils when unprotected by a covering of plants, such as grass, shrubs, or forest growth, is one of the most serious calamities that can befall a country. It is especially formidable in hilly regions, which may become wholly uninhabitable if the forests are cut off and the turf on the hillsides is destroyed by too constant grazing and tram- pling of sheep or goats. Immense areas of land once valuable for timber and for grazing have thus been ruined throughout southern Europe, and the same process is under way in our own country all the way from New England to the Pacific coast region. One of the clearest ways in which the loss by washing away of the soil can be presented is by considering how the land is carried into the sea by great rivers. The delta of the Mississippi covers an area of more than 12,000 square miles. It consists of material brought down by the river in the form of mud, now forming a deposit of unknown thick- ness, probably averaging more than 500 feet. It is calculated that the river every vear carries enough solid matter to form a layer one foot thick over an area of about 268 square miles. Remembering that this mud consists mainly of the choicest part of the rich soil of the Mississippi basin, it is easy to see that the land is robbed every year of the material to support enormous harvests x (see Chapter XXIV). 1 See "Forest Influences," Bulletin 7, Division of Forestry, U. S. Dept Agr., 1893. BOOTS 29 30. Relation of earth roots to air and water. The soil at moderate depths contains much air in its pores, the amount being largest in light loams and sand, and least in stiff clays. This air is essential to the health and growth of ordinary roots. Many kinds of plants growing in earth are quickly killed when transferred to a glass battery jar with a lead cover sealed on, if water enough is poured in through a thistle tube FIG. 19. Cypress trees (Taxodium) growing in a swamp The conical " knees " growing from the roots and nearly always above water are thought to serve as channels to supply air to the roots to fill the jar almost to the exclusion of air. In the same way, if water is backed up a stream when a dam is built across it, most of the trees that are surrounded by the pond formed by the retained water are killed. They have been drowned, and die for lack of air. Even the lower forms of green plants (Figs. 156-168) will soon die for lack of it, if kept in a tightly stoppered jar or bottle full of water. Most aquatic plants which have leaves or green stems exposed to the air like pond lilies, some rushes, cat-tails, and so on convey air down into the submerged parts by means of numerous 30 PRACTICAL BOTANY air passages, which lead from the leaf, through the stem, down into the roots (Fig. 360). It is supposed that " cypress knees," curious outgrowths from the roots of the American cypress (Fig. 19), absorb air, which passes down into the roots. A supply of water is, as already suggested, even more evidently necessary for earth roots than is a supply of air. The appearance during a drought of fields planted with ordi- nary crops is familiar to most people. The dwarfed condi- tion to which plants can be brought by a scanty supply of water is less well known. Many annuals; if given barely enough water to keep them alive, will flower and bear seed after reaching a height of hardly a greater number of inches than they would measure in feet under favorable conditions. When the water supply is wholly withheld from ordinary potted plants they soon wilt and die, as every one knows. 31. Water roots. Most aquatic perennials, like the cat-tails, arrowheads, pickerel weeds, pond lilies, and many grasses and sedges, form mainly earth roots. On the other hand, some plants not aquatics, as many willows, can develop roots indif- ferently either in earth or in water. A row of willows along a brook usually sends great numbers of roots into the earth, and also produces a multitude of fibrous roots which dangle in the water of the brook. Cuttings of Wandering Jew {Zebrinci), geranium (Pelargonium), and many other common plants, root readily in water, and grow for a long time if supplied only with ordinary river or well water. The number of kinds of seed plants which float, and therefore produce only water roots (if they have roots at all), is rather small. Some of the commonest are the so-called "water hyacinth" and the little duckweeds (Fig. 357) so often seen on the surface of stagnant pools and streams. 32. Air roots. Roots may be produced by portions of the stem above ground, in the case of plants which root in the earth. Well-known examples of these are the brace roots of corn, often originating a foot or more above the earth and usually at length extending into the soil, and the tough, fibrous roots by means of which English ivy and poison ivy KOOTS 31 FIG. 20. Aerial roots of an orchid (Cattleya) (Fig. 46) climb. Air roots are also borne by many kinds of air plants which do not root in the earth at all. Such plants are usually natives of moist, warm climates. Good examples of air plants are many orchids (Fig. 20), and some plants of the FIG. 21 Aerial roots of a wild tig tree and lianas in a tropical forest BOOTS 33 Pineapple family. Aerial orchids frequently possess roots of peculiar structure, covered with a papery, absorbent layer which takes up water freely when exposed to rain or dew. One air plant, the Spanish moss (Tillandsia) (Figs. 367, 368), common in the Gulf States, has no roots, but it imbibes water freely by means of special absorbing hairs scattered over the surface of the plant. The Tillandsia is a characteristic feature of many Southern regions, often appearing as tangled, rope- like masses hanging from the trees. 33. Reproduction by means of roots. Roots are often capable of producing buds which may develop into new individuals and thus serve to propagate the plant. The sweet potato is a good instance of this, each root if buried in moist sand being capable of giving rise to several new plants (Fig. 22). Roses are propa- gated by root cuttings, and some trees, such as the silver-leaved poplar (Populus) and the black locust {Robinia), are very troublesome because of the readiness with which young sprouts (sometimes called suckers) spring up from the roots. Many bad weeds, such as the field sorrel (Rumex) and the Canada thistle (Cirsium), are reproduced by roots. In case of desirable plants that can be propagated either by pieces of root or by seeds, it is generally better to use root cuttings, as they will grow much faster. 34. Duration of life and storage of food and water in roots. It is usual to divide plants according to their duration of life into three classes : annuals, living one year or less ; biennials, living two years; perennials, living more than two years. The boundaries between these classes are not always definite ; FIG. 22. Vegetative reproduction of the sweet potato The potato was buried in moist sand and began to sprout, that is, to send out shoots from adven- titious buds at various points. Each shoot may grow into a new plant. About half natural size 34 PRACTICAL BOTANY for example, winter wheat is an annual, though it does not seed until the next summer after it is planted. And the cot- ton plant, the lima bean, the tomato, and the castor bean are instances of plants which with us are cultivated as annuals, but in warm climates live several years ; the castor bean, in- deed, grows there into a large, almost tree-like shrub. Very commonly plants which live for more than one year have food stored in their roots. j FIG. 23. Clustered, fleshy roots of the dahlia, with much stored plant food, in early spring st, remains of last year's stem ; sh, young shoots beginning to sprout from the upper ends of the roots. One fourth natural size Such biennials as beets, carrots, and parsnips store up much food in the root 1 during the first summer's growth, and form a large tuft or rosette of leaves, but do not develop much stem above ground. During the second summer the stored food is consumed in the production of leafy stems, bearing flowers and fruit, and in the autumn the root appears quite withered and nearly dry. 1 The underground part of the carrot and the parsnip is part stem and part root. ROOTS 35 Herbaceous perennials, like the dahlia (Fig. 23) and the common rhubarb, store food in the root during the summer, and consume part or all of it in the growth of the following spring. Trees and shrubs in temperate or cold climates store starch and other foods in the roots, as well as the stem, dur- ing the winter. It is the stored food in the root that enables such plants as rhubarb, the peony, some buttercups, sweet cicely, the dandelion, and many others to make a quick growth in the spring before the weather is warm enough for the man- ufacture of much plant food. The starch, sugar, and proteins which abound in many roots or root-like portions of plants make them valuable for food, as in the case of beets, turnips, carrots, parsnips, sweet potatoes, salsify, and in the cassava plant, from which tapioca is made. It is frequently the case that desert plants store large quantities of water in their roots or in combinations of roots and underground stems, and are thus able to survive long periods without rain. 35. Roots in relation to other organisms. The roots of the higher plants often enter into complicated relations with plants of other species or with animals. Before discussing these re- lations it is necessary to state briefly what some of them are. A plant or animal which feeds in whole or in part on the sub- stance of another living organism is called a parasite. Familiar examples of animals parasitic on other animals are fleas and ticks. The organism which supports a parasite is called the host. Organisms which live together in a mutually helpful way are said to be mutualists or sometimes are called mess- mates. Roots may be : (1) Parasitic on other roots or stems. (2) Hosts for parasitic roots. (3) Hosts for parasitic animals. (4) Messmates or mutualists with other organisms. 36. Parasitic roots. A good many of the higher plants feed altogether or partially on the sap which they draw from other living plants. Those which live entirely at the expense of the 36 PRACTICAL BOTANY host are total parasites, while the others are partial parasites. The dodders (Fig. 351) are practically leafless, of a yellow- greenish or whitish color, and incapable of photosynthesis. The mistletoes and many other half parasites have green leaves and can do photosynthetic work, so that they may depend on the host only for water and mineral subtances, but make for themselves starch or other carbohydrates from the raw materials. Root parasites (Fig. 309) are often attached to the roots of the host at some distance from the stem of the latter, so that few but botanists recognize the real state of the relations between the two plants. The sucking roots of parasites, known as haustoria, are of peculiar structure and have the power of penetrating rapidly into the substance of the host. In the dodder, at any rate, this power is partly due to the presence of ferments, liquid or semi-liquid substances manufactured by the haustorium and capable of dissolving cellulose. 37. Partnership of roots and bacteria. Bacteria are exceed- ingly minute plants of very low organization (Fig. 150). Their forms and structure are shown in a general way by the figure. They differ greatly in their habits of life, as is shown in Chapter XL Those which inhabit little tubercles on the roots of most leguminous plants (as those of the Pea family are called) are of the highest value to the farmer. The tu- bercles occur in the greatest abundance, 4572 having been counted on the roots of a single pea plant. Fig. 305 shows their mode of occurrence on the roots of red clover. Each tubercle contains multitudes of root tubercle bacteria, which are able to change the free nitrogen of the air, contained in the pores of the soil, into a combined form in which it can be absorbed by the plant. Without the action of these or other bacteria or other agents to transform atmospheric nitro- gen into a soluble form it is perfectly useless to the higher plants. 1 1 It is certain that other bacteria besides those of root tubercles render nitrogen available, but the extent of their action is not fully known. BOOTS 37 In order to ascertain how much nitrogen is produced by any given crop it is necessary to make chemical analyses of care- fully selected and weighed samples of the clover, alfalfa, or other crop studied. In this way it was found in one series of experiments that a single crop of alfalfa yielded 95 pounds, red clover 102 pounds, and crimson clover 134 pounds to the acre. As about two thirds of this nitrogen is taken from the air by the plant, turning under by plowing any of these legu- minous crops adds greatly to the available nitrogen of the soil. A ton of barnyard manure contains only about 10 pounds of nitrogen. Therefore an acre of alfalfa plowed under might add to the soil as much nitrogen as could be gained from 16 tons of manure, though the manure would add other desired substances to the soil. A crop of corn of 50 bushels per acre would remove from the soil (in both grain and fodder) about 74 pounds of nitrogen per acre. A wheat crop of 25 bushels per acre would remove from the soil about 48 pounds of nitrogen per acre. Experiments continued for a series of years upon worn-out land, treated year after year with lime and leguminous crops plowed under, show great gains in fertility. In one set of experiments lasting from 1902 to 1907 the soil which had been thus treated produced a little more than six times as large a crop of oats as a similar untreated area. On common prairie land in Illinois the value of the nitrogen gained by the root tubercles of a single crop of alfalfa was found to amount to $25.80 per acre, reckoning the nitrogen as worth the usual fertilizer price for it, 15 cents per pound. What part of this improvement is due to better cultivation is a matter still under discussion. The poorer the land is in nitrogen the more effective is this process of "green manur- ing " with leguminous crops. Provided the tubercle bacteria are present, clover can make a vigorous growth without any soluble nitrogen in the soil at the beginning. 1 1 On the general subject of maintenance of fertility by plowing under leguminous crops, see Hopkins, Soil Fertility and Permanent Agriculture, chap, xvi, and Part III. Ginn and Company, Boston. 38 PRACTICAL BOTANY 38. Partnership of roots and filaments of fungi. Many of the flowerless plants known by the general name of fungi form a dense network of very minute threads. Such a network is found in intimate association with the roots of many kinds of flowering plants. It is especially com- mon on the roots of those which cannot manufacture plant food by photosyn- thesis, but it also occurs on other plants with green leaves, such as pines and beeches. On the roots of the beech the fungus filaments are found united into a sort of membrane, covering the tips of the young roots and extend- ing back for a considerable distance (Fig. 24). In such plants as the heaths, blueberries, and their relatives, the fungus threads form little tangled masses inside the cells near the sur- face of the root and send out free ends into the surrounding soil. In any case the whole filamentous mass living in connection with the root is called a mycorrhiza. Roots provided with my- corrhiza usually form few or no root hairs, and it is supposed that the fungus threads to some extent perform the work of root hairs in absorbing soil water. The subject is not yet well understood, but it would seem that certain trees, such as pines and oaks, do not flourish as well when grown in a soil which does not develop a mycorrhiza upon their roots. 1 i See "Experiments in Blueberry Culture," Bulletin 193, Bureau of Plant Industry, U.S. Dept. Agr. FIG. 24. Tip of a root of European beech, covered with mycorrhiza The coating has been stripped off for a little way at the top to show the thickness of the mycorrhiza. Magnified 30 diameters. After Pfeffer CHAPTER IV THE STEM AND THE LEAF 39. Stem and leaf as coworkers. In a general way it may be said that the stem and the leaf together do the work of making plant food from the raw materials (Sect. 17). In most of our commonest seed plants the stem is mainly impor- tant as the part of the plant body which bears leaves, maintains them in the- most advantageous position to receive sunlight, carries to them water and dissolved salts from the earth, and carries away from the leaves the newly made plant food which is to serve for the immediate needs of the plant body or to be stored for use later on. The stem and the leaf are so intimately associated that it is often convenient to have a single name for the two together. The stem and its leaves collectively are known as the shoot. 40. Photosynthesis done by stems. In some practically leaf- less plants, such as the cacti, the photosynthetic work of the plant is all done by the stem, which is covered with layers of chlorophyll-containing cells. Stems flattened so as to expose a good deal of surface for photosynthesis are shown in Fig. 25 and still more expanded ones in Fig. 26. In the shrubs known as switch plants (Fig. 365), common in some regions where the summers are hot and almost rainless, the leaves (if there are any) are borne for only a few months of the year, usually in the spring. During the rest of the year photosynthesis is slowly carried on by the green layer of the bark, which is abundantly supplied with chlorophyll. Even among the trees and shrubs of temperate North America there are many species, such as the wahoo, box elder, sassafras, and some roses, which have much green bark on the younger twigs and probably accomplish a good deal of photosynthesis through 39 40 PRACTICAL BOTANY these. As the twigs grow older the green layer is shut away from the light by the corky layer outside of it and soon dies. Most of our useful annuals of the farm and garden, such as corn, potatoes, tomatoes, squashes, and so on, have green stems which do photosynthetic work. 41. The stem raises leaves into the light. Many plants which cover the ground rather closely do not need to raise them- selves much from the earth in secur- ing their share of the light. Good examples of these are such familiar creeping plants as white clover, black medic (Medicago), moneywort (Lysi- macliia), and some species of wild ev- erlasting (Anten- naria). But very commonly plants compete for light against each other, as may readily be seen in almost any cornfield. When the corn is only a little way above ground it is neces- sary to keep it free from rank, quickly FIG. 25. Branches of Muehlenbeckia, a plant with ffrowm p- weeds by flattened stems which do most of the photosynthetic J work of the plant frequent cultiva- /, flowers; I, leaves; s, stems. One half natural size tion. If this Work THE STEM AND THE LEAF 41 is neglected, the young corn plants will be overshadowed and dwarfed and the crop greatly injured. But as soon as the cornstalks have lengthened enough to carry the spreading leaves above the tops of ordinary weeds and leave them in the shade, the corn plants are safe from further competition with these plants, though other species that can thrive in weak light may develop later. In the same way wild plants kill off other species by overshadowing them. Under a close thicket of dogwoods ( Cornus), hazels, FIG. 26. Stem of "smilax" (Myrsiphyllum) I, scale-like leaves; cl, cladophyll, or leaf-like branch, growing in the axil of a leaf; ped, flower stalk, growing in the axil of a leaf or buttonbush, hardly any smaller plants can grow, and the most successful competitors with the bushes are such climbers as the cat brier {Smilax, Fig. 49), 1 climbing false buckwheat (Polygonum), wild morning-glory, and climbing hemp weed (Mikania). These support themselves on the bushes or other plants, and secure all the light they need by running along the tops of the supporting plants. 1 This is not the familiar greenhouse plant shown in Fig. 26, which is usually called smilax by florists. 42 PEACTICAL BOTANY As a result of competition with each other to secure light, plant stems often become greatly lengthened. Any one who is observant and familiar with things out of doors must have noticed the different form (habit it is called by botanists) of such plants as giant ragweed (^Ambrosia) or hemp as they grow tall and little-branched when in dense clumps, or low and spreading when they stand singly. And full-grown trees such as pines are nearly branch- less for most of their height, when growing in dense forests, but low and broad-topped with many lateral branches when growing alone in a pasture (Fig. 246). A tree growing on the edge of a patch of dense woods may develop the pasture habit on its exposed side and the forest habit on the side toward the woods, like the tree in Fig. 27. 42. Danger from excessive height of stems. Wheat, oats, or corn plants are sometimes blown down by severe winds, and a field of grain in this con- dition is said to be " lodged." Large tracts of forest may also be greatly damaged by severe storms, particularly when the trees are loaded with sleet (Fig. 28), and the area covered with broken-down tree trunks is known as a " windfall." But neither tall grain nor forest trees can be blown down as easily when growing massed together as when standing singly, since every FIG. 27. Pruning as an effect of shade The large American beech in the fore- ground has developed no considerable limbs on the right, because, until it was well grown, another beech stood within fourteen feet of it, on that side THE STEM AND THE LEAF 43 FIG. 28. Cottonwood trees on the day after a sleet storm Many branches have been broken off by the weight of the sleet individual in the interior of the field or forest is much sheltered from the wind by its neighbors, and all together present enough resistance partially to impede the wind. Scientific foresters in clearing the trees off a large tract begin on the sheltered side and cut toward the quarter from which severe storms usually come. 44 PRACTICAL BOTANY 43. Growth in length. Under favorable conditions the younger portions of the stem for a good while increase con- tinually in length. The rate of growth varies greatly in dif- ferent plants : sunflowers and giant ragweed (Artemisia) may grow to a height of 10 or 12 feet, and climbers like gourds and hops to a length of perhaps 40 feet, in a single summer. On the other hand, pine seedlings during their first summer only grow to be from 1 to 3 inches high, and oak seed- lings less than 5 inches. The growth per year for a time continues to increase and then diminishes. For example, the long-leaf pine (Fig. 261) grows only about three quarters of an inch the first year. For the first fifty years it makes an average annual growth of 14 or 15 inches; for the next fifty, 4 or 5 inches ; and from one hundred years to extreme old age, about one and one-half inches. It usually lives about two hundred years. The growth of the younger nodes of most plants is quite un- equal, as may be learned from the study of a rapidly growing stem, such as the morning-glory. 1 It will also prove interest- ing to measure such plants as corn, broom corn, hemp, and pole beans, to determine whether they elongate more during the day or the night, and during warm or cool weather. 44. Internal structure of the young dicotyledonous stem. 2 The structure of the fully developed stem can best be under- stood by tracing its development from the time when the em- bryo begins to grow in the sprouting seed. That, however, is a rather difficult process to follow, so this brief account will begin with the stem already considerably developed. In common language the dicotyledonous stem is said to con- sist of bark, wood, and pith. These regions are very distinctly 1 See Bergen and Davis 1 s Principles of Botany, p. 17. 2 See also Sects. 45-48. The stem of many gymnosperms (e.g. trees of the Pine family) in its general structure much resembles the dicotyledon- ous stem. For a general account of the stem structure of dicotyledons and monocotyledons see Coulter, Barnes, and Cowles's Textbook of Botany, chap, iv, A. ANGIOSPERMS. THE STEM AND THE LEAF 45 seen in the youngest twigs of most of our dicotyledonous trees and shrubs, such as willow, poplar, sassafras, and elder. The early structure of dicotyledonous stems is in some ways best shown in the stems of woody climbers. Fig. 29 shows e b c p EIG. 29. Diagrammatic cross section of one-year-old Aristolochia stem e, region of epidermis ; 6, hard bast ; o, outer or bark part of a bundle (the cellular portion under the letter) ; w, inner or woody part of bundle ; c, cambium layer ; p, region of pith ; m, a medullary ray. The space between the hard bast and the bundles is occupied by thin-walled, somewhat cubical cells of the bark. Consid- erably magnified FIG. 30. Diagrammatic cross section of sunflower stem p, pith ; fv, woody or fibrovascular bundles ; e, epidermis ; b, bundles of hard bast fibers of the bark. Somewhat magnified. After Frank the relative position of the structural components of the one- year-old stem of Dutchman's-pipe, as seen in a cross section. The outer cylinder (e-c) is bark ; the central portion (^?) is pith. Between bark and pith, extending both inward and out- ward from the cambium layer (w-i;re?f.-.?5ViV- -n FIG. 34. Arrangement of strengthening tissue A, J5, in stems; (7, in the root A, cross section of a young elder twig; B, cross section of flower stalk of Eryn- gium ; C, cross section of a small root ; coll, collenchyma ; cort, brittle cortex ; cyl, tough central cylinder ; /, fibrous cylinder around a central hollow portion ; p, pith; w, woody bundles surrounding the pith. After Strasburger case of dicotyledonous trees the stiffness of the trunk, resisting the severest storms, is mainly due to the immense number of tracheids and fibers in the wood of the annual cylinders. The stems of woody climbers need to be at once tough and flexible. Many such vines have, while young, the structure shown in the cross section of Dutchman's-pipe (Fig. 29), with the bundles arranged in a discontinuous series around the central pith and not united into a cylinder. This makes the stem flexible in the same way that a wire cable is more flex- ible than a solid metal rod. Roots (except prop roots) do not need to possess much stiff- ness ; it is necessary for them to be tough to resist lengthwise 50 PRACTICAL BOTANY -- m pulls, but laterally they are supported by the earth. Accordingly it is usual to find young roots with a fibrous central cylinder of comparatively small di- ameter, surrounded by a coating of much weaker tissue (Fig. 34, (7). 47. Limited thicken- ing of annual stems. In stems of large dicoty- ledons which die to the ground every year, such as sunflowers, iron weeds, hemp, giant ragweed, and so on, growth in thick- ness goes on throughout the summer. The outer cells of the cambium con- tinually split up, by the formation of tangential partitions (parallel to the bark), and so form new layers of bark. The inner cells of the cam- bium, in a similar way and to a still greater extent, form new wood, and thus the stem goes FIG. 36. Cross section of a stick of oak wood on increasing in thick m, medullary rays, running from bark to pith ; ness - But m sucn plants r, "annual rings"; 6, boundaries between as those just mentioned " rings," porous from presence of many ducts ; . > . . . , / , i t, interior fibrous layers of dead bark ; pi, hard the activity of the cam- plates of dead bark, splitting away from each bium is strictly limited. other but attached to bark beneath. Reduced Af ^ ^ ^ giyen ^ to a certain amount of new tissue, growth stops and the stem dies down to the ground. The death of annual stems in the autumn is often thoughtlessly supposed to be due to the THE STEM AND THE LEAF 51 arrival of cold weather, but it occurs just as certainly, and often after a briefer period of growth, in regions where there is no cold winter. 48. Annual thickening. In stems such as those of dicotyle- donous trees and the trees of the Pine family and other cone bearers, which live for many years, the cambium forms a new layer of bark and of wood every year. 1 These annual layers are usually more noticeable in the wood than in the bark, because the wood cylinders thus formed remain closely joined together (Fig. 35). The newer lighter-colored portions of the wood are known as sapwood, and the older portions, often darkened by the deposit of coloring matter, are known as heartwood. Not infrequently the heartwood decays and leaves the tree hollow. (1) How old is the stick of wood shown in Fig. 35 ? (2) Did it grow equally fast during each year of its life ? Dis- cuss this question. (3) Why is the name " annual rings " not an accurate one ? What are they really ? (4) Is each year's growth uniform all round the stem? (5) Had this stem any branches in the portion shown by the section ? How could the age of the stem, at the time when a branch began, be known (Fig. 37)? The hardwood trees show great differences in the rate at which their trunks increase in thickness. Poplars, bass woods, willows, or red oaks, growing in good soil and unshaded, may for forty or fifty years form annual rings as much as three eighths of an inch thick. But old beeches and sugar maples in the forest, after they have passed the hundred-year limit, often grow not more than about one sixteenth of an inch per year. When very old, though still sound, they may grow only about one twenty-fifth of an inch per year. Two of the most important of our coniferous or needle- leaved timber trees are the white pine and the long-leaf pine. A white-pine tree, overtopping most of its fellows in the forest, is, on the average, at ten years 0.9 inch in diameter, 1 In the tropical regions, where there is no marked change of seasons, the wood often grows rather evenly all the year round. 52 PRACTICAL BOTANY at one hundred years 17.2 inches, and at two hundred years 31 inches. The average thickness of the " annual rings " during the life of the tree throughout its second century is therefore about one fourteenth of an inch. In the Southern long- leaf pine, growth is slower. The increase in thickness of a tree two hundred and twenty years old and 17| inches in diameter was only one inch during the last forty years, or one fortieth of an inch per year. In successful white-pine trees (that is, the taller and only slightly shaded ones of a forest) the total amount of wood formed in the trunk per year is, at fifty years, about one fourth of a cubic foot, at sixty to seventy years one cubic foot, at one hun- dred years one and one half cubic feet. 1 49 o Origin of branches. The branches of dicotyledons be- gin as little elevations or FIG. 36. Diagrammatic section through the growing tip of a dicotyledonous shoot, showing origin of branches g, the growing tip of the shoot ; I, leaves, those at the upper part of the shoot the youngest; 6j, 6 2 , 63, 64, branches of various ages, arising in the axils of the leaves. Note that only the older leaves and branches have fibrovascular bundles, connecting with those of the main portion of the shoot (all deeply shaded in the diagram) . After Luerssen rounded outgrowths from the axis of the leaf bud, which often terminates the stem. 2 The extreme tip of the stem is the growing point (. FIG. 41. Alternate arrangement of leaves An apple twig in the autumn THE STEM AND THE LEAF 57 54. Leaf positions on horizontal stems, and overshadowing. If a rapidly growing plant, as a sunflower, is bent over so as to lie flat on the ground, its younger leaves soon readjust them- selves to the new position. Horizontal branches of trees and shrubs are very different from vertical shoots as regards the position of the leaf blades with reference to the stem. Though the opposite or the spiral arrangement of the leaf origins is the same, a twisting of the stem, or a lengthening, or twisting, or FIG. 42. Rosettes of evening primrose Two species are shown : CEnothera rhombifolia on the left, and (E. biennis, a very widely distributed species, on the right. Photograph by W. J. G. Land other change of position of the leafstalks usually occurs. This comes about in such a manner as to put the leaves in a favor- able position to receive the sunlight (Fig. 40). Prostrate stems, like those of pumpkins, squashes, cucumbers, poison ivy, English ivy, and a host of others, when lying on the ground, arrange their leaves much as do horizontal branches of trees. Trees that have fallen in such a way as to leave the roots in the soil may have one or more branches assume the form of a tree. 58 PRACTICAL BOTANY 55. Leaves of apparently stemless plants. Many plants have a stem so short that they are commonly spoken of as stemless. Most of these are perennials, such as the Iceland poppy, the common plantain, the true primroses (Primula), and the dan- delion. There are also numerous biennials, such as the parsnip, the carrot, some species of wild let- tuce, many evening- primroses ( (Eno- thera), and other plants, which form a tuft of leaves close to the ground the first year and then send up a leafy stem which flowers and fruits the sec- ond year. Such a FIG. 43. Wild ginger, an apparently stemless plant A, the entire plant, with running rootstock ; B y top view of flower ; (7, lengthwise section of flower ; I, limb of calyx ; o, ovary. Reduced tuft of leaves as that of the dandelion or the evening primrose (Fig. 42) is called a rosette, and plants in which the appar- ently stemless condition, with a cluster of radiating leaves, is permanent are known as rosette plants. Many of these are natives of alpine regions, and some, such as the century plant (Agave, Fig. 62), are found in hot, dry climates. Quite generally the shape of the leaves in rosette plants secures economy of THE STEM AND THE LEAF 59 light, as they are either narrowed at the base or borne on long leafstalks, so that they do not overlap and shade each other at the bases. The leaves of the century plant are broad at the base, FIG. 44. Leaf mosaic of a begonia The leaves are so disposed that little shading of one leaf by another occurs but this portion is pale and much thickened and does hardly any photosynthetic work, serving rather as a storehouse for plant food. At flowering time this food is removed, the leaves droop, and after the seeds are ripe the leaves die (Fig. 63). FIG. 45. Mosaic formed by leaves of unequal size Top view of a branch of deadly nightshade. After Kerner 56. Leaf mosaics. Any combination of leaves, whether found in rosette plants or on longer stems, in which the space is very fully occupied by leaves, with few spaces horizontally between them, is called a leaf mosaic (Figs. 44 and 45). Walls 60 PEACTICAL BOTANY covered with Japanese ivy furnish beautiful examples of leaf mosaics on a large scale, and many of our common house plants illustrate the same phenomenon. In any leaf mosaic many of the leaves occupy a very different position from that which they would have if borne on a vertical stem. FIG. 46. Poison ivy, a root climber Reduced 57. Obtaining better illumination by climbing. While the "stemless" plants and low mosaic formers uti- lize light very advantageously by the disposition of their leaves, many plants get an increased light sup- ply by climbing. On account of the great height and dense growth of tropical forests, climbing plants or lianas reach their greatest development in those regions, often running hundreds of feet to emerge at last into the blazing sunlight above the tree tops. FIG. 47. Twining stem of hop THE STEM AND THE LEAF 61 Climbers are, however, quite generally distributed, and many are familiar plants of our own flora. They may be roughly classed into (1) scramblers, (2) root climbers, (3) twiners, and (4) tendril climbers. Scramblers sprawl among and over the tops of bushes and thickets. Examples are some kinds of asparagus, our common climbing rose, and cleavers (Gralium Aparine). FIG. 48. Woodbine or Virginia creeper, a tendril climber Reduced Twiners raise themselves by winding the stem about any slen- der upright support that offers itself. Well-known examples are pole beans, morning-glories, and the hop. The details of the process by which twiners wind themselves about a supporting object cannot be very briefly stated. If carefully watched, the growing tip of the shoot will often be found to describe revolving movements like those of the hands of a watch. When the movement is arrested by contact of the shoot with an ob- ject not too large for the climber to twine about, the resistance which the young moving stem encounters causes it to wind permanently around the resisting object (Fig. 47). Usually the direction of the coils for any given plant is the same. 62 PRACTICAL BOTANY Tendril climbers attach themselves to the stems or branches of other plants or to inanimate objects by means of special, slender, thread-shaped, leafless organs called tendrils. These are modified leaves or parts of a leaf, as in the pea (Fig. 306) ; or modified branches, as in the grape, the Virginia creeper (Fig. 48), and the passion flower. When a living and active tendril comes into contact with a support, this contact causes growth to take place more rapidly on the exterior side of the FIG. 49. A tropical Smilax, a tendril climber a, tendril coiled about a portion of the stem ; I, tendril coiled about a leafstalk ; br, a young branch ; t, young unattached tendrils tendril (that side which does not touch the foreign object), and thus the tendril is made to coil about the support. The sensitiveness of some tendrils is almost inconceivably great. Those of the star, wild, or bur cucumber (Sicyos) are stimu- lated to curve by a moving weight of -j o-oViJo" ^ a g ram > or one eighth of the smallest amount which can be perceived by the most sensitive part of the human skin (the face). After a tendril has become attached the free portions are also thrown into coils and thus the plant is drawn closer to the support. As a result of its attachment the tendril becomes stronger and often considerably thicker. In some plants, as the "Virginia creeper, the tendrils are enabled to fasten FIG. 60. An English ivy (Hedera) grown in front of a south window WW, the line of the window casing ; all to the right of this is unlighted wall. The tips of the shoots (f) avoid the light ; the young leaves (I) have assumed no defi- nite position ; the mature leaves are nearly at right angles to the light coming from the direction of the arrow ; r, aerial roots 63 64 PEACTICAL BOTANY themselves to flat surfaces, as of stones or bark, by developing disks which act as suckers. These may stick so fast to the sup- porting surface that the tendril can be broken without tearing them away. 58. Leaf posi- tions avoiding ex- cessive illumina- tion. While the leaves of plants growing in the FIG. 51. Nearly vertical leaves , , f of the olive shade of ten suf - fer from lack of sunlight and are usually so arranged as to utilize most fully what light there is (Fig. 50), it is possible for leaves in exposed situations to have too much light. It seems certain that the most powerful sunlight may injure the chloroplasts and therefore cripple the power of the leaf to do its work of photosynthesis. Compass plants, such as the common prairie species (>SVZ- phium) and the prickly lettuce, have leaves somewhat erect, with edges directed nearly north and south, thus se- curing good illumination during the cooler morning and evening hours, but pre- senting the leaves nearly edgewise to the sun at noon. Many other plants maintain some or all of their leaves in a nearly vertical posi- tion, but with the edges not directed north and south. In the olive (Fig. 51) many leaves point nearly upward, while in the commonest species of Eucalyptus the leaves hang vertically downward. FIG. 52. A leaf of red clover At the left, leaf by day ; at the right, the same leaf at night. Natural size THE STEM AND THE LEAF 65 In a great number of trees the young leaves from recently opened buds stand erect or hang straight down. In one tropical species 1 it is estimated that these young drooping leaves do not get more than -5^ as intense illumination as is received by the most exposed of the mature leaves. 59. Daily movements of leaves. It is com- mon to find leaves assuming different posi- tions during different portions of the day, or even whenever (as from the long continuance of clouds over the sky) the intensity of the sunlight is much altered. These daily changes of position are particularly frequent in plants of the Pea family, and many of these have a special cushion-like organ, the pulvinus, at the base of the leafstalks or of the leaflets, which produces the movements. Sometimes, as in Fig. 52, there are only two principal positions assumed during the entire twenty- four hours, one for the day, the other for the night. In other cases there are at least three well-defined positions, as in the case of the black locust leaf. In this the leaflets droop at night, remain nearly horizontal in ordinary daylight, and stand erect in full sunlight. It is certain that the plant gains some ad- vantages from the change from horizontally placed to vertically placed leaflets, and the reverse. The horizontal position is (as already stated) favorable for photosynthesis in mod- erate light, and the vertical position hinders undue absorp- tion of intense sunlight by the chloroplasts. What benefit the plant gets from the assumption of the night position by the leaves, and of how much importance this is, are questions as yet unsettled. 1 Amherstia nobilis, from Burma. FIG. 53. The purple wood sorrel, with the leaves in the nocturnal position One third natural size 66 PEACTICAL BOTANY 60. Self-pruning of leaves and twigs. Many trees and shrubs begin to shed some of their leaves even in the spring, very soon after the leaves are well grown. Examples of this are the lilacs, the syringa (Philadelphus~), the cottonwood, the horse-chestnut, the box elder, and some lindens. Still more common is the loss of leaves during the summer, which may amount to 30 per cent of the total number of leaves. This leaf fall, coming long before the leaves are cast off in the autumn as a preparation for winter, affects mostly the leaves inside the crown of the tree, which have such scanty light that they can- not accomplish much photosyn- thesis. Leaves, twigs, and even larger branches which are not getting an adequate sup- ply of light or of water are pruned away by the tree. Were it not for this, the dense growth in the interior of the tree top and along the trunk would soon render further branching me- chanically impossible. What one sees on looking up along the trunk into the top of a large tree is mainly dead or dying branches, with few leaves. It is this self -pruning and pruning by neighboring trees which makes the straight trunks, free from knots and most valuable for timber, in trees grown in woodlands, where they stand moderately close together. In some instances, as the so-called snap willows, the cotton- wood, and the large-toothed aspen, live twigs fall very freely from the tree during wind or snowstorms, or when it is loaded FIG. 54. A leaf of acacia A, as seen by day ; B, the same leaf at night. After Darwin THE STEM AND THE LEAF 67 with sleet (Fig. 28). These may be blown over crusted snow or floated along by brooks or rivers near which the trees grow, and doubtless often lodge in spots where they take root and grow into new trees. 61. Aerial, floating, and submerged leaves of water plants. Many plants which grow rooted under water have only aerial leaves. To this class belong many arrowheads, the cat-tails, FIG. 55. Victoria regia and other tropical and sub-tropical water lilies at the nurseries of Henry A. Dreer, Philadelphia The Victorias have the largest known floating leaves, sometimes six feet in diameter and, like rafts, capable of supporting large water birds wild rice, pickerel weeds, and other familiar species. A few common plants like the pond lilies and Victorias have floating leaves only (Fig. 55). Some water crowfoots and pondweeds have all their leaves submerged, while other species of these plants and some arrowheads have part of their leaves ex- posed to the air and others wholly under water. Submerged leaves are often made up of many thread-like divisions, apparently to enable them to present as much 68 PRACTICAL BOTANY surface as possible to the water, in order that they may ab- sorb from it the gases dissolved in it. Their shape somewhat resembles that of the gills of fishes, and the thread-like divi- sions of the leaf and the gill both have to do the work of absorbing dissolved gases. 62. Leaves in relation to water supply. The form and size of leaves are frequently dependent on the water supply which the plant receives. In many plants which grow in moist soil or even in swamps the leaves are large and often entire, as in the Cypripedium, skunk cabbage, white hellebore, papaw, and the magnolias. In very dry soils or where the rainfall is scanty or lacking during a considerable part of the warm months, there occur many plants whose leaf surface is very small, as in some Eu- phorbias, aloes, and heaths (Erica) ; or is even practically wanting, as in most cacti (Fig. 65). This reduced leaf surface evidently fits plants admirably to resist death from excessive transpiration during droughts. When the soil temperature is nearly at the freezing point most plants are unable to absorb much water by their roots. It is probably mainly due to this fact that our ordinary winter deciduous trees owe their habit of shedding the leaves at the approach of winter. If their actively transpiring leaves were to remain at work while the ground was almost or quite frozen, the tree would suffer a fatal loss of water. Winter deciduous- ness is not a perfectly definite phenomenon, always setting in at precisely the same season. For example, the common Jap- anese honeysuckle, which is deciduous in the late autumn or early winter in the Northeastern States, is almost or quite ever- green in the South, and the trumpet honeysuckle is deciduous in. the North and perfectly evergreen in the South. Such de- ciduous trees as the American tulip tree (Liriodendrori) and the English oak become irregularly evergreen in the very uniform climate of West Java ; that is, they show in December and January (on separate boughs) a state of things correspond- ing to their winter, spring, and summer condition in their THE STEM AND THE LEAF 69 native countries. The process of shedding the leaf is a some- what complicated one, being brought about by the formation of a waterproof layer of tissue at the base of the leafstalk, FIG. 56. An evergreen rhododendron, typical of leathery-leaved non-deciduous dicotyledons, in very early spring A deciduous rhododendron (azalea) is seen leafless in the foreground Photograph by Robert Cameron thus cutting the leaf off from communication with the stem. Before this is formed, the plant food in the leaf has usually been conveyed into other parts of the plant, so that when the leaf falls it takes with it little of value. 70 PRACTICAL BOTANY Some trees and many shrubs in countries like the Medi- terranean region and California, where the hotter months are B C FIG. 57. Hairs which protect leaves from excessive loss of moisture A, T-shaped hairs of wormwood ; B, silky hairs of Convolvulus; C, shield-shaped scaly hairs of Elseagnus. All considerably magnified. After Kerner nearly rainless, are summer-deciduous, losing almost or quite all of their leaves at the beginning of summer. Twigs in this leafless summer condi- tion have been found to lose only about ^ as much water in a given time as they do when in full leaf. 63. Hairs and other cover- ings of the leaf surface. The leaves of many kinds of plants are covered with a layer of wax or of a var- nish-like material ; some are coated with a deposit of FIG. 58. Part of epidermis of geranium (Pelargonium), surface view lime salts, and all of these substances appear to hin- der excessive loss of water from the leaves. A similar purpose is subserved by a A, hairs, the one at the left consisting of one cell, the one at the right several-celled and bearing a gland at its tip ; e, stout cells of the epidermis, which serve to support the hair. Between the hairs a stoma is seen, Considerably magnified THE STEM AND THE LEAF 71 clothing of dry hairs, which often assume very curious forms (Fig. 57). These may completely cover one or both surfaces of the leaf (usually the lower one). Such hair-clad leaves are very commonly found on mountain and desert plants and on those which grow in regions with a long and rainless summer, and it has been experimentally proved that the hairs greatly lessen evaporation from the leaves. Speaking of the flora of the summer-dry Mediterranean region, the distinguished Aus- trian botanist Kerner says: "The trees have foliage with gray hairs ; the low undergrowth of sage and various other bushes and semi-shrubs ... as well as the perennial shrubs and herbs growing on sunny hills and mountain slopes, are gray or white, and the preponderance of plants colored thus to restrict evaporation has a noticeable influence on the charac- ter of the landscape. He who has only heard from books of the evergreen plants of the Greek, Spanish, and Italian floras, feels at the first sight of this gray vegetation that he has been in some degree deceived, and is tempted to alter the expression ' evergreen ' into ' ever gray.' " Hairs which contain liquid, like the gland-bearing one in Fig. 58, do not serve to prevent evaporation, but are some- times of much use for other purposes, as in carnivorous plants (Chapter XXI). CHAPTER V UNDERGROUND STEMS ; STORAGE IN STEMS AND LEAVES ; REPRODUCTION 64. Characteristics of underground stems. The popular notion of what a stem is, includes the idea that it is an aerial part of the plant. It is easier to recognize as roots such structures as the aerial roots of corn and of poison ivy than it is to rec- ognize as stems the thickened underground portions of iris, jack-in-the-pulpit, dragon-root, trillium, or potato. Frequently, like aerial stems, underground stems are divided into nodes and internodes ; and many of them bear scales which repre- sent leaves, and produce buds in the axils of these scales. Such buds are well shown in the underground stems of some grasses. Dicotyledonous underground stems usu- ally have distinct bark, wood, and pith, while most dicotyledonous roots do not have pith, though some do. FIG. 59. A May-apple plant, showing the history of the rootstock 1 is the oldest surviving portion of the rootstock ; 2 is a year younger ; 3 a year younger than 2, and so on. At each figure the cluster of roots marks the position of the base of the upright stem for that year, as is shown at 6. b, bud for the new year's growth ; br, bract at the base of the present stem. One sixth natural size 72 UNDERGROUND AND AERIAL STEMS 73 Some of the principal forms of underground stems have for convenience been given special names. The elongated forms like that of the May apple (Fig. 59), mints, couch grass, and many other plants, and some stouter kinds like that of trillium and Solomon's-seal (Fig. 60), are known as rootstocks or rhizomes. The very short shoots with disk-like stems and a covering of scales, familiar in some lilies, the hyacinth (Fig. 61), and the onion, are called bulbs. Much like bulbs, ex- cept that the stem is more developed and that the scales are almost lacking, are tu- bers, like those of the Jerusalem artichoke (Fig. 67), the potato, and the crocus. 1 The potato is a particularly good tuber for study, as it has well-defined nodes and internodes ; the buds ("eyes") are arranged in a distinctly spiral manner, and are borne in the axils of little scales which represent leaves, and not infrequently the tuber is considerably branched. 65. Aerial outgrowths of underground stems. Some under- ground stems produce a leafy aerial stem, while others send up leaves but have no stem above ground. A good example of the former class is the lily or the Jerusalem artichoke ; of the latter, the ferns of temperate regions, many grasses, wild ginger (Fig. 43), and some of the commonest violets (Fig. 124). In any case the aerial parts of herbs, in cold or tem- perate climates, usually die to the ground at the beginning of winter. In regions with a long, rainless summer they fre- quently die soon after the end of the spring rains. The buried 1 Such very short underground stems as that of the jack-in-the-pulpit and the crocus are often called corms. FIG. 60. Rootstock of Solomon's-seal rh, rhizome or rootstock; 6,6', buds; r, roots; s, stem. The scar where an old stem was attached is seen just above 6" 74 PRACTICAL BOTANY part of the plant body, with its terminal bud or sometimes lateral buds, is comparatively safe from extremes of cold or dryness, and serves to carry the life of the plant over from one growing season to another. 66. Water storage in stems. All living stems of plants con- tain water, and in the case of plants ex- posed to long peri- ods of drought the water stored in the stem may be abso- lutely necessary to tide over the rainless months. Some cacti and other succulent desert plants con- tain enough water to make it possible for men and other animals to drink from them when they are cut open. The amount of water stored in some desert plants is sufficient to carry on growth and FIG. 61. Lengthwise section through a young hyacinth plant *t the cushion-shaped stem at the base of the bulb ; reprO( iuction for ten 6, the young bulb from which the next year s growth would proceed; sc, bulb scales; f.s, flower stalk, years or more Wlth- Eeduced out renewal from outside sources. The trunks of certain South American trees are so swollen as to constitute something like aerial tubers, STOEAGE IN STEMS AND LEAVES 75 and great numbers of desert plants have bulbs or rootstocks much exceeding in bulk the rest of the plant body, and con- taining large quantities of water, protected from evaporation by heavy exterior layers of cork. 67. Water storage in leaves. Many of the most striking examples of succulent or fleshy-leaved plants occur among species which are natives of dry countries or of regions where there are long rainless periods. The century plants (Agave) (Fig. 62), ice plants (MesembryantJiemurn)^ aloes (Alo'e), and Echeveria are good instances of this kind of leaf. The leaves are sometimes cylindrical or prismatic, thus offering little surface for evaporation, and contain great quantities of water in the form of a thin mucilage, not easily dried up. In many such leaves the water is largely stored in special layers of the epidermis, while in others the water-storage tissue is in the interior of the leaf. During droughts fleshy leaves gradually lose their firmness and become flabby in the same way as the leaves of the purslane do when the plant is hoed up and left on the surface of the ground. In tliis case the plant may live for weeks and then take root and grow again after the first rain. Sometimes plants which grow in moist soil have leaves with water-storage layers. The oleander, for instance, grows along water courses but is exposed for months to very dry, hot air, during the nearly rainless summers of the Mediterranean region. The common rubber plant (Ficus), which in India grows to be an immense tree, is one of the most familiar examples of water storage in the leaves of a species growing in moist soil. Such leaves are able to withstand the great changes of tem- perature and moisture in the air of the tropics during every twenty-four hours, the air for two thirds of the time being almost saturated with moisture, while during the remaining hours the moisture is relatively low and the temperature under a nearly vertical sun extremely high. Plants with fleshy leaves are often found in cool, damp cli- mates, but they usually grow on rocks or in other situations where the water supply is at times nearly or quite cut off. 76 PRACTICAL BOTANY 68. Air storage in stems and leaves. In many marsh and water plants very extensive supplies of air are stored in the interior of the roots, rootstocks, the ordinary stems, and the leaves. This stored air consti- tutes what has been well called an inner atmosphere, by means of which the respiration of the plant is much aided, especially at times when the whole plant body is temporarily submerged. In those marsh or water plants which have the most extensively developed air passages and cav- ities they form a complex system which extends all the way from the stomata to the tips of the roots. Often a large part of the bulk of the plant body is occu- pied by such air cavities, sur- rounded by slight walls of solid material. In the leaves of Pistia, a floating aquatic belonging to the Arum family, 71 per cent of the volume is occupied by air spaces, while in ordinary land plants these spaces may occupy less than 7 per cent of the total volume of the leaf. An important mechanical use is often subserved by stems or leaves inflated with air, in buoy- ing up the plant, as is well shown by the duckweeds, the water hyacinth (EicTihomicT), and the water chestnut (Trapa). Many seaweeds, as the rockweed, are thus buoyed up. FIG. 62. A century plant, nearly ready to blossom The flower stalk considerably devel- oped and the outer leaves beginning to shrivel and droop from loss of food transferred to the flower stalk. Photograph by G. D. Fuller STORAGE IN STEMS AND LEAVES 77 69. Storage of food. Aerial stems contain plant food, often in great quantities. In the trunks of trees this food is present in various forms, as starch, sugar, oil, and proteins. Many kinds of sapwood turn deep blue or black if tested with iodine for starch in the autumn. During the winter much of this starch is often converted into sugar or oil. The presence of proteins in wood is so general that the cheaper grades of white paper, largely made of wood pulp, at once turn yellow on being mois- tened with nitric acid (protein test). When thus tested, paper made wholly of cotton, or of linen rags, shows little change. The plant food stored in wood is most abundant in the younger portions (sapwood), and above all in the cambium layer. Underground stems often con- tain large quantities of stored food, and are thus useful in tiding over the period of the year when no food can be made, just as they have already (Sect. 66) been shown to be of serv- ice in storing water. There are many shade plants such as trilliums, dogtooth violets (Fig. 66), wild ginger (Fig. 43), May apple (Fig. 59), and others which leaf and blossom early in the spring and do a large part of the storing of food for the next season in their rootstocks, FIG. 63. The century plant of the preceding figure as it appeared nearly two months later The leaves have given up their stored food to the flowers and flower stalk and are now withered and valueless. Photograph by G. D. Fuller 78 PRACTICAL BOTANY tubers, or bulbs, before the trees under which they grow are in full leaf, so as to shut out the abundant light necessary for photosynthesis. Fleshy leaves often contain much stored food, as in the familiar century plant (Figs. 62 and 63). This receives its name from the commonly received idea that it must store food for a century before it can blossom. In hot climates, however, such as that of Arizona, near Tucson, it flowers at the age of fifteen years or but little more. By the end of the flowering season the leaves have lost more than 90 per cent of their weight, which has been expended in producing the immense flowering shoot. This may reach a height of over 33 feet and a weight of some 500 pounds. Its average growth in height during the month of most rapid elongation has been found to be about five and one half inches a day. Not only the plant food, but also nearly all of the water for this rapid growth is furnished by the leaves. 70. Food for reserve stores brought from elsewhere. In all plants of high organization the reserve food is carried from the cells in which it was manufactured into other cells. In plants with fleshy leaves, like the houseleek, the century plant, the common purslane, and many others, the greater part of the stored starch and other nutritive materials has only been carried from the outer portions of the leaf, where photosyn- thesis and other manufacturing processes go on, into the leaf interior. The distance traversed may be only a small fraction of an inch. But in case much of the food is stored in under- ground parts of the plant it may have been carried for long distances, in large trees even much more than a hundred feet. 71. Form in which plant food is carried. As is suggested in Sect. 17, the first visible product of photosynthesis in most plants is starch. This is deposited in or about the substance of the chloroplasts, during their exposure to daylight, in the form of very minute grains. In the course of the night these disappear, so that testing a leaf with iodine 1 shortly before 1 This turns starch grains blue or almost black. STORAGE IN STEMS AND LEAVES 79 daylight usually gives no result. However, in case the leaf is cut off from the stem before nightfall, it responds readily to the iodine test for starch in the morning. This, of course, shows that the starch made during the day had no outlet and there- fore remained in the leaf cells where it was formed. Very generally starch carried away from any part of the plant body to another part is first changed to sugar and travels in the form of a very weak solution of sugar in water. On its arrival at the storage region (as in the case of the potato plant at the tuber) the dissolved sugar is re- converted into starch by the action of minute colorless corpuscles of proto- plasm known as leucoplasts. The starch grains deposited for storage (Fig. 64) are many times larger and show a far more definite structure than those formed in the chloroplasts during photosynthesis. 72. How plant food is carried; diffusion. If a little molasses is poured into a straight-sided jar and water is carefully added, a disk of porous paper being first laid on the surface of the molasses to prevent instantaneous mixing, the water will for a considerable time appear clear and colorless. Only after some hours will the molasses rise and mingle much with the water, or the latter perceptibly thin the molasses. This process by which two liquids in contact become mixed by the interchange of inconceivably minute portions (molecules) of both liquids is called diffusion. The interchange of diffusi- ble liquids through a membrane without visible pores, such as an ordinary cell wall, is called osmosis. Ordinarily in osmosis the stronger flow is from the less dense to the denser liquid. In the case of the starch-loaded leaf (Sect. 71) it is evident that, as fast as the starch grains temporarily deposited in the chloroplasts are changed into sugar, some of the sugar FIG. 64. Starch from root- stock of Canna. Magnified 300 diameters 80 PEACTICAL BOTANY in the denser cell sap thus produced will pass on to the more watery sap of adjacent cells. From these cells in turn por- tions of sugar will pass on to other more distant cells. In a similar way, when a potato tuber is planted and begins to sprout, the sugar formed from the reserve starch in the potato will pass into the more watery sap contained in the sprouts. This sap is constantly losing sugar that is used as building material for the young growing stems and leaves, and its strength can be maintained only by the addition of new por- tions of sugar coming from the tuber. 1 73. Channels by which plant food is carried. Many kinds of living tissue serve as channels for the conveyance of food from one part of the plant body to another. The main route for the transportation of food in flowering plants is through special tubular cells forming the sieve tubes, so called from the perforated plates which are found at the ends or along the sides of the nearly cylindrical cells of which the tubes are built up. These sieve tubes in dicotyledons occupy a region of the stem immediately outside of the cambium, as shown at o in Fig. 29. The fact that most of the plant food prepared in the leaves is carried down through the sieve layer of the bark is well shown by the behavior of a willow cutting from which a ring of bark has been removed. If the cutting is stood with its lower end in water but with the girdled part out of water, enough constructive material will pass down through the sieve layer to send out roots from the upper edge of the ring, but few or none will appear at its lower edge. Water meantime is freely carried upward through the sap wood. In early times the process of clearing woodlands for farming purposes was made less laborious by girdling the trees, which soon died and at length fell and were burned. Would the gir- dling process be more effective if a good deal of the sapwood were removed from the ring as well as the bark ? Explain. 1 It is not possible here to go into details concerning the transportation of other kinds of plant food than starch and the sugars. That of proteins is especially difficult to trace. STORAGE IN STEMS AND LEAVES 81 FIG. 65. Prickly-pear cactus It seems certain that a good deal of the transportation of food substances inward from the sieve tubes toward the cen- ter of the stem is done by the medullary rays (Fig. 35, m). 82 PEACTICAL BOTANY 74. Stems as sources of animal food. The life of men and of many species of the lower animals is largely sustained by vegetable food obtained from the stems of plants. Cane sugar and maple sugar are respectively derived from the stem of the sugar cane and of the maple tree. The sugar maple is tapped for its sap for sugar-making in early spring. The flow of sap is most abundant during moderately warm days suc- ceeding freezing nights. A single tree usually yields from 30 to 50 or more quarts of sap, from which 3 or 4 pounds of sugar can be made. One tree has, however, been known to yield 23 pounds of sugar in a single season. Asparagus, cabbage, and a few other vegetables consist of aerial shoots. Sago is made from the starchy pith of East Indian palms and West Indian cycads. Potatoes, onions, and Jerusalem arti- chokes are well-known examples of underground stems used as food. Many familiar animals such as rabbits (more prop- erly called hares), deer, and moose live largely by brows- ing on the twigs of trees and shrubs. In pioneer times it was sometimes necessary to feed to horses cottonwood and other twigs in winter for lack of hay. Young cornstalks with the leaves (corn fodder) form an important article of horse and cattle food, and the preparation of fermented cornstalks known as ensilage is widely used. The stems of prickly-pear cactus (Fig. 65) deprived of their thorns (or of thorn less varieties of this cactus), are used as food for cattle in the semi-desert regions of the Southwest. 75. Reproduction by portions of the stem. The number of seed plants which are naturally reproduced by means of por- tions of the stem is very large, and there are many others which are artificially propagated by this means. Some of the principal varieties of reproduction by pieces of stem or special shoots for the purpose are : (1) By aerial bulblets. (2) By underground bulbs, rootstocks, tubers, and so on. (3) By offsets, stolons, and runners. (4) By broken-off branches (Sect. 60) or cuttings ("slips"). FIG. 66. Steps in the development of the yellow dogtooth violet (Erythro- nium americanum) from the seed to the seventh year The diagram for the most part explains itself. The student should note that the seed begins to germinate late in the first year, becoming a seedling early in the second year. The cotyledon of the seedling accomplishes enough food making by photosynthesis to enable the plant to form a small bulb. This is maintained with- out much increase in size throughout the third year. During the fourth, the fifth, and the sixth years the increasing size of the leaf permits the production of larger and larger bulbs, until in the seventh year enough plant food has been accumu- lated in the bulb to send up two leaves and produce a flower and fruit. The third bulb may repeat itself indefinitely, not gaining much in depth. In this case the interval between germination and flowering would be more than six years (the time indicated in the diagram). Each well-developed bulb may (in this species) form runners, rh, which bring about vegetative reproduction, the small bulb at the end of each growing into a new plant. Modified after Blodgett 84 PRACTICAL BOTANY 76. Reproduction by bulblets and by underground stems. Many plants bear small aerial bulbs or tubers on some portion of the stem and are commonly reproduced by these. Familiar examples among cultivated plants are the onion and the tiger lily. The bulblets known as " onion-sets " are for sale at every seed store, and in some parts of the country are almost exclu- sively planted by onion growers, while in other sections the seed is more generally planted. The black bulblets of the tiger lily are borne in considerable numbers along the stem, in the FIG. 67. Roots, rootstocks, and a tuber of the Jerusalem artichoke (Helianthus tuberosus) A, base of a plant with two long rootstocks, about one twelfth natural size ; B, a full-grown tuber, beginning to sprout, slightly reduced ; st, aerial stem ; r, roots ; rh, rootstocks ; I, lateral buds of tuber ; t, terminal bud of tuber. A, modified from report of Kansas Agricultural Experiment Station leaf axils, and may be found on the ground, rooting in the late autumn and the following spring. Some of our wild plants, including certain, ferns, are propagated by bulblets. Underground stems of various kinds are so common as means of reproduction that only a very few of them need be mentioned. Some of the worst weeds are those which have running root- stocks, like the couch grass or quack grass and the Canada thistle, which may be cut up by the hoe and produce a new plant from every node ; and the nut grass (Cyperus), which produces many little tubers. Among cultivated plants a great number REPRODUCTION BY STEMS AND LEAVES 85 of the earliest blooming herbaceous kinds, such as squills, hyacinths, tulips, crocuses, and snowdrops, are grown from bulbs or other forms of underground stem. The commonest of all instances of propagation by this kind of stem is that of the potato, which is never grown from seed except for the production of new varieties. As every farmer and market gar- dener knows, each potato will produce as many new plants as it has buds ("eyes"); though it is better not to cut the potato into too small pieces for propagation, or the plants will grow slowly at first. FIG. 68. Propagation of the strawberry plant by runners A, the parent plant; J5, the young plant; r, runner; 6, bract. Half natural size 77. Reproduction by offsets and similar branches. An offset is a lateral branch for vegetative reproduction, usually rather short, as seen in the cardinal flower and the houseleek. Some- times the offset ends in a leafy rosette ; in any case the branch readily takes root and begins life as a new individual. A stolon is an ordinary branch which roots at or near the tip and so forms a new plant, as is often seen in the black raspberry. A runner is a very slender stolon, leafless except near the tip, where it roots and grows into a new plant, as in the straw- berry (Fig. 68), the silverweed, and other cinquefoils. 1 1 The word runner is also used, for lack of a better term, for the slender underground stems shown in Fig. 66. 86 PRACTICAL BOTANY 78. Reproduction by detached branches. A few words were said in Sect. 60 about how some trees, such as snap willows, are reproduced by broken-off twigs, rooting like cuttings. A good many water plants, such as the common bladder- wort, produce leafy buds or branch tips (Fig. 36 2) which become detached from the parent plant. In late autumn the latter usually dies, and in the spring new individuals arise from the buds which have lain dormant all winter at the bottoms of the ponds or slow streams where they grew. Numerous woody plants, such as willows, grapevines, currant bushes, gooseberry bushes, and geraniums, and some herbaceous plants such as the hop vine and the Wan- dering Jew, are usually grown from cuttings. Many others, such as the French marigold and the garden portulaca, not usually thus grown, may be readily propagated by cut- tings. In the case of woody plants the cutting should be taken from well-matured twigs of the previous season. In order to avoid too much loss of water and consequent wilt- ing, leafy cuttings are often FIG. 69. A geranium cutting, show- , ' i ing growth of many young roots which ke pt covered for a short time, spring from a node near the cut end with a tumbler Q? feell glass* BEPBODUCTION BY STEMS AND LEAVES 87 Layering is a modification of reproduction by cuttings, and consists in bending down a living branch and covering it for part of its length with earth, so as to form a sort of artificial stolon. Some trees and shrubs, such as the apple, pear, plum, and quince, are much easier to grow by layering than by mak- ing cuttings, and they root more readily if the shoot is deeply notched or has a ring of bark removed on the buried portion. ABC FIG. 70. Propagation by budding A, a bud cut from a tree of the desired variety, with a piece of the underlying bark; B, the bud inserted in a T-shaped slit in the bark of the stock; C, the same, with the bark bound in place by strips of raffia (a fibrous material obtained from the leaves of the raffia palm) . Modified after Percival 79. Budding and grafting. The process of budding consists of detaching an uninjured bud from the stem of one plant and inserting it under the bark of the stem of another plant (Fig. 70). Peaches and cherries are familiar examples of trees commonly propagated by budding. The operation should be performed at a season when the cambium layer is active, so that the transplanted bud will at once unite with the wood of the stem into which it is set. In the case of peaches the young seedling trees grown from seeds planted the same spring are budded in June or September. Those budded late do not grow much until the next season, but then make rapid 88 PRACTICAL BOTANY progress. As the top of the seedling is cut off not far above the bud, all further growth of the shoot partakes of the quality of the bud ; and the fruit borne by the tree, when it is large enough to bear, will be of the kind characteristic of the tree from which the bud was taken. Grafting is removing a piece of stem with its buds from one plant and inserting it into a portion of stem of another living plant so that the cambium layer of each will be in contact with that of the other (Fig. 71). The plant into which the stem is inserted is called the stock, and the por- tion of shoot which is set into the stock is called the scion or graft. There are many kinds of woody plants which may readily be grafted, but the process is of practical importance mainly for the grower of apples and pears. Various plans are adopted in different fruit-growing regions. One of the commonest methods for the propagation of apples is root grafting. Seedling trees a year old are dug in the autumn and the roots grafted with one-year-old scions of desired varieties of apples, each cut to the length of about six inches. The grafted roots, wound about the joined surfaces with waxed cord, are packed in sand in a cool and not too dry cellar and left until spring. By that time the cambium layers of root and scion have united .and the roots are ready to plant. Tongue grafting is practiced either with young seedlings or with twigs of larger trees (Fig. 71) in the spring. Top grafting consists in cutting off limbs one or two inches in diameter, splitting the portion remaining attached to the tree for a short distance, and inserting at each part of the split, where it crosses the cut surface, a small scion, and then FIG. 71. Grafting At the left scion and stock are shown ready to be united; at the right they are joined and ready to cover with grafting wax. After Percival REPRODUCTION BY STEMS AND LEAVES 89 covering all exposed parts well with grafting wax. Root graft- ing has the advantage that it results in a tree with trunk and branches wholly of the desired variety of apple. Tongue grafting of small branches does not interrupt the growth of the tree and is done with very little trouble. Top grafting is mainly resorted to in order to renew old trees that are not bearing the desired variety of apple. The main object of budding and grafting is to propagate the varieties of fruit which the horticulturist desires. This cannot be done merely by growing seedling trees, since every seedling of hundreds grown from any valuable kind of apple or pear may differ from all the others of the same lot and not one of them be worth cultivating. Grafting often succeeds on plants of different species, 1 as the peach on the plum, the apple on the pear, and the pear on the quince. Sometimes it succeeds between different genera 1 of the same family, 1 as the tomato on the potato and the Spanish chestnut on the oak. Many technical details must be attended to in order to bud or graft successfully, and these are best learned from a practical horticulturist. 80. Reproduction by leaves. Not very many plants can re- produce themselves by means of their leaves. The best-known examples are begonias, which are largely propagated by cut- ting off leaves, slitting them, and then laying them on moist sand under a bell glass until buds and roots are produced at one or more points of the cut surface. A not uncommon greenhouse plant of the Live-forever family, the Bryophyllum, is still more easily propagated, as the leaflets readily produce buds and roots at the notches along their margins when placed on moist earth. 1 For the definition of the terms "species," "genus," and "family," see Chapter X- CHAPTER VI BUDS AND BRANCHES 81. Naked buds and scaly buds. When people who are not botanists speak of buds, as, for example, in referring to the signs of leaf- ing or flower- ing of fruit trees in the spring, they always mean Fi'j. 72. Twigs of black walnut with buds in winter condition Two thirds natural size the scaly winter buds or resting buds, such as are familiar on most of our hard-wood trees and shrubs (Figs. 72-86). This is, however, a narrow view of the meaning of the term. Herbs like our common gar- den annuals, such as the bean, the pea, the cucumber, and the morning-glory, are as well provided with buds in proportion to their size as are ordinary trees. In the tropical rain forest, where the tempera- ture is always high and there are violent rains almost daily, there are few scaly buds. Most of the trees in such regions have naked buds like those of the common greenhouse hydrangea (Hydrangea Hortensia) or the geraniums (^Pelargonium). Generally speaking, scaly buds occur in woody plants which grow in cold or temperate climates, where such buds are well suited to resist the sudden winter changes from heat to cold, and the reverse. Some of our common trees and shrubs have buds which are only slightly protected by scales, but these buds are usually small, and often more or less hidden under the bark, as in the syringa (Philadelphus) and the Ailanthus. 90 BUDS AND SEARCHES 91 82. Nature of the bud and its coverings. A bud is an unde- veloped shoot; or, in other words, a bud is a group of undevel- oped parts which, under favorable circumstances, will grow into some kind of stem and leaves. If it is a leaf bud, like the majority of the buds on most forest trees familiar to us, it will grow into a leafy branch or con- tinue the growth of the main stem at its tip. If it is a flower bud, it will grow into that kind of spe- cialized branch which we call a flower. If it is a mixed bud, it will grow into one or more flowers and will also develop some ordinary leaves. The scales which cover buds are often dwarfed and otherwise modified leaves or leafstalks, as is well shown in some buckeyes in which the opening buds present a series of gradations between mere scales and foliage leaves (Fig. 73). In other cases, as in oaks, beeches, lindens, and mag- nolias, the scales represent the appendages (stipules') found at the bases of many leaves. 1 Fre- quently bud scales are covered with a dense layer of hairs or down, and sometimes, as in the balm-of-Gilead poplar, they are cemented together by a resinous varnish. These coatings on the scales of materials which do not readily conduct heat in- crease their value as a protection against sudden changes in the weather during the colder months. 1 See Kerner-Oliver, Natural History of Plants, Vol. I, pp. 351-353. Henry Holt and Company, New York. FIG. 73. Dissected bud of sweet buckey e,'showing transitions from bud scales to leaves 92 PRACTICAL BOTANY \--ax 83. Position of buds. Buds are either terminal, growing from the tip of the stem ; or lateral, growing from its side (Fig. 74, lat). The plumule (Fig. 126) is the first terminal bud of the young seedling. Commonly the terminal bud is stronger than any of the lateral ones, and makes more rapid growth than they do. Lateral buds are usually axillary ; that is, they arise from the axil, or angle, formed by the leaf with the stem, as shown in Fig. 74, ax. Many plants also produce accessory buds; that is, buds a little outside of the leaf axil, which may either stand above the axillary bud, as in the butternut, or on either side of it, as in the box elder (Fig. 75). Adventitious buds are those which spring, without any definite order, from roots, stems, or leaves. These are often of great value in propagating plants by means of cuttings or layers. 84. Form of trees dependent on growth of buds. If the uppermost bud of the main stem of a tree continues year after year to be stronger than any other bud, the general form of the tree becomes roughly conical, as is well shown in the pine tree (Fig. 246), and in firs, spruces, and the European cypress. If, on the other hand, some of the branches grow in length as fast as the main trunk, the tree will be- come round-topped and spreading, like an apple tree, an elm, or most of our hard-wood trees, when they grow in open ground. Not uncommonly the terminal bud of most branches is a flower bud, as in the magnolias, or no terminal bud is devel- oped, as in the lilac. In these cases the main branches cannot FIG. 74. Twig of hick- ory in winter condition sc, scar of last year's leaf; lat, a lateral bud; I, a last year's leafstalk ; ax, a lateral bud in the axil of the leafstalk ; t, terminal bud. Reduced BUDS AND BRANCHES 93 run out from the trunk for long distances, remaining much larger than any of the branchlets, as they do in the spruces and in many pines (Fig. 329). Why can they not? Such trees are round-topped, with many forking branches. 85. Competition among buds and branches. Of all the buds yearly produced by a medium-sized tree only a small propor- tion can survive even for a year or two, and a much smaller proportion still can grow into branches. The killing-off proc- ess is mainly one of light- starvation. Looking up into the crown of a tree along a line nearly parallel to its trunk, one is able readily to see that the tree top is not a rather dense mass of leaf- covered twigs, as it appears to be when looked at from without. It is more nearly a hollow cone or (in the case of very round-topped trees) a hemisphere, like an open umbrella, the main branches answering to the ribs of the umbrella. The interior por- tion of the tree top is too much shaded for rapid growth of buds or young twigs, and parts of it are dark enough to kill them outright, since their growth depends upon the plant food which they can make by photosynthesis. Some simple counts and calculations may serve to make clearer the fact of competition and consequent death of the interior members of the tree top. On a well-grown box-elder tree, perhaps twenty-five years old, the condition of the lateral twigs springing from six-year-old portions of the smaller branches was carefully noted in March. On the branches most fully exposed to the sun, on the south side of the tree, li FIG. 75. Accessory buds of box elder (Acer Negundo). Magnified A, front view of group; B, two groups seen in profile 94 PRACTICAL BOTANY the number of lateral twigs on the six -year-old portions of the branches ranged from to 9 and averaged 3.2. 1 On the north side of the tree, and somewhat inside its circumference, only FIG. 76. Development of leaf bud of pear A, a leaf bud of pear in autumn; , a leafy shoot derived from A, as seen in the middle of the following summer, with flower bud at tip ; C, the fruit spur (5) in autumn, after the falling of the leaves. After Percival FIG. 77. Fruit bud of pear (same as C of Fig. 76), showing its development A, opening in spring ; B, later, developing flowers and leaves ; C, later still ; only one flower has produced a fruit, the rest having fallen off. Below it, is a lateral bud which will continue the spur next year. After Percival 1 Average of ten counts. BUDS AND BKANCHES 95 one branch out of ten had any live twigs. The sunlighted branches, then, had 32 times as many twigs on the portions counted as the shaded ones did. A similar study of a large thorn bush (^Cratcegus) gave for the ten sunlighted branches 74 live twigs and for the shaded ones only 2, or 37 times as many for the sunny side. 1 A study of the relative amount of growth of the tips of branches during the year preceding the observations showed that those on the sunny side of the thorn grew 21 times as fast as those on the shady side. 2 86. Definite and indefinite annual growth. In such trees as the hickories, walnuts, butternuts, elms, poplars, and so on (Figs. 72, 74, 82), the branches usually produce vigorous, well-matured buds at their tips ; that is, they form definite shoots, and each terminal bud develops promptly in the spring. But some trees, like the honey locust, and such shrubs as sumachs, roses, raspberries, and blackberries, form indefinite shoots, which grow until their tips are killed by the frost. Trees of this sort necessarily have a top much broken up into minor branches. Why? 87. Fruit spurs. A fruit spur is a short fruit-bearing twig borne on the side of a branch (Figs. 76 and 77). Apple, pear, plum, and cherry trees afford capital examples of the production of fruit spurs. At the tip of the spur a flower bud (or a mixed bud) is borne, and this usually develops into a cluster of flowers, one or more of which may mature into fruit. In the apple and pear (Fig. 77), though the flower bud contains a good many blossoms, only one fruit is generally produced from each bud. In cherries a single bud produces a cluster of fruits. Why ? If the terminal bud of the spur contained leaves as well as flowers, a leaf bud is likely to grow in the axil of one of the leaves and thus provide for the growth of the spur during another year. This process may go on for a good many years. 1 Comparing three-year-old portions of branches. 2 The illumination in the shade (measured by "solio" photographic printing paper) was, for the box elder, about one twentieth and for the thorn about one eightieth that of the sunny side at noon in early July. 96 PRACTICAL BOTANY Evidently when the spur produces a terminal bud contain- ing flowers it cannot grow straight ahead but must turn aside FIG. 79. Cross section of a poplar bud sc, bud scales ; I, leaves ; st, stipules. Magnified 15 diameters. After Strasburger FIG. 78. A lengthwise section of bud of thorn tree (Cratcegus) br, brown outer bud scales ; o, pale bud scale ; t, innermost rudimentary leaves ; gr, growing point at apex of twig, consisting of cells in a condition to sub-divide and multiply rapidly at the beginning of the growing season. Somewhat magnified slightly. Since a large part of the plant food carried into the spur is used in produc- ing the flowers and fruit, it is clear that a fruit spur cannot grow as rapidly as an ordinary twig. A little study of an old fruit spur will show that of the .scars left by the flower buds FIG. 80. American elm, March 11 The large buds are flower buds, the smaller, more numerous ones, leaf buds. Reduced FIG. 81. American elm, April 3 flower buds seen in Fig. 80 are fully opened. Reduced 97 98 PRACTICAL BOTANY some are much larger than others. The large scars mark seasons when the fruit matured, and much smaller ones show that it dropped before it was full grown. Do fruits generally mature on any given fruit spur two years in succession ? l 88. Structure of leaf buds. Scaly win- ter leaf buds consist, as shown in Figs. 78 FIG. 82. Twig of cotton- wood with buds in winter condition b.sc, bud-scale scars. Two thirds natural size J FIG. 83. Cottonwood twigs, April 15 The flower buds (developing into catkins) are fully open, but the leaf buds are still closed. Reduced and 79, of (a) one or more outer layers of scales ; (>) rudimen- tary leaves ; (e) a central axis, at the tip of which is the growing point (Fig. 36), a region of cells capable of rapid sub-division, by means of which the elongation of the shoot is produced. 1 See Bailey, Lessons with Plants, Part I. The Macmillan Company, New York. BUDS AND BRANCHES 99 The rudimentary leaves are stowed in the bud in a Avonder- fully compact manner. There are several plans of arrange- ment, all of which have received technical names. The mode FIG. 84. Cottonwood fruits, April 28 , Reduced of arrangement is best shown in a cross section of the bud like that represented in Fig. 79. In mixed buds, as a rule, the flowers are inclosed by the leaves and usually develop earlier than the leaves (Fig. 83). 89. Opening of buds. Winter buds are not absolutely inac- tive during the colder months. Often a gradual increase in the size of the bud can be noted for many weeks before it 100 PEACTICAL BOTANY gives any other external sign of getting ready to open. This swelling is caused by the growth and development of the leaves or other contents of the bud. When the begins to open, the scales spread apart contents to emerge; sometimes they off. It is this time when the flowers to open that is a particularly the fruit grower. Peaches, for to blossom before the last season are over, and the FIG. 85. Rapidly grown twigs of horse- chestnut in winter condition b.sc, bud-scale scars ; ii, i%, i s , internodes ; I, lateral buds ; t, terminal buds ; sc, leaf scars. The portion i^-i^ and the large terminal bud grew during the preceding spring and summer. The opposite lateral twigs are of the same age as the portion ii-i s . One third natural size the coldest month is often March or April, after the young olive leaves are fairly well grown and are not easily injured by cold. bud actually and allow the promptly fall are beginning anxious one for example, often begin freezing nights of the entire crop may often be cut off by a single very cold night. For this reason peach- growing in the North is safest in regions, like the east shore of Lake Michigan, where the spring is usually rather late in coming. A curious instance of the importance of the sea- son at which frosts occur is found in European olive culture. In the Crimea, on the north shore of the Black Sea, the temperature during most years sinks a good deal lower than it does in southern France. Yet in Languedoc the olive culture fails, while in the southern Crimea it succeeds, because in the former region severe frosts occur in January, just when the olive buds are opening, while in the latter region BUDS AND BRANCHES 90. The record borne by the twig. In most cases the twig bears upon its surface and in its rings of wood a fairly com- plete record of the most important events of its Me. Some of the principal markings on the surface of a twig which enable us to make out its history are : (a) bud-scale scars (from leaf buds) ; (5) fruit scars ; (c>) leaf scars. Other mark- ings are found which tell less of the life history of the twig than those just enumer- ated, but which should also be considered, namely, (cT) lenticels. The bud-scale scars, as the name implies, are the markings (Figs. 82 and 85, b.sc) left by the falling of the scales when the bud opened. Plants like geraniums, with naked buds, do not show such scars. As the twig or branch in most cases is prolonged by the growth, spring after spring, of its terminal bud, each ring of scars marks the beginning of a new season's growth. In many trees it is easy to determine the age of twigs or branches by counting the number of such rings (Fig. 86). The distance be- tween the rings of scars depends upon the rapidity of growth of the shoot in length, varying all the way from a fraction of an inch to ten or more feet per year. If a twig were cut across smoothly, just above and just below a ring of bud-scale scars, would the number of rings of wood in the two sections be the same ? Why, or why not ? 91. The record; fruit scars. Fruit scars of the same species are often quite unequal in size, the smaller ones marking the positions of unsuccessful fruits, and the larger ones of fruits which grew to maturity. Sometimes in mixed buds the young FIG. 86. A slowly grown twig of horse- chestnut in winter condition d, dormant buds ; fs, flower-cluster scar. The internodes are numbered in succes- sion (beginning at the bottom) with the respective years dur- ing which they were formed. One third natural size 102 ^PRACTICAL BOTANY FIG. 87. Leaf scar of horse- chestnut fv, scars marking position of fibro- vascular bundles ; len, lenticels. Twice natural size flowers may be destroyed by frost as the bud opens, and in that case no fruit scar will be left at the end of the season, the bud developing much like an ordinary leaf bud. The only way in which one can become thoroughly familiar with the course of development of shoots, flowers, and fruits from buds is to mark some buds like that shown at A in Fig. 76. This may be done by tying a bit of twine loosely above each bud ; its history is then to be fol- lowed for at least a year and recorded by means of frequent drawings. 92. The record; leaf scars. A leaf scar is the place which was occupied by the base of the leafstalk while it remained attached to the shoot. Some of the things which can be learned from the study of leaf scars are the number, position, and arrangement of leaves on the shoot for several years back, the relative sizes of the leaves, and the mode of bud-bearing of the spe- cies studied, i.e. whether there were accessory buds, or the buds were all axillary (Figs. 75 and 85). On careful examination of any large leaf scar, as that of ailanthus, horse- chestnut (Fig. 87), coffee bean, it is seen to be dotted with a considerable number of minute projections, fv. These mark the course of the fibro- vascular bundles from the leaf into the stem. In leaves of dicotyledons there are usually about as many such dots on the scar as there were principal veins in the leaf. Why ? B FIG . 88. Lenticels, wild black cherry A, soon after the destruction of the stomata, to which the len- ticels succeed; B, at end of first season's growth. One and one-half times natural size BUDS AND BRANCHES 103 93. Lenticels. On the general surface of the bark of many kinds of twigs and young branches for example, of birch, cherry, elder, and sumach there are found many dots, or markings with a rough surface, known as lenticels. These are nearly circular on the younger twigs, but on branches of moderate size they become lengthened at right angles to the length of the branch. In many kinds of birch and most FIG. 89. Lenticels, wild black cherry From a tree fifteen or twenty years old. One and one-half times natural size cherries the lenticels finally become narrowly oblong or lens- shaped (Fig. 89). This is due to the fact that as the branch increases in diameter the lenticel is drawn out by the trans- verse expansion of the bark. Lenticels originate as stomata (Sect. 14) in the epidermis of the young shoot. On growing older the interior of the lenticel becomes filled with a spongy mass of thin-walled cells. Air is admitted into the interior of the stem and gases can pass out through the lenticels far more freely than through other parts of the bark. CHAPTER VII FLOWERS 94. What is a flower ? A little has been said in Chapter II about the structure and work of the flower, but it will be necessary in the present chapter to take up these matters somewhat more Corolla /\ ^ m detail. First may come the question as to what a flower really is ; that is to say, to what other organs of a plant the parts of a flower cor- respond. Put in more technical language, this question would be, What is the morphology of the flower ? A flower is a specialized and highly modified branch or shoot for reproduction of the plant. If this is true, then the sepals or divisions of the calyx, petals or divisions of the corolla, stamens, and pistils (Fig. 90) must represent leaves. It would take too much space to present here the evidence of the branch-like nature of the flower. Much of this evidence rests upon the study of the lower plants, and especially on the investigation of the steps by which the higher kinds of plants have in the course of ages been developed from these. 104 ^Stamen ^Pistil FIG. 90. The floral organs of alpine azalea (Loiseleuria) A good example of a flower in which the floral organs do^jot all spring separately from a knoh-like receptacle. Here the calyx is very slightly and the corolla decidedly bell-shaped. The stamens are distinct from each other, but the pistil is single and represents several united carpels. A, an exterior view ; B, a lengthwise section of the flower. After H. Miiller FLOWERS 105 95. The arrangement of the organs of the flower. Many of the most familiar flowers have the four sets of organs shown in Figs. 90 and 92. Sometimes there are intermediate forms, B C D E F FIG. 91. Transitions between petals and stamens in the yellow pond lily A, external view of flower ; J5, a sepal ; C, a petal ; D, E, transitional forms ; F, a stamen transitional between the parts of one set and those of another, a fact easily understood if all the floral organs represent leaves. The organs are generally arranged in cycles or whorls, that is, in circular fashion around the axis, which is known as the receptacle. 1 Often (but not always) the parts of each FIG. 92. Flower of stonecrop A typical example of the kind of flower in which the members of all four sets of floral organs (sepals, petals, stamens, and carpels) spring separately from a knob- like receptacle. A, entire flower ; />, vertical section. Bothmagnified. After Decaisne set stand opposite the spaces between the parts of the adjoin- ing sets; e.g. the petals opposite the spaces between sepals, stamens opposite the spaces between petals, and so on. 1 In the lowest seed plants, the gymnosperms (pines, spruces, cedars, and so on), the parts of the flower are arranged in a spiral fashion. So, too, are some of the floral organs in the arrowhead (Sagittaria), the pond lily, and the buttercup. 106 PRACTICAL BOTANY FIG. 93. Apetalous flower of buckwheat (Fagopyrum esculentum) A, flower ; B, section of flower. Both somewhat magnified. After Marchand Frequently the arrangement of the floral organs differs from that just described by reason of the absence of one or more sets of organs or from the multi- plication of the whorls. In the buckwheat, for example (Fig. 93), only one whorl surrounds the stamens and pistil. In such cases it is usual to assume that the missing flower leaves are the petals, and the flower is said to be apetalous (without petals). Sometimes neither sepals nor petals are found (Fig. 94). On the other hand, many flowers have both calyx and corolla, with the number of petals equal to that of the sepals, but with indefi- nitely numerous stamens, as in buttercups. 96. Unisexual flowers. Among many families of plants the flowers do not contain both stamens and pistils. One kind of flower has stamens only, and is called a staminate flower, while the other A kind has pistils only, and is called & pistillate flower (Figs. 94 and 96). Such flowers are said to be unisexual or diclinous. D FIG. 94. Dioecious flowers of white willow (Salix alba) A, staminate catkin, natural size ; B, pistillate catkin, natural size; C, a staminate flower, magnified ; D, a pistillate flower, magnified. After Cosson and De Saint-Pierre FLOWEBS 107 Sometimes, as in corn and cucumbers, one plant bears both staminate and pistillate flowers. Such plants are said to be monoecious (meaning "of one household"). Many plants, such FIG. 95. Catkins of willow Pistillate catkins at the left ; staminate at the right. Slightly reduced as willows and poplars, bear the staminate and the pistillate flowers on different individuals. Such plants are said to be dioecious (meaning "of two households"). 108 PRACTICAL BOTANY, It is often a matter of much practical importance to recognize the partially or completely dioecious character of cultivated plants, or, at any rate, the fact that many or all of the individ- uals of a species or variety produce no good pollen. This is well known to be true of strawberries, and so staminate varieties must be planted among those which produce little or no pollen. 97. Symmetry of the flower. The calyx and corolla of most flowers of the higher seed plants show some kind of symmetry or orderly arrangement of the parts ; that is, the divisions of the calyx or corolla either radiate FIG. 96. Begonia flowers, monoecious A: a, staminate flower; 6, pistillate flower. B, twisted stigmas, enlarged from a central axis, like the spokes of a wheel from the hub (Fig. 97, .#), or they are arranged with corresponding halves on either side of a central axis (Fig. 98,^). Flowers on the former plan are said to have radial symmetry or to be actinomorphic (ray- shaped), and those on the latter plan are said to have bilateral symmetry or to be zygomorphic (yoke-shaped). It is considered that the zygomorphic type of flower is in a general way more specialized and of a higher type than the actinomorphic one. 1 98. The receptacle. 2 The parts of the flower are borne by the more or less enlarged extremity of the flower stalk, which is 1 For illustrations consult any good modern flora, e.g. Gray's Manual of Botany, seventh edition. 2 To THE TEACHER. Unless the class is to do a good deal of work in deter- mination of species of seed plants by means of a flora, most of Sects. 98-105 should be omitted. FLOWERS 109 known as the receptacle shown in Fig. 92, B. This varies much in shape in different kinds of flowers, being sometimes nearly flat-topped, as in the lotus (Nelumbo) ; usually convex, as in the buttercup, raspberry, and strawberry; sometimes very concave or even flask-shaped, as in the sweet-scented shrub and the rose. 99. The perianth. The calyx and co- rolla taken together are known as the perianth. It is con- venient to have a name which includes them both, as in many flowers, such as those of the Lily family, it is difficult or impos- sible to detect any marked distinctions between sepals and petals. In most flowers the sepals are green or greenish and the petals of some other color, ranging FIG. 97. Flowers of common asparagus A, staminate flower, with perfect stamens (s) and rudimentary pistil (rp) ; jB, pistil late flower, with fully developed pistil (p) and rudimentary stamens (rs). Such a flower is practically unisexual, but would seem to have become so by descent, with modifica- tion, from bisexual ancestors. After H. Miiller W FIG,, 98. Bilaterally symmetrical corolla of sweet pea A, side view ; B, front view dissected ; s, standard ; w, w, wings ; k, keel B from violet to red. There are, however, plenty of exceptions to this rule. What are common instances of such exceptions ? 110 PRACTICAL BOTANY The flowers of monocotyledons and of dicotyledons very commonly have separate sepals and separate petals (Fig. 92). The sepals and petals are then said to be distinct. In the more specialized and higher families, both of monocotyledons and of dicotyledons, the receptacle often bears a tubular or cup- like outgrowth, and the peri- anth is borne upon this. In such cases the sepals, the pet- als, or both, appear as if grown together into a tube, upon the free border of which are seen teeth, or lobes, which indi- cate the number of divisions of which the perianth is com- posed (Fig. 97). 1 Sympetalous corollas occur of many extraordinary forms, enabling them to aid in seed production. The only such co- rolla shown in this book is Baillon and Luerssen the fypripedmm of the Orchis family (Figs. 281 and 282). 100. Forms of the stamen; union of stamens. A common form of stamen is that shown in Fig. 100, A, consisting of an enlarged portion called the anther, borne by a slender stalk called the filament. When the filament is lacking, the sta- men is said to be sessile. Sometimes the filaments appear to be united, thus joining the stamens into one, two, or more 1 When the sepals are distinct the flower is said to be chorisepalous (sepa- rate sepals) ; when the petals are distinct, choripetalous. When the sepals or petals appear only as teeth or lobes on the margin of a tubular or cup-like outgrowth of the receptacle, the calyx is said to be synsepalous and the. corolla sympetalous (syn signifies " together "). The terms gamosepalous and gamo* petalous are also used (gamos signifies ''marriage" or "union"). FIG. 99. Diagrams to show struc- ture of an anther A, younger stage, with four chambers or locules(loc) containing pollen mother cells dividing to form pollen grains; B, an older stage in which the pollen grains (p) are fully formed and each pair of locules is uniting to form a pollen sac, which will split open and discharge along the line of dehiscence (d) . After FLOWERS 111 groups (Figs. Ill and 121). In such cases the stamens are said to be monadelphous, diadelphous, triadelphous, polyadelphous (in one, two, three, many brotherhoods). The function of the stamen is to produce pollen, a powdery or pasty substance com- posed of separate grains (Figs. 105 and 106), which is formed within four cavities in the anther (Fig. 99). The two cavities on each side generally join to form a single larger pollen sac as the anther matures. Pollen is discharged from the mature anther in various ways, as shown in Fig. 100. The special significance of some of these modes of discharge is explained in Chapter VIII. 101. The carpel. The simplest form of the organ which bears ovules or rudimentary seeds is called a carpel (from a Greek word meaning "fruit"). The most elementary kind of carpel is found in the lowest seed plants, and often consists, as in the pines and other cone-bearing trees, of a single scale, with a naked ovule borne at its base (Fig. 252). In the higher seed plants the carpel con- tains an ovule-bearing cavity (Figs. 14 and 101), in which the ovules are completely inclosed while they are maturing. 102. The pistil. The entire carpellary portion of the flower of the higher seed plants is called a pistil (Latin for pestle). 1 In flowers which have but one carpel, pistil and carpel mean 1 It would be better to call it, as some botanists do, gynceceum, but the word pistil is so much in use in descriptive botany that it seems likely to be retained for a good while, FIG. 100. Various types of anther A, iris, discharging pollen by a longitudinal slit; B, barberry, discharging pollen by uplifted valves ; C, nightshade; D, bilberry, discharging pollen through holes or pores at the top of the anther. A, B, C, after Baillon ; Z), after Kerner 112 PRACTICAL BOTANY the same thing, but in flowers with two or more carpels, each carpel is one of the units of which the pistil consists. A one- carpeled pistil is simple (Fig. 14), a several- carpeled pistil is compound (Figs. 102, A, and 104, A). The parts usually found in a pistil (Fig. 101) are the ovary, or enlarged ovule- bearing portion, and the style or stalk, on which is borne the stigma, which is usually expanded, knob-like, or ridged, and with a rough moist surface. When there is no style the stigma is said to be sessile, and the stigma is borne on the ovary. A compound pistil may consist of many separate carpels, as in the stonecrop (Fig. 92), strawberry, and buttercup. Frequently the carpels are more or less completely united (Figs. 102, A, and 295). The ovary of a com- pound pistil may be formed of the united ovaries of the carpels, or a considerable part of the ovary may consist of a cup-like or tubular growth beneath the carpels. 103. Locules of the ovary; placentas. Compound "ovaries sometimes have but one ovule-bearing cavity, but more gener- ally they consist of several separate chambers, known as loc- ules (Latin, loculi," little compartments"). They are then said to be unilocular, bi- locular, trilocular, and so on. Ovules are not borne by all parts of the interior of the ovary, but are usually produced only along cer- tain regions. The ridge, column, or ovary FIG. 101. A pistil, with the ovary cut through lengthwise stig, the stigma ABC EIG. 102. Three modes of bearing ovules A, ovary three-loculed, with the ovules borne on the axis (central placenta) formed by the united partitions ; .B, ovary one-loculed, ovules borne on the ovary wall along three placentas ; (7, ovary one-loculed, ovules borne on a. free central placenta. After Behrens FLO WEES 113 other ovule-bearing portion of the ovary is called a placenta. Some common types are shown in Fig. 102. 104. Superior, half-inferior, and inferior ovaries. The posi- tion of the ovary with reference to the other whorls of the flower is a matter of great importance in the classification of plants and is described by the use of appropriate names. When the pistil is borne nearer FIG. 103. Part of a flower cluster of evening primrose br, bracts; ca, calyx; co, corolla; ov, ovary; p, pod; t, tube of perianth, appearing as if it sprung from the tip of the ovary. Slightly reduced the extremity of the receptacle than any of the other whorls the ovary is said to be superior (Fig. 93). When, however, the end of the floral axis is expanded in a more or less cup- shaped manner, so that the stamens (and the divisions of the perianth) seem to spring from around the ovary, the latter is said to be half-inferior. When the concave floral axis, 114 PRACTICAL BOTANY on the margin of which the stamens are borne, appears to be grown fast to the ovary, the latter is said to be inferior^ (Fig. 103). 105. Floral diagrams. Lengthwise sections through the flower greatly help the student to understand its structure. But still more is to be learned from a suitable cross section. Diagrams like those in Fig. 104 are constantly used in flower descriptions to show the relations of the floral organs. Such a diagram is not simply a sketch of the cut surfaces made by BCD FIG. 104. Floral diagrams J, Lily family ; B, Heath family ; C, Madder family ; D, Composite family. The dot above the diagram indicates the position of the stem or axis which bears the flowers. The sepals are distinguished from the petals by being represented with midribs. In B the alternate stamens are printed lighter, since some flowers of this family have five and some ten stamens. After Sachs dividing the flower crosswise near its center; it is rather a representation of what would be shown if all the whorls of the flower were brought into the best position for making a characteristic section, which would pass through the middle portions of sepals and petals and through the anthers of the stamens and the ovaries of the carpels. Note that the sepals are distinguished from the petals by being represented with midribs. If any part of the flower is lacking (as in the case of antherless stamens, represented only by filaments), the position of the missing or incomplete organ may be indicated by a dot. 1 Often flowers with superior, half-inferior, and inferior ovaries are said to be respectively hypogynous, perigynous, and epigynous. CHAPTER VIII POLLINATION AND FERTILIZATION 106. Pollination. By the term pollination the conveyance of pollen to the pistil is meant. Some of the various means by which this result is secured are discussed later on in the ^ present chapter. In whatever way fl% i A the pollen is carried from the sta- mens to the pistil (usually by the wind, by ani- B ^ss^ JT~ > L mals, or by contact of the anthers with the stigma), FIG. 105. Types of pollen grains A, dandelion ; B, hemp ; C, gentian ; D, squash. All greatly magnified. After Kerner FIG. 106. Types of pollen grains A, evening primrose, the grains united by sticky threads; B, marsh mallow. Greatly magnified. After Kerner its lodging place in the higher seed plants is on the stigma. This generally has a rough, often moist and sticky surface. 107. The pollen grain and its germination. 1 Pollen grains are of many forms, a few of which are shown in Figs. 105 and 106. 1 The logical order of treatment would be to say all that is to be said about pollination before dealing with its result, fertilization. It is, however, more convenient to discuss the minute structure of pollen and the pistil soon after Chapter VII is completed, and then to give details of some of the modes by which pollination is secured. 116 116 PRACTICAL BOTANY Each mature grain contains a generative nucleus and a tube nucleus (g and , Fig. 107, A). After the pollen grain lodges on the stigma the inner coat of the grain becomes slightly distended by osmosis, pro- duced by contact with the moist stigmatic surface. The distention of the inner coat causes it to protrude through the outer coat and it at length develops into the wall of a pollen tube (Fig. 107). This tube has the nucleus (T) at its tip and a generative cell (#) somewhere within the tube. Finally the genera- tive cell divides in- to two male nuclei, these develop into male cells (Fig. 10 7, Z?) , and the tube nu- cleus disappears. 108. Course of the pollen tube: fertilization. The pollen tube makes its way from the stigma to the ovary either through a canal or passage (Fig. 108), or by directly trav- ersing the cellular tis- sue of the style, upon which it acts so as to eat its way along by means FIG. 107. Germination of the pollen grain of a dicotyledon J, an early stage in the germination ; 7?, later stage, with the tube rather fully developed ; <7, generative cell ; t, tube nucleus ; Sj, s 2 , male cells formed from the generative cell. It is ap- parent that when the growth of the tube is far advanced the tube nucleus (t) almost disappears. Much magnified. After Bonnier and Sablon of ferments (Sect. 36) secreted by the tube. The tube may require a day or more to reach the ovule. Food materials from the style are dissolved by the enzymes and used in promoting the POLLINATION AND FERTILIZATION 117 growth of the pollen tube. 1 When the tip of the tube reaches the ovary it usually penetrates to the interior of an ovule by FIG. 108. Pollen grains produc- ing tubes, on stigma of a lily. Much magnified <7, pollen grains ; t, pollen tubes ; p, papillae of stigma ; c, canal or passage running toward ovary means of the little opening (micropyle) at one end of the ovule (Fig. 109). 2 One of the male cells now unites with FIG. 109. Diagram to illustrate course of the pollen tube during fertilization p, pollen grains ; t, pollen tube ; n, nucel- lus, or body of the ovule ; a, antipodal cells of embryo sac ; en, endosperm nu- cleus of embryo sac ; egg, the egg ap- paratus, consisting of the egg cell and two cooperating cells ; m, the mi?ropyle, or small opening through which, in most ordinary flowering plants, the pollen tube makes its way to the egg at the tip of the embryo sac the egg nucleus of the ovule. The other male cell in many cases unites with the cen- tral nucleus of the embryo sac to form the endosperm nucleus 1 See Green, Vegetable Physiology, chap. xxvi. P. Blakiston's Son & Co., Philadelphia. 2 In some plants the tube makes its way directly through the tissue of the ovule. 118 PKACTICAL BOTANY (Fig. 265). The result of fertilization is to cause the egg of the ovule to develop into an embryo. One of the first steps of embryo formation is shown in Fig. 267. The fertilization of the egg within the ovule may result from the proper placing of a single pollen grain, but the result is more certain if there are several grains. 109. Advantages of reproduction by seed. As has already been shown (Sects. 33 and 75-80), reproduction may readily be accomplished by buds produced on roots, stems, or leaves, vegetative reproduction. This method is much quicker than that by the agency of seed, as is well shown in the case of the potato. It would seem that sexual reproduction, repro- duction by means of seed, a more complicated process, would hardly have originated unless on the whole it were of advan- tage to plants. 1 It is evidently desirable for the continuation of the various kinds of plants to have such a comparatively portable, heat-, cold-, and drought-resisting structure as the seed to disseminate plants over large areas and to maintain plant life under unfavorable conditions. But some botanists have been led to think also that sexual reproduction is of distinct advantage to plants by giving them greater vigor than is secured by long-continued vegetative reproduction, as in the case of potatoes grown for years by planting the tubers. It is also of advantage to the plant to reproduce by means of seed, because this secures variations in the offspring which may result in greater fitness to meet the conditions of its existence (Chapter XXIII). 110. Ecology. Plant ecology (from two Greek words meaning "house" and "discourse") is the subdivision of botany which discusses the relations of the plant to its surroundings. Defin- ing the subject more in detail, it may be said that ecological botany treats of the effects upon plants of the various forces and forms of energy, such as gravity, heat, light, electricity, currents of air and water, as well as of the effects of chemi- cal elements and compounds. It also comprises the study of 1 For a brief account of the beginnings of sex in plants see Chapter XIII. POLLINATION AND FERTILIZATION 119 the social relations between plants and other injurious or help- ful plants and animals. 1 The ecology of flowers is largely concerned with the ways in which pollination is brought about. 2 This subject is of suffi- cient importance to have accumulated an extensive literature, the principal treatise upon it being Knuth's "Bliithenbiologie," em- bracing nearly three thousand pages. There is also an excellent English translation of this remarkable book. 3 111. Pollination and floral characteristics. Some of the most obvious divisions of flowers into everyday groups, such as are made by children and other unscientific people, are those into scented and scentless, showy and inconspicuous kinds. Another less obvious but important distinction is based on the presence or absence of the sweet liquid (com- monly called honey, but more properly known as nectar) so familiar at the tips of colum- bine spurs and in clover and honeysuckle blossoms. Such characteristics as those just mentioned have much to do with the way in which flowers have their pollen transferred from anthers to stigma. Flowers with feathery stigmas (Fig. 110) and dry, dust-like pollen are usually polli- nated by the wind. Flowers with stigmas which, before they wither, curve so as to bring the anthers into contact with the stigma (Fig. Ill) are usually self-pollinated. 1 A great deal of what was said about the behavior of roots, stems, and leaves in Chapters III- VI is to be classed as plant ecology, though it was not given a separate name in those chapters. 2 See Kerner-Oliver, Natural History of Plants, Vol. II. Henry Holt and Company, New York. 8 Knuth-Davis, Handbook of Flower Pollination. Clarendon Press, Oxford. FIG. 110. Pistil of timothy with feath- ery stigmas sti, stigmas. Mag- nified about twenty times 120 PEACTICAL BOTANY Flowers of any other color than green, or which are fragrant, have nectar, or show marked deviations from radial sym- metry (Figs. 98 and 281), are generally more or less wholly dependent upon animals (commonly insects of some kind) for pollination. 1 112. Wind-pollinated flowers. The number of plants which depend upon the transference of pollen by the wind is very great, embracing as it does large families, such as that of the cone-bearing trees (Pine family), the grasses, and the sedges. It is easy to see that pollen-carrying by the wind must be a very wasteful process, since only now and then a pollen grain is likely to alight on a stigma of the species of plant which produced it. Accordingly, flowers which have their pol- len carried by the wind yield it in enormous quantities. It is estimated that a medium-sized plant of Indian corn produces about 50,000,000 pollen grains ; a pine tree must produce an unimaginably great number. The stigmas of wind-pollinated flowers which catch the dust-like flying pollen are brush-like, as in the hazels ; feathery, as in most grasses (Fig. 110); or pro- longed and thread-like, as in Indian corn (Fig. 336). Wind- pollinated flowers frequently appear before the leaves of the plant which bears them. What advantage is there in this ? 113. Self-pollinated flowers. As a rule, inconspicuous flowers with moist, sticky pollen are wholly self -pollinated or can pol- linate their own stigmas when pollen from another flower is not supplied to them. Familiar examples of such flowers are pigweeds, 2 knotgrass, 3 the common chickweed, 4 the round- leaved mallow 5 (Fig. Ill), the low cudweed, 6 and the com- mon groundsel. 7 It is not infrequently the case that flowers^ when they first mature,, have the anthers and the stigma far enough apart to make it impossible for pollen to lodge upon 1 See Bergen and Davis, Laboratory and Field Manual of Botany, Sect. 149. Ginn and Company, Boston. 2 Chenopodium, various species. 6 Malva rotundifolia. 8 Polygonum amculare. 6 Gnaphalium uliginosum. * Stellaria media. 7 Senecio vulgaris. POLLINATION AND FERTILIZATION 121 the stigma as long as the flower remains undisturbed ; but at a later period in the development of the organs, anthers and stigmas may grow into contact with each other and self-polli- nation be secured (Fig. 111). It is a remarkable fact that when a stigma is pollinated with pollen from the same flower or from another flower of the same plant, and also with pollen from another individual of the same kind, generally only the latter pollen takes effect in fertilizing the egg. In other words, foreign pollen is prepotent over pollen from the same individual. 1 114. Self-pollination and cross-pollination. The process of self-pollination is usually rather simple, as may have been inferred from Sect. 108. Not infrequently the be- ginner in botany may be led to wonder whether it would not be advantageous to the plant world if all flowers were bisexual and pollinated their own pistils. The matter is not, however, quite as simple as it ap- pears to be. The earliest seed plants were doubtless remotely related to our evergreen cone-bearing trees of to-day (such as pines, spruces, and cedars), and these cone-bearers have unisexual flowers (Figs. 251 and 262) and are wind-pollinated. Bisexual flowers came later. It is likely that, later still, plants with unisexual flowers have come into existence by descent, with gradual modifications, from ancestors which bore bisexual flowers. One proof of this is drawn from the fact that there are many cases of flowers which are practi- cally unisexual but show rudimentary pistils in the staminate flowers and rudimentary stamens in the pistillate ones, as in the common asparagus (Fig. 97). Occasionally the asparagus has perfect stamens and pistils in the same flower. 1 See Darwin, Cross and Self Fertilisation in the Vegetable Kingdom, chap. x. D. Appleton and Company, New York. FIG. 111. Stamens and pistils of round- leaved mallow The flower has heen open for a consider- able time, and the stigmas have curved so as to come into contact with the sta- mens and insure self- pollination. AfterH. Miiller 122 PRACTICAL BOTANY By cross-pollination is meant the process of transferring for- eign pollen to the stigma. The effect in fertilization is the same whether the pollen is carried by the wind or otherwise. 115. Advantages of cross-pollination. As already stated (Sect. 113), foreign pollen is usually more effective than the pollen from the same individual. Charles Darwin, the great English naturalist, showed by experiments continued through eleven years that in many cases the plant derives great advan- tages from cross-pollination. 1 He found that in plants the flowers of which are not especially suited to self-pollination if left to themselves, but which he pollinated thoroughly by hand, the plants grown from the seeds of cross-pollinated flowers usually much exceeded in height, weight, and fertil- ity those from self-pollinated flowers. It was found, for in- stance, that when the yellow monkey flower (Mimulus luteus) was self-pollinated to the ninth generation the plants thus produced were -ffa the height of plants which came from those self-pollinated to the eighth generation and then cross* pollinated with a plant of another stock. In fertility the two kinds (self-pollinated to the ninth generation and cross-polli- nated at the end of the eighth generation) were in the ratio T -|^. Cabbages were raised by Darwin from seeds of a third self-pollinated generation and also from those of the second self-pollinated generation crossed with a plant from a distant garden. The self -pollinated cabbages were only -ffo the weight of the cross-pollinated ones. These two examples may serve as extreme instances of the benefits of cross-pollination. In many cases less advantage is gained by it, and there is a considerable group of plants which seem to be indifferent to the source from which the pollen comes, that from the same flower answering as well as that from another individual of the same species. The practical value of a knowledge of the effects of different kinds of pollination is often very great (Chapter XXIII). 1 See Darwin, The Effects of Cross and Self Fertilisation in the Vegetable Kingdom, chaps, i and vii-ix. D. Appleton and Company, New York. For facts about flowers which do not need cross-pollination see Sects. 121 and 126. POLLINATION AND FERTILIZATION 123 -ti 116. Insects as carriers of pollen. Most flowers which re- quire or are benefited by cross-pollination and which are not wind-pollinated depend upon insects as pollen carriers. It is not an overstatement to say that, in general, flowers seem to have acquired their colors (other than green) and their odors as means of attracting the attention of insects which may serve to cross-pollinate them. Insects vary greatly in their efficiency as pollinators, the small ones with smooth sur- faces on the head, legs, and ab- domen, such as ants and many beetles, carrying little pollen, while bees, moths, and butterflies often carry considerable quan- tities. Many bees in particular are provided with a special collecting apparatus for pollen (Figs. 112 and 113). Although the portion which they carry to the hive or nest for food is of no use for pollination, much of that which is smeared over the general surface of the body serves to pollinate the stigmas of flowers which they afterwards . . , A -, , . -, .,, , . * ,, FIG. 113. Right hind visit. A good practical illustration of the leg of a bee $ acropis) importance of insect visits is afforded by Thetibiaiscover edwith the case of cucumbers grown in winter pollen of the common under glass. It is found necessary to keep loos ^ S^' hives of bees in the cucumber houses in order to insure pollination and consequent crops of cucumbers. Some idea of the number of insect visits may be gathered from the fact that in a single locality dandelion flowers have FIG. 112. Pollen-carrying apparatus of leg of honeybee A, right hind leg of a honeybee (seen from behind and within) ; B, the tibia (ti), seen from the outside, showing the collecting basket formed of stiff hairs. After H. Miiller 124 PKACTICAL BOTANY been seen to be frequented by 100 kinds of insects. 1 The sta- tistics of visitors to the flowers of yarrow, Canada thistle, and the willows are fully as remarkable. 117. Attractions offered by insect-pollinated flowers. Insects are led to visit flowers for the sake of procuring food. This is usually either pollen as in the flowers of many species of meadow rue, Clematis, Anemone, poppy, rose, Spiraea, and St- John's-wort or both pollen and nectar, as in most kinds of conspicuous flowers. Nectar is usually secreted by nectar glands, small organs which are often to be found near the base of the flower, as in buckwheat (Fig. 114). Sometimes the nectar remains on the surfaces of the glands, sometimes it trickles down into the bottom of the flower, and sometimes as in the columbine and the honeysuckle it is stored in pouches called nectaries, situated at the bases of separate petals or at the bottom of the sympetalous corolla. Honey is nectar which has been swallowed by the bee and, by partial digestion in its crop, has undergone slight chemical changes. 118. Odors of flowers as attractions to insects. It is evident from familiar facts that many insects have an acute sense of smell. The way in which flies are attracted by decaying meat or fish, and bees and wasps by a cider press at work, or by fruit-preserving operations, is a matter of common observa- tion. A single cluster of carrion-scented flowers has been known to attract carrion flies and dung beetles from a distance of hundreds of yards. Some flowers such as those of the FIG. 114. Flower of buckwheat Lengthwise section, showing nectar glands n. Five anthers are discharg- ing pollen ; the other three here shown are not quite mature. After H. Miiller 1 See Knuth-Davis, Handbook of Flower Pollination, Vol, II. Clarendon Press, Oxford. POLLINATION AND FERTILIZATION 125 \ 7 irginia creeper (Psedera), the Dutchnian's-pipe, the blueber- ries, and many others are so inconspicuous that apparently their numerous insect visitors must be attracted by an odor which is almost or quite imperceptible to us. It seems certain that the odors of flowers have been devel- oped with reference to the sense of smell in animals (usually insects), and that these odors serve as a most efficient means of insuring insect visits. It is a most interesting fact that many flowers give off their scent mainly at the time of day when the insects which polli- nate them are most active. Thus some catchflies, the petu- nias, some kinds of tobacco, and several honeysuckles have little odor by day, but are very fragrant at night when the moths which pollinate them are on the wing. On the other hand, many plants of the Pea family, which are pollinated by day-flying bees and butterflies, give off their scent mostly by day, and especially in strong sunshine. 119. Colors of flowers as attractions to insects. There has been much discussion among botanists as to how far insects are led to visit flowers by displays of color. It appears to be fairly certain that no insects can make out the forms and sizes of objects at a distance of more than six feet, and that many are unable to see clearly even two feet. 1 In spite of this, however, it seems probable that the colors of flowers are an important means of attraction for many flower-frequenting insects. 2 The commonest method of color display is that in which the color (other than green) is mainly found in the corolla, as in the flowers of the poppy, rose, sweet pea, and morning-glory. Sometimes the calyx also is bright-colored, or, as in the Hepat- ica, the Anemone, and the Clematis, the corolla is wanting and the showy calyx looks like a corolla. Not infrequently the 1 See Packard, Text-Book of Entomology. The Macmillan Company, New York. 2 See Kerner-Oliver, Natural History of Plants, Vol. II. Henry Holt and Company, New York. Also Knuth-Davis, Handbook of Flower Pollination, Vol. I ; and Andreae, Inwief ern werden Insekten durch Farbe und Duft der Blumen angezogen, Beiheft, Bot. Centralblatt, 15, 1903, pp. 427-470. 126 PRACTICAL BOTANY display is all made by an enlarged and conspicuous set of specialized leaves (bracts) which surround the flower, as in the flowering dogwood and many euphorbias (Fig. 292), or even by highly colored ordinary leaves, as in the poinsettia. 120. Degrees of specialization for insect visitors. Flowers with a spreading perianth and radial symmetry like those of the stonecrop (Fig. 92) and the live-forever, the buckwheat (Fig. 114) and the caraway (Fig. 295), buttercups, poppies, roses, and hun- dreds of other familiar kinds are open to all comers, and are frequented by many sorts of in- sects, from flies to bees. Flowers with bilateral symme- try like vio- lets, wild balsam (Fig. 119), most flowers of the Pea family (Fig. 98), mints, and many others are usually not suited to indiscriminate visitors, but only to those insects which can get at the nectar, the pollen, or both. In violets, for example, the pollen is abundant, but is concealed within the throat of the corolla, and the nectar is deep down in the spur of the corolla. Both pollen and nectar are easily reached by the tongues of bees, but not by small insects. In the snap- dragon the mouth of the corolla is firmly closed, so that small insects cannot enter it. Larger ones, such as bees, can, how- ever, readily overcome the elasticity of the hinge at the junc- tion of the lips and enter the flower (Fig. 115). There are some flowers which appear to be dependent on pollination by a single kind of insect only, and therefore are FIG. 115. Flowers of snapdragon A, with lips of corolla tightly closed ; JB, with the lips forced open by a visiting bee POLLINATION AND FERTILIZATION 127 unable to set any seeds if that species of insect is not at hand to carry their pollen. One famous example of this depend- ence of the flower on a particular insect is that of the common fig, which may bear large and juicy fruits without insect visits, but cannot produce seed that will grow without being polli- nated by a small species of wasp. Another instance is that of the yuccas (Sect. 121). 121. Pollination in yucca. The yuccas are mainly plants of desert or semi-desert regions, especially characteristic of the southwestern United States and Mexico. One species, the Adam's-needle, or Spanish dagger, is a native of the Atlan- tic and Gulf coast, and commonly cultivated. The flowers of yuccas are white or nearly so, mostly with large spreading corollas, and borne in great clusters, of one of which Fig. 116 represents only a small portion. The stamens are somewhat shorter than the carpels, with abundant sticky pollen, and the pistil consists of three carpels which are joined to form a tube, which is stigmatic on its inner surface. Pollination is impos- sible without insect aid, and this is furnished by a small moth (Pronuba). Unlike most cases of insect-pollination, that per- formed by the yucca moth is self-pollination. The flowers of yucca are fully open and in condition for pollination during only a short period. Throughout the day the female moth remains at rest within the flower, almost hid- den by the stamens (Fig. 116). At dusk she begins active work, first crawling to the anthers, on the surfaces of which the pollen generally remains in a lump after its expulsion from the pollen sacs. She collects pollen into a mass, held as shown in Fig. 117, which is sometimes three times the size of her head. She then crawls over or within the flower, with occasional sudden starts, until finally she takes a position astride of one stamen and with her head toward the stigma, as shown in the top flower of Fig. 116. Lowering the abdo- men between the stamens, she now thrusts the sharp tip of the egg-depositing apparatus (ovipositor) into the soft ovary wall and inserts an egg into an ovule. After depositing an egg, FIG. 116. Flowers of yucca visited by the moth Pronuba The work of the moth is suggested by its position in the several flowers. In the first flower (the lowest), the moth is gathering pollen ; in the second, she is polli- nating the stigma ; in the third, she is in the position of rest during the day ; in the fourth, in the position of rest when disturbed ; in the fifth, ovipositing 128 POLLINATION AND FERTILIZATION 129 FIG. 117. Head of Pronuba moth. Magnified p, mass of pollen held in posi- tion hy spinous appendages of the moth's head the moth runs to the top of the pistil, as shown in Fig. 116, uncoils the organs which hold the pollen mass, and with her tongue tlirusts the pollen vigor- ously into the stigmatic opening for several seconds. As the stigma is usually pollinated after every depo- sition of an egg, in cases where ten or a dozen eggs are introduced into a single pistil it is pollinated as many times. After the hatching of the eggs, each little grub that is pro- duced from them eats up the ovule in which it was depos- ited, leaving, however, many other ovules to mature into seeds. It then bores its way out through the capsule, drops to the earth, and makes a cocoon of silk a few inches underground. It probably does not assume the form of the adult (winged) in- sect until near the next bloom- ing time of the yuccas. The relations of the yucca moth to the plant afford a most remarkable example of cooper- ation between a plant and one of the lower animals. Without pollination by the moth, yuccas produce no seeds, while, on the other hand, without yucca capsules and their contents the larvae hatched from the eggs of the moth would starve. 1 1 See Proceedings of the American Association for the Advancement oj Science, 1880, Vol. XXIX, paper entitled " Further Notes on the Pollination FIG. 118. Pod of a tree yucca p, perforations caused by escape of larva of yucca moth. Somewhat reduced. After Thirteenth Annual Report of Missouri Botanical Garden 130 PRACTICAL BOTANY 122. Bird-pollinated and snail-pollinated flowers. Although by far the greater part of the pollination done by animals is due to insects, birds also perform this office for many flowers. Those which are most efficient in this work are the sunbirds of Asia, Africa, and other hot countries, and our own humming birds. Most bird-pollinated flowers are large and showy, many of them scarlet or deep orange in color. Among the most famil- iar of our wild flowers much visited by hum- ming birds are the wild balsam or jewelweed (Fig. 119), the trumpet creeper, and the cardinal flower ; among cultivated ones are the scarlet salvia, the gla- diolus, and the trumpet honey- suckle. 1 Snails are not so abundant in most parts of our own country as to be important agents in pollinating flowers, but in some parts of Europe they swarm in almost countless numbers on the foliage and the flowers of many species of plants, and are known to pollinate some flowers, particularly those of the Arum family, related to our jack-in-the-pulpit and dragon- root (Fig. 277). of Yucca, and on Pronuba and Prodoxus," by C. V. Riley ; also the same reprinted as a pamphlet by the Missouri Botanical Garden, 1883. See also the Thirteenth Annual Report of the Missouri Botanical Garden, 1902, paper entitled < f The Yuccese," by William Trelease. 1 Other flowers are the buckeye, horse-chestnut, canna, century plant, cotton, evening primrose, milkweed (Asclepias), oleander, painted cup, petunia, tobacco. FIG. 119. Wild balsam (Impatiens biflora) The spurred flowers are much visited by humming birds POLLINATION AND FERTILIZATION 131 123. Prevention of self-pollination, dichogamy. Of course dioecious flowers like those of the willow cannot be self-polli- nated. Monoecious ones like those of Indian corn (Figs. 335 and 336) are likely to be pollinated with pollen from another plant. As regards bisexual flowers, it is evident that there are many opportunities for self-pollination. But in all cases in which cross-pollination produces more seed or stronger plants, or both, it is clear that any- thing in the structure or mode of development of the flower FIG. 120. Dichogamous flowers of plantain (Plantago lanceolata) A, earlier stage, pistil mature, stamens not yet appearing outside the corolla ; J3, later stage, pistil withered, stamens mature. Six times natural size FIG. 121. Dichogamy in the high mallow In A the stamens are mature but the stigmas are pressed together into a club-shaped mass (hidden by the numerous stamens). InJB the anthers are withered and the stamens droop, while the stigmas have separated and are ready for pollination. After H. Mtiller which tends to secure cross-pollination is highly advantageous. One of the most effectual means of preventing self-pollination in bisexual flowers is the maturing of the stamens at a different time from the pistils, known as dichogamy. In some flowers, as in the figwort and some plantains (Fig. 120), the pistils mature first. In such cases the pollen from older flowers (in the stami- nate condition) is transferred to the stigmas of recently opened flowers (in the pistillate condition). Pollination of the plan- tain shown in Fig. 120 is due to the wind. 132 PRACTICAL BOTANY Usually, as in some mallows (Fig. 121) and in Clerodendron (Fig. 122), the stamens mature first. An insect visitor to a flower in the staminate condition becomes somewhat covered with pollen. Then flying to a flower in the pistillate condition, he is sure to leave pollen on the stigmas and thus in- sure cross-pollination. It is common to find the stamens of a flower matur- ing a few at a time, as in " nasturtium," buckwheat (Fig. 114), and many other flowers. This gives more opportunities for insects to carry away the pollen than would be possible if it all matured at once. 124. Prevention of self- pollination: dimorphism. A means of preventing self- pollination, even more ef- fective than is dichogamy, is found in the structure of flowers in which some have a long pistil and short stamens, others a short pistil and long stamens. This condition occurs in the flowers of bluets (Fig. 123), the partridge berry, the primrose, and some other common flowers. It is easy to see that the head of an insect smeared with pollen by contact with the anthers of Fig. 123, A, would just come into contact with the stigma of B, and that the insect's abdomen covered with pollen in B would just touch the stigma of A. All the flowers on an individual plant are of one kind (either long-styled or short- styled), and the pollen is of two sorts, each kind sterile on the stigma of any flower of similar form to that from which it came. FIG. 122. Dichogamous flower of Clero- dendron in two stages In A (the earlier stage) the stamens are mature, while the pistil is still undevel- oped and bent to one side ; in B (the later stage) the stamens have withered and the stigmas have separated, ready for the reception of pollen POLLINATION AND FERTILIZATION 133 125. When self-pollination is advantageous: cleistogamous :flowers. Some flowers are usually self-pollinated unless cross- pollinated by accident or by human agency. Wheat is a :notable instance of the kind, and apparently self-pollination can go on in this grain for a long period without injury to the fertility or the robustness of the offspring. 1 Experiments in raising selected varieties of tobacco seem to show that in this plant self-fertilization, for several generations at any rate, produces better results than cross-fertilization. 2 Whenever cross-pollination by the wind or by the agency of :animals is impossible, it is evident that self-pollination would be advantageous, since it is infinitely better than no pollination ;at all. Examples of the impossibility of cross-pollination are the -cases of plants which grow isolated or in localities in which the special pollinating ;animal is not found, a ' ;as American yuc- cas in European botanic gardens. Many highly suc- cessful weeds owe part of their pre- dominance to the fact that they seed well after self- pollination. Since occasional cross-fertilization appears to be sufficient to keep up the strength and fertility of many kinds of plants, it would seem to be an advantageous plan for these to unite the certainty which characterizes self-pollination with the re- newal of strength which comes from cross-pollination. Violets and many other less familiar plants unite the two methods 1 See "Wheat : Varieties, Breeding, Cultivation," Bulletin 62, University of Minn. Agr. Exp. Sta., 1899. 2 See "Tobacco Breeding," Bulletin 96, Bureau of Plant Industry, U, S. Dept. Agr., 1907. FIG. 123. Lengthwise section of dimorphous flower of bluets A, long-styled form ; J3, short-styled form ; a, anthers; s, stigmas. About three times natural size 134 PEACTICAL BOTANY by producing ordinary showy flowers and also inconspicu- ous closed or cleistogamous flowers. The latter are, in violets, borne on flower stalks close to the ground (Fig. 124), and FIG. 124. A violet, with cleistogamous flowers The objects which look like flower buds are cleistogamous flowers in various stages of development. The pods are the fruit of similar flowers and contain great numbers of seeds. The plant is represented as it appears in late July or earJy August, after the ordinary flowers have disappeared POLLINATION AND FERTILIZATION 135 usually before maturing become partially buried in the earth. The cleistogamous flowers produce many more seeds than the showy ones, but the latter insure occasional cross-pollination. 1 1 On the general subject of pollination of flowers and illustrations of special cases see : Knuth-Davis, Handbook of Flower Pollination. Clarendon Press, Oxford. Darwin, The Effects of Cross and Self Fertilisation in the Vegetable Kingdom. D. Appleton and Company, New York. Darwin, Different Forms of Flowers on Plants of the Same Species. D. Appleton and Company, New York. Darwin, The Various Contrivances by which Orchids are fertilised by Insects. D. Appleton and Company, New York. ; Kerner-Oliver, Natural History of Plants, Vol. II. Henry Holt and Com- pany, New York. Gray, Structural Botany. American Book Company, New York. | Weed, Ten New England Blossoms. Houghton Mifflin Company, Boston. CHAPTER IX \--e SEEDS AND SEEDLINGS; SEED DISTRIBUTION 126. Gross structure of seeds. The definition of the term seed has already been given (Sect. 22). The structure of seeds varies so greatly in details that in this place it will be possible to describe only a very few typical forms. 1 The most important parts of ordinary seeds are : (1) The embryo, or miniature plant. (2) The plant food stored elsewhere than in the embryo, usually known as endosperm? (3) The seed coat or coats. All of these parts are well shown in Figs. 125 and 126. The embryo differs greatly in P seeds of the various groups into which or- dinary seed plants are assembled on account FIG. 125. Length- of tn eir relationship to wise section of each other. Many em- bryos show a fairly well-defined set of or- gans, the hypocotyl, orli ledons, or seed leaves ; ] -hyp squash seed hi, hilum, or scar, marking place of attachment to the ovary ; hyp, hypo- cotyl ; p, plumule ; c, cotyledon ; e (in- nermost layer next to cotyledon), en- FIG. 126. A common bean stem ; the coty- split ope ^ soakin " h, hypocotyl, lying on one of dosperm ; t, testa. and the plumule, or the cotyledons ; g, groove in Two and one-half n ' * the other cotyledon where times natural size seed bud. the hypocotyl lay ; p, plumule 1 See also Gray, Structural Botany, chap. viii. American Book Company, New York. 2 When this reserve food is formed outside of the embryo sac it is called perisperm. 186 SEEDS AND SEEDLINGS 137 C-- 127. Classification according to number of cotyledons. The seeds of one great division of seed plants, the monocotyledons, comprising grasses, sedges, palms, lilies, and many other groups, have one cotyle- don (Fig. 127). The reserve food is, as is shown in that figure, mainly stored outside the embryo. The seeds of the other and still larger division, the dicotyledons, have two cotyle- dons (Figs. 125 and 126). The plant food in the seeds of dicotyledons is often stored in the embryo itself (Fig. 126), as in the chest- nut, hazel, beech, oak, bean, and sun- flower; or often, like that of the monocotyledon ou s onion(Fig. 127,^4), outside of the em- bryo, as in buck- wheat, four-o'clock, castor bean, honey locust, and morn- ing-glory. 128. Forms of reserve material. The study of the forms of the food stored in seeds is in many ways most important. For a time, usu- ally, the seedling plant depends for its growth largely on the reserves in the seed from which it springs. And the most concentrated vegetable food used by FIG. 127. Seed and seedlings of onion A, seed ; B-F, successive stages in development of the seedling ; c, cotyledon ; e, endosperm ; /, first true leaf ; 7i, hypocotyl ; s, slit from which /emerges; r 1? primary root; r2, secondary root. A, considerably magnified 138 PRACTICAL BOTANY man and other animals generally consists either of seeds them- selves, as in the case of the grains, nuts, beans, and peas, or of manufactured products, such as oatmeal, corn meal, flour, cornstarch, cottonseed oil, derived from seeds. The principal plant foods found in the seed are proteins of many kinds ; carbohydrates in the form of starch, sugar, or cellulose ; and fats or oils. The characteristics of these vari- ous substances can be learned only by means of careful labo- ratory work, though some of them are tolerably familiar to most people. Not infrequently the different kinds of reserve material are localized in special parts of the seed. In the grain of wheat and of corn the proteins are especially abundant in the trans- lucent flinty outer part of the endosperm, while the starch lies mainly in the interior white portion (Fig. 333). The oil of the corn grain is stored mainly in the embryo, so that kinds which have large embryos contain a high percentage of oil and those with small embryos have a low percentage (Fig. 334). Every seed must contain some protein material, since this is indispensable to the building of protoplasm, and no growth can take place without it. But it does not seem to make much difference whether the non-nitrogenous food in the seed consists mainly of starch as in rice, of oil as in Brazil nuts, or of cellulose as in coffee and date seeds. Along with much starch, many of the grains, particularly millet, contain a good deal of gum, sugar, and fat. The fact that sugar is not usually abundant in seeds may be due to the readiness with which it dissolves in water, which might lead to some of it becoming lost in the soil during germination. 129. The seed coat. The seed coat protects the embryo (and the endosperm, when present) from mechanical injuries. In order to allow germination to begin, either the general surface of the coat must, as in most seeds, be porous enough to absorb FIG. 128. Diagram of lengthwise sec- tion of a grain of wheat en, endosperm ; em, embryo. Somewhat magnified SEEDS AND SEEDLINGS 139 sc v.c-- moisture, or, in such hard-shelled seeds as the coconut, hick- ory nuts, walnuts, and butternuts, there must be a thin or soft-walled place through which water can enter. Usually the little opening in the ovule, known as the micropyle (Fig. 109, w), remains in the seed and serves to admit moisture. The coats of many seeds have wings or outgrowths of hairs which aid in their dis- persal, as already mentioned. Other modifications in the coats of seeds apparently, in some cases, serve as aids in their dispersal, and others as means of preventing the seed from being eaten by animals. 130. Conditions for germi- nation. A sound, live seed will germinate or sprout when suit- able conditions are present. The requisites for germina- tion are : per r.c~- f (1) The proper tempera- ture. (2) Enough moisture. (3) Air or oxygen. 1 The temperature most fa- FIG. 129. Lengthwise section (some- what diagrammatic) through the em- bryo end of a grain of wheat en, endosperm ; sc, scutellum, or absorb- ing portion of cotyledon; c.t, cellular tissue (containing much oil) in which the cotyledon is embedded ; v.c, vegetative cone or growing point; h, hypocotyl; r.c, rootcap ; per, periderm, or coating of grain ; /, scar to which the f uniculus or seed stalk was attached. After Warming. Magnified about 26 diameters vorable for germination varies with the kind of seed ; for any given kind there seems to be a lowest limit, a most favorable (optimum) temperature, and a highest limit. The approximate temperatures for a few species are given on the next page (in Fahrenheit degrees). 2 1 Some seeds begin to germinate without air, but soon die unless it is supplied to them. 2 See Detmer, Keimungsprocess der Samen, chap. iii. G. Fischer, Jena. 140 PEACTICAL BOTANY GERMINATION TEMPERATURES LOWEST HIGHEST MOST FAVORABLK Barley 32-41 100 4 84 Wheat . 32-41 107 6 84 Scarlet runner . . . ' > 49 115 91.4 Indian corn 49 115 91.4 Squash . . .15.19 , ..,.-= .. 6.62 Boston . .:.'. . . '..... .... .11.76 ... ., .. 6.34 Baltimore '. . '. ". \". ''''. 7M V . . 4.99 Chicago 8 / . .14.29 . . . 5.13 An estimate of the number of lives saved annually in New York and Chicago will further illustrate the benefits from the use of antitoxin. 1 Certain disastrous cases where impure antitoxin was used, resulting in infecting patients with other disease germs, are inexcusable. These cases, however, should not lead people to decline to use antitoxin. 2 Jordan, E. O., General Bacteriology, 1908. 3 Use of antitoxin begun in 1895-1896 ; drop from 12.01 (1895) to 7.62 (1896). 174 PRACTICAL BOTANY 159. Watercourses as means of distribution of bacteria of disease. As may be expected, water courses are means of dis- tribution of some kinds of bacteria. To what extent this is true for all kinds is not known, but in case of the typhoid bacteria there has been much conclusive investigation. The following illustration is one of a number that might be cited. The southern part of New Hampshire and the northern part of Massachusetts are drained by the Merrimac River. In the region thus drained are many industrial cities and towns. In 1890-1891 there occurred in this region a great epidemic of typhoid fever. The water of the Merrimac River and its trib- utaries was the means of carrying away the sewage for the entire region, and the cities of Lowell and Lawrence, which took their water supply from this river, took sewage-polluted water. The cities of Concord, Nashua, and Haverhill did not get their water from the Merrimac. The epidemic began in Lowell, and this was soon followed by a more severe epidemic in the city of Lawrence, situated downstream from Lowell. There is a small stream, Stony Brook, which flows through a suburb of Lowell and empties into the Merrimac three miles above the point at which the Lowell water supply was taken. The first cases of typhoid were along Stony Brook, and these cases polluted the water, thus in turn polluting the supply for the main part of Lowell. Furthermore, the Lowell sewers entered the Merrimac nine miles above the water intake for Lawrence, and thus polluted the water supply so that typhoid fever was well distributed throughout those parts of Lawrence where this water was used. The other cities in this same valley had very little typhoid fever, while Lowell and Lawrence suffered many deaths, reaching in twelve months (1890) 187 per 10,000 population in Lawrence and 195.4 per 10,000 population in Lowell. There are many such cases showing the effect of typhoid- polluted water. 160. Tuberculosis: the great white plague. The disease commonly known as tuberculosis is so generally distributed THE BACTERIA (SCHIZOMYCETES) 175 and so destructive that it has been called " the great white plague." Its universal importance demands that a separate paragraph be given to a brief statement concerning it. It is the most destructive disease that affects the human race, and in the United States it causes about one ninth of all deaths. It costs the United States many hundreds of thousands of dollars annually, and, if a money estimate could be placed upon the many untoward circumstances that accompany and follow tuberculosis, the sum would be appalling. The tubercle bacilli may infect almost every part of the human body. Though the lungs are the regions most fre- quently attacked, the bones and joints, the intestines, the throat, skin, and other organs often are the regions of growth of these bacilli. The growth of tubercle bacilli in the body is usually very slow, and months or years may pass before conspicuous con- sequences follow infection. Furthermore, the germs may live upon a handkerchief, in the floor of a house, in a public building, in public transportation vehicles, in the dirt of the street, etc., for a very long time, and then grow when they are introduced into the human body. Some of the lower ani- mals (cattle, hogs, poultry, etc.) are subject to tuberculosis, and while there seems to be some doubt whether it is of exactly the same kind as tuberculosis of human beings, the dangers are such that careful disposition should be made of all tuber- culous animals. The usual source of infection is through the organs of breathing, though the germs may be carried into the mouth and other organs by means of milk and other food. Since the dried or partially dried tubercle bacilli may be transported by the air, it is evident that the greatest precaution should be taken to keep the air from becoming contaminated with these germs. Furthermore, it is known that when tubercle bacilli are moist, the direct light of the sun has a destructive effect upon them, and that fresh air is likely to contain fewer tubercle bacilli than the " close " air of rooms in which many 176 PRACTICAL BOTANY people have been. Plenty of fresh air, sunshine, and whole- some food are most important factors in preventing attacks of tuberculosis, and these, together with good general vitality of the body, are one's best guaranty against this disease. On the other hand, poor food, bad air, dark rooms, and low vital- ity render the body a favorable growing place for these disease germs when once they are introduced. These predisposing factors are of tremendous importance in relation to tubercu- losis, and too much emphasis cannot be given them. The nature of the occupation and habits of men have much to do with predisposing and exposing them to tuberculosis. This was proved by an Englishman named Newsholme, in 1898, when by means of records he showed that for each 100 agri- culturists who died from tuberculosis and other respiratory diseases, there were 453 potters and earthenware workers, 407 cutters, 373 plumbers, and 335 glassmakers who died from these same diseases. At a time when so much is known about how to prevent tuberculosis it seems a needless waste of human life to allow so many people to become affected by it. 161. Prevention of disease. Bacteria are distributed into al- most every nook and corner of the earth, in soil, air, water, dust, and upon and within the bodies of plants and animals. Disease-producing bacteria are common, though less abun- dantly distributed than forms which do not cause disease. A good deal is known regarding the methods of distribution and infection of the most dangerous disease-producing forms, though our knowledge is by no means complete. Polluted water and milk have often been the means of wholesale dis- tribution of typhoid germs (Fig. 151). The house fly is one of the most dangerous agents of distribution of typhoid and probably of other disease bacteria. The atmosphere is an efficient means of carrying bacteria of tuberculosis. They must, however, be dry in order that they may be thus carried. Every possible effort should be made to remove the breed- ing places of flies (refuse from stables, exposed and decaying sewage, etc.) and to keep them out of public and private THE BACTERIA (SCHIZOMYCETES) 177 dwelling places ; to insure a pure and well-kept supply of milk and water ; to keep vegetables and other foods that are handled in public places free -from dust and flies and promiscuous fingering ; thoroughly to disinfect all known or suspected FIG. 151. A chart illustrating the number of deaths from typhoid fever before, during, and after the introduction of improved systems of sewage disposal and water supply Five prominent cities of the world are selected. The figures indicate the num- ber of deaths per each 10,000 inhabitants. Rearranged from a chart in Abbott's Hygiene of Transmissible Diseases 178 PRACTICAL BOTANY disease-bearing materials of all kinds ; l to have large quan- tities of fresh air; to have all the sunshine possible, for sun- shine is destructive of many disease germs. 2 It is of great importance also that a high standard of vigor be maintained as a means of preventing bacterial disease. Many people have had disease-producing bacteria introduced into their bodies without any serious consequences, indeed without even being conscious of danger. Their bodies were in such vigorous condition that the initial growth of bacteria was prevented. An instructive experiment relative to this point was performed by Pasteur. Ordinary domesticated fowls are not readily susceptible to anthrax. Pasteur found, how- ever, that if he kept the fowls at lower temperatures than was normal for them, they were very susceptible to anthrax and that under such circumstances it proved deadly to them. This is a common principle in hygiene. When through excessive fatigue, loss of proper sleep or nourishment, or for any other reason, bodily vigor is greatly reduced, susceptibility to disease is increased. Modern bacteriology has offered the human race the means of escape from many diseases. Ignorance, lack of care, and financial greed are often the only excuses that can be offered when certain diseases occur. If only those who are responsible for them might be attacked by these preventable diseases, the matter would not be so serious, for in that case disease and the resulting deaths would tend to eliminate those who do not act upon the knowledge of sanitation which we now 1 In Bacteria, Yeasts, and Molds in the Home, by H. W. Conn (Ginn and Company), there is an excellent popular discussion of the nature of bacteria and the effects of their growth. 2 In Germany it is unlawful for filtered water to contain more than 100 bacteria per cubic centimeter, and it should always contain less. Boston has a legal standard which requires that market milk shall not contain more than 500,000 bacteria per cubic centimeter; and Rochester, New York, and Milwaukee, Wisconsin, have legal standards of 250,000 per cubic centimeter. Some kinds of certified milk may contain less than 10,000 Jbacteria per cubic centimeter. On the other hand, in impure milk the number may run from several hundreds of thousands to several millions. THE BACTEEIA (SCHIZOMYCETES) 179 possess. This, however, is a public matter, and innocent people must now suffer from the lack of precaution of others. 1 162. Classification. The thallophytes are divided into the fission plants (schizophytes), the algae, and the fungi. The fission plants are divided into the bacteria (schizomycetes) and the blue-green algae (schizophyceae or cyanophyceae). Formerly the bacteria were included with the fungi, and the blue-green algae with the algae, but resemblances in structure and methods of reproduction are such that the two groups are now classed together as the schizophytes. The name means "splitting plants," or "fission plants," and refers to the formation of new individuals by the division of the old ones. Likewise the technical name of the bacteria, schizo- mycetes, means " splitting fungi," or " fission fungi," and that of the blue-green algae, schizophyceae, means " splitting algae," or " fission algae." The classification of the bacteria and the blue-green algae is as follows : Plant Kingdom Thallophytes Schizophytes Class I. Schizomycetes (bacteria) Class II. Schizophycese or Cyanophyceae (blue-green algse) 1 Why are some public drinking places so arranged that one must drink from running water ? Why do some states have a law prohibiting railway trains from carrying public drinking cups ? What is the nature of the water supply and care of the drinking water for your school ? CHAPTER XII THE BLUE-GREEN ALGJE (CYANOPHYCEJB) 163. Introductory. The life habits, size, and structure of the blue-green algae are such that we can obtain the best notion of the whole group by selecting for discussion a few represent- ative plants. " Representative plants " cannot fully represent this or any other group, any more than three or four selected students would adequately represent an entire school. How- ever, in an elementary textbook it is not advisable to present a large number of plants from each group. 164. Where found. The blue-green algse are found in pools of stagnant water, along shores of streams, lakes, and oceans, in places where the water contains considerable organic matter. They may appear as coatings to sticks, stones, etc., as float- ing pieces of dirty, bluish-green material, or as small masses free-floating or attached and held together in jelly-like balls. Usually they may be readily distinguished from other algae by the distinct bluish-green color. 165. Glceocapsa: structure and nutrition. In stagnant water such as is found in old pools, horse tracks in open fields, and sometimes in aquarium jars in the laboratory, the plant known as Gloeocapsa may appear as bluish-green fragments floating or adhering to the sides or bottom of whatever may contain the water in which it is growing. These fragments are made up of a great many plants, each one so small that when alone it cannot be seen without magnification. The appearance of the masses of many plants may be thus determined, but that of a single plant can be determined only by the aid of a com- pound microscope. 1 A single plant when separated from the 1 In the first studies of the single-celled algae it is often better to use a good specimen under a compound microscope as a demonstration than to 180 THE BLUE-GREEN ALGM (CYANOPHYCE^) 181 others (Fig. 152) is spherical in its general form. It has a well-defined wall, the cell wall, inside of which is the living substance of the plant, the protoplasm. Although in higher plants the protoplasm is clearly divided into different parts, cytoplasm, nucleus, and chloroplasts (Sect. 8), in Grloeo- capsa these different parts are not evident. The protoplasm of G-lceocapsa is granular, and there is a blue-green stain distrib- uted throughout it. It is only when these plants are massed together that the characteristic blue-green color is seen. In a single plant this coloring matter is present in such small quantities that when observed under a microscope the color is not easily detected. The living protoplasm builds the wall that surrounds the inner part of the cell, but the wall itself is not alive. Some of the water in which Crloeocapsa lives is absorbed by the wall, which causes the older outer parts to swell, thus producing layers of jelly-like material around the protoplasm and the inner cell wall. Also through the wall the food material is absorbed. Even with the small amount of chloro- phyll and blue pigment present in one of these plants photo- synthesis (Sect. 17) can be carried on. Since the plant lives in stagnant water, in which there is much decaying organic matter, it is not impossible that it may absorb and use directly as food some of these decaying organized foods. In times of drought these plants may become dry, although, being pro- tected by means of the heavy gelatinous covering, they dry very slowly, and when favorable conditions again come they may continue to grow. have the student attempt to find a good specimen without any notion as to what single-celled plants are. Individual studies will then be more intelligible and more successful. FIG. 152. Glceocapsa, one of the simplest of the blue- green algae. Magnified 300 times A-E, successive changes in the development of new in- dividuals from a parent cell 182 PRACTICAL BOTANY 166. Glceocapsa: reproduction. After a G-lceocapsa plant has been growing for a time it may divide into two new plants. The wall divides, completing the separation of the protoplasm ... into two cells and thus two new plants are formed (Fig. 152). The separation of the protoplasm really begins before the walls push inward, but this protoplas- mic division cannot readily be observed. The new plants, before they '/ become free from the mass of jelly inclosing them, may again re- produce themselves, so that four, eight, or even a much larger number may be united in one colony. In such cases the plants are held together so very closely that they of- ten do not assume the spherical form. Each new Gloeocapsa plant is essentially the kind that its parent was before the divi- sion occurred. In fact the parent plant by division becomes di- rectly two new indi- viduals. This method of reproduction by division or fission (splitting) is the simplest known in the plant kingdom, and is characteristic of the simplest animals as well as of the sim- plest plants. FIG. 153. Nostoc At the left (A) are several of the Nostoc balls, which appear as glistening, rounded masses (natural size). At the right (Z>), inclosed in gelatinous material, are a few chains of Nostoc plants which have been taken from one of the balls and greatly magnified. In the chains several of the enlarged heterocysts may be seen THE BLUE-GKEEN ALG^E (CYANOPHYCE^E) 183 167. Nostoc: structure and nutrition. In regions such as those mentioned as the living place of Crloeocapsa^ and also upon damp soil or floating upon standing water, there may be found the jelly-like balls of Nostoc. Instead of the rather ragged fragments of the Crloeocapsa masses, Nostoc usually is found in irregularly rounded compact balls (Fig. 153, A), which have a dark bluish-green color. The ball is a colony of plants, but when it is taken in the fingers no evidence of the existence of single plants can be obtained. Under magnification the ball is seen to be composed of granular jelly, through which are interwoven thousands of chains of cells, each of which is a Nostoc plant. Usually two kinds of cell are found in the chain, one or more larger ones called Jieterocysts (which simply means " different cells " ), and ordinary cells (Fig. 153, J5), each one resembling a G-loeocapsa plant. These ordinary cells of Nostoc manifest an evident dif- ference from those of G-loeocapsa; the jelly-like mass about Nostoc plants is not in layers about each cell, as is true in Crloeocapsa. The cells are loosely held together in chains by attachments of their walls, thus making a slightly more com- plex plant than Crloeocapsa. In nutrition, Nostoc may absorb directly through the cell walls the materials that are needed for photosynthesis, or it may, per- haps, absorb organized foods, since much food of this kind is in the water in which the plants live. Since the jelly mass is often quite large, obviously there must be absorbed through the outer part of the Nostoc ball the food needed not only for the outer- most plants but also for those that are more deeply situated. In times of drought the gelatinous nature of the Nostoc balls results in extremely slow drying, though if the drought be long- continued the whole ball may become so dry as to crumble be- tween the fingers. Even when as dry as this, not all of the plants are killed, and a large number of them proceed to grow when furnished the needed moisture. This covering of jelly and the consequent slow drying seems to be of the greatest importance in the life of both Nostoc and Crloeocapsa. 184 PRACTICAL BOTANY 168. Nostoc: reproduction. If a single Nostoc cell is sepa- rated within the mass from the chain in which it has grown, it soon divides in essentially the same way as does the Crloeo- capsa plant; but in the case of Nostoc, the new cells thus formed are likely to remain together, and will redivide in the same direction as did the cell at first, and thus form a new chain. Nostoc is not, however, usually reproduced by one cell's becoming free and behaving as just described. Divisions of the cells do occur as stated, sometimes all or nearly all of the cells of a chain dividing at the same time. This, if contin- ued, would soon produce a plant of great length, a result which does sometimes occur. Usually, however, in one or more cells of the chain the protoplasm dies and the cell wall greatly enlarges, thus producing a heterocyst. This hetero- cyst apparently weakens the connection between the adjoin- ing cells, and the chain separates at this point, the heterocyst usually adhering to one of the new chains (Fig. 153, Z?). The presence of two or more heterocysts may result in breaking the chain of cells into three or more new Nostoc chains at the same time. This Wgd of reproduction resembles that which wls seen in G-lceocapsa, in as much as the cells divide to repro- vdiice the plant. It differs in the fact that new plant chains are formed by an additional reproductive structure, the heterocyst. 169. Oscillat oria : structure and nutrition. In the same kind of regions in which Grloeocapsa and Nostoc are found, but more abundant and more widely distributed, is the plant Oscillatoria. Oscillatoria filaments grow together, sometimes forming mats of a dark green, dirty-looking growth. At times when a few plants are seen growing free from others, they present a beau- tiful clear green growth in which very little bluish coloring matter can be detected. The mats, though often slimy, are not covered by the masses of gelatinous substance that are seen in the two preceding forms. Some of the Oscillatoria plants are so large that if placed in a dish of water they may be studied in a general way without magnification. They are thread-like plants, the length of each THE BLUE-GKEEN ALG^ (CYAKOPHYCE^) 185 individual greatly exceeding its thickness. Some of them per- form a peculiar swinging or oscillating movement, from which the generic name Oscillatoria is taken. They may, however, move forward as well as sidewise. Under a compound microscope Oscillatoria is seen to con- sist of a great many cells held very closely together in a common tubular sheath (Fig. 154). If free from the sheath, one of the cells assumes the spherical form. But normally the cells are compressed so closely in the sheath that the separate walls appear as one common wall. A plant there- fore consists of many of these cells held together in a common wall. It may grow in length by having the cells divide, which they regularly do. As compared with Gloeocapsa and Nostoc, Oscillatoria contains a great deal of chlorophyll, which may be much or little obscured by blue coloring mat- ter. It lives in water, often at the outlets of sewers and drains, or upon damp surfaces, from which it absorbs the needed materials for the construction of foods. It grows vigorously, being able to thrive throughout a wide range of temperature and other climatic conditions. 170. Oscillatoria : reproduction. Division of cells in this plant does not necessarily mean reproduction of the individual, but may signify merely its growth. A single Oscillatoria cell may, if free, grow until it has reproduced a plant similar to the one from which it came. This is not, however, its usual method of reproduction. In a long specimen usually one or more cells die, thus weakening the sheath that holds the cells together. This allows the plants to break at these points, and each piece FIG. 154. Oscillatoria A, tips of several plants; B, part of one plant enlarged to show cellular structure. Both magnified, B much more than A 186 PEACTICAL BOTANY that is set free is a new plant and may continue to grow until it assumes the proportions of the old one. This is essentially the same kind of reproduction that is seen in Nostoc, except that here, instead of having a heterocyst, the dead cell does not become enlarged. Oscillatoria plants may also break at any point to produce new individuals. 171. General characteristics of the blue-green algae. In addition to the types of blue-green algae that have been dis- cussed, many other kinds are abundant. They are found in the same kinds of regions as those that have been presented in the preceding paragraphs. Members of this group have the characteristic blue-green color, with this color pretty evenly dis- tributed throughout the interior of the cells. The blue-green algae are extremely simple in structure, being one-celled plants (as G-lceocapsa), or plants made up of cells arranged in rows so as to form simple chains (as Nostoc), or filaments (as Oscil- latoria). Some of the members of the group are more complex than Oscillatoria, as Grloeotrichia and Rivularia, which are com- monly found as small, glistening, jelly-like balls attached to sticks and to the stems of other plants. They are usually found in shallow fresh-water lakes, or sometimes free-floating. The entire group consists of plants that are relatively simple in form Und structure. The cells are simple, and definitely organized chloroplasts are not present. Nuclei of the kind known in the other algee and in the higher plants have not been demonstrated in this group, although fragments that resemble the nuclei of higher plants have been found. Most of the members of the group have a jelly-like cover- ing, and in many forms this holds the plants together in colo- nies. This covering seems to be of advantage to the plants during periods of drought by regulating the rate of drying. The water or moist habitat and the simplicity of structure suggest the simple way of securing food material, namely by absorbing it directly through any part of the wall of the plant. By means of chlorophyll, members of this group may manu- facture foods through the process known as photosynthesis. THE BLUE-GREEN ALG.E (CYANOPHYCE^E) 187 New plants are established by the blue-green algae in the simplest ways that are possible. Reproduction takes place by means of fission of the single-celled forms, or by the breaking into two or more parts of the chains or filaments of the less sim- ple forms. Sometimes in certain species of Nostoc reproduction is said to occur by means of a special heavy -walled cell which, after lying quiet for a time, may grow into a new plant. The growing plant is often spoken of as the vegetative plant, and when reproduction occurs as it does in the blue- green algae, by division to produce new plants, the process is known as vegetative reproduction. Such reproduction is charac- teristic of the blue-green algae. The blue-green algae have a very wide distribution. They are found in both fresh and salt waters, in warm and cool tem- peratures, and at high and low altitudes. They thrive in water, and also upon land, provided they have a supply of moisture. Many of them are most luxuriant near the mouths of sewers, in case light and temperature conditions are favorable. In re- gions where moisture is intermittent they thrive part of the year and are dormant the rest of the time. Often they grow in such numbers as to tinge the water with green, or whatever other color the plant may have. Fresh-water lakes are often distinctly green from the growth of Rivularia, GrloBotrichia, and other forms. The Red Sea owes its hue to the abundant growth of a reddish-brown member of this group. The margins of some of the pools about geysers and lakes in the Yellowstone National Park, and shores of lakes and streams, are often so colored. 172. Classification of the Fission Plants (Schizophytes): Thallophytes Schizophytes Class I. Schizomycetes (bacteria) Illustrated by numerous type forms and various methods of living Class II. Schizophycese, or Cyanophycese (the blue-green algae) Leading genera used as illustrations, Glceocapsa, Nostoc, Oscillatoria CHAPTER XIII THE GREEN ALGJE (CHLOROPHYCEJE) AND OTHER ALGJE 173. General considerations. The green algae are found in almost all inland waters, floating freely upon the surface, ly- ing in heavy mats near or below the surface, forming masses upon the bottom, and often attached to various solid sub- stances in the water. A few are marine in habit. They are widely and abundantly distributed and may be found by any observing student. Not infrequently they are spoken of as " pond scums," " water mosses," and " seaweeds." Usually it is easy to distinguish green algae from most other algae by the fact that in members of this group the chlorophyll is not obscured by any other coloring matter. Various shades of green are presented in different plants, and indeed in the same kinds of plants at different growth periods, but the color is not readily confused with that of the other groups. 174. Pleurococcus: structure and habitat. This green alga grows in great abundance upon the partially shaded portions of trees, fences, rocks, and old buildings, and when moist it presents the appearance of a coating of green paint. Some- times it is called " green slime." It adheres so closely to the object upon which it grows that few people recognize it as a plant. It is one of the most widely distributed of all plants. When examined under suitable magnification it is seen that the green slime is composed of thousands of single-celled plants, each so small that as a separated individual it is not visible to the ordinary observer (Fig. 155). A careful meas- urement of a number of plants showed their average diameter to be about -$$$-$ of an inch (.014 mm.). In other words, if a row of these plants side by side should be arranged across 188 THE GKEEN A.LGM (CHLOEOPHYCE^E) 189 the unsharpened end of an ordinary lead pencil, approximately 500 plants would be required to complete the row. How many would be required to occupy one cubic inch ? Each plant is somewhat spherical and has a well-defined cell wall. Within this wall is the protoplasm, which is colored green by the chlorophyll. The chlorophyll is usually confined to a special part of the protoplasm, this part being called the chloroplast, which means " a body which bears chlorophyll." Often it is not possible to distin- guish the chloroplasts in Pleura- coccus^ the chlorophyll appearing to be evenly distributed throughout the plant. The nucleus is another special part of the protoplasm. It is a mass of protoplasm denser than the other portions, usually lies near the center of the cell, and is a structure of great importance in the activities of the plant. When chloroplasts are evident it is possible also to see about them a thin, almost colorless, pro- toplasmic substance, the cytoplasm. A single Pleurococcus plant, there- fore, consists of the cell wall and the protoplasm that is contained by this wall. The protoplasm may be divided into chloroplasts, cytoplasm, and nucleus. In some cases, also, there may be seen vacuoles, which are regions within the cell surrounded by cytoplasm but containing air or cell sap. 175. Pleurococcus: nutrition. The protoplasm of this plant contains chlorophyll, and if carbon dioxide and water are ob- tainable it can carry on photosynthesis. Carbon dioxide may be secured from the air. The bark, or other support upon which the plants grow, is often sufficiently moist to enable Pleurococcus to obtain water from it. Rains and heavy dew FIG. 155. Green slime (Pleuro- coccus) a, single plants showing cell wall, granular cytoplasm, and nucleus ; b, plants in process of reproduc- tion by division or fission ; c and d, further divisions sometimes re- sulting in formation of colonies of plants. Greatly enlarged 190 PRACTICAL BOTANY supply water more or less intermittently. Possibly water may be absorbed directly from a moist atmosphere. If dry bark with Pleurococcus on its surface is placed within a moist bell jar, the plants soon become bright green, thus indicating that they are at work. Heat, cold, and the extreme drought either of summer or of winter are some of the great extremes which this plant must undergo in order to live. Exposed as it is, it nevertheless is able to pass through such periods and grow luxuriantly within a short time after the return of favorable conditions. If in zero weather Pleurococcus is brought into the laboratory and moistened, within a few hours it begins to grow. 176. Pleurococcus: reproduction. Pleurococcus cells divide, thus forming new plants directly, as has been seen to occur in Grloeocapsa. This vegetative reproduction in favorable weather results in a rapid multiplication of the plants. Divisions follow one another in such a way that whole colonies, the descendants of one individual, are often found grouped together (Fig. 155). Sometimes, in near relatives of Pleurococcus that live in the water, another kind of reproduction occurs. Within the cell wall the protoplasm divides so as to form several (eight, six- teen, or thirty-two) small bodies. Each of these has a nucleus and cytoplasm which are obscured by chlorophyll, an extremely thin cell wall, and two small hair-like extensions, the cilia (sin- gular, cilium). After a time the old plant wall breaks, and these bodies, by means of the active cilia, begin to swim about in the water. Soon they become quiet, the cilia are lost or are withdrawn into the main body of the cell, and the cell begins to grow and develop into a new plant like the one that formed it. Thereafter it may reproduce itself vegetatively or by the process just described. These cells that are specially made for the work of repro- duction are called spores. In the study of other kinds of plants we shall find several kinds of spores ; and while they may differ in .the ways in which they are formed, they are alike in that all may reproduce the kinds of plants that form them. THE GREEN ALG^ (CHLOROPHYCE^) 191 Spores that have special structures by means of which they swim are called zoospores, meaning "animal spores," or "mov- ing spores." They were thus named when it was supposed that self -caused movement is a distinguishing fea- ture of animals. Plants which have swimming spores have means of more ready distribution than do those that reproduce entirely by means of fission. 177. Spirogyra: its habitat and structure. The algse commonly spoken of as "pond scums" are found in standing water, often floating upon its sur- face. One of the most abundant of these is Spirogyra. Within the water, it appears as long threads of a clear green color, at times -n FIG. 156. Spirogyra ch, the spirally arranged chloroplast; n, the nu- cleus which is supported by the bands of cyto- plasm (c?/) ; cytoplasm also appears just within the cell wall. The central cavity of the cell is usually occupied by one or more large vacuoles. At the right are two cells of one plant. At the left are parts of two plants whose cells have conjugated to form zygospores (Z). Greatly enlarged attached by one end to some support; when floating upon the sur- face of the water, it commonly appears in yellowish-green mats in which are many bubbles of gas or air. It is soft like silk, and may thus be distinguished from most other algae likely to be found in similar places. 192 PKACTICAL BOTAKY When magnified, the cells that compose Spirogyra are seen to be very large as compared with those of any alga yet stud- ied. They are joined end to end, thus forming the filamentous plant. Each cell has a cylindrical cell wall which contains one or more peculiar spirally arranged chloroplasts, each of which extends almost or quite the entire length of the cell (Fig. 156). Different species of Spirogyra may have different numbers of chloroplasts in each cell, and this is one of the ways of distinguishing the species from one another. If the chloroplast were uncoiled, it would be like a ribbon with the edges more or less indented. A layer of cytoplasm lies just within the wall, and the cytoplasmic threads run from all sides to the nucleus, which the cytoplasm surrounds. Much of the interior of the cell is occupied by one or more vacuoles. The cytoplasmic layer and the nucleus may be made more conspicuous by mounting the plants in an iodine solution, which pulls the cytoplasm away from the cell wall and also stains the nucleus and the threads which support it. 178. Spirogyra: nutrition. The supply of water for this plant is secured from the surrounding medium in which are dissolved the carbon dioxide and other inorganic materials from which foods are made. Indeed there is much water within the plant. By carefully drying, it may be demonstrated that sometimes as much as 98 per cent of Spirogyra is water. That photo- synthesis is carried on is often made evident by the oxygen bubbles that arise from the active plants. It is possible to collect the oxygen that is produced by alga) approximately, as shown in Fig. 12. A test tube is placed over the small end of a glass funnel, both being under water in order to exclude all air from them. While under water the large end of the funnel is placed over a mass of algse. The apparatus is then made secure and left in an upright position. As the plant con- tinues its work, oxygen bubbles arise and accumulate in the closed end of the tube, thus forcing out a similar volume of water. The oxygen may be tested by the ordinary tests for this gas. Because of the size and the length of this plant, and THE GREEN ALG^E (CHLOROPHYCE^E) 193 the size of its chloroplast, it can expose more chlorophyll to the light and hence do more photosynthetic work than any plant yet studied in the present chapter. When Spirogyra cells divide, the division wall is at right angles to the length of the plant. Such division results in an increase in the number of cells and usually in growth in length of the whole plant. Growth occurs so rapidly that within a few days after the plants are first seen in the spring they become so abundant that they may pollute the water in which they grow. FIG. 157. Spirogyra in process of spore formation A, conjugating cells; a and b, conjugating tubes; c, a tube from a cell which has begun to conjugate with one that is already paired ; d, a second tube from a paired cell. Such secondary tubes rarely develop. B, a and 6, tubes through which the protoplasm is passing to unite with that of the pairing cells ; c, a tube similar to c in A. Greatly enlarged 179. Spirogyra: reproduction. Plants may become broken into two or more pieces, and each piece may grow into a sepa- rate plant, thus securing vegetative reproduction. At times, however, there occurs a kind of reproduction quite different from any that we have as yet studied in the algae. The cells of two plants that lie near one another unite in pairs, this union being made by means of tubular outgrowths from the pairing cells (Fig. 157). These tubes meet between the old cell walls, their ends fuse and form a continuous passageway 194 PRACTICAL BOTANY from one cell to the other. Then the protoplasm from one cell passes through the tube and unites with that from the other cell. About this mass of protoplasm, which has now be- come greatly condensed, there forms a very heavy cell wall (Fig. 156). This heavy-walled body is a spore and may grow into a new plant. It is formed by union of cells and not by cell division, as was true in the case of the zoospores of plants related to Pleurococcus. Reproduction by cell union is sexual? and by cell division is asexual. The spore of Spirogyra is a sexual spore. Because it is formed by the union of similar cells, it is called a zygospore, which means a "yoked spore." Cells that unite to form sex spores are called gametes ; hence a zygospore is a sexual spore that is formed by the union or conjugation of similar gametes. Dozens of Spirogyra cells in two adjacent plants may con- jugate to produce zygospores. Usually the different pairs in the united filaments will be found in about the same stage of spore formation, though occasionally there will be some varia- tion. Sometimes the cells from one plant will unite with cells from more than one other plant. Also occasionally one cell may unite with the adjoining one in the same plant. Some- times the contents of cells that have not united with other cells will assume the form and characteristic coverings of the zygospore, and such spores may grow into a new plant. Zygospores are set free by the decay of the old cell walls. After a period of rest, as during drought or winter, they ger- minate and produce new Spirogyra plants. It is of obvious advantage to the plant to have a heavy-walled resting spore which will carry it through unfavorable periods. 180. Cladophora: habitat and structure. Various species of Cladophora are found attached to objects along shoals in streams, over dams, about waterfalls, sometimes in heavy floating mats along the margins of ponds, lakes, and even the oceans. It is a most widely distributed genus, and one of the few green algse ever found in salt waters. Cladophora usu- ally has one end attached to some kind of support, and is THE GKEEN ALG.E (CHLOROPHYOE^) 195 extensively branched (Fig. 158). When growing vigorously, new branches are constantly being formed at the upper ends of some of the segments. Each segment appears to be one cell, though really a good many nuclei with their ac- companying masses of cyto- plasm are contained within each wall. Such a structure is called a ccenocyte, and though this same condition is found in another plant that we shall study (Vaucheria, Sect. 183), it is not common in the plant kingdom. For our purpose we may think of each segment of Cladophora as like one cell. All of these branching segments may to- gether compose a plant of great size as compared with the smaller dimensions of a Nostoc, an Oscil- latoria, a Pleuro- coccus, or even a Spirogyra. In each seg- ment there are FIG. 158. Branching of Cladophora manv small cmo- J After Collins roplasts, crowded together so closely as to present an almost solid green color even when viewed under considerable magnification. 196 PRACTICAL BOTANY 181. Cladophora: nutrition. Cladophora is well supplied with the food materials that it needs. It grows chiefly in moving water, which is better aerated than still water. This FIG. 159. One of the filamentous algae (Ulothrix) A, the base of a plant showing the attaching or holdfast cell and a few vegetative cells ; B, a group of vegetative cells ; (7, cells in which gametes have formed ; D, two cells in which zoospores have formed, and one cell from which the zoospores have escaped; E, swimming zoospores; F, a, b, c, d, gametes uniting to form a zygospore ; G, the zygospore, after a period of rest, grows and finally produces zoospores ; H, a zoospore germinating to produce a new Ulothrix plant. All greatly enlarged. E, F, and G after Dodel-Port water also carries in solution more or less inorganic sub- stances from the soil. The holdfast usually holds the plant se- curely in this favorable environment. Furthermore, its system THE GREEN ALG.E (CHLOEOPHYCE^) 197 of branching enables it to expose much chlorophyll to the light. Its rapid and luxuriant growth is evidence that it is a successful plant. 182. Cladophora: reproduction. It is probable that Cladoph- ora reproduces itself vegetatively by continued growth of broken parts. Like Spirogyra, it does not have any regular method of bringing about vegetative reproduction. At times, however, in some of the segments, the contents divide into large numbers of small zoospores. These escape from the old wall, swim about for a time, and then become attached and grow into new Cladophora plants. This method of spore formation is much like that of the relatives of Pleurococcus, except that zoospores of Cladophora are formed in much greater numbers, by a special cell rather than by the whole plant, and under con- ditions suited to abundant and wide distribution. In Fig. 159 is shown the method of reproduction of Ulothrix, an unbranched plant which in its reproduction is quite similar to Cladophora. Plants such as Cladophora and Ulothrix have still another method of reproducing themselves. At times the cells, in- stead of forming zoospores, form bodies which are like the zoospores in form and movement, but smaller. It seems that one of these alone cannot reproduce the plant, or, if it should germinate, it produces a plant that does not live. It is not a spore, since it cannot directly reproduce the plant which formed it. Two of these bodies may unite and form a cell which is capable of reproduction. These zoospore-like bodies are gametes and unite to form a zygospore, which then pro- duces a new plant. In Cladophora and other plants ( Ulothrix, Draparnaldia, Fig. 160) that reproduce themselves as it does there are interesting suggestions as to the origin of sexual re- production among plants, namely, the origin of gametes from small and apparently weakened zoospores. By the union of these simple zoospore-like gametes there is formed the simplest kind of sex spore, the zygospore. Spirogyra forms its zygospore in somewhat the same way as does Cladophora, but the process is more complex and no relation of gametes to zoospores is shown. 198 PEACTICAL BOTANY 183. Vaucheria: habitat and structure. Vaucheria is com- monly called "green felt," a name which suggests the charac- teristic appearance presented by it as it grows upon the moist surface of the earth, in pots, on growing tables in the green- house, or upon damp shaded soil out of doors. It also grows FIG. 160. A branch of the alga, Draparnaldia After Conn in pools of water, where it may be distinguished from many other algae by its coarseness. Certain species of Cladophora are coarser than Vaucheria, but their greater length and more extensive branching will ordinarily enable one to distinguish them. If the earth upon which Vaucheria is growing is exam- ined, the plants will be found to penetrate slightly into the soil, their size enabling one to see parts of them without THE GREEN ALG^ (CHLOEOPHYCE^) 199 magnification. Plants that have been kept in a closed dish within the laboratory for a few days grow into a heavy moss- like mass and are good material for study. Under low-power magnification the whole body may be traced through its intertwining with its neighbors. It branches considerably (Fig. 161), the branches arising irreg- ularly and rebranching to a small extent. The newest branches are the greenest and most active, and as they grow forward older portions may die, thus sep- arating the branches from one another and resulting in the formation of new individuals by vegetative reproduction. No cross walls appear in the vege- tative part of the plant; hence the whole plant is a ccenocyte (Sect. 180). 184. Vaucheria: nutrition. Water may be absorbed from the earth upon which T7 . 7 . FIG. 161. Branch of a Vauchena Vaucherm grows. In case plant Of those Species that live in Considerably enlarged the water the food supply is secured as in other floating algae. The abundant chlorophyll suggests considerable ability to manufacture nutrient sub- stances, but this plant is not so well suited to secure abundant exposure to light as is Cladophora. It is to be noted that, living on the land as these plants often do, they do not have the pro- tection against extremes of light and temperature that water algae enjoy; also that in nature Vaucheria plants are found in shaded and otherwise protected places. If direct sunlight falls upon these plants for very long, they are not able to live. 200 PRACTICAL BOTANY 185. Vaucheria: reproduction. As suggested in Sect. 183, it sometimes occurs that branches are left as separated in- dividuals by the death of the older portions of the plant. This re- sults in vegetative re- production. Asexual reproduction may be started by having the end of a branch cut off by a cross wall. The part that is thus cut off proceeds to form an immense zoospore (Fig. 162, ^, 5). The wall which contains it breaks, and it slowly emerges, and, after a period of separate ex- istence in the water, it germinates and forms a new plant (Fig. 162, C). This zoospore is composed of many cells. It is therefore a com- pound zoospore, and is coenocytic. But the compound zoospore produces only one new plant. Forma- tion of zobspores may be induced in the lab- oratory by keeping Vaucheria plants in a dish of shallow water. Another kind of re- production may occur at the same time that zoospores are being formed, though it usually occurs at other times. Upon the sides of the plant FIG. 162. The formation of zoospores by Vaucheria A, a piece of a plant at the tip of which a section has been cut off to produce the zoospore (z) ; B, a zoospore which has become free from the plant which formed it, and has assumed the rounded swimming form ; O, a zoospore germinating to form a new plant. Considerably magnified FIG. 163. The sexual reproductive structures of Vaucheria (V. sessilis) o, oogonia ; A, antheridia. Note the opening in the antheridium for exit of sperms, and in the oogonia for their entrance to the large eggs. Greatly enlarged THE GREEN ALG.E (CHLOKOPHYCE.E) 201 special short branches are formed. In one species of Vaucheria (V. sessilis) two kinds of branches arise near one another (Fig. 163). One of these is short and irregularly spherical, and has a beak at its free end. This branch forms one large cell within it. The other branch is longer, somewhat coiled, and has a terminal cell that is cut off by means of a cross wall, which is much farther from the main plant than in the other branch. In the terminal segment many small cells are formed. Through a small opening in the tip of this coiled branch these cells escape, some of them entering the beak of the other branch, and one of them uniting with the large ce>H. This union forms a spore which proceeds to develop a heavjr protecting wall. After a period of rest this spore -, germinates and produces a new plant. 1 If this spore had been 111 FIG. 164. A vegetative cell of a common formed by the union of gpedes of cEdogonium similar gametes, we then Greatly enlarged should have called it a zygospore ; but it is formed by the union of gametes that are very unlike, one large gamete, the egg or oosphere, and the other a small gamete, the sperm, and the resulting spore is called an oospore, which means "egg spore." When similar gametes unite to form a zygospore, the process is called conjuga- tion, but when dissimilar gametes unite to form an oospore, the process is called fertilization. The special sex organ which produces the sperm is the antheridium, and that which pro- duces the egg is the oogonium, which means the "egg case." Vaucheria has three methods of reproduction, vegetative,, by asexual spores (zoospores), and by sexual spores (oospores). One plant may use vegetative reproduction at one period of growth, asexual spore reproduction at another, and sex spore re- production at another, but two methods are rarely used at once. 1 To THE TEACHER. No attempt is made to present the difficult and tech- cic&l questions relative to alternation of generations in the thallophytes. 202 PRACTICAL BOTANY 186. Increase in complexity of sex organs and gametes. It is to be especially noted that in other algae which we have studied reproduc- tive bodies were formed from cells which at the out- set were vegeta- tive cells. In Vau- cheria sex organs are made primarily for the work of reproduction, an interesting divi- sion of labor in the plant. In some green algae, as (Edogonium (Figs. 164 and 165), vegetative cells are thus formed into oogonia and antheridia. It is also im- portant to note that in Pleura- coccus the entire plant might divide A, holdfast cell and two vegetative cells; B, part of f f - i f a plant in which are an oogonium (o), containing egg, e V and two groups of antheridia (a), which have not yet formed sperms ; (7, part of a plant in which is an oogo- nium (o), which, by breaking away of one vegetative cell, has made a place for the sperm to enter, so that a fertilized egg or oospore has been formed, as is shown by its heavy inner wall ; D, a zoospore of (Edogonium, D redrawn from Pringsheim. All greatly enlarged FIG. 165. Reproduction in (Edogonium nodosum two new plants ; or, in relatives of Pleurococcus, the entire plant might become a spore case (spo- rangium), producing zoospores. In Cladophora, zoospores are formed, together with zoospore-like gametes, the latter uniting THE GKEEN ALG^E (CHLOKOPHYCE^E) 203 to form zygospores, which constitutes the simplest kind of sexual reproduction. In Spirogyra, zygospores are formed by the union of similar gametes, the conjugation being brought about by siphon-like tubes which unite the cells from which the gametes come. In Vaucheria the gametes are differentiated into an egg and a sperm, which, by fertilization, produce an FIG. 166. Zygnema A, two vegetative cells showing the central nucleus which lies between the parts of the dumb-bell-like chloroplast. B, conjugation to form zygospores; a, 6, c, conju- gating tubes ; z, zygospore fully formed. Both greatly enlarged, but A more than B oospore. These differentiated gametes are found in specialized sex organs made primarily for reproductive work. 187. Other green algae. 1 The green algae are more abundant than all others in inland waters, and it is not possible or de^ sirable to mention many of them in this connection. Some of the following may be collected, however, in regions in which those already discussed are found. Sphcerella, a unicellular 1 It is more important that the student should have an impression of the kinds of plants found among the algae than that he should remember names of different genera. 204 PRACTICAL BOTANY form somewhat like Pleuroeoccus, is frequently found in stag- nant water. It sometimes grows so luxuriantly in barnyard and roadside pools as to give the water a bright green appear- ance, and its resting spores may impart -a dark red color to the drying pools in which the plants have flourished. Of the near rela- tives of Spirogyra there are several kinds, some of which are Zygnema )P %.(Fig, 16), Mesocarpus (Fig. 167), , and the desmids (Fig. 168). The desmids are pe- culiarly fantastic forms, one-celled, but often found in colonies. They usually appear in stagnant waters. As in Spirogyra, these plants repro- duce themselves by formation of zygospores. Con- ferva, which re- sembles Ulothrix (see Fig. 159), is fairly abundant in ponds and along margins of lakes. Draparnaldia is a branching form (Fig. 160) which resembles Cladophora and Vaucheria ; Ulva, or sea lettuce, is a peculiar large salt-water form ; while Coleochcete (Fig. 169) is a disk-like or plate-like form. Ohara, or stonewort (Fig. 170), is a complex alga that is found in great abundance upon the bottom of shallow lakes and streams throughout the continent. It has a heavy coating FIG. 167. Mesocarpus c, conjugating cells which have bent toward one another and are producing conjugating tubes; p, a start toward conjugation with a third plant. Greatly enlarged THE GREEN ALG^ (CHLOEOPHYCE^) 205 of calcareous material, which, as the plant dies, falls to the bottom of the pond or stream. Char a' grows in such luxuri- ance that its deposits eventually form deep layers of this cal- careous material, or marl as it is called. Marl has been found of great value in the manufacture of cement, and not a few of the lakes in which OJiara grows are being dredged to secure the marl deposits for this important manufacture. 188. Algae and water supply. Many of our large cities have found it advisable to construct reservoirs for water. These are open pools, lakes, tanks, etc., and they are intended to hold water enough so that in times of scarcity there will be at hand a sufficient supply. Such reser- voirs have proved so admirable as growing places for algae that these plants have often become a nuisance. Their presence in water for domestic use is not at- tractive, and, besides, they may stop up the water pipes ; but far more serious than these objec- tions is the actual pollution of the water because of their pres- A,Micrasterias; B,B',Staurastrum ence. When they die they "be- (two views); c, ciosterium. After come the food for decay-produc- ing organisms (Sect. 154), and often positively injurious sub- stances may thus be generated. It has been found that by tow- ing about in such reservoirs a quantity of copper sulphate, 1 inclosed in coarse sacking, minute quantities of the salt be- come dissolved and the algse are thus killed. The solution is" not strong enough to render the water unwholesome for use. FIG. 168. Desmids 206 PRACTICAL BOTANY This treatment has been an important factor in improving the water within reservoirs used as sources of water supply for many American cities. 1 189. The brown algae: general characteristics. The blue- green and the green algae are predominantly fresh-water groups, and are considered the chief representatives of algae. The remaining groups, though almost exclusively salt-water FIG. 169. ColeocTicete, a flat-bodied green alga, which is a single layer of cells in thickness. It sometimes branches extensively After West plants, have such striking characteristics that brief mention of them must be made, and pupils who live near the seacoast will be interested in extending this study. The brown algae, or brown seaweeds (Phceophycece), are found along the shores of all the oceans. They grow attached, by means of strong holdfasts, to rocks, piling, or any relatively fixed support that is available. 1 See ff A Method of destroying or preventing the Growth of Algse and Certain Pathogenic Bacteria in Water Supplies," and ff Copper as an Algi- cide and Disinfectant in Water Supplies," Bulletins 64 (1904) and 76 (1905) respectively, Bureau of Plant Industry, U. S. Dept. Agr. Whipple, "Microscopy of Drinking Water," chap. xii. John Wiley & Sons, New York, 1906. THE GREEN ALG^ (CHLOROPHYCE^E) 207 From high-tide mark to a little below low-water mark Fucus and Ascophyllum (known as rockweeds) often form dense coat- ings upon rocks. At low tide these rockweeds hang loosely over the exposed rocks. Such masses exhibit the dark olive-green color that is characteristic of the group. 190. Sargassum and the Sargasso seas. Some of the brown algse may become detached and be carried hun- dreds or even thousands of miles from their original growing places. This is true in the case of Sargassum, some species of which thrive along the shores of tropical oceans. In the North Atlantic Ocean, north of the Canary Islands, is a body of water known as the Sargasso Sea. Its entire area is more or less filled with floating Sar- gassum and other forms of plant and animal life. In other similarly quiet parts of the seas occur large regions filled with floating algse. Sargas- sum, as is also true of some other brown algse, is peculiarly fitted for floating by the presence of " air bladders," which are swollen regions of the leaf -like expansions (Fig. 171). In mid- ocean one may see small floating masses of these plants, which have been carried sometimes hundreds or even thousands of miles from their original homes. FIG. 170. The stonewort alga (Chara) A, a slightly magnified piece of a plant showing the general appearance ; B, a more highly mag- nified illustration showing the oogonium (o) and the antheridium (a) , hy means of which repro- duction takes place 208 PEACTICAL BOTANY 191. The kelps. The giant kelps belong to the brown algae, .and are represented by such forms as Laminaria, Postelsia, and Macrocystis. The cylindrical stem-like growth of the Macrocystis is said to reach a length of from 800 to 900 feet, while Laminaria, or " devil' s-apron," grows into strap-like or widely spread, tough, leathery expansions. All of these forms have heavy root- like holdfasts, which furnish attachments so strong that the plant usually will break else- where before it will pull away from its sup- port. The great length of these plants is not dis- posed vertically in the water, but FIG. 171. Rockweed (Fucus) the strO ngstem- A, the base of a young plant showing an early stage in formation of the holdfast, which attached the plant to a .piece of wood. B, tip of a plant; b, air bladders; a, spe- cialized regions in which reproductive organs are formed ; c, new leaf-like growth where the plant had been broken. A little less than natural size like and leaf- like outgrowths trail out in a semi-upright po- sition. 192. Reproduction. Vegetative reproduction in the brown algae is secured by the breaking apart of branches from old plants. There is no known special method resulting in vege- tative reproduction, as in Pleurococcus, Nostoc, etc. Some members of the group {Ectocarpus and others) are reproduced by zoospores and by the formation of zygospores THE GREEN ALG^l (CHLOKOPHYCE^E) 209 that are the result of the union of similar motile gametes, as in such green algae as Ulothrix and Cladophora. Others, of which Fucus is a representative, reproduce by means of oospores that are formed by the union of sperms and eggs. 1 193. Uses by man. At one time the world's supply of iodine was derived from the brown algse ; now it can usually be pre- pared more economically by chemical means. Soda was for- merly secured from these plants, but chemical processes have driven out the laborious methods of securing that substance directly from plants. Gelatinous foods and a sugar known as mannite are se- cured from some species of brown algae. In some coastal portions of this country the farmers collect and carry inland great quantities of brown algse and spread them over the cultivated land as a fertilizer. 194. The red algae. The red algge (Rhodophycece) chiefly inhabit deeper water than do the brown algse. The class is almost wholly confined to salt water, and the few that do live in fresh water do not exhibit well the color characteristics of the class. One com- mon fresh-water genus is Batrachospermum (Fig. 172). The marine forms of this group present most striking shapes and colors. They are of different shades of red, varying from the most brilliant to those that are dark and somber, while some are a deep purple. Chlorophyll is present, but often is completely obscured by the other colors. Sometimes all the colors are obscured by deposits of calcareous material upon the plants. 1 If desired to study further the details of reproduction of the brown algae, see Coulter, Barnes, and Cowles, College Botany, Vol. I ; also Bergen and Davis, Principles of Botany. FIG. 172. A red alga (Batracho- spermum}, which is fairly com- mon in fresh waters Slightly magnified 210 PEACTICAL BOTANY There are no known unicellular red algse. Usually the plants are quite complex and present expanded leaf-like structures FIG. 173. A red alga (Gigartina spinosa) Attached by means of its holdfast to a small stone (Fig. 173) or are extensively branched (Fig. 174). They have basal holdfasts, which in general resemble those usually found in the brown algse. Red algse are, as a rule, smaller and THE GKEEN ALG.E (CHLOKOPHYCE^) 211 more delicate than the brown forms. 1 There are often many branches, the smallest ones becoming quite thread-like, so that the entire plant looks to the beginning student like a sparsely branched stem with many finely divided leaves. In their asexual reproduction the red algae may form spores in groups of four (Fig. 175). FIG. 174. A red alga (Dasya) 1 The best way for the teacher to give a general notion of brown and red algae is to secure card mounts or bottled material for class demonstrations of a few of the leading types in each group. These may be obtained from the Woods Hole Biological Laboratory, Woods Hole, Massachusetts, and from other reliable supply houses. Well-prepared card mounts preserve the natural colors, and may be kept indefinitely for laboratory use. 212 PRACTICAL BOTANY 195. Uses of red algae. Several genera of the red algse are used as food. They may be dried and thus kept for long periods. The gelatinous mate- rial that is secured from them forms a delicacy much de- sired by some people. In the North Sea and elsewhere in the Atlantic Ocean occurs a red alga known as "Irish moss," which is collected in large quantities and employed in the preparation of jelly, to be used both directly as food and as the basis for the prep- aration of other foods. One of these gelatinous products of red algae is agar-agar, which is extensively used as a growth medium in bacteriological work, and in similar work with some of the lower fungi. FIG. 175. The asexual reproduction of a red alga (Callithamniori) At the left there is a branch upon which is a sporangium. Within its wall its di- vision into four spores has taken place. At the right these four asexual spores have escaped from the sporangium. Much magnified. After Thuret 196. Classification of the algae : Thallophytes Algse Class I. Chlorophyceae (the green algae) Leading genera used as illustrations, Pleurococcus, Spirogyra, Cladophora, Ulothrix, Draparnaldia, Vaucheria, Zygnema, CEdogonium, Chara Class II. Phaeophyceae (the brown algae) Leading genera used as illustrations, Fucus, Sargassum, Lami- naria, Ectocarpus Class III. Rhodophyceae (the red algae) Leading genera used as illustrations, Gigartina, Dasya, Calli- thamnion CHAPTER XIV THE ALG^E-FUNGI (PHYCOMYCETES) 197. General characteristics of the fungi. The algae-fungi, as the name suggests, are fungi which resemble the algae. It was noted in the discussion of the bacteria that the fungi are thallophytes which do not possess chlorophyll. Some of the fungi are so much like the algae in general structure that if chlorophyll were added to them they might easily be classi- fied together. There are other fungi which are very unlike the algae. Absence of chlorophyll suggests the absence of ability to manufacture foods from water and carbon dioxide (Sect. 17). "In order to live, fungi must secure their carbohydrate food already prepared for them, and the first great question that arises relates to the ways in which non-chlorophyll-bearing plants secure their food. 198. The dependent habit of living. The dependent habit is characteristic of the fungi, though there are many dependent plants that do not belong to the fungi. Dependency may appear in any one of several forms. Such fungi as toadstools, mushrooms, and puffballs live upon decaying plant and ani- mal material, old leaves, logs, stumps, manure heaps, etc., and when so living are called saprophytes. Sometimes depend- ent plants live upon living plants or animals, as in the case of tree-destroying fungi, wheat rust, and some of the bacteria of the human body. These, as we have seen, are called parasites, and the organism which furnishes the food material is the host. Two living organisms, plant or animal, may live together in such a way that each benefits from the presence of the other, and sometimes these are called mutualists, meaning " mutually helpful," and sometimes they are called helotists, meaning that 213 214 PRACTICAL BOTANY one organism is held by the other in a condition of slavery. In case of some dependent plants it is not easy to determine the nature of their dependency. 1 199. Bread mold (Rhizopus nigricans). If a piece of slightly moistened bread is placed in a glass jar or covered in a dish for a few days, an abundant supply of mold soon appears upon it. There may even be several kinds of molds developed upon the bread under such conditions within a very few days. The common bread mold, or black mold, is the one which usually appears. It grows about our homes in great abundance, soon appearing when bread, fruits, and other favorable nutrient substances are left exposed. When young the mold is white, only assuming its blackish appearance when spores are formed. 200. Bread mold : vegetative structures. A mass of growing bread mold is composed of many white threads greatly entangled one with another. This entanglement is due to the forward growth of the many free ends of these threads. Each thread is called a hypha (meaning "a single web"), and the whole net- work of hyphce is the mycelium, or fungus mass. The mycelium is the interwoven network of which one hypha is a single thread. Careful examination also shows that some of the hyphse have grown down into the nutritive substratum (supporting substance), and if one could see through the bread after mold has grown on it for a few days, much of the mycelium would be seen within the bread. Branching downward from some of the superficial hyphas are special root-like hyphse (rhizoids) (Fig. 176), which descend and spread out within the nutrient material. At such places upright hyphae also are formed. From these areas long runner-like branches (stolons) may extend over the surface a little way. From the stolons a new set of rhizoids and upright hyphae may be formed. This method of vegetative extension gave rise to a much-used name, Mucor stolonifer, meaning " the stolon-bearing mold." 1 Dependent plants are treated more fully in a separate chapter, but plant dependency necessarily receives attention throughout ttus, discussion of the fungi. THE ALG^-FUNGI (PHYCOMYCETES) 215 Under magnification hyphse of bread mold are seen to con- sist of heavy tubular cell walls in which the granular proto- plasm is not separated by trans- verse walls, as it is in most of the algae. If the nuclei could be seen, which is not possible in unstained material, many of them would be found within the tubular hyphal wall. This plant, therefore, is a coenocyte, like the green alga VaucTieria (Sect. 183). If Rhizopus pos- sessed chlorophyll, it would re- semble the vegetative structure of Vaucheria. FIG. 176. Black mold Below is a slightly magnified illustration of plants, one of which has given rise to the other by means of a runner, or stolon. Descending are the rhizoids and as- cending are the aerial branches, upon the tips of which spores are borne within sporangia. Above and at the right a more highly magnified sporangium is shown. Its wall (w) incloses many spores (s), through which may be seen the columella (c), which is the swollen tip of the stalk upon which the sporangium is borne. This wall may be broken away, so as to leave some of the spores lying upon the columella, as is seen in two cases of the plants shown below 201. Bread mold: nutrition. Bread mold lives upon and within its nutrient substance and absorbs food material directly from it. Parts that are in contact with the substratum do the 216 PRACTICAL BOTANY work of food absorption. Food is carried through the tubular cells to the parts of the mycelium that are above the food material. 202. Bread mold : effect upon the substratum. If a piece of bread upon which bread mold is growing vigorously be -kept moist, the mold will not, usually, continue to grow' until the bread is completely consumed. Either because of having se- cured all the food it can extract from the bread, because of having secreted substances that prevent its further growth, or because of being unable to hold its own with other organisms (molds and bacteria), the bread mold after a time ceases to grow. Other molds and bacteria may appear, one kind follow- ing another for weeks, until the decay of the bread is almost or quite complete. If kept tightly sealed, however, growth stops before all the food material is used. Molds often grow for a time in jars of fruit, forming upon the top of the fruit a coating which remains until the jar is opened. If this coat- ing is removed and a fresh supply of air is admitted, a new growth soon appears. 203. Bread mold: asexual reproduction. In addition to vege- tative reproduction by means of stolons, this mold also repro- duces itself both asexually and sexually. There arise from the main body of the mycelium upright hyphse, upon the ends of which sporangia are produced (Fig. 176). The upright stalks are called sporangiopliores (meaning " sporangia bearers"). In the development of the sporangium, first a transverse wall cuts off a small tip of the upright stalk. This tip cell grows rapidly until it has become a large spherical body. Meanwhile the transverse wall has extended into the spherical sporangium, thus producing a little column (the cdumella) upon which the sporangium contents rest. The protoplasm of the sporangium divides into many small spores, which, when the sporangium wall breaks, are scattered widely into the air. The musty odor which is detected when we smell mold may be due to the presence of large numbers of these spores, or to gases that r have been produced within the nutrient material. THE ALG^-FUNGI (PHYCOMYCETES) 217: If bread that has not been exposed to the air is cut in a room in which the air is quiet, and if one piece 'is covered directly in a glass dish, another similarly covered after five minutes' exposure to the air of the room, and another after five minutes' exposure on the outside window sill, an interest- ing test of the abundance of spores in the atmosphere will be afforded. One class of students, in performing this experiment, .secured the development of mold upon all three pieces of bread, having in all five kinds of mold. 204. Bread mold : sexual re- production. Bread mold rarely reproduces itself by sexual proc- esses, but does so under some circumstances. The tips of hy- phse approach one another, and end cells are formed by means of transverse walls. These end cells gradually unite to produce a spore, and a heavy dark wall is formed about it. Since this spore is produced by the union of similar cells it is called a zy- gospore. It is a well-protected spore, and seems fitted for en- during great extremes in physical conditions.- The germi- nation of the zygospore of Rhizopus nigricans is an occurrence that is difficult to demonstrate in the laboratory, thougK it and closely related molds (Mucor mucedo and Sporodinia) form zygospores that have been seen to germinate and thus repro- duce the mold plants. The similarity between the formation of zygospores in molds and in Spirogyra is worthy of note. 205. Water mold (Saprolegnid). Although there are several kinds of water molds, this is the most common one. It lives in the water, upon dead insects, fish, and other animals. FIG. 177. Water mold growing on the body of a wasp The fungus has grown upon the host until an extensive white fluffy mass has been formed 218 PRACTICAL BOTANY Sometimes living fish that are confined in close quarters become infested with this mold and die. In such cases the mold is first a parasite, but upon the death of its host it becomes a saprophyte. In late summer and early autumn, flies and other insects often become infected with water molds and related fungi (as Entomopktliora). If these insects, when found lying on the floors and window sills, are placed in a dish of water, the mold sometimes grows rapidly, soon producing a "collar" of fluffy hyphse about the thorax of the insect, and may cover the entire body (Fig. 177). 206. Water mold: vegetative structures and nutrition. The mycelium of Sapro- legnia branches and extends itself through- out the tissues of its supporting material. As in Mucor and Vaucheria, the plant is a coenocyte. It absorbs its food material directly, and when the supply of food is abundant it may grow with striking ra- pidity. This plant is effective in bring- ing about decay of dead animal bodies in the water. 207. Water mold: asexual reproduction. At times the numerous hyphse which extend from the nourishing material may form transverse walls, which separate large swollen tip segments from the bases of the hyphse. Within each tip segment many zoospores form (Fig. 178). These escape into the water in very large numbers and swim about quite actively. Upon coming in contact with favorable nutriment the cilia are withdrawn and the zoospore germinates into a new hypha, which by growth may produce a new mycelium. 208. Water mold : sexual reproduction. From the tips of short hyphae large spherical cells (oogonia) are formed, in each of which one to many eggs are produced. In some FIG. 178. A water mold bearing a sporangium (s), from which zoo- spores (z) are escaping After Schenck THE ALGLE-FUNGI (PHYCOMYCETES) 219 species groups of oogonia are formed upon a single hypha. Antheridial branches come in contact with the oogonia (Fig. 170). A tube grows from the antheridium and pierces the wall of the oogonium. Sperms from the antheridium escape and fertilize the eggs, thus forming oospores which can repro- duce the plant. In some cases when Saprolegnia eggs are not fertilized they develop heavy walls, and after- wards germinate as if they had been fertilized. Such development of eggs into oospores without fertiliza- tion is known as partheno- genesis. It is a method of reproduction that is met with in some other plants and in some animals. 209. The grape downy mildew (Plasmopara viti- cola). There are numerous so-called downy mildews ; the one here used as a type frequently appears upon the under surface of leaves of the grape. In the Cen- tral States, which region is Some of the hyphse bear oogonfa (o) and an- , . , ., . . , theridia (a), and within the oogonia are the supposed to be the original eggs (e) . After K iebs home of this parasite, it has been an injurious pest for many years. Its downy white growth upon the surface of the leaves (Fig. 180) is its most con- spicuous distinguishing characteristic, but it also often grows upon green shoots and fruit. When conditions are thoroughly favorable (proper soil, moisture, and temperature) for the growth of grapevines, the parasite when present may do little damage. At other times it may all but destroy the crop and greatly reduce the vigor of the host plant. FIG. 179. Sexual reproduction of a water mold 220 PRACTICAL BOTANY 210. Grape mildew : vegetative structures and nutrition. The downy patches that appear upon the leaves are merely the superficial parts of the parasite, since within the leaf the FIG. 180. A leaf of the grape, upon which may be seen the white, fluffy patches of grape mildew Photograph by H. H. Whetzel mycelial hyphse have grown for some time before the downy patches are produced. These ccenocytic hyphse grow between the cells and send into the interior of the cells short branches THE ALGLE-FUHG1 (PHYCOMYCETES) 221 (hamtoria), which absorb food directly from the cell contents of the host (Fig. 181, -B). When the mildew has thus grown within the leaf for a time, it sends through the stomata on the under surface numer- ous branches which consti- tute the super- ficial downy patches char- acteristic of the parasite. 211. Grape mildew : asex- ual reproduction. Some of the aerial hyphse branch and upon tips of these branches produce spore-like bodies, the conidia (Fig. 181, A). These conidia fall from the conidiophores (conidia bear- ers), and when favorable moisture (dew, rain, etc.) is present they germinate. Instead of producing new hyphse they usually act as sporangia and produce ZOO- FIG. 181. Grape mildew (Plasmopara) From the mycelium within the cells of the grape leaf haustoria (Z?) are formed. Upright hyphse (A) bear conidia. These conidia divide, as at D, and form zoo- spores (E). Within the leaf oospores (C) are formed. After Duggar spores (Fig. 181, D and E). The z oospores may swim about for fifteen or twenty minutes, and then lose their cilia and begin to produce new hyphae. If favorably located, the new hyphse may find entrance to a leaf through its stomata and begin anew the growth therein. 222 PRACTICAL BOTANY 212. Grape mildew: sexual reproduction. In the interior of the leaf short hyphal branches develop into obgonia and an- theridia (Fig. 181, (7). Each obgonium develops an egg, which, when fertilized by one of the many sperms from the anther- .idium, becomes an obspore. This obspore has a heavy wall and also is within the tissues of the leaf, so that apparently it is well fitted to endure severe winter conditions. Upon the decay of the leaf the obspores are set free. They probably ger- minate to produce new plants, but " much work needs to be done in the way of determining to what extent the obspores are necessary in the annual propagation of this species." 1 213. Grape mildew: preventive measures. Usually it is pos- sible to control the growth of this parasite so that serious damage is prevented. In 1881 the Frenchman Millardet began experi- menting with the Bordeaux mixture 2 as a method of treating grape mildew. His experiments resulted in a chemical mix- ture which, when properly used as a spray, will obviate most of the ill effects of grape mildew. The same mixture has been found of great value in treating many other plant diseases, and almost all the state agricultural experiment stations issue special directions concerning local uses of this mixture. 214. Potato blight (Phytophthora infestans). This parasite is a near relative of grape mildew. Its vegetative characteristics closely resemble those just described. Its asexual reproduc- tion by conidiospores and the consequent z obspores gives it very ready and wide distribution. The parasite may infest leaf, stem, or tuber of the potato, and is one of the several fungous diseases that have proved very destructive of potato crops. It may be held in check by proper spraying (Fig. 349) with the Bordeaux mixture. 3 1 Duggar, B. M., Fungous Diseases of Plants. Ginn and Company, Bos- ton, 1909. 2 The preparation as most commonly used consists of materials mixed in the following proportions : copper sulphate, 5 pounds ; stone lime, 6 pounds ; water, 50 gallons. Other proportions are often used. 8 "Potato Spraying Experiments in 1906," Bulletin 279, N.Y. Agr. Exp. Sta. ; "Certain Potato Diseases and their Remedies," Bulletin 7,Vt. Agr. Exp. Sta. THE ALG.E-FUNGI (PHYCOMYCETES) 223 215. Other phycomycetes. Of the forms that have here been discussed, Rhizopus, Saprolegnia, and Plasmopara, each represents an important subdivision of the phycomycete class of fungi. There are many molds closely related to Rhizopus, and some of them usually appear wherever there is decaying organic matter. Several kinds of water molds are known, and other parasitic forms which resemble Saprolegnia are the cranberry-gall fungus (Synchytrium Vacdm), which attacks the stem, leaves, flowers, and fruit of the cranberry plant; the " damping-off " fungus (Pythium DeBaryanum), which, in plant-house seed beds and sometimes in open fields, kills seed- ling plants by attacking their cells at or near the soil, thus causing them to wilt ; the brown rot of the lemon and other citrous fruits (Pythiacystis citrophthora), which is especially injurious in California and is often a forerunner of the blue mold (JPmicillium). Important plant parasites which in struc- ture and habit resemble the grape mildew and potato blight are the white or downy mildew ( Cystopus candidus, sometimes called Albugo Candida) of plants of the mustard family ( Oru- ciferce), as shepherd's-purse, the common radish, horse-radish, cress, mustard, and turnip ; also another white mildew (Pero- nospora parasitica) which infests many members of the mus- tard family, including most of those mentioned for Cystopus, as well as others ; downy mildew (Plasmopara cubensis) of the cucumber, pumpkin, and watermelon ; onion mildew (Peronos- pora Schleideni) ; downy mildew of lettuce (Bremia Lactucce) and downy mildew of lima beans (PhytopTithora Phaseoli). 216. Summary of phycomycetes. In structure and methods of reproduction this group resembles some of the green algae. The frequently occurring ccenocytic body suggests Vaucheria and its relatives among the green algse. In reproduction zobspores, zygospores, and ob'spores are formed, and the spe- cialized sex organs, oogonium and antheridium, are present. In some of the phycomycetes specialized asexual structures, the conidia, are formed, and these germinate, usually producing one or more zoospores. Evidently these conidia are sporangia 224 PRACTICAL BOTANY which fall from the parent plant before the spores that de- velop within them are set free. A careful review of type plants used in the study of green algae and phycomycetes will show striking similarity in reproductive processes. The saprophytic and parasitic habits of living of this group give them very great economic significance. Agriculture, hor- ticulture, gardening, fish industries, and water supplies are seriously affected by members of the group. 217. The groups of fungi. The classification of dependent plants into saprophytes, parasites, mutualists, and helotists is FIG. 182. Slime mold (Fuligo) growing from a decaying board Two masses have exuded from the crevices of the board and are rounded into position for forming spores. Natural size based entirely upon the ways in which plants live. Fungi are also classified upon the basis of their structure, and this classi- fication is the one generally used in speaking of them. 1 The leading groups or classes are the phycomycetes, ascomycetes, lichens, and basidiomycetes. The schizomycetes (bacteria) are sometimes treated in this connection, but by reason of sim- ilarity of structure and methods of reproduction they and the blue-green algae are now discussed together (Chapters XI and XII). The last part of the name of each class (mycetes) means "fungi," and the first part refers to a distinguishing 1 The simplest acceptable classification of fungi has been adopted. Certain technical groupings that are quite proper in a more advanced treatise are omitted from this elementary statement. THE ALG.E-FUNGI (PHYCOMYCETES) 225 characteristic of the class. Thus phycomycetes literally means " seaweed fungi," and we call them algae-fungi ; ascomycetes means "sac fungi," since some of the spores are formed in a peculiar sac ; and the basidiomycetes are the " stalk fungi," or " club fungi," since some of the spores are borne upon a stalk or club-like base. In each of these classes many kinds of fungi are found, but only a few kinds in each class can be consid- ered in an elementary treatment. 1 The lichens are peculiar plants, which are treated in this connection merely for lack of better classification for them, as will appear later. 218. Classification: Thallophytes Algae Fungi Class I. Phycomycetes. Leading genera used as illustrations, Rhizopus (bread mold), Saprolegnia (water mold), Plasmopara (grape downy mildew), Phytophthora (potato blight), Cystopus, and others Class II. Ascomycetes Class III. Lichens Class IV. Basidiomycetes 1 The " slime molds," or myxomycetes, are usually classed with the fungi, though some students regard them as animals. They often appear as ge- latinous, sticky, yellow, brown, or brightly colored masses exuding from crevices in old stumps, logs, old board walks, upon decaying leaves, and sometimes upon very rich soil (Fig. 182). At other times these masses pro- duce stalks, globules, or one or a few rounded masses. These are the spore- producing structures. So different are these two stages one motile like some of the lower animals, the other forming spores like some plants that students formerly thought the two stages were different organisms, of which one was animal, the other plant. CHAPTER XV THE SAC FUNGI (ASCOMYCETES) ; THE LICHENS; THE BASIDIUM FUNGI (BASIDIOMYCETES) THE SAC FUNGI (ASCOMYCETES) 219. General characteristics. More of the fungi belong to this class than to any other, and since most of the ascomycetes are parasitic, it is evident that the class is one of great im- portance. There is wide variation in form and structure in this group. The mycelium of the parasitic forms grows mainly upon instead of within the host, and sends into it short haus- toria which absorb food material. The hyphse of the mycelium are divided into many cells, and branch extensively. Many of the known structures are difficult to understand, and many of the facts are not known regarding the life cycles of some of the plants which belong in this class. In a general way, the fungi of this class are subdivided into two groups, those which have their spore-forming sacs opening into cup- like structures, and those which have the spore sacs inclosed, or almost inclosed, in heavy-walled and more or less spheri- cal cases. Common illustrations of the class are the mildews which grow upon leaves of the plantain, smartweed, and lilac, the cup fungi, the morel, and yeasts. Of the many represent- atives, but a few types will be used to give some general notions of the structure and importance of the class. 220. Peziza and Sclerotinia. In damp soil, attached to decay- ing sticks or roots, may be found the pink or reddish cup fungus, Peziza. Peziza plants sometimes appear singly and sometimes in clusters or rows, and in color some of them are very striking. Growing from old plums and peaches which have shriveled and dried (become mummified), sometimes there are found similar though brownish cups, which contain the reproductive 220 THE SAC FUNGI (ASCOMYCETES) 227 organs of another ascomycete, Sderotinia (Fig. 183). In case of both Peziza and Sderotinia, the cups are external indica- tions of a much larger internal growth of the fungus. In Sderotinia^ commonly called the brown rot of the stone fruits (peach, plum, apricot, cherry), the infection of the host long precedes the production of cups. Mycelial hyphse penetrate the fruit or the flower and grow extensively in it, often extending to the twig. After a period of such growth there appear upon the surface of the fruit, which is now shriveling or decaying, FIG. 183. Brown rot (Sderotinia) growing upon old plums At the right are some of the fruiting cups; in the middle is a greatly magnified portion of the cup, showing the spore-bearing areas ; and at the left is one of the spore-bearing threads still more magnified. After Duggar many tufts of light-brown hyphse. Among these tufts are conidiophores, upon which conidia are produced. These con- idia are scattered by wind, by contact with insects, etc., and, alighting upon favorable growing places, produce new myce- lial growths. It is thought possible that these conidial spores may persist throughout the winter. Infected fruits may be- come dried and shriveled, and hang upon the tree or fall to the ground. When favorable growing conditions return in the next season, or even in a later season, the brown cups are pro- duced from the mass of mycelium in the old fruit. These cups are composed of many hyphse closely pressed together. In the tips of some of these hyphse in the bottom of the cups the spores 228. PRACTICAL BOTANY are formed (Fig. 183). The wall of a spore-containing hypha is the sac or ascus, and the spores which are formed therein are the ascospores, or sac spores. These spores, when favorably placed, again produce the mycelium of the parasite. This repre- sents the chief method of spring and early summer infection of fruits with the brown rot. 221. Destructiveness of Sclerotinia. All kinds of stone fruits seem to be susceptible to attacks of this disease. It is said 1 : " It would appear that among peaches the sorts densely covered with hairs or down, such as Alexander, Hill's Chili, and Triumph, are usu- ally susceptible. Among the more resistant sorts are to be found the Carmen, Early Crawford, Elberta, Chinese Cling, and some others. Among the plums the Jap- anese varieties suffer gen- erally in most sections of the country. The American group of plums is also sus- FIG. 184. A group of "morel" mush- . rooms (Morchella) Note the depressions in the surface, in which the sacs and ascospores are formed. , Three fourths natural size ceptible, and apparently more susceptible at the South than farther north. The Wild Goose and Marietta plums are much less affected in all regions. The native cherries are more resist- ant than such as the Montmorency." The total amount of the damage is enormous. In 1887 Maryland and Delaware were reported to have had a peach-crop shortage, from this cause, of 800,000 baskets of fruit. In 1900 Georgia had an estimated loss of 40 per cent of the peach crop, or a money loss of be- tween $500,000 and S700,000. 2 The disease may be checked 1 Duggar, Fungous Diseases of Plants. Ginn and Company, Boston, 1910. 2 "The Brown Rot of Peaches, Plums, and Other Fruits," Bulletin 50, Georgia Agr. Exp. Sta., 1900. THE SAC FUNGI (ASCOMYCETES) 229 by destroying the infected fruits and twigs. Spores are so gen- erally distributed that spraying is also necessary. Different sprays have been used, but with such varying success that the advice of local experiment stations should be sought for the special needs in each state. 222. The morel (Morchelld). Another representative of the open-fruiting ascomycetes is that commonly called the "morel mushroom" (Fig. 184). Its mycelium grows in earth that is FIG. 185. Leaves of lilac upon which lilac mildew appears in whitish patches. Also the small dark reproductive bodies are shown very rich with decaying organic matter. It is usually found in woods among the leaves and about old logs and stumps. The fruiting body, the mushroom, is the only part usually noticed, and under favorable conditions of moisture and temperature it develops in a very short time, growing at the expense of food material that is gathered by the underground saprophytic my- celium. In the deep, wrinkle-bordered pits of the mushroom are the ascus-bearing hyphse. The ascospores form in great numbers and are so light that they may be widely distributed. 223. The powdery mildews: lilac mildew (Microsph&ra alni). Good illustrations of the inclosed-fruited ascomycetes are had in the powdery mildews. They are frequently found upon the surfaces of leaves of lilac (Fig. 185), and related mildews are 230 PRACTICAL BOTANY found upon the willow, aak, some of the smartweeds, and upon many other plants. The powdery mycelium lives upon the surfaces of the leaves. Haustoria, by means of which nutrient material is extracted from the host, are sent into the leaf from the superficial hyphse. The fungus is therefore a superficial parasite. At times upright hyphse form transverse walls, cutting from their tips rows of small cells, the conidia. The powdery appearance of the mildews is due largely to the pres- ence of large numbers of these conidia. The co- nidia, if favorably placed, are the means of produc- ing new growths of the ascocarp mildew. Another complex method of reproduction results in forming asco- spores. Two superficial hyphse unite their tips, and fusion of the nuclei of these tip cells takes place. Then there grows, as a result of this fusion, a relatively large, heavy- walled body, the asco- carp, so called because it is the hard-walled body which con- tains the asci and ascospores. Within the developing asco- carp, division of the tissue finally results in forming several asci, in each of which there are four to eight ascospores (Fig. 186). In late summer the ascocarps may, without mag- nification, be seen as small black bodies upon the surface of lilac leaves. From the walls of the ascocarp peculiar arms extend, and in the lilac mildew and some other kinds these have strikingly branched tips, which sometimes serve as one means of distinguishing the species. FIG. 186. The spore-sac case of lilac mildew (Microsphcera alni) The central, heavy-walled body (ascocarp) contains the sacs (asci) in which spores are formed. Upon the wall of the ascocarp are stalks, sometimes called arms, which have peculiar branches at their tips. About 60 times natural size THE SAC FUNGI (ASCOMYCETES) 231 O, The heavy-walled ascocarp is resistant to unfavorable cli- matic conditions, and may pass through the winter and in the following spring break open, thus freeing the thin-walled asci. Upon escaping, the spores may be blown or carried about and germinate upon new host leaves. 224. Blue mold or green mold (Penicillium). This mold fre- quently appears upon discarded leather, upon shoes or gloves which when damp have been left in a dark warm place, upon old lemons, and upon cheese and other dairy products. Various species have distinct shades of color, so that the common names of blue or green mold can be taken only as applying in a general way. Certain species of Penicillium are supposed to give characteristic flavors to cheese in which they grow, as Penicillium Roqueforti of Roquefort cheese and Penicillium Camemberti of Camembert cheese. These species are widely dis- tributed, however, and are found growing upon many substances other than cheese. It has been suggested that these are not different species, but that they merely show different features, dependent upon the kind of material upon which they grow. While it is true that these as well as species of other molds do show different characteristics when grown in different ways, recent investigations indicate that the species are distinct. 1 Penicillium is an ascomycete which has almost lost the habit of reproduction by means of ascospores, the ascus being 1 An interesting discussion of various species and their cultural reac- tions is " Cultural Studies of Species of Penicillium," by Charles Thorn, Ph.D., Mycologist in Cheese Investigations, Bulletin 148, Bureau of Animal Industry, U. S. Dept. Agr., 1910. FIG. 187. The blue mold (Penicillium) At the left is the tip of a hy- pha, with the characteristic branches, on the ends of which are the spores; at the right are germinating spores. After Thorn. Much magnified 232 PRACTICAL BOTANY rarely formed. It reproduces itself very .abundantly by means of conidia. Plants branch profusely at their ends, and from the tips of these branches conidia are formed (Fig. 187). The number of these conidia is often so large that when the sub- stance supporting the plants is slightly shaken a small cloud of spores arises. 225. Yeasts. The yeasts (Saccharomycetes) constitute a group of plants of somewhat doubtful classification. Since occasion- ally they form an ascus-like sac in which spores are formed, they are often classed with the ascomycetes. They are extremely simple, and are more interesting because of their manner of life than because of their structure. A yeast plant is a single cell FIG. 188. Yeast plants (Saccharomycetes) _ (Fig. 188). It usually repro- a, a plant from which a bud has begun 2 . ' , , ,11 to grow; b and c, plants with two buds, duces itself by a method Note the vacuoles in the plants. Greatly o f vegetative reproduction known as budding. The buds, before becoming separated from the parent cells, may bud again- and again until a chain of plants is formed. If a cake of commercial yeast is examined, it is found, in addition to the large starch grains nearly always occurring in yeast cakes, to consist of thousands of yeast cells, some single and some in process of budding. If a cake of yeast is kept at room tempera- ture, the plants soon continue their growth, and other organisms (bacteria and molds) also grow, so that the yeast " spoils." When yeast plants are placed in dough they grow with great rapidity. They live upon the solutions in the dough, and in so doing break down the sugar, thus forming from it small quantities of alcohol and carbon dioxide. The carbon- dioxide gas forms the "air spaces" in the dough, which cause the phenomena known as " rising." 1 In cooking the dough 1 Salt-rising bread owes its peculiar quality to the fact that instead of yeasts certain bacteria produce a putrefactive fermentation within the dough. THE SAC FUNGI (ASCOMYCETES) 233 the air spaces are enlarged and at the same time the alcohol is evaporated. In former methods of bread baking pure cul- tures of yeast were less likely to be secured, " wild " yeasts very frequently appearing. With modern methods, quite sim- ilar to those used in bacteriology, pure cultures may be ob- tained, and it is therefore possible to secure the exact kind of fermentation of the dough that is desired. 1 The processes of fermentation by yeasts are used in the manufacture of alcohol, wine, beer, and other liquors which contain alcohol. Certain definite kinds of yeasts produce cer- tain kinds of alcoholic fermentation, and it is necessary for the brewer to keep pure cultures of the desired yeasts in order to insure the particular quality of his product. It is worthy of note that the difficulties which brewers formerly had from impure yeasts furnished the occasion for the development of the basis of modern bacteriology. The brewers of Germany appealed to the great scientist, Louis Pasteur, to assist' them in this difficulty. He succeeded, in 1856, in devising methods of pure culture by isolating single yeast plants and growing a colony from each. Thus the particular result to be secured could be determined by the kind of yeast selected for use in fermentation. It was this method of pure culture which opened the way for bacteriological investigations. 226. Other ascomycetes. The number of destructive asco- mycetes is too large even to be enumerated in this elemen- tary treatise. Some of the more important ones besides those discussed above are here given. Upon heads of rye the dis- ease known as ergot (Claviceps purpurea) sometimes develops. Its mycelium infests the whole plant. Within and about the developing grains masses of summer spores are formed. Later the same mycelium produces dark compact masses (Fig. 189), which completely replace some of the grains. These fall to the ground and lie dormant through the winter, and from them in the spring the ascospores for new growth develop. The spore 1 An especially interesting paper is "Bread and the Principles of Bread Making," by Helen W. Atwater, Farmers' Bulletin 11%, U. S. Dept. Agr., 1900. 234 PRACTICAL BOTANY masses are poisonous, and, as ergotine, are sometimes used for medicinal purposes. A parasite known as root rot ( Thielavia la- sicola) attacks the roots of tobacco, horse- radish, and violets, and of peas and other leguminous plants. 1 The rose and peach mildew (Sphoerotheca pannosa)? which oc- casionally appears as light-colored downy patches upon the fruit of the peach, attacks the leaves of roses and is very destructive. The wilt disease of cotton, cowpea, and watermelon (Neocosmospora vasinfecta) 3 is widely distributed over the Southern states and attacks the vascular bundles in such a way as to cut off the plant's water supply. A common disease of plum and cherry trees is black knot (Plowrightia morbosa). 4 The familiar and very destructive dark and shrunken patches on the fruit of the apple are due to bitter rot {Grlomerella rufomaculans)? The value of fruit des- troyed by it sometimes amounts to millions of dollars in a single year. In addition to the conidial forms already considered in connection with their asco- sporic forms and used as types of their re- spective groups, there remain thousands of species whose life histories are not known. Many are saprophytes and many, are parasites, some of which are very destructive to crops. 1 Clinton, G. P., "Root Rot of Tobacco," Conn. Agr. Exp. Sta., 1906. 2 "Peach Mildew," Bulletin 107, Colo. Agr. Exp. Sta., 1906. 8 "Wilt Disease of Cotton, Watermelon, and Cowpea," Bulletin 17, Divi- sion of Vegetable Pathology, U. S. Dept. Agr., 1899. *Lodeman, E. G., "Black Knot," Bulletin 81, Cornell University Agr. Exp. Sta., 1894. 6 "The Bitter Rot of Apples," Bulletin 44, Bureau of Plant Industry, U. S. Dept. Agr., 1903. FIG. 189. Ergot which has grown on a head of rye After Duggar THE LICHENS 235 LICHENS 227. General characteristics. The lichens are not simply fungi. A lichen is not even a single plant, but is a com- bination of fungi and algae living together in such a close relationship that it looks like a single plant. There may be many individual fungi and many individual algae in this rela- tion, but the combination is spoken of as the lichen plant. The fungal part of the lichen is usually, though not always, a member of the ascus-bearing class of fungi, and consequently lichens are often classified with ascomycetes. This is obvi- ously a somewhat questionable classification, but for lack of a better one we shall dis- cuss the class in this con- nection. The algae that enter into the formation of lichens are usually uni- cellular forms resembling Pleurococcus, but may be filamentous green algae or even some of the blue- o-TAon alrr FlG - 19 - A foliaceous lichen (Parmelia) LiJ.v?"ll CtJ.fi ct% , _ _ , 3 T . , , . , , upon a piece of bark Lichens live upon bark ^ , , . * .Natural size of trees, stones, and upon soil (Fig. 190). They thrive under conditions of exposure and in moisture and temperature variations which do not permit most plants to grow. They are found at as great altitudes and with as great range north and south as any plants. In "stony places lichens often form heavy mats made up of lichen bodies, mosses, and decomposed rock. These masses when upon upright faces of rock may by their own weight fall and become the soil for growth of other plants. New growths soon start where the old ones were, and by a con- tinuation of this process these plants may slowly wear away large masses of stone. It is probable that consider- able chemical action is exerted upon the rock by the hyphae, 236 PEAGTICAL BOTANY resulting in decomposition of the substratum. Examination of almost any stone pile that is but a few years old will show the presence of these forerunners of other plant life. x ^ We have, therefore, a combination of alga and fungus, neither of which alone could keep alive in places of such great ex- posure, living together and instrumental in building up soil where at first no other plants could live. FIG. 191. A hanging lichen (Usnea) which is often called the "bearded moss." Also upon the dead spruce twig which supports this lichen there is another foliose lichen (Parmelia). Upon the Usnea plant there are shown several of the disk-like cups in which ascospores are formed 228. Form, structure, and reproduc- tion. Those lichens which adhere like leaves to the material upon which they grow are called foliose (Fig. 190) ; those that form closely adhering, scale-like growths are crustaceous forms; "those that branch and are partially free from the substratum swefruticose (Fig. 191); while a few are mucilaginous or ge- latinous forms. Foliose forms are com- mon upon the rougher-barked trees, fences, etc. ; crustaceous forms grow upon smooth-barked trees and upon THE LICHEFS 237 stones ; while fruticose forms grow upon the ground or hang from branches of trees. Illustrations of the latter group are the reindeer moss (Gladonia rangiferina) and other cladonias (Fig. 193), and the bearded moss (Usnea barbata). In sections or carefully made dissections of a lichen body usually the fungus is seen to compose the outer covering for the whole body. The algae are within, and often closely wound about by the hyphae of the fungi (Fig. 194), which absorb food from the cells of the algae. The fruiting cups usu- ally resemble some of those of the ascomycetes. Within the base of the cup in most lichens the fungal hyphse form asci and ascospores, as do many ascomycetes. These spores belong to the fungus. The algal part of the lichen when it is a one-celled alga like Pleurococcus reproduces by division, as we have al- ready found that it does in the green algae. This repro- . c The branches hear the fruiting cups, and auction 01 the alga OCCUrs branches may also grow from the cups, quite independently of the The open sides of the cups are shown in 6, J and the reverse surfaces m c reproduction of the fungus. 229. Economic importance of lichens. Probably the greatest economic importance of lichens is found in their relation to formation of soils. Any freshly bared rock soon becomes the FIG. 192. A detail of a small piece of Usnea barbata 238 PRACTICAL BOTANY home of small crustaceous lichens. As these grow, die, and decay, and are replaced by others of their kind, the living and decaying bodies tend to disorganize the rock. Weathering processes also assist in crumbling the rock, and after a time there is soil enough to permit the growth of other lichens and mosses and finally of larger plants. These pioneer plants are eventually driven from the rock by others that can live in the meager soil that is pro- duced by the li- chens and mosses. Certain kinds of crustaceous lichens are looked upon as the forerunners of higher vegeta- tion in rocky re- gions which are too bare to per- mit other forms of vegetation to live. They are almost universally distributed over the earth. The time required for the production of soil sufficient for the growth of other plants depends largely upon the nature of the rock and upon the climate. Upon some lava beds it is said l that after almost two hundred years from their formation crusta- ceous lichens in places are still the only plants to be found. Lichens as food for herbivorous animals are of considerable importance in regions where other foods are scanty or where for parts of the year cold and snow render other vegetation 1 Warming, CEcology of Plants, chap. xvii. FIG. 193. A cup lichen (Cladonia) This lichen often appears on moist ground, and at times forms the cup-like reproductive bodies, even sometimes having some of these form upon other cups. Two and one-half times natural size THE LICHENS 239 unavailable. Reindeer moss (Cladonia rangiferina) grows upon earth and rocks in great abundance throughout the north tem- perate and frigid zones, and at high altitudes in most mountain ranges. In winter it is eaten by animals, which find it green and nutritious when they remove the snow from above it. A few lichens are sometimes used as food for men, though they are not especially nutritious. A mucilaginous and starchy food is prepared from Cetraria islandica, a lichen which is known as Iceland moss. This and other food lichens are more or less bitter, and when used regularly in large quantities are FIG. 194. A small piece of a lichen, showing in detail the relation that exists between the mycelium of the fungus (/) and the algal cells (a) . Magnified 500 diameters. After Bonnier said to have caused disagreeable intestinal disturbances. Other lichens have been ground with wheat in making wheat flour, as in parts of northern Africa. The lichens, while adding some nutrient matter, also add considerable non-nutritious calcare- ous material, so that altogether the bulk of the flour is in- creased at the expense of the quality. In Sweden one very bitter lichen (Sticta pulmonacea) is sometimes used as a sub- stitute for hops in processes of brewing. Various dyes are prepared from lichens. These were once more commonly used than they are to-day, and are known in the markets under the names of orchil and cudbear. Litmus, used in preparing litmus or blue test paper, a common and fairly delicate test for the presence of acids, is prepared from lichens. 240 PRACTICAL BOTANY BASIDIOMYCETES 230. Different groups of basidiomycetes. The prominent groups of basidiomycetes are : the smuts, which frequently ap- pear in the heads of oats, wheat, and barley, and upon the ears and stalks of corn; rusts, which are universally distributed wherever wheat is grown, and which also grow upon many other hosts ; the toadstools, mushrooms, and puffballs. Next to the ascomycetes, this is the largest class of fungi, and is one of great economic importance. FIG. 195. Sprays of oat plants (Avena sativa) The grass-like leaf character I is well known in this plant ; the plant at the left has developed normally, while in that at the right the grains have been destroyed and replaced by oat smut and the growth of the entire plant is checked. Both one third natural size THE BASIDIUM FUNGI (BASIDIOMYCETES) 241 231. The smuts. All the smuts are parasitic. They are par- ticularly destructive to the grains and are widely distributed. In the United States it is estimated that the injury caused by smuts to wheat, oats, and barley exceeds $25,000,000 annually. The oat smut (TJstilago Avence) is present in almost every field of oats. It is generally recognized by means of the black sticky masses of spores that form in the positions previously occupied by the devel- oping grains (Fig. 195). The spore mass, however, is the external indication that the smut mycelium has previously permeated the host. The smut usually matures at about the time the oat heads are in full flower, and prevents the normal develop- ment to such an extent that the annual damage in this country is estimated to reach $6,500,000. Upon germination of these heavy-walled spores a short hypha is produced. This soon produces four thin-walled spores (Fig. 196). Since these thin-walled spores appear at about the same time that oat seedlings are growing, they produce hyphae which penetrate the host plant. Under favorable growing con- ditions the smut mycelium, which contin- ues its growth throughout the host, does not markedly retard the growth of the infected oat plants. The spores that are formed in the heads have heavy resistant walls. They may adhere to the grains, lie in the granaries, or lie upon the ground in the fields until favorable conditions for growth occur. Probably the grain used for seed is itself one of the chief means of spore distribution. It has been found that by treating seed oats with hot water (132 to 133F.), or with water containing four tenths per cent formalin, the smut may be killed. 1 1 " The Grain Smuts," Farmers' Bulletin 75, U. S. Dept. Agr., 1898; "The Smuts of Grain Plants," Bulletin 122, Minn. Agr. Exp. Sta., 1911. FIG. 196. A stage In the loose smut of oats (Ustilago Avence) The small hypha that is produced by the ger- minating spore soon produces bud-like co- nidia. Greatly magni- fied. After Duggar 242 PEACTICAL BOTANY sm Corn smut ( Ustilago Zece) infests many of the corn plants in an ordinary field, and when abrasions of the plants occur the unattractive smut masses frequently appear. They most often appear in the tassel or ear, and may completely or partially destroy both (Fig. 197). 1 232. The rusts. The intricate struc- tures and habits of living of the rusts are objects of great interest to bota- nists. Their effect upon useful and decorative plants that serve as their hosts gives them great economic im- portance. A given species of rust may live for a time upon one kind of plant and later upon host FIG. 197. An ear of corn within and upon which corn smut (Ustilago Zece) has grown The bracts which inclose the ear (E) have peculiar leaf-like extensions of their tips. Masses of the spores of the smut (sm) have grown and extruded at the tip of the ear plants that belong to other groups. In each of these stages the parasite has distinctly dif- ferent structures and produces quite different effects upon its host. So unlike are these stages that formerly they were named as distinctly different plants, and it is only recently that enough has been learned about them to enable us to know some of the different appearances they may assume. 1 " Corn Smut," Ind. Agr. Exp. Sta., 1900. THE BASIDIUM FUNGI (BASIDIOMYCETES) 243 233. Black rust of grain (Puccinia graminis). Wherever wheat and oats are grown, black rust, sometimes called red rust, is a dreaded pest. It also grows upon many other grasses, includ- ing barley and other cereals. The damage done to the world's crops by this fungus is very large indeed, and in the United States it has been estimated to exceed $15,000,000 in a single year. Much money has been expended in making stud- ies of the life habits of this parasite, with the hope that means of preventing its ravages may be discovered. The first conspicuous appearance of rust in the late spring or early summer is in the form of reddish-brown patches upon stalks and leaves of wheat and oats (Fig. 198). The patches are composed of large numbers of "summer spores" (uredospores'). A section cut through the host leaf (Fig. 199, A~) enables one to see that the uredospores are formed upon the ends of hyphae. The spore-bearing ends of hyphaB are continuations of hypha3 which have pushed their way among the leaf cells from which they have absorbed their nourishment. At the time uredospores are formed the host plant is usually thoroughly infested with the mycelium. The uredospores are readily carried about by currents of air or contact with animals. If placed upon wheat or oat plants, these spores germinate, and the young hyphse penetrate the host and produce new mycelium. Later in the summer the same mycelium which produced uredospores may produce a heavy-walled two-celled spore (Fig. 199, (?) known as the " winter spore " (teleutospore). When formed in large quantities these spores FIG. 198. Apiece of a stalk of wheat upon which spots of the rust para- site have formed FIG. 199. Black rust (Puccinia graminis) A, A small section of a wheat leaf upon which the parasitic rust is growing: ra, mycelial hyphae of the rust; y. tt, young summer spore, or uredospore; u, fully formed uredospore ; st, upright hypha upon which uredospore is formed. B, ger- mination of uredospore: st, old hypha; u, old uredospore wall ; m, new mycelial hyphae. C, winter spore, or teleutospore : st, hypha; t, two-celled spore. D, ger- mination of teleutospore: st, old hypha; p, new hypha, or the promycelium ; s, spores or sporidia. E, section of the barberry leaf showing secidiospore stage of rust: ej upper epidermis, and e 2 lower epidermis; p, wall of cup or aecidium; s, aecidiospores. Rearranged from Duggar's "Fungous Diseases of Plants." All much enlarged 244 THE BASIDIUM FUNGI (BASIDIOMYCETES) 245 appear as blistery patches, much like those made by the red- dish spores except for the difference in color. The teleuto- spores are scattered over the ground and upon wheat and oat straw. After a period of dormancy, usually lasting through the winter, these spores germinate. From each cell of the teleutospore in the spring there grows a small hypha (Fig. 199, Z>), quite resembling the one which grows from the smut spore (Fig. 196). Similarly, each cell of this hypha may form one of the thin-walled spores (sporidia). Puccinia graminis sometimes has another stage in its life cycle. In regions as in the New England States where a shrub known as barberry is common, the sporidia when alighting upon leaves of the barberry may grow and produce within the leaf an extensive growth of mycelium. When this mycelium produces spores, they appear in a peculiar cup on the underside of the barberry leaf (Fig. 199, E). These spores, being different from any of the three described and being formed in a cup, are called cecidiospores, or cup spores. jEcidiospores may reproduce the rust plant upon wheat and oats. When the life cycle of black rust was discovered, it was thought that all four stages are essential to it. It is now known, however, that the barberry stage may sometimes be omitted. The native barberry, not the Japanese variety, is the one on which this rust grows, and efforts are being made to destroy this plant with the hope of reducing the rust disease on wheat and oats. Uredospores persist through the winter in sufficient quantity to reproduce the rust upon oats and wheat in the following spring. No satisfactory pre- ventive for this fungus has been discovered. Some progress has been made by learning which varieties of wheat and oats are most resistant to attacks by the parasite. 1 234. Other rusts. Upon the leaves and stems of carnations an injurious rust ( Uromyces caryophyllinus) sometimes appears. Asparagus rust {Puccinia Asparagi), probably introduced into this country from Europe but a few years- ago, is now generally 1 "Rusts of Cereals," Bulletin 109, S. Dak. Agr. Exp. Sta., 1908 246 PEACTICAL BOTANY distributed over asparagus beds. 1 The hollyhock and many other members of the mallow family (Ma&vacecey, to which the hollyhock belongs, are often all but destroyed by the holly- hock rust (Pucdnia Malvacearum). ^Ecidial stages of other rusts appear upon many common plants, as the May apple, jack-in-the-pulpit, burdock, sunflower, and blackberry. Apple rust and " cedar apples," produced by the rust Grymnospo- rangium macro- pus, offer a strik- ing life cycle. Upon red cedar trees in the late autumn, winter, and early spring branches may be found with hard brownish knots upon them (Fig. 200). The knots are outgrowths produced by the internal myceli- um of the rust. Near or before the period in the spring when apple trees are in flower or setting young fruit, the brownish knots or " cedar apples" become gelatinous, and from them yellow projec- tions protrude (Fig. 201). These projections are made up of hyphse bearing teleutospores. The teleutospores germinate at once, producing from one to three hyphse from each cell. Sporidia are formed, and since these are blown about in great profusion, some of them alight upon young leaves, flowers, or 1 "The Asparagus Rust: its Treatment and Natural Enemies," Bulletin 129, N. J. Agr. Exp. Sta., 1898. FIG. 200. A " cedar-apple" parasite (Gymnosporan- gium) as it appears in winter condition upon its host, the red cedar (Juniperus Virginiana) Natural size THE BASIDIUM FUNGI (BASIDIOMYCETES) 247 fruit of the apple tree, or other members of the apple family. The apple tree is thus infected, and during the summer the cups bearing secidiospores are formed. Some of the secidio- spores may fall upon the cedar and reinfect that host. In late summer and autumn "cedar apples" are again produced. 1 235. Toadstools and mush- rooms. These fungi are char- acterized in general by the fact that the mycelium lives entirely within the material which fur- nishes its nourishment, and oc- casionally sends up into the air the spore-bearing structure that is called the toadstool or mush- room. Scientifically there is no accepted distinction between toadstools and mushrooms. Those forms that are known to be good to eat are popularly spoken of as mushrooms, while those that are not edible, or that are poisonous, are called toadstools. Even this distinc- tion, which is wholly popular and was made solely upon the basis of real or supposed edibil- ity, is not easily applied, since little is known regarding the edibility of many species. Furthermore, in a given genus some species may be excellent for food, and others poisonous. Cer- tain edible species are easily learned and are not readily con- fused with those which are poisonous. 2 There are over one thousand edible fungi which grow in the United States. 1 "The Cedar-Apple Fungi and Apple Rust in Iowa," Bulletin 84, Iowa Agr. Exp. Sta., 1905. 2 The United States Department of Agriculture publishes several bulle- tins upon poisonous and edible fungi. FIG. 201. A "cedar apple "(Gymno- sporangium) in its spring condition The extrusions are made up of hyphae and teleutospores. Three eighths nat- ural size 248 PRACTICAL BOTANY 236. Toadstools and mushrooms : structure and reproduction. The mycelium often becomes very extensive, and may form moldy or cobweb-like threads within the rich earth, decaying wood, or other nourishing substratum. When it grows, the mycelium helps to bring about the decay of the material which nourishes it, and therefore may be very destructive. The FIG. 202. A large toadstool Note the stalk, the ring, the crown, and the gills. One third natural size mushroom spawn, which is sometimes especially prepared and sold in bricks to those who wish to grow mushrooms, is sim- ply a mass of mycelium. At times there form aggregations of the mycelium, which are whitish, bud-like growths called " buttons," and which are the beginnings of the structures known as toadstools or mushrooms. They grow and push their way to the surface. As the "button" elongates, its top begins to expand into the umbrella-like form, and finally opens out as the crown or pileus, with its center attached to the upper THE BASIDIUM FUNGI (BASIDIOMYCETES) 249 FIG. 203. Gills of a toadstool On the faces of the gills the spores are formed. Seven and one-half times natural size. After Buller end of the stalk (stipe) (Fig. 202). As the pileus opens, it is joined to the stalk beneath by means of a layer of hyphse (the veil). This in some species, in breaking away from the pileus, forms a ring or annulus about the stalk. The underside of the pileus is made up of plate-like growths (jjills), which radiate from the point of attachment to the stalk. The flat surfaces of the adja- cent plates face one another (Fig. 203). Some of the hyphse which compose the gills grow in such a way that their tips extend a little way from the surface of the gill. Upon this extended tip (ba- sidium) four (rarely two) branches are formed, and upon the tip of each branch a spore (basidiospore) is formed (Fig. 204). When the spores fall upon moist, warm, nutrient material, they produce a new mycelium. By cutting the pileus of a ripe toadstool from the stalk and placing it with the gills downward upon a piece of ordinary white or black paper, after a few hours there will be made a "spore print" composed of thousands of spores. 237. Toadstools and mushrooms: different forms and habits. The type form just described is representa- tive of the most common toadstools &iid mushrooms. The commonest Cultivated mushroom (Agaricus cam- pestris) has long been a well-known article of food. Some of the same type of toadstools form " fairy rings " (Figs. 205 and 206), which in constantly widening circles may appear in the same locality" year after year. The phenomenon is doubtless due FIG. 204. Basidia arid spores of a toadstool Three hundred seventy times natural size. After Buller FIG. 205. A group of toadstools Note the stalk, crown, ring about the stalk, and the gills FIG. 206. A "fairy ring" formed by toadstools This ring appeared with successively widening circles for at least six years. Many known rings have reappeared for much longer periods of time 250 THE BASIDIUM FUNGI (BASIDIOMYCETES) 251 to the fact that the underground mycelium either exhausts all available food, or deposits within the circle secretions which for a few years prevent further growth of this fungus. Upon logs, trees, and stumps many kinds of toadstools are found, as those shown in Figs. 207 and 208. But most abundant are the various species of Polyporus (meaning many pores) and other genera (Fig. 209). These often are hard FIG. 207. A group of small toad- stools (Marasmius) growing from decaying wood Natural size FIG. 208. The oyster toadstool growing upon the dead and de- caying branch of a tree Three eighths natural size and woody, and instead of gills they have many small pores upon the under surface, within which the basidia bear the spores. In some species of Polyporus the reproductive body may continue its growth annually for many years. Meantime its mycelium, which feeds it, has been growing within the tissues of the host and gradually bringing about its decay. Another toadstool (Hydnum septentrionale), the mycelium of which produces the heart rot of the sugar maple, forms a reproductive body which, though its general form is like the 252 PRACTICAL BOTANY FIG. 209. A tree-destroying fungus (Polyporus sulphureux) growing at the base of a red-oak tree About one sixth natural size common mushroom, has its spores produced upon spines. In deep, moist woods, upon old logs, a species of the Hydnum sometimes produces an immense (twenty to twenty-five pounds) edible, coral- like, reproductive body. A coral- like toadstool is Clavaria (Fig. 210). The toadstools and mushrooms, both saprophytic and parasitic, are widely distributed. Forest and or- chard trees are in great danger of infection by them whenever open wounds are left from broken limbs or pruning. It has been FIG. 210. A coral-like toadstool (Clavaria) One half natural size THE BASID1UM FUNGI (BASIDIOMYCETES) 253 shown 1 that a single Ayaricus campestris may produce not less than 2,000,000,000 spores ; that the " shaggy-mane " mush- room (Coprinus comatus) may produce 5,000,000,000 spores; and that Polyporus squamosus may produce 11,000,000,000 spores. It is also inter- esting to note that the same authority estimates that in Polyporus squa- mosus one spore in about 1,000,000,000,000 has a good chance to start a new life cycle. 238. The puffballs. These are basidiomycetes whose mycelium usually grows in rich soil, and which have a globular reproductive body that incloses the basidia and spores. Puffballs may range from the size of a pinhead to those that are a foot in diameter (Fig. 211). When ripe they burst open, usually at the top, and small clouds of spores may be emitted at intervals for months and even years. The largest known puffball is Lycoperdon yiganteum. One specimen of it which measured sixteen by eleven inches was estimated 2 to contain 7,000,000,- 000,000 spores. It was also estimated that some of the puffballs 1 Buller, A. H. R., Researches on Fungi. Longmans, Green, and Com- pany, 1909. 2 Buller, A. II. R., loc. cit. FIG. 211. Two species of puffballs of the genus Lycoperdon Those above are one half natural size, and that below is two ninths natural size 254 PRACTICAL BOTANY may each shed spores at the rate of 1,000,000 per minute, and may continue this for several days. Another puffball is called the " earthstar " ( Geaster). It grows in sandy and waste places. When its reproductive body is mature the outer surface peels back from the tip, thus exposing the central body, which contains the spores. A closely related form is the stinkhorn fungus (Fig. 212). The nest fungi are peculiar puffballs which grow within and upon rich earth, well-decayed wood, old manure piles, etc. The reproductive body opens, and re- sembles a small cup or nest. Within the nest are a few egg-like bodies (Fig. 213), each of which contains a mass of spores. 239. Summary of the fungi. Because of their ex- treme simplicity and their close relation to the blue- green algse the bacteria or schizomycetes were treated first in this series of classes. Then in the chapter follow- ing the algse the class of fungi called phycomycetes, FIG. 212. The stinkhorn fungus (Phallus) which in many respects resemble green algse, was discussed. In this chapter classes that are very unlike algse the ascomycetes and basidiomycetes and the lichens are discussed. The bacteria are so simple in struc- ture that they are generally regarded as the simplest living organisms. They reproduce themselves almost wholly by vege- tative processes, occasionally by simple resting spores. In their At its spore-forming period this has a very foul odor, that attracts flies, which are said to distribute the spores. When young the whole hody is a whitish, egg-shaped mass. From this there emerges the stalk, upon the end of which is the spore-bearing crown. One half natural size THE BASIDIUM FUNGI (BASIDIOMYCETES) 255 life processes they are of the greatest importance, since they are instruments of decay and soil enrichment, and bear an im- portant relation to various industries. As producers of diseases of plants, animals, and men, they have great significance. Phycomycetes are sometimes saprophytic and sometimes parasitic. As saprophytes they are instruments of decay, and as parasites they often kill their hosts and then as saprophytes disorganize them. The simpler phy corny cetes, as bread mold, FIG. 213. Nest fungi growing in soil in which is decaying wood Within the cup-like plants are the egg-like bodies which contain the spores. Natural size reproduce themselves by asexual spores and by forming zygo- spores, as do some of the green algse. One of the more com- plex forms, water mold, lives in the water and reproduces by means of zobspores ; it also forms oospores by means of special sex organs. Sometimes its oospores are produced without fer- tilization. Such forms as the downy mildew of the grape are parasites. They bear conidia, or sporangia-like bodies, upon the leaves of their hosts, and produce oospores within these leaves. Ascomycetes have conidia, but are distinguished by the fact that some of their spores are formed in sacs at the tips of hyphse. These sacs are in open cups, as in Morchella, Peziza, and Sclerotinia ; or inclosed, or almost so, as in the lilac mil- dew. Some forms (^Penicillium and yeasts) seem to have lost part of the usual ascomycete life cycle. The life habits of 256 PRACTICAL BOTANY ascomycetes are of great importance in relation to dairy indus- tries, fermentation, and to diseases of economic plants. Basidiomycetes comprise extremely diversified forms, many of which (smuts and rusts) are not conspicuous except in their spore formation. Striking polymorphic life cycles are shown in the rusts. The rusts and smuts are destructive para- sites of the greatest importance. The toadstools and mush- rooms, though representing a very large number of forms with world-wide distribution, have a comparatively simple life cycle. They are chiefly saprophytic, though several forms, as the tree-destroying fungi and others, attack living hosts. Puff- balls are almost exclusively soil saprophytes. The lichens exhibit a remarkable case of mutualism or of slavery in which algae and fungi live together in such a way as to compose a new organism. In these organisms the algae do the necessary chlorophyll work, and the fungi, it seems, protect the whole organism, thus making life possible in places and under conditions that would otherwise be impossible for both mutualists. Algae and fungi of the lichen combination reproduce themselves in the ways that are peculiar to the algae and fungi, and not as a new lichen organism. 240. Classification Thallophytes Algae Fungi Class I. Phycomycetes Class II. Ascomycetes. Leading genera used as illustrations, Peziza (cup fungus), Sclerotinia (brown rot), Microsphcera (lilac mildew), Morchella (morel), Penicilliinn (blue mold), Saccharomyces (yeast), Claviceps (ergot), etc. Class III. Lichens. Leading genera used as illustrations, Parmelia, Usnea (bearded moss), Cladonia, etc. Class IV. Basidiomycetes. Leading genera used as illustra- tions, Ustilayo (smut), Puccinia (rust), Uromyces (rust), Gymnosporangium (cedar apple), Agaricus, Polyporus, Hydnum (toadstools or mushrooms), Lycoperdon (puft'ball), etc. CHAPTER XVI MOSSES AND LIVERWORTS (BRYOPHYTES) 241. Introductory statement. There are two classes of this division of the plant kingdom, the mosses (Musci) and liver- worts (Hepaticce). The name Bryophytes means " moss plants." Liverwort literally means " liver plant" or " liver root," so called from the supposed resemblances in form between the liverwort plants and the .human liver. There is a rather com- mon flowering plant (Ifepatica) which is sometimes called liverleaf or liverwort. This flowering plant should not be con- fused with the true liverworts. Also there is a common habit of calling all small green plants "mosses," but when we dis- cover what kind of plants mosses are, we shall find the proper use of this term. In some respects liverworts are simpler than the mosses, and they are given as the first or lowest class. But it;is so much easier to get clear notions of some aspects of bryophytes by a study of mosses that we shall first consider them. MOSSES 242. The moss plant: the protonema. Mosses of various kinds are widely distributed. Careful observation of a moss plant enables one to see that it has green leaf-like structures arranged around a very small stem. Sometimes also there ap- pears upon this leafy stem a slender stalk with a swollen pod- like tip or capsule (Fig. 216). In this tip are many simple asexual spores, and we shall begin the life cycle by following the germination of one of them. When an asexual spore germinates there grows from it a filamentous, branching body. Its cells contain chloroplastids 257 258 PRACTICAL BOTANY and closely resemble cells of many of the green algse (Fig. 214, A). Mats of this growth form upon or within such sub- stances as soil, logs, etc., which are moist and shaded. These FIG. 214. The moss plant A, the alga-like protonema with branches (a) ; a young bud (c), and one (6) which has divided and produced several cells. -B, a bud which has grown until young leaves (c) and rhizoids (6) are formed. The old protonema (a) is still seen. Both considerably enlarged growths are so alga-like that in the absence of considerable magnification it is not possible, ordinarily, to distinguish them from the algae. At times some of the cells become swollen, MOSSES AND LIVERWORTS (BRYOPIIYTES) 259 divide by oblique walls, and form buds (Fig. 214, A, &). These buds continue to grow, the outermost cells develop leaves, the central ones become the stem, and from the lower ones root-like hairs (ihizoids) descend into the soil (Fig. 214, B, 6). The buds, there- fore, are the beginnings of the leafy moss plant (Figs. 215 and 216). Young buds may grow directly into leafy plants, or become dormant for a time and then resume their growth. Since the alga-like growth is that which precedes and produces the leafy moss plant, it is called the protonema, mean- ing " primitive thread." 243. The moss plant: nu- trition. Dense growths of moss plants may form from a single mat of protonema. The rhizoids, embedded in soil, humus, or de- caying timber, bring these plants into close relation with the water supply. The whole dense growth may serve as a sponge, so that the plants may then be virtually immersed in water. Some mosses really live part or all of the time in streams or bodies of still water. In exposed regions mats of moss may become dry enough to crumble into powder when handled, but, if undisturbed, may pro- ceed with their growth upon the return of moisture. Some mosses also show remark- able ability to withstand extremes of heat and cold. The stem and leaf arrangement that exists in the mosses exposes chlorophyll to the light in a different way from that which was found in the algae. With the leaves arranged FIG. 215. A fully formed leafy moss plant Z, leaves; s,stem; r, rhizoids. Ten times natural size FIG. 216. A leafy moss plant upon which the sporo- phyte has grown Lp, the leafy plant; s, seta; c, capsule. Five times natural size 260 PRACTICAL BOTAHY I J radially about the stem much more chlorophyll is exposed than could be exposed in the same space by a prostrate plant. The importance of the stem in holding these leaves up into the air, thus making the radial arrangement possible, is evident. It is also possible that no less importance should be attached to transpor- tation of water through the stem to the leaves, though it is not- known to what extent moss leaves get their water directly through their surfaces or through the stem. The expanded portions of the leaves are a single layer of cells in thickness, while the median por- tion may consist of several layers of cells. In the middle (midrib) there are rows of elongated cells running from base to tip of the leaf. These constitute the vein of the leaf. 244. The moss plant : sexual reproduction. The sex organs are borne upon the upper end of the stem. If the terminal leaves are FIG. 217. Archegonia of a moss carefully removed from plants that are in reproductive condition, two kinds of sex organs together with some sterile filaments (para- physes) may be found. In some kinds of mosses but one kind of sex organ grows upon a single plant, while in other kinds both may grow upon the same plant. Magnifica- tion is needed in studying them. At A is shown the tip of a stem of a leafy moss plant, with the frag- ments of leaves (T) surrounding a group of archegonia (a). At B is an enlarged archegonium, in the swollen part of which is the egg (e), above it the neck (ri), contain- ing the neck canal cells, and at the end of the neck are the cells (m) which later open to form the place of entrance for sperms. A, magni- fied 100 times; B, magnified 500 times. After Sachs MOSSES AND LIVERWORTS (BRYOPHYTES) 261 One of the sex organs, the archegonium', is flask-like, the neck being greatly elongated (Fig. 217, A and B). In the swollen part of the archegonium the female gamete or egg is formed. When the egg is mature the central cells in the neck disor- ganize and the tip of the neck opens, thus leaving a, gelatinous passage- way into the open end of the arche- gonium and through the neck to the egg. The other sex organ, the antheridium, is club-shaped (Fig. 218), being attached by its smaller end to the end of the stem. Within each antheridium thousands of male gametes or sperm cells form. When abundant moisture is present (dew or rain) the antheridium swells, its tip bursts open, and the contents escape. The biciliate sperms swim about actively, and if some of them come into the vicinity of the arche- gonium neck they make their way down through the gelatinous pas- sageway. One of the sperms unites with the egg, thus producing the oospore. It is evident that the diffi- culty of securing fertilization of the egg in this case is greater than in such plants as VaucTieria and (Edogo- nium. But the very large number of sperms produced in moss antheridia helps to make it possible for sperms to be widely spread, thus making fertilization more probable. 245. The moss plant : the oospore and its product. The oospore begins to grow almost as soon as formed. It grows from the place in which it was formed, and soon elongates and thickens until its lower end pushs down into the end of FIG. 218 An antheridium (a) of a moss. From its tip the sperms (&) are escaping, and one of them is shown enlarged at the side (c). a and 6, magnified 350 times; c, magnified 800 times. After Sachs 262 PKACTICAL BOTANY the stem upon which the archegonium grew. This gives the lower end a foothold in the stem, and by reason of its close contact this end, or foot as it is called, absorbs food material from the stem. The young stalk also bears chlorophyll and may manu- facture some of its own food. The upward end elongates rapidly and carries up with it the old arche- gonium wall, which meantime has grown somewhat (Figs. 216 and 219). This elongated structure is called the seta, which means a "bristle" or "hair." Since this old archegonium now changed is like a hood, it is called calyptra, which means " hood." Beneath the calyp- tra, at the end of the seta, there is formed the enlarged capsule. Within the capsule, by division of certain specialized cells, large numbers of spores are formed. At the extreme tip of the capsule, beneath the calyptra, is the mouth, oiperistome, which is covered by a lid known as the operculum, mean- ing the "cover" or "lid." When the spores are ripe the calyptra may fall off and the operculum be thrown off by swelling of the cells immediately below it. There then appears around the margin of the mouth a row of teeth (Fig. 220). The number of teeth in a capsule is definite for each species of moss, and sometimes special students of FIG. 219. Growth of the moss oospore to form the sporophyte At A is a diagram of the oospore after it has gone through several cell divisions and has spread the archegonium wall. B shows the tip of a plant stem with parts of leaves ahout. The oospore has grown into a stem-like structure (), has its lower end inserted in the old plant stem (gr), and the other end has carried up the en- larged archegonium wall (a) as the hood or calyptra. After Sachs MOSSES AND LJVEEWOKTS (BRYOPHYTES) 263 mosses use this number as the basis of distinguishing one species from another. On account of the regular thickenings upon the teeth they are readily affected by moisture changes ; that is, they are hygroscopic. When they extend within the capsule the spores adhere to them. As they straighten and extend outward they move with a jerking motion which serves to throw the spores about. A moss may be made to repeat the characteristic tooth movements under a hand lens or low power of a microscope, by being moistened and then fanned until dry. The spores developed within the capsules are made entirely by cell division and are therefore asexual spores. As seen in Section 242, they t may germinate and produce protonema. Because of the large number and wide distribution of asex- ual spores, abun- dant production of protonema occurs when the favorable conditions of mois- ture, light, and tem- perature exist. 246. The moss plant : alternate stages in the life cycle. It is evident that in the mosses sexual and asexual reproduction are limited, each to a distinct part of the life cycle. It is also evident that each of these parts of the life cycle forms a kind of spore which, upon germination, produces not the same part of the life cycle, but the other part. The asexual spore that is formed in the capsule germinates and produces protonema, which, by means of buds, produces the leafy plant; the oospore, which is produced by union of gametes, the egg and sperm, germinates and produces the foot, seta, and capsule. The FIG. 220. Tips of moss capsules A, a side view of a moss capsule showing the teeth (t), and the mouth or peristome (p), to which the teeth are attached. (Considerably enlarged.) B, an end view of a moss capsule. Note the peculiar spiral arrangement of the teeth and the transverse thicken- ings upon them. (Greatly enlarged) 264 PRACTICAL BOTANY part of the life cycle which produces the asexual spores is called the sporophyte, meaning an asexual spore-producing plant. The part which pro- duces the obspore is called the gametopliyte, the gamete- producing plant. The spo- rophyte, therefore, is the asexual generation of moss, and the gametophyte is the sexual generation. The rela- tion that these two bear to one another in the complete life cycle is called the alter- nation of generations. The fact that the proto- nema and leafy shoot are distinct structures does not introduce a third genera- tion, since one of those struc- tures grows from the other without the in- tervention of FIG. 221. Sphagnum A, an entire plant which bears capsules upon its tallest branch (natural size) ; B, two sporophyte capsules and stalks enlarged ; C, tip of a vegetative branch enlarged MOSSES AND LIVERWORTS (BRYOPHYTES) 265 a spore. It must also be kept in mind that alternation of generations refers to alternation between the sexual genera- tion and the asexual one. In case of several kinds of asexual spore reproduction, such as were seen in some of the parasitic fungi, the term alternation of generations does not apply in its usual meaning, though obviously in such cases there is a series of stages that make up the life round. A more detailed discussion than we have given might show a real alternation of generations in algse and fungi, but for an elementary study this is not advisable." 247. Kinds of mosses. There are hundreds of different species of mosses, and nearly all of them follow closely the life cycle already outlined. The moss used for the illustra- tions (Figs. 215-220) is Funaria hygrometrica. Another com- mon moss and one of the larger ones is pigeon-wheat moss (Polytrichurni). In forests it commonly produces thick cush- iony patches, and when sporophytes are present they are quite prominent and bear unusually large calyptras. Peat-bog moss (Sphagnum) is a very striking form, which with other plants may form peat. It is common in bogs every- where, and grows about the edge of the water or upon the extremely wet soil that has been formed by the partial decay of plants. Due to the peculiar structure of the leaves these plants hold water in great quantities, and from a handful of the plants water may be pressed as from a wet sponge. The gametophyte or leafy shoot of Sphagnum continues its growth at the plant tip from year to year, and the older buried or submerged portions gradually become partially decayed and 'intermingled with other plant material. Dense peat masses are thus formed. Such material forms peat fuel, which is com- pressed, dried, and kept for sale in some markets. The sporo- phyte of Sphagnum is quite unlike that of the moss described above, since it is merely a spherical capsule upheld by the elon- gated stem of the gametophyte (Fig. 221). Sphagnum is used quite commonly as a packing material; it is also used as a covering for holding moisture within the soil of potted plants. 266 PRACTICAL BOTANY LIVERWORTS 248. Riccia. Among the bryophytes the liverworts are sim- pler than the mosses, and some of the liverworts are extremely simple. Upon moist soil at the margins of ponds and streams and sometimes free-floating in quiet water, the small, green, disk-like Riccia or Ricciocarpus plants may be seen (Fig. 222). Upon careful observation, root-like projections (rhizoids) may be observed upon the lower surface. The plant is two-lobed, with a depression or notch between the lobes. This body is frequently spoken of as a thallus, though it is not like the thallophyte body. The rhizoids extend downward and backward from the notch. The upper surface of Riccia is greener than the lower surface. Near its margin the plant may be but one or a few layers of cells in thickness. Evidently Riccia, though a prostrate plant, is much more complex than any of the algae. It is more complex in that it has distinct upper and lower surfaces, with root-like hairs grow- ing from the lower surface. It is also to be noted that it has a distinct apical or growing end and a basal end. Chlorophyll is borne in the compact body cells, and living as the plant does, upon damp earth or in water, it can readily secure the materials from which foods are manufactured It is more complex than the protonema of moss, but less so than the leafy shoot. In reproducing itself each individual plant of Riccia forms within its tissues both kinds of reproductive organs. One of these is an archegonium, the tip of which just reaches the upper surface of the plant. In the swollen part of the arche- gonium is the large egg cell, which is therefore deeply em- bedded in the plant tissues. The antheridia also open to the FIG. 222. A simple liver- wort (Ricciocarpus) It has distinct upper and lower surfaces, bears rhi- zoids (r) on the under surface, and branches from a midrib into leaf- like structures (I) . About five times natural size MOSSES AND LIVER WORTS (BKYOPHYTES) 267 upper surface. From these there escape large numbers of cells, each of which produces a sperm. Sperms enter the neck of the archegonium and one unites with the egg, thus producing an oospore. The oospore does not grow directly into a new plant, but produces an enlarged spherical body which is embedded in the tissues. After a time all of this spherical body except a single layer of outside cells divides into spores. These escape by the breaking down of the tissues of old plants. They may grow into new Riccia plants. The main Riccia body is the gametophyte, since it produces the gametes which form the oospore. The sporophyte which develops from the oospore is very simple. It is entirely em- bedded within the gametophyte body. All of it forms spores except a single outside layer of cells. Alternation of genera- tions is as truly present as in the mosses but is not nearly so conspicuous. 249. Marchantia: vegetative characteristics. This liverwort grows in moist places, such as swampy regions, shaded river banks, and protected rocky ledges. Sometimes it forms exten- sive mats, completely covering the material upon which it grows. Single plants may become several inches in length and breadth and many layers of cells in thickness. Its well- differentiated upper and lower surfaces, apical and basal regions, and masses of rhizoids, which are sometimes an inch or two in length, are features which were less developed in Riccia. The plants grow forward, the lobes continuing to branch, until at times quite extensive growths are produced (Fig. 223). Older portions may die, leaving the younger branches as new and independent plants. The nutritive tissues of Marchantia are highly developed. There are chains of special chlorophyll-bearing cells in the upper tissues. These semi-open spaces or chambers are near the upper surface of the plant. The surface outline of these is diamond-shaped. Each diamond-shaped superficial layer of cells has in its center a chimney-like pore through which there 268 PRACTICAL BOTANY is atmospheric contact with the internal chlorophyll region. The lower layers of tissue bear less chlorophyll, but they com- pose the main supporting part of the plant. From these the rhizoids descend. In vegetative structure Marchantia is more complex than Riccia, or perhaps than mosses, and very much more complex than any of the green algae. FIG. 223. A common liverwort (Marchantia) The plant shown at the left is an archegonial or female plant : rh, rhizoids ; c, cupules, in which are buds or gemmae ; s, stalk of the archegonial branch ; r, radiating, finger-like projections of the head ; a, region in which the archegonia are borne. At the right is an antheridial plant : a, antheridial head. Both plants show the leaf- like expansion (I) and the midrib (m) . About one and one-half times natural size 250. Marchantia: vegetative reproduction. Upon the upper surface of Marchantia in the midrib region there are frequently developed cup-like outgrowths (cupules), within which many buds (gemmce) are formed (Fig. 223, ove outlined has been criticized on the ground that little or no attention is paid to the productiveness of the plant used as the source of pollen. A new sys.tem devised by Professor C. G. Williams, of the Ohio Agricultural Experiment Station, provides for equally careful selection of the staminate and of the pistillate parent. The system in its barest outlines, as stated by Professor Williams, provides for : 1. The usual ear-row test. Only a portion (usually about one half) of each ear is planted. The remnant is carefully saved, and when the ear-row test has shown which ears are superior, recourse is had to the remnants to perpetuate these ears. 2. An isolated breeding plot in which are planted the four or five best ears as demonstrated by 1. Not the progeny of the best ears, but 1 For details about corn breeding see De Vries, Plant Breeding, Open Court Publishing Co., Chicago; Bulletin 100, Illinois Agricultural Experi- ment Station ; and Circular 66, Ohio Agricultural Experiment Station. 424 PRACTICAL BOTANY the original ears. Usually the best ear is used for staminate plants and planted on each alternate row in the small breeding plot. All the plants from the other ears going into the plot are detasseled. The pedigreed l strains produced in the breeding plot are multiplied for general field use and also furnish ears of varying worth for a second ear-row test, if it is desired to continue the improvement. The ear-row test need not be isolated, for no seed is taken from it. Neither is there any need for detasseling until the breeding plot is reached. 388. Sugar beet breeding. Almost all the sugar that is used by civilized peoples is manufactured from sugar cane and sugar beets, the latter furnishing the greater part of the world's supply. Beets of many varieties have been cultivated since the sixteenth century or earlier. But it was only as late as the middle of the nineteenth century that scientific efforts were made by Louis Vilmorin to increase the percentage of sugar in beets grown for sugar-making. The sweetest roots are usually the heaviest in proportion to their bulk, 2 and therefore Vilmorin tested whole beets or pieces cut from them by placing them in brine strong enough to float all of the roots except those which contained an unusually large per cent of sugar. The sugar beet is ordinarily (though not always) a biennial, and the root produced in one year is used for grow- ing seed in the second year. These selected beets were planted for seed and became the parents of valuable new races. At present the process of producing beets of the highest value for the manufacture of sugar is a long and complicated one, consisting, as usually carried out, of the following steps- (1) Planting the best seed that can be bought. (2) Chemically testing average samples of the roots that are grown from the seed of (1) to see if they are good enough to breed from. (3) Selecting the best single roots by a chemical test. Less than one half of one per cent of all the beets tested pass this examination in a satisfactory way. 1 Pedigreed, because the pedigree on both sides is a matter of record. 2 That is, have the highest specific gravity. PLANT BREEDING 425 (4) Planting the mother roots selected in (3) for the production of what is called "elite seed." (5) Growing from elite seed small beets which are planted to secure commercial seed. It requires five years to obtain seed in large quantities from the very few selected roots with which the process of securing improved seed is begun. 1 Some notion of the thoroughness with which European seed growers choose their beets may be gathered from the fact that in 1889-1890 one of the most important firms tested 2,782,300 roots, from which it selected only 3043 to be planted for seed production. Constant pains must be taken in main- taining the best possible seed supply, as the quality becomes lowered at once when the seed is grown without special pre- cautions. This is due to the fact that the variations in beets are not elementary species (Sect. 383), and therefore are not sure to come true from the seed. Two of the most serious ways in which a poor stock of sugar beets falls short are in the low percentage of sugar and in the production of many worthless annual plants. In central Europe the annual indi- viduals sometimes constitute 20 per cent of the entire crop. The average yield of sugar from American-grown beets is at present 12 per cent or less. Exceptional beets have been found to contain more than double this amount. It is impos- sible at present to produce the roots in large quantities with anywhere near this high percentage of sugar, but decided gains may easily be secured, and an increase of 2 per cent in the yield would mean a gain of something like $ 100,000 per year in the beet-sugar production of the United States. 389. Constant and inconstant varieties. Beets, as stated in Sect. 388, do not long remain true to type unless there is con- tinued selection of the seed. There is a constant tendency of the high-bred sugar beet to " run out," that is, to revert to the average sweetness of beets grown from unselected seed. In this respect beets differ sharply from the cereals, most of 1 Sec Yearbook of the Department of Agriculture, 1904. 426 PRACTICAL BOTANY which do not quickly revert to the original type, unless as a result of miscellaneous crossing. Plant breeding, as a science, is much too young to enable us as yet to answer the question how far varieties tend to " run out " and what plants are most subject to this reversion. 1 It is probable that most cultivated plants grown from seed will be found to be decidedly less constant in maintaining their character for years than are the grains. 390. Hybridizing. Hybridizing, as the term is now gen- erally used, means the production of seed by the action of pol- len of one variety or species on the ovule of another variety or species. In order to produce seed that will grow, both species must usually belong to the same genus. Frequently different species of the same genus hybridize with difficulty; that is, the result of the attempted cross is to produce no seed, or seed that does not grow well. The offspring produced by hybridi- zation are known as hybrids. It has long been known that hybrids are often extraordi- narily variable, but the law (Mendel's law) which in many cases, though not in all, determines their characteristics and their mode of variation, was not discovered until 1865, 2 and did not become well known until some thirty-five years later. Recently much use has been made of hybridizing in order to set plants to varying, and the most desirable varieties thus produced have then been selected and used in breeding as already described. 391. How hybrids are artificially produced. Hybridizing, or crossing plants, is sometimes an easy, sometimes a rather dif- ficult, process. It is simplest in unisexual flowers, for exam- ple, in those of Indian corn. Here the "tassel" (Fig. 335) is a cluster of spikes of staminate flowers, and the "ear" (Fig. 336) is a spike of pistillate flowers, each thread of the " silk " rep- resenting a stigma and style attached to an ovary (grain of 1 See Bailey, The Survival of the Unlike, Essay XXIV. The Macmillan Company, New York. 2 See Bailey, Plant Breeding, chap. iv. The Macmillan Company, New York. PLANT BREEDING 427 corn). In hybridizing corn it is only necessary to tie a paper bag over the ear before the silk appears, in order to keep off stray pollen, and leave it covered until full-grown ; then re- move the bag, dust the silk thoroughly with pollen from tas- sels of the desired crossing variety of corn, and thereafter keep the ear covered until the silk is entirely withered. Sometimes in hybridizing corn the stalks are detasseled just before the ears are ready to receive pollen. If all the stalks of one kind or one row are thus detasseled, it is made probable that pollen, if received at all by the ears of the detasseled stalks, must come from another row or another kind of corn. The detas- seling of alternate rows is a rather common mode of insuring cross-pol- lination. In most cases of hybridiz- ing with bisexual flowers it is nec- essary to carry out processes similar to the following ones : (1) Select the flower to be pollinated before it opens or its own pollen is mature. If it is one of a cluster of flowers, as in the wheat or the apple, remove from the cluster of the flowers all that are not to be operated on. (2) Open the remaining flowers and remove the stamens by taking hold of the filaments with fine forceps, or cut away all the stamens at once, as shown in Fig. 338. Then cover the flower or the entire twig with a paper bag until the stigma is mature. (3) When the stigma is mature, pollinate it with the de- sired kind of pollen. This may be done with the finger tip, or FIG. 338. A peach flower prepared for hybridization A, flower cut round for removal of the stamens, with the removed parts of the young flower showing above ; B, longitudinal section of a flower showing level (s) at which the cut was made in A 428 PRACTICAL BOTANY with a cameFs-hair brush or other implement. It is safer to take pollen from a flower that has been kept covered with a paper bag to keep off foreign pollen. (4) Cover the pollinated flower again with a paper bag until the fruit has grown considerably. 392. General results of hybridizing. As was men- tioned before (Sect. 390), hybrids are likely to be extremely variable. Not only may they differ from either parent, but they may also be unlike each other. The differences include such features as the form, size, quality, and other characteristics of the entire plant or of its roots, stems, leaves, flowers, fruit, and seeds. Physiological differ- ences, such as early or late maturing, ability to grow in new conditions of soil and climate, unusual sus- ceptibility to or immunity from the attacks of para- sitic fungi, may appear and are sometimes (Sect. 398) of great economic impor- tance. It is much easier to perpetuate new varieties unchanged in the case of plants propagated by vegetative means, as by cuttings from roots or stems- or by bulbs or tubers, than in the case of those grown from seed. If a desirable variety of potato is obtained by hybridizing and then plant- ing seeds from the berries ("potato balls"), the hybrid can FIG. 339. A hybrid wheat and the parent forms The hybrid is in the middle. It is somewhat intermediate between the parents, being nearly (but not quite) beardless like the right-hand parent, with a length of head intermediate between the two and with the grains and their covering bracts stout, as in the left-hand parent. Photograph by Minnesota Agricultural Experiment Station PLANT BREEDING 429 be perpetuated with certainty by planting tubers of the new variety. But if a hybrid bean, pea, or wheat plant is produced, only a few of its seeds will " come true to seed " ; that is, the offspring of the hybrid seeds will, many of them, be what breeders call " rogues," or undesirable varieties, not closely resembling their hybrid parent. Year after year, for several generations, the garden plots containing descendants of the new hybrid must be rogued, or gone over plant by plant, FIG. 340. Variation in wheat, the hybrid offspring of hybrid parents After figure redrawn from Transactions of the Highland and Agricultural Society of Scotland in order to destroy all individuals but those of the desired variety. In the case of wheat, after the fourth generation some plants are usually to be found that will "come true to seed." 393. Results of hybridizing the grains. In this country especial attention has been given to hybridizing Indian corn and wheat. Some valuable varieties of corn have already thus been obtained, and many more seem likely to be secured. Hybrid wheats are of importance for use -as stocks from which to breed and select. At the agricultural experiment stations of the great wheat-growing states much time is now spent in hybridizing wheats for breeding purposes. 430 PRACTICAL BOTANY 394. Results of hybridizing small fruits. The most familiar hybrids among small fruits are grapes. It is probable that the Delaware and the Catawba are hybrids, and the Salem, Brigh- ton, and Diamond certainly are. Many varieties are directly or remotely descended from hybrids between the European wine grape and our northern fox grape, two wholly distinct species. d FIG. 341. Hybrid plums a, a stoneless wild plum ; b, c, d, fruit of hybrids of a with the French prune plum All drawn to the same scale A favorite blackberry, the Wilson Early, is a hybrid between two common wild species, the high blackberry 1 and the dew- berry. 2 Among the descendants of hybrids between an almost inedible species 3 from Siberia and an edible one 4 from Cali- fornia is a new constant species (not a variety), the Primus blackberry. Hybrid plums in the greatest variety have been produced by plant breeders, especially by the well-known grower of horticultural novelties, Luther Burbank. The amount of vari- ation in the offspring of a single hybrid is suggested by Fig. 341. One fruit of great value, the Climax plum, was bred by Burbank as a hybrid between a bitter, tomato-shaped Chinese plum and a Japanese plum. 395. Results of hybridizing citrous fruits. Most valuable and interesting work in hybridizing plants of the Orange fam- ily has been done by the United States Department of Agri- culture, under the direction of Dr. H. J. Webber. 5 The hardy 1 Eubus allegheniensis. 8 R. cratcegifolius. 2 R. villosus. 4 R. mtifolius. 6 See Yearbook of the Department of Agriculture, 1904. PLANT BREEDING 431 trifoliate orange, which resists our winters as far north as Phila- delphia, but bears a small, bitter, worthless fruit, was hybridized with the common sweet orange. Three valuable hardy hybrids known as citranges were produced. One of them makes a good substitute for grape fruit, another for lemons, and the third for rather sour oranges. They may be grown from two hundred to four hundred miles farther north than ordinary oranges. Another citrous hybrid is that between the tangerine and the grapefruit. This is called the tangelo, and has character- istics somewhat intermediate between those of the parent spe- cies. It is smaller in size, and the pulp is less bitter and acid than that of the grapefruit, while the " kid-glove " skin, readily peeled off with the fingers, is like that of the tangerine. Our most valuable citrous fruit is the Washington navel orange, nearly or quite seedless. It originated from chance seedlings found in a swamp along the Amazon and brought from Bahia, Brazil, to the United States Department of Agri- culture in the early seventies. This orange forms by far the greater portion of the entire California crop of over 10,000,- 000 boxes a year. 396. Results of hybridizing ornamental flowers. Some of the most showy flowers of our gardens and greenhouses are hybrids. Among the most important examples are the gen- era Canna, Amaryllis, and G-ladiolus. Orchids, too, have been hybridized to such an extent that a dictionary of hybrid orchids has been prepared. In most cases of flowers which have been bred and hybrid- ized for many years, the process of improvement has been due partly to crossing and partly to selection. It is often impos- sible to find out how many parent species or varieties have entered into the production of the final hybrid. 397. Summary of methods and results. Successful plant breeding requires a continuous effort to get better plants, either by picking out and growing chance varieties, or by con- tinued selection, first of a set of choice parent plants, then of their best offspring, and so on for several generations. 432 PRACTICAL BOTANY Hybridizing sometimes (but not nearly always) aids the plant breeder by giving him a large number of marked variations from which to select. High cultivation, together with plant breeding, has brought about many astonishing results. Plums three inches long have recently been produced. A hybrid beach plum bears so abun- dantly that the twigs are entirely hidden by the fruit. The largest cultivated apples are many hundred times the bulk of their remote wild ancestors. A new variety of blackberry plant covers one hundred and fifty square feet of soil and bears a bushel or more of fruit. 1 Most cultivated roots and tubers have been greatly changed from their wild condition, losing in the proportion of woody fiber which they contain, and gaining immensely in size. 398. Securing varieties immune to disease. One of the most important problems for the plant breeder is how to secure varieties immune to diseases. Two of the most notable achievements of our Department of Agriculture in this direc- tion have been the production of a disease-resisting variety of sea-island cotton and of watermelon. The soil of valuable cotton plantations had come to harbor a fungus (Fusarium) which attacked the roots of the plants, plugged the vessels with its hyphse, and destroyed almost the entire crop. In consequence of this many planters gave up cotton growing. Observation showed that often in a field where nearly all the plants were killed, here and there an individual survived, blossomed, and ripened its capsules. For four years plants were bred from the seeds of these resistant individuals until a variety was secured which withstood the attacks of the fungus and made it possible to resume cotton growing on the abandoned plantations. Extensive areas in the South, once devoted to the culture of watermelons, became so infected with a fungus that melon growing was no longer possible. The destruction was so 1 See the article by D. S. Jordan, ff Some Experiments of Luther Bur- bank," Popular Science Monthly, January, 1905. PLANT BREEDING 433 complete that no process of selection could be adopted, as in the case of the cotton. It was, however, found that the roots of the so-called "citron," a plant of the watermelon genus, were not attacked by the fungus. Watermelons were hybridized with "citrons," and about a thousand varieties were grown from the seeds thus obtained. Many of these proved resistant, but only one was found to be resistant and at the same time desirable in most other respects. This one variety is now grown with good success even on fungus-infected soils. 1 COLLATERAL READING The terms " Yearbook," "Farmers' Bulletin" "Bulletin . . . Bureau of Plant Industry," all refer to the .publications of the United States Department of Agriculture. A very detailed list of books and articles on plant breeding will be found in Bailey, Plant Breeding. The Macmillan Company, New York. Other titles not already referred to in this chapter are as follows : GENERAL Yearbook, 1898, " The Improvement of Plants by Selection." Yearbook, 1906, " The Art of Seed Selection and Breeding." Farmers' Bulletin 334, " Plant Breeding on the Farm." Bulletin 167, "New Methods of Plant Breeding," Bureau of Plant Industry. Cyclopaedia of American Horticulture, article "Plant Breeding." The Macmillan Company, New York. Cyclopaedia of American Agriculture, article "Plant Breeding." The Macmillan Company, New York. The Principles of Breeding, Davenport. Ginn and Company, Boston. SPECIAL Farmers' Bulletin 229, " Production of Good Seed Corn." . Yearbook, 1906, " Corn-Breeding Work at the Experiment Stations." Yearbook, 1902, " Improvement of Cotton by Seed Selection." Farmers' Bulletin 342, " Potato Breeding." 1 See an address by Dr. Erwin F. Smith on " Plant Breeding in the United States Department of Agriculture," before the Royal Horticultural Society's conference on genetics. CHAPTER XXIV FURTHER DISCUSSION OF PLANT INDUSTRIES 399. Introductory. Agricultural and horticultural indus- tries are fundamental, since they produce most of the things upon which people live. A scientific study of what plants are and how they live has been the means of raising these indus- tries to their present high efficiency. In preceding and in later chapters there is frequent reference to the practical nature of a knowledge of the principles of botany, but in the present chapter there are presented three topics which relate specifi- cally to agriculture and horticulture. The topics presented are: I. The Soil and the Plant; II. Special Care of Plants; III. Leading Agricultural and Horticultural Plants. I. THE SOIL AND THE PLANT 400. Composition of the soil : rock material. One of the most important lines of botanical study has to do with the interrelations of plants and the soil in which they live. Any extended consideration of agricultural and horticultural indus- tries must involve a comprehensive study of the soils, but in the present connection only an outline of the subject is given. In a general way it may be said that the basis of soils consists of more or less finely divided rock. A study of the dumping ground of a stone quarry will show that weathering processes are bringing about the disorganization of some of the stones, and as a result soil is made possible. Sometimes water freezes and expands within the crevices of the stone ; or roots of trees and other plants may grow in these crevices, and by expanding may break the stone. Organic material from plants and animals may help in disorganization, -and landslides 434 DISCUSSION OF PLANT INDUSTRIES 435 may crush the stones, or streams of water may wear them into smaller pieces. In ancient times great glaciers crushed and wore the stones, reducing enormous masses to smaller ones, gravel, and finely pulverized material. All these agencies and others have reduced the rocks so that in soils we are sometimes unable to find sand particles except by means of the microscope. EIG. 342. Production of humus in the soil A partially reclaimed swamp in which dead plant material several inches deep is decaying. In the foreground is a cluster of young skunk-cabbage leaves, and just back of these and in front of the tree is a cluster of unfolding leaves of Clayton's fern In a gravelly soil there are present small pebbles which usually show by their form and sometimes by their markings the kind of treatment they have undergone. In sandy soil the reduction of the rock is more uniform and has gone further. In clayey soil the particles are so small and fit together so compactly that the rock origin is not very evident. Peaty soil contains comparatively little rock material but much more of the results of partial decay of plant and animal bodies. There are all possible gradations between these different kinds of soils. 436 PRACTICAL BOTANY 401. Composition of soils: organic matter. A brief study of soils under the microscope would show that in addition to rock in different stages of decomposition, there is usually present considerable other material. Leaves, twigs, wood, her- baceous plants, and the bodies of animals decompose, and the products make up a most important part of the soil (Fig. 342). In almost all soils some organic matter may be found. When a large quantity of plant material lies upon the surface of the earth and partially decomposes, it is usually spoken of as humus. In undrained or poorly drained swamps into which little soil washes from adjacent hills, the deposit at the bottom of the standing water is almost pure organic matter, which is the peaty material often found in regions which once were swampy. 402. Composition of the soil : water and air. Around and between the particles of the more or less decomposed rock, and absorbed by organic matter, there is always some water, though it may be present in amounts so small as to be difficult of detection. Some water adheres closely about solid particles of the soil. Water also may fill the spaces between the par- ticles of solid material, and such water is known as the free water of the soil. Water may take into solution some portions of the soil. The amount of water in the soil varies largely and depends upon many factors. If there is little rainfall and the supply is not replenished from below, the coarse soils (gravel and coarse sand) will soonest become dry. But the amount and nature of the organic matter in the soil has much to do with ability to hold water. A good supply is usually held by fine sandy and clayey soils in which there is an abundance of organic matter. At times of continued heavy rainfall all kinds of soil may become filled with water, and the prevention of dangers from this surplus is discussed in the later sections of this chapter. In the spaces between the solid particles of the soil air is also found. Even in soils that are below ponds and streams DISCUSSION OF PLANT INDUSTRIES 437 there is some air, though its amount is usually so small that only water-enduring plants can grow therein. Observation of any porous soil immediately after a heavy rainfall will enable one to see bubbles of air emerging from the soil as the spaces which they have occupied begin to be filled by the water. After prolonged rains most of the air of the soil may have been ex- pelled, and it is generally supposed that in such cases it is the absence of air as much as the overabundance of water that brings injurious results to suddenly submerged plants. Obvi- ously the quantities of water and air in the soil are factors that are constantly varying in amount. As a given soil becomes dry it may also become compact, and it by no means fol- lows that the total space occupied by water and air together remains constant. 403. Composition of the soil: living things within it. A highly important factor of the soil consists of the many kinds of living things that inhabit it. Microscopic plants and animals of many kinds and in great numbers live upon one another, upon plant roots, or upon dead organic matter, and as they do so are constantly affecting the composition of the soil. Then the roots of living plants, the molds, and the burrow- ing animals such as the larvse of insects and the earthworm, constantly take from, add to, or otherwise change the soil. Earthworms eat their way through the soil, and as they do so they make it more porous and excrete materials that add to its available organic matter. Certain groups of soil bacteria have already been discussed (Sect. 343). The living things of the soil may be said to constitute an extensive and intricate society of plants and animals living close together and greatly affecting the nature of the material in which they live. 404. Drainage. The annual rainfall in different parts of the United States varies from ten inches or less to more than sixty inches per year (Fig. 381). In some parts of the country the total annual rainfall occurs within a short period, while in other regions it is usually fairly well distributed throughout the year. In all regions shortage of water is often a source 438 PRACTICAL BOTANY of danger to plants, and surplus water may also be injurious, Some of this surplus water may run off the surface without ever entering the soil (Sect. 408). If much of it enters the soil and remains for a long time as free water, it may drown the roots of plants. Sometimes the slope of the land surface is such that the free water of the soil runs off with sufficient rapidity to prevent drowning of plant roots, but in most cases growth of plants is enhanced by artificial methods of under- ground drainage. Ditches are made and earthen tile placed in them, thus forming drainage courses which hasten the nat- ural underground flow of the water. The cereals ordinarily thrive best in soils which contain from 50 to 60 per cent of their total water-holding capacity. In swampy places artificial drainage, which furthers the growth of economic plants, also restrains the growth of those swamp plants which ordinarily thrive in wet soils. Much of our best land has been made available by drainage, and there are enormous areas that would be most valuable if only they were properly drained. It has been estimated by Professor Shaler that along the Atlantic coast alone there are over 3,000,000 acres of swamp lands that it is possible to reclaim by drainage. The estimates of the United States government indicate that in our country there are nearly 100,000,000 acres of swamp land. There are thirty-five states in the eastern half of the United States in which there are over 30,000,000 acres of swamp lands. Much of this vast area can be drained, and may then become the growing place for valuable economic plants instead of the relatively valueless swamp plants. When underground drainage for ordinary cultivated fields was first advocated, opponents asserted that while it might be helpful in removing surplus water during times of abundant rain, the same drains would be the means of depletion of the water during times of drought. Practice has shown, however, that if surplus water is removed in rainy seasons, plant roots grow deeper into the soil and are thereby better placed for enduring subsequent dry periods. Furthermore, the thin films DISCUSSION OF PLANT INDUSTRIES 439 of water which adhere to soil particles are not removed by drainage, and plant roots are better located to avail themselves of this supply than if they are placed near the surface, as happens in wet soils. Within the last decade it has been shown that at least some of the cereals secrete and leave within the soil substances which are injurious to the kinds of plants which produce them. 1 Adequate drainage probably assists in removing some of these poisonous materials. Drainage ditches help to aerate the soil, and in this way are of great benefit to the growth of economic plants. 405. Tillage and water supply. In olden times agriculturists advised against cultivating corn and other crops during times of drought, because they thought that if constantly stirred the soil would lose its moisture more rapidly. People now know that it is of the greatest importance to till the soil during droughts in order that it may not lose its moisture. An illus- tration will help in studying this matter. If two pieces of loaf sugar are placed one upon the other, the lower one held in the thumb and finger and the other left lying loosely upon the first and not touching the fingers at all, and if the lower one is then placed in contact with water, two important facts are shown. The lower piece takes up water freely, but the upper one, though lying upon the lower wet piece, becomes wet only after a long time. Close connection between the solid particles is necessary for the rapid upward passage of the water. When soils are compact, moisture from the deeper portions passes upward freely, as in the lower lump of sugar, and evap- orates into the air. If, however, the surface is kept loose and finely pulverized, so that the particles are less closely conr nected, moisture does not readily pass through it and there is less loss from evaporation. The roots of plants being more 1 Schreiner, 0., and Reed, H. S., Some Factors influencing Soil Fertility. "Bur. Soils," Bulletin 40, U. S. Dept. Agr., 1907. Also,, " The Production of Deleterious Excretions by Roots," Bulletin 34, Torrey Bot. Club, 1907. 440 PRACTICAL BOTANY . deeply placed, are in contact with the moist soil from which a supply of water may be secured. The depth to which roots are known to go in regions where the water is found only at great depths is discussed in Sect. 27. For a long time it was supposed that the chief reason for cultivating plants was to keep down the weeds, but we here see that this is but a small part of the truth. Weeds have been of much advantage to agriculture, since in keeping them down the farmer has tilled the soil so as to help regulate the moisture supply for the growing plants. 406. Dry-land farming. It has been shown that the culti- vable area of the earth may be extended by drainage of un- used swamp areas ; but it may be greatly extended if water in proper quantity and at the proper times is placed upon arid lands. It is said that approximately two fifths of the area of the United States is too dry for cultivation without irrigation. Dry-land farming is one method now being tried in regions where there is some rainfall, but an amount that is insufficient to produce a good crop. By careful tillage of the soil the scanty rainfall is conserved, and in this way most of the rain- fall of two or more years may be used for one crop. Good crops have been grown in this way, but it is evident that much work over a long period is necessary in order to accu- mulate enough water for one crop. It is hoped that drought- enduring and drought-resisting varieties of economic plants, especially wheat and other cereals, may be found or devel- oped, thus increasing the outlook for dry-land farming. 407. Irrigation. The practice of irrigating lands is in some parts of the earth a very old one. Its extensive use in the United States is recent and both the government and private enterprises have expended enormous sums of money in sup- plying water from lakes and rivers to lands which previously were non-productive. In some cases this has involved damming the mountain streams and diverting the water over, around, or through mountains, and finally to the valleys to be culti- vated. With control of the water supply, fertile soil, abundant DISCUSSION OF PLANT INDUSTEJES 441 sunshine, and freedom from sudden changes in climate, it is evident that there is a great future for irrigated lands. Already over 13,000,000 acres are under irrigation, and other projects that are now under way will add largely to that amount. Even with this large acreage added to our tillable soil, it must be kept in mind that only a very small portion of the arid lands has been or apparently can be supplied with water from the sources that are now available. 408. Removal of soil by winds and water. Currents of air constantly carry particles of dust. During periods when the earth's surface is dry the amount of dust thus carried is large. If a pane of glass that has been moistened with oil is exposed for a time to the wind on a dry day, and then examined with a strong magnifying glass, it will furnish a good demonstra- tion of the dust-carrying power of moving air. Further illus- trations are found in the dust that strikes our faces on windy days, and in that which is deposited on window sills. Win- dow panes in the houses near the end of Cape Cod finally become translucent, like ground glass, from the action of sand driven by the wind. When cultivated fields become dry the wind may carry away large quantities of soil. This is some- times well shown in winter when snow covers the ground in such protected places as the leeward slopes of hills. Soil which has been frozen dry is often carried from other regions by the wind and dropped upon these leeward snow banks in such quantities as to bury the snow completely. Good windbreaks about cultivated fields help to prevent loss of soils by wind. Rapidly running surface water often carries away part or all of the fertile soil. In grasslands, meadows, and forested areas, surface water is retarded in its rate of flow, and conse- quently does not carry away much soil. In regions that were once forested and from which the timber has now been largely removed, the surface water soon erodes ditches (Fig. 343), which, with rapidly deepening channels and developing tribu- taries, will in a few years carry away much of the fertile soil of the forest floor. After forest fires, which themselves destroy 442 PRACTICAL BOTANY much of the humus of the forest soils (Fig. 344), the surface water, which is no longer retarded and absorbed by humus, flows with increased rapidity. In so doing it carries away large quantities of soil, sometimes uncovering the burned roots until the trees are easily overturned by winds. An area once for- ested may soon be cut into trenches and ridges until the only FIG. 343. Erosion of the soil following removal of the forest This land was covered with a heavy pine forest, and had a good soil, which was held upon the forest floor. When the timber was removed, erosion soon cut ditches through the pasture land remaining evidence, if any, of its previously forested condition is seen in the presence of a few plants such as young trees that are trying to grow in the poor soil that is left (Fig. 346). There are several means of preventing much of this loss of soil by erosion. In wooded regions judiciously cutting part of the timber each year rather than cutting all of it at once gives opportunity for new plants to occupy and hold the soil. There FIG. 344. Humus of the soil, and roots of red spruce and balsam fir burned by forest fire. Photograph by United States Forest Service 443 444 PRACTICAL BOTANY are many kinds of soil-holding plants which, if properly placed, will prevent erosion in its earliest stages, and these should be used. In open, 'hilly fields which are exposed to erosion, grass and meadow crops are desirable, since their roots help to hold the soil throughout the whole year. In such cases the roots and stems help to prevent the rapid run-off of the surface water. The very things that need to be done in the cultiva- tion of plants increase the danger of loss of soil where rapid flow of the surface water cannot be prevented. In hilly fields FIG. 345. A Mississippi hillside farm, newly cleared It is plowed and planted in rows around the hill to retard erosion. In such regions the soil when plowed washes away rapidly. Photograph furnished by W. N. Logan it is often difficult, sometimes impossible, to prevent erosion. In some localities the rows of growing plants are arranged across the slope of the hill (Fig. 345), thus assisting some- what in retarding the surface flow of water. If cultivation is continued in such places, the soil soon erodes, and it is with extreme difficulty that any plants gain a foothold (Fig. 346). In some foreign countries hillsides have been saved for cultiva- tion by a process of terracing. The terraces are constructed in such a way that the soil upon each is level or slopes toward the hill, thus retarding or preventing erosion (Fig. 347). 446 446 PRACTICAL BOTANY Terraced farms sometimes are desirable for vineyards, but it is obvious that for ordinary crops such elaborate care will prove profitable only where available land is extremely scarce. FIG. 347. Landward slope of an Italian promontory, the loose, loamy soil terraced to prevent erosion when under cultivation as a vineyard Modified from a photograph 111 localities with moderate slope of the surface, underground drains may prevent erosion except at times of extremely heavy rains. Many ditches that were formerly supposed to be too large to be taken underground have been so placed with great advantage. DISCUSSION OF PLANT INDUSTEIES 447 409. Soils and plant nutrition. Soils differ widely in their ability to support vegetation. Even the roots from one plant may develop quite differently in different soils, as is shown when the roots are arranged so that part of them grow in clean sand and part in rich loam (Fig. 348). A comparison of plants of the same kind that have been grown in regions that have different kinds of soil will show wide differences. From the point of view of the growth of our economic plants, FIG. 348. Effect of quality of soil on growth of roots The cucumber plant shown in the figure was grown in a shallow box, one end of which was filled with sand and the other with rich loam. The seed was planted in the sand, quite near the partition (p) of mosquito netting, which separated the sand from the loam. When the plant was one foot high the earth and sand were washed away and the roots sketched. Those grown in the loam weighed nine times as much as those in the sand. Three eighths natural size that soil is best which with the proper amount of cultivation will produce the best and largest yield of plant material. Such a soil is said to be fertile. There are now in progress many experiments relative to the nature of soil fertility, and many disputed questions are involved. Into these difficulties we shall not enter. How- ever, a study of the way in which plant foods are built up (Sect. 17), and of the chemical analyses that have been made of plants and of soils, enables us to know some of the facts 448 PEACTICAL BOTANY concerned. Carbon dioxide comes from the air, water from the soil, and with the water there are carried into the plants compounds of nitrogen, potassium, phosphorus, magnesium, calcium, iron, sulphur, etc. Uncombined nitrogen exists in the air, but as such it is unavailable to green plants. In the soil, when nitrogen exists in combination with oxygen as a nitrate (NO 3 ) green plants may use it. The following tables show the amount of these substances contained in the soil and the amount used in a given quantity of plant product. RELATIVE ** SUPPLY AND DEMAND " OF SEVEN ELEMENTS l SUBSTANCES Pounds in 2,000,000 pounds of the aver- age crust of the earth Pounds in 100 bushels of corn (grain only) 2 200 17 49200 19 48 000 7 68,800 u 88,600 1 Sulphur . . * 2 200 1 4 Pounds above one acre of ground 70,000,000 100 MINERAL PLANT FOOD IN WHEAT, CORN, OATS, AND CLOVER 2 PRODUCE Phos- phorus (pounds) Potas- sium (pounds) Magne- sium (pounds) Calcium (pounds) Iron (pounds) Sulphur (pounds) KIND AMOUNT Wheat (grain) 50 bu. 12 13 4 1 .3 .1 Wheat (straw) 2 tons 4 45 4 9.5 1.5 2 Corn (grain) 100 bu. 17 19 7 1.3 .4 .2 Corn (fodder) 3 tons 6 52 10 21 4.8 5.8 Oats (grain) 100 bu. 11 16 4 2 .5 .6 Oats (straw) 2 tons 5 52 7 15 2.8 3 Clover (seed) 4 bu. 2 3 1 .5 .1 Clover (hay) 4 tons 20 120 31 117 4 6.4 1 After Hopkins, C. G., Table 8, Soil Fertility and Permanent Agricul- ture, 1910. 2 Ibid., Table 13. DISCUSSION OF PLANT INDUSTRIES 449 410. The nitrogen supply. The nitrogen supply of plants has already received attention in Sect. 343, Chapter XXI, which should be reviewed in the present connection. Long before the action of the soil bacteria was known, agricultur- ists knew of the value of clover and other leguminous plants as a means of helping to maintain or regain the fertility of the soil. It is now known that when soils are poor in nitrogen compounds it is possible to replenish the nitrates from the atmospheric nitrogen by the use of clover and its relatives, upon the roots of which grow tubercles containing the nitro- gen-fixing bacteria. Sometimes it is difficult to get clover to grow in old and much-worn soils. This may be due to the fact that there are no nitrogen-fixing bacteria in the soil to start the tubercles. In such cases they must be introduced from a soil in which they are growing, or from artificial cul- tures. The best way of introducing them consists in scatter- ing over the impoverished field some soil from fields in which tubercle-bearing plants have grown. Successful clover fields and waste places in which the common sweet clover (Melilo- tus~) grows, furnish good soil for infecting worn-out lands. Some much-used soils have become quite acid, and this acidity seems to interfere with growth of the tubercle-forming bacteria. It has been found necessary in many cases to coun- teract this acidity with limestone before the tubercle bacte- ria can flourish upon the clover roots and thus produce the nitrates that are needed for nutrition of the clover and the enrichment of the soil. 411. Is fertility permanent? It is a fact of common obser- vation that when a given crop of plants is cultivated upon the same soil for a long period, of years the yield of the crop diminishes. Agriculturists learned a very long time ago that by growing different crops in rotation better yields were secured. But even with this rotation of crops and with careful cultivation, the annual yield decreases unless the soil is replen- ished in some way. The oldest experiments of which there are complete records are still in progress at the Rothamsted 450 PEACTICAL BOTANY Experimental Station, Harpenden, England. Some of these began in 1848. Certain crops have there been grown year after year upon the same soil. A barley field, which has been unfertilized since the experiments began, produced in the year 1849 a little over 40 bushels per acre. Each year thereafter, with no fertilization, barley has' been grown on the same field, and the yield has steadily decreased, so that dur- ing the twenty years closing in 1909 the average per year was less than 15 bushels per acre. Another piece of ground was used for wheat, turnips, and clover, in rotation, with three years given to each rotation, and was fertilized by use of nitrogen and mineral fertilizers. Considering only the wheat records, we have the following : In the first twenty years the average yield of wheat for the years in which wheat was grown was 35.3 bushels per acre ; in the second period of twenty years the average yield was 32 bushels per acre ; and in the third period of twenty years the average yield was 36.4 bushels per acre. In the second twenty-year period one year of general wheat failure materially reduced the average for that period. 412. Soil improvement. Since plants use such large quantities of the materials that are named in the tables given above, it is apparent that any soil to be fertile must contain these materials. Merely containing them, however, does not make a soil fertile. They must be in the particular combination in which plants can take them ; the soil must be of such a texture and physical nature as to permit the processes through which plants secure their foods. Such chemical substances within the soil as strong solutions of injurious salts, if present in sufficient quantities, will prevent the passage of materials into the plant. A fertile soil, then, is one that has the following requisites : a favorable water content, a good supply of mineral substances necessary to plant growth, freedom from harmful chemical substances, and favorable texture and physical composition. Many soils that once were fertile have become almost or quite unproductive, either through exhaustion of food elements, or through accumulation of harmful substances, and vigorous DISCUSSION OF PLANT INDUSTRIES 451 study is now being made regarding the nature of these limit- ing factors. The Rothamsted experiment and hundreds of others that have been made in the United States show the good effects upon soil fertility that may be secured by proper rotation of crops and proper care of the soil. II. SPECIAL CARE OF PLANTS 413. Horticulture and gardening. Scientific study has aided much not only in the matter of the better growth and care of field crops and the forests, but in gardening and agriculture as well. All that has been said about what a plant is and how it lives, and about soils, cultivation, and plant food, applies in some way to gardening and agriculture ; it must be recognized, moreover, that each garden or orchard crop is a specialty in itself, and requires special study for mastery. Almost every kind of garden or orchard plant thrives and yields best in cer- tain climates, in certain kinds of soils, often with certain kinds of exposure to light; has its own peculiar diseases, and re- quires particular treatment in caring for its matured product. It can be no part of this general discussion of botany to deal with such matters in detail, but two or three kinds of special care should be discussed as illustrations of the nature of the work that is being done. 414. Pruning. In Sect. 60, Chapter IV, there was a discus- sion of the way in which natural pruning occurs. Artificial pruning has become a general practice, and the botanical relations of the process are therefore significant. In injured plants, whose branches have been broken by wind or other destructive agencies, cutting away the broken parts discontinues the passage of food into the injured portions, makes it possible for new branches to grow into the space occupied by the injured branches, and decreases the danger of disease infection. Often the last result is not secured because the cut area is not treated so as to prevent entrance of fungus spores, bacteria, or insect parasites. When the wound that is 452 PEACTICAL BOTANY made by pruning is small, the cambium layer sometimes grows over the cut surface, the wound thus healing without becom- ing the place of infection. But large wounds are almost cer- tain to become infected with fungus spores before they heal, and they thus become the means of injury or destruction of the whole plant. A heavy coat of paint placed upon the cut sur- face usually prevents the entrance of destructive organisms. At transplanting, all injured roots are pruned away and new, vigorous roots are soon developed. During the time when the roots -are becoming established, transpiration of water from the aerial parts may greatly endanger the plant. This is one of the reasons for heavy pruning of the top at the time of transplanting. After the top has been pruned new growth develops, and by the time the root system is established and is thus in position to take up water, the increased transpiring surface produced by the new growth may be supplied with water. When transplanting potted plants into the garden it is often necessary to cover or otherwise protect them against excessive transpiration until the roots are established. This serves the same purpose that pruning does in transplanting woody plants. Indeed, succulent potted plants are sometimes pruned when they are transplanted. Pruning for better form is extensively practiced in caring for the shrubs and trees of lawns and parks. By pruning to determine just what part of a plant may develop, almost any desired form may be produced. In this way apple trees have been made to grow as vines, roses have been made to grow like box hedges, and grapevines have been made into upright and self-supporting shrubs. In pruning for better flowers and fruit, only a comparatively small number of vigorous buds or branches are permitted to grow. In this way each bud which grows receives proportion- ately much more nourishment from the whole plant than would be true if all the parts had remained. If all but one or two of the flower buds of a tomato plant are pruned away, larger and better fruit is produced. Chrysanthemums and DISCUSSION OF PLANT INDUSTRIES 453 roses are often treated in the same way with striking results. Many of the large and perfect flowers and fruits that are shown in exhibitions are developed in this way. Successful orchard growers prune their trees moderately each year, and thus main- tain the quality and quantity of woody branches from which the largest yield of good fruit may be secured (Fig. 350). Checking FIG. 349. Photograph by the New York Agricultural Experiment Station illustrating the results of spraying potatoes to prevent disease Those that were not sprayed yielded at the rate of 161 bushels per acre ; those sprayed three times during the season yielded at the rate of 350 bushels per acre ; those sprayed every two weeks yielded at the rate of 380 bushels per acre. In other experiments the results are even better. In this same station, during the year 1904, the average gain per acre in the yield for three sprayings is 191 bushels, and for spraying every two weeks is 233 bushels the vegetative growth of the plant at the right time seems to stimulate flower and fruit production. All kinds of orchard trees are more productive when properly pruned. In recent times pruning in order to facilitate proper spraying has become a prominent feature of the work. The various factors that are now involved in the practice of pruning are of such importance that the subject has become almost a specialty in itself. 454 PRACTICAL BOTANY 415. Checking and removing disease. The prevalence of plant diseases has been made apparent in preceding chapters. Although the nature of many of these diseases is not known, scientific study has contributed methods of prevention, control, or elimination in many cases. Oat smut, which on an average is said to destroy each year from one dollar to five dollars' worth FIG. 350. Results of proper pruning and spraying in growing Jonathan apples, Spokane, Washington The number and average size of the apples are increased and the quality is improved. Photograph by August Wolf of oats per acre, can be removed by application to the seed of a formalin solution at a cost of a few cents per acre. It is not uncommon for the yield of an apple orchard to be doubled by proper spraying, and the accompanying improvement in the quality of the fruit changes it from a, poor quality with a poor market, if it has any at all, to a good quality with good market. A very carefully recorded experiment in the value of con- trolling the disease known as potato blight illustrates the DISCUSSION OF PLANT INDUSTRIES 455 possibilities of such treatment (Fig. 349). Three rows of potatoes were planted side by side, the planting and cultiva- tion of all being the same. The results from different kinds of spraying, as shown in the legend under the figure, indi- cate clearly the great importance of this treatment. If you will ascertain the price of potatoes in your local market, and estimate the value of the increased yield, its significance will be more fully seen. It costs as much in money and labor to plant and cultivate a poor crop as a good one. 416. An artificial association of plants. By draining or irri- gating, cultivating and fertilizing the soil, planting the seed or plants at the right time and in the best way, caring for them and fighting their diseases, a highly artificial and depend- ent association of plants has been developed. None of these plants would naturally grow alone and unmixed with other plants. They have been cultivated and protected until, when this cultivation and protection are discontinued, their produc- tivity rapidly decreases. They would soon be unable to hold their own against the many natural plants that would begin to occupy the previously cultivated region. Many of the charac- teristics for which cultivated plants are valued, such as tender stems or foliage, seedless fruits, and double flowers, tend to weaken their capacity to succeed in the struggle for existence. III. LEADING AGRICULTURAL AND HORTICULTURAL PLANTS 417. Commercial importance of the cereals. Under the name cereals are included many economic plants of the Grass family. They produce grains (seeds or fruits) in which food material is stored in compact form. The principal cereals named in the order of their yields for the whole world, stated in tons of 2000 pounds, are: Corn t . . . . 109,000,000 Rice 53,500,000 Wheat 103,500,000 Rye 40,500,000 Oats . .... 57,000,000 Barley 31,000,000 456 PRACTICAL BOTANY In the United States the average annual value of the grain and hay crops for the five years 1903-1907 was as follows 1 : Corn ... O. '' . . . . .$1,132,000,000 Hay 587,000,000 Wheat . 503,000,000 Oats 293,000,000 Barley 70,000,000 418. Indian corn. Indian corn is an American plant, well known to the Indians and cultivated by them long before the coming of white people. Its food value per acre is about double that of other grains. The United States is the chief corn-raising country, pro- ducing more than three quarters of the world's crop, mainly in the " corn belt " of the Middle West. This region, with its fertile soil, its sunny summers, a fairly heavy rainfall, and a high summer temperature, 2 is especially adapted for corn grow- ing. In northern Europe corn is grown in botanic gardens as a curiosity, but does not succeed as a field crop because the summer temperature is not high enough and there is not suffi- cient sunshine. In the Mediterranean region the soil is fertile and the summers are sunny and hot, but the scanty summer rainfall sometimes less than an inch during three months affords unfavorable conditions for corn growing. The most important types of corn are flint corn, dent corn, and sweet corn. The flint varieties have a large proportion of hard, translucent endosperm. The dwarfed, quickly matur- ing kinds, which can be harvested in ninety days or less from the time of planting, and which are therefore grown in the northernmost states and Canada, are all flint varieties. The dent varieties have much soft endosperm and indented kernels (Fig. 332). The plants sometimes reach a height of eighteen feet or more, and require nearly six months to mature. Dent corn is much more productive, as a rule, than the flint varieties, 1 See Yearbook, U. S. Dept. Agr., 1907. 2 Averaging between 70 and 80 F. for the month of July. DISCUSSION OF PLANT INDUSTRIES 457 and therefore a more profitable crop. Sweet corn contains more sugar in the grain than other kinds, particularly when in the milk stage. It is much grown on the farm for home use, and by market gardeners on a far larger scale to supply canning establishments. 419. Wheat. Wheat is the most highly prized of the cereals, and has been cultivated for some thousands of years through- out large parts of the region extending from China to southern and western Europe. Most people prefer wheat preparations to those from other cereals. Wheat flour, containing a large percentage of the sticky protein material known as gluten, is particularly well adapted for bread-making. There are two well-known classes of wheats, based on the time of sowing ; spring wheat, which is planted in the spring as soon as the ground is dry and warm enough for tillage; and winter wheat, which is planted in the autumn, grows but little before winter, finishes its growth in the following spring, and is harvested in the summer. Both winter and spring wheats include hard and soft varieties, the former containing much gluten and the latter less gluten but more starch. The hardest of all are the macaroni wheats, which have a very high food value but are not usually considered well adapted for bread-making unless mixed with softer wheats. Wheat can be grown in a cooler climate and with less sum- mer rainfall than is needed for corn. For semi-arid regions, such as a large area in Texas and portions of Oklahoma and Colorado, the macaroni or durum wheats are extremely well adapted. Wheat will grow well on a more clayey soil than is best for corn, and in general throughout the corn belt the wheat crop takes a secondary place, often being planted on land that for some reason is not wanted for corn growing. 1 420. Other cereals. Oats, rye, and barley may all be grown in cooler and moister climates than are suited for corn and wheat. They are therefore much cultivated in northern Europe. 1 On varieties of wheat and wheat culture see Bulletin 24, Division of Vegetable Physiology and Pathology, U. S. Dept. Agr., 1900. 458 PRACTICAL BOTANY Oatmeal cooked in various ways, barley bread, and rye bread are therefore more used than wheat by the poorer classes throughout that region. Oats and barley are both much used as feed for horses, and barley is largely employed by brewers in the manufacture of malt. Rice is the great cereal crop of Asia, and a good deal is grown in South Carolina and the Gulf States. The territory in which rice is grown has been much extended in the United States within the past decade. The crop is generally cul- tivated on land that is overflowed during part of the year (Fig. 274). 421. Grasses cultivated for hay, forage, or pasture. In addition to the high value already stated for the hay crop, there are many grasses which are used directly as feed, with- out being cut and dried as hay. It would be difficult to esti- mate the annual value of the forage grasses and the pasturage of the United States, but it must run into hundreds of millions of dollars. Only three or four of the most important grasses that are cultivated or somewhat protected in their growth can here be mentioned. Timothy is the leading grass for hay, especially in the more northerly states. Redtop ranks next after timothy as a source of hay, though in its quality it is somewhat inferior to the former. Kentucky blue grass is the most valuable pasture grass in America. There are many grasses of great value in semi-arid regions, as the buffalo grass. Formerly some of these dried, as they stood, into a kind of natural hay on which the vast herds of buffalo of the Great Plains fed throughout the winter. 1 Red clover and alfalfa are also very valuable hay-producing plants. They do not belong to the Grass family, however, but to the Pea and Bean family (Leguminosse). 422. Cotton. The most valuable fiber plant of the world is the cotton plant, which is a member of the same family as the mallows and the hollyhocks. It is grown extensively in India, 1 On the grasses see G. F. Warren, Elements of Agriculture, chap. vii. The Macmillan Company, New York. DISCUSSION OF PLANT INDUSTRIES 459 Egypt, and in our own Gulf States. In 1907 the United States produced a crop worth about $675,000,000, which was approximately three fifths of the world's crop. This country ordinarily produces from 9,000,000 to 13,000,000 bales of 500 pounds each, the total value ranging from one third to two thirds of a billion dollars in value. The cotton consists of hairs which surround the seeds. Different lengths of cotton fibers are produced by different species. There is also much variation in the same species when grown in different parts of the world and under more or less favorable conditions. The cotton plant is an annual. When grown in tropical and semi-tropical countries it requires a relatively long season for maturing. In regions which have shorter growing seasons certain kinds, as the " sea-island " cotton (Grossypium Barbadense), will mature in ninety to a hundred days, and it has been known to mature in seventy. 423. Fruits of the Rose family. As the cereals are found in the Grass family, the majority of fruits are found in the Rose family. A large proportion of the edible fruits of the temperate region (using the word fruit in its popular sense) is produced by this family. These fruits may be divided into (1) pome fruits, such as the apple, pear, and quince ; (2) " berries," which are fruits that are commonly but in- correctly called berries, as the blackberry and strawberry ; (3) stone fruits, such as the peach, apricot, plum, and cherry. 424. The pome fruits. Apples are the most important rosa- ceous fruits. They have been cultivated for several thousand years. The wild species from which they are thought to have originated, flourished in ancient times over a large area in the region about the Caspian and Black seas in southern Europe. This supposed ancestral apple is still represented by wild forms that live in Europe, the fruit of which is small, hard, extremely sour, and unpalatable. From the original wild form thousands of different kinds have developed, and these range to such extremes in size, color, quality, and time of ripening, that it is difficult to conceive of them as having a common 460 PEACTICAL BOTANY ancestry. Cultivation has increased the bulk of the fruit sev- eral hundred times; moreover, in the plants now cultivated only one flower, or a few flowers, of the cluster develop fruit, as is also the case with the pear. The importance of the apple industry may be realized from the fact that a full crop for the United States and Canada amounts to about 100,000,000 barrels. Apples are grown on a large scale in most of the cooler portions of the United States, but there are large areas of good orchard land not thus utilized, particularly in the cen- tral Appalachian region. Apple growing in irrigated lands is rapidly increasing in the United States. Pears are much less extensively grown than apples. Cali- fornia pears, as is well known, are usually the largest and the finest that are grown. It is interesting to note that while the finest pears consumed in England were formerly of French growth, the United States is now exporting pears for the English market. Quinces are not of much commercial impor- tance, being used for little else than as a basis for preserves and jellies. A large part of those produced are ordinarily grown for home use on one or two trees in a corner of the garden or orchard. 425. " Berries. " In the so-called berries of the Rose family the ovaries ripen together, forming a thimble-shaped fruit upon the end of the flower stem, or receptacle, as in the black- berry; or it may be the receptacle itself which ripens, and, with its seeds upon its surface, forms the fruit, as is true in the strawberry. Cultivated strawberries are mostly descended from a Pacific coast species which was introduced into cultivation from Chile some two hundred years ago. The plant occurs wild along the North American coast as far north as Alaska. Strawberry growing in the United States began with the once famous Hovey seedling, about 1834 or 1835, but was of little impor- tance until after 1840. Strawberries grow readily in almost all good farming lands of the country. In favorable situations DISCUSSION OF PLANT INDUSTRIES 461 the crop is very profitable, as the yield may exceed four hun- dred bushels per acre. Strawberry raising on a large scale was long confined chiefly to gardens in the neighborhood of cities which served as a market. With improved quality and better facilities for shipping it has now become an extensive indus- try, and the season for some consumers has been extended from a few weeks to five or more months, beginning in Jan- uary with the product of the Gulf States and ending in July with Canadian berries. There are at least five species of raspberries in cultivation, but none of them bear transportation especially well. They are grown considerably for shipment over comparatively short distances. The red species, whether wild or cultivated, is much used in preserving-factories in making jam, and at times is prominent in the fruit markets. Blackberries, of which, including the Pacific coast forms, there are five or more species in cultivation, are known as commercial fruit only in America. Their cultivation began before 1841, and was slow to reach its present importance. Most of the favorite varieties were for years only chance seedlings of the upright wild species, but at present improved kinds that are descended from the trailing dewberries are coming into favor. 426. Stone fruits. Our most common stone fruits are peaches, plums, and cherries. Of these three fruits the two latter occur wild, but only plums have been much used in the wild state. Of the thousands of acres of wild-plum thickets once widely scattered over the Middle West, few now remain. Peaches are of Chinese origin, and were early introduced into America from Europe. They cannot be safely cultivated except where there is little danger of frosts after the trees have blossomed. Favorite peach-growing portions of the United States are the southerly part of the region bordering the Great Lakes, parts of Georgia and Alabama, southern Illinois, Missouri and Kansas, western Colorado, Texas, and most of California except the mountainous portion. As 462 PRACTICAL BOTANY peaches are yery perishable, most of the crop (as is the case with strawberries) must be taken to market in refrigerator cars. Nectarines, apricots, and almonds are very closely related to peaches. Plums, cultivated in various parts of the United States, belong to about ten groups, of Asiatic, European, and Ameri- can origin. Some highly successful varieties are of hybrid origin (Fig. 341). One of these is derived from the little beach plum 1 so well known along the Atlantic coast, and the common wild plum 2 which ranges from New England to Colorado and Texas. This hybrid is extraordinarily hardy and prolific. Among the most valuable plums are those which can be dried whole for prunes, and these are now extensively grown in California. Cherries in cultivation are of two types, the sour and the sweet, both derived from European species. The sour varie- ties are grown throughout a large portion of the country, the sweet ones principally in California. 427. Citrous fruits. The plants which bear oranges, grape- fr,uit, and lemons, are not hardy but thrive in tropical or semi- tropical climates. They may grow in regions where frosts are rare and light. In the United States the leading citrous-fruit orchards are in Florida and California. The wild orange is probably a native of southeastern Asia. Its fruit is sour, but the tree is more hardy than some of the improved sweet varie- ties. Because of this hardiness the sweet varieties are some- times grafted upon the wild stock in order to make use of the stronger wild plants. By means of experiment and cultivation many hundreds of varieties of oranges have been produced. Attempts are still being made to produce trees which will withstand the colder winters of the region farther north and at higher altitudes than where they are now grown. These efforts have been partially successful. Oranges, lemons, and the grapefruit or pomelo, as well as the more recently developed varieties, as the tangerine and 1 Prunus maritima. 2 Prunus americana. DISCUSSION OF PLANT INDUSTKIES 463 kumquat, have peculiarly valuable shipping qualities, which make it possible for these fruits to be shipped anywhere and to be kept for very long periods. 428. The grapes. The fruit of the grape is known to have been used by the earliest civilized peoples. From the wild grapes, which though sour are edible, more than a thousand varieties have been developed. These differ in color, as white, black, blue, or red ; and in texture, from the soft juicy grapes from which wine is made, to the more solid ones which are dried in making raisins. The leading grape-producing states are New York, Ohio, Michigan, and California. Perhaps the best-known and the most widely distributed kind of cultivated grape that is native to the United States is the Concord grape, which was discovered by Ephraim Bull at Concord, Massachusetts. Part of the original vine still grows on the lawn of the old Ephraim Bull homestead. The European grapes, which form the basis of the very large and important wine industries of France, were developed out of a different stock from that of the American cultivated grapes. Since the French grapes produced a quality of wine that differed from that made from the grapes of the United States, European grapes were brought to this country. Their roots were soon attacked, and the plants well-nigh destroyed, by a small parasitic insect known as phylloxera (Sect. 343). It was found, however, that the roots of the American grapes were able to withstand attacks from phylloxera and were not seriously affected by it. It was also found that when Euro- pean grapes were brought to this country and grafted upon American stock, the quality of the European fruit might be secured without the accompanying dangers from the insect. But when grape growers transplanted American grapes into Europe the phylloxera was also transferred, and soon the na- tive grapes of Europe were attacke.d and serious damage was done in the vineyards of France. In order to protect their vineyards many French grape growers adopted the practice of planting American plants and then grafting their own 464 PRACTICAL BOTANY grapes upon this introduced stock. The grape industry of France has been greatly increased by thus growing French grapes upon the stronger and more productive American stock. Some French grape growers, still believing that the quality of their grapes would deteriorate if grown upon American stock, use carbon disulphide as a means of protection against phylloxera, but this treatment is still too expensive to be used in the ordinary vineyards. 429. Garden vegetables. Another group of plants which form the basis of a great industry includes those generally known as vegetables. The vegetables come from many plant families. According to one authority, 1 there are at least two hundred eleven distinct species of garden vegetables, and many of these species are represented by very large numbers of varieties. The parts of these plants used as food may be the roots (sweet potato, radish, etc.), the combined stem and root (beet, parsnip, carrot), the underground stem (white potato, Jerusalem arti- choke), stem and leaves (lettuce, cabbage), and the fruit (to- mato, squash, cucumber, eggplant, string beans). The list of vegetables is too long and varied for any common characters to be given for it. 1 Vilmorin, in The Vegetable Garden. CHAPTER XXV WEEDS 430. What is a weed ? It is not possible to put into a short sentence a complete statement of what is meant by a weed. It is often said that a weed is a plant that is not wanted. Perhaps a better definition, from the farmer's point of view, would be : A weed is a plant which interferes with some crop. The word crop must, in this case, be taken in a very gen- eral sense. The dandelions which interfere with the growth of grass on a lawn, or the raspberry bushes which spring up in burnt-over clearings in white-pine woods and crowd out young tree seedlings, must be reckoned as truly weeds as the ragweeds and the pigweeds 1 that are so troublesome in cornfields. Cultivated plants may become very injurious weeds. Horse- radish, and Johnson grass, 2 which is valued in the South as a hay plant, are good instances of this. In the ordinary sense the term weed is applied only to flowering plants or to the larger representatives of the lower groups, such as ferns and horsetails. The many bacteria and higher fungi which do so much harm in the farm and garden are never spoken of as weeds. 431. Classes of weeds. Weeds may be classified in many ways, according to the kinds of resemblances and differences taken into account in grouping them. 3 The kind of classifica- tion which would first suggest itself to most botanists is that into families, such as the Grass family, the Nettle family, and the Buckwheat family. Another kind of division would be into annual, biennial, and perennial plants ; still another into 1 Amaranthus. 2 Sorghum halepense. 8 See Percival, Agricultural Botany, Part V. Henry Holt & Co., New York. 465 466 PRACTICAL BOTANY sun plants and shade plants, or into drought-enduring and moisture-loving plants (Sects. 441-446). We are fortunately as yet but little troubled in this country by one obnoxious group of weeds, the parasitic flowering plants. The clover dodder (Fig. 351) is one of the most important of these, causing much trou- ble in fields of clover and of alfalfa. The farmer would often class weeds accord- ing to the kind of crop with which they interfere; for example, into weeds of pas- tures and those of culti- vated ground, subdividing the latter group into weeds of cornfields, weeds of oat and wheat fields, weeds of clover fields, and others. 432. Qualifications for suc- cessful weeds. Not many wild plants of any region can become, even in the ter- ritory to which they are native, successful weeds. The trilliums, columbines, A, habit sketch of part of the parasite and pepperroots, fire pinks, wild the host ; B, portion of stem of the dodder, ginger (Fig. 43), Dutdl- showing protuberances from which haus- , i i i -, -t toria pass into the stem of the host; C, man S-breecheS, and Wild a single flower of the dodder. B and C SW66t William {Phlox), SO familiar among the early wild flowers of the Middle West, are there practically unknown in cultivated fields. For various reasons the conditions of life in tilled ground are promptly fatal to them. In order to push its way among com- petitors, to win in the struggle for existence, under natural FIG. 351. Clover dodder, parasitic on red clover considerably magnified. Modified after " Flora Danica " WEEDS 467 conditions and with the farmer and gardener against it, the weed must possess exceptional powers of reproduction or of FIG. 352. J., corn cockle, a weed of the Pink family, troublesome in grain- fields. The seeds are poisonous. One third natural size. .B, cocklebur, a very troublesome weed of the Composite family, in rich land throughout a large part of the country. Two thirds natural size resistance to unfavorable influences. Some of the chief quali- fications which distinguish weeds are : (1) The power of vegetative reproduction. (2) Deep, tough roots, or relatively extensive development of the underground portion. (3) The power to produce many seeds. 468 PRACTICAL BOTANY (4) Capacity for self-pollination (if necessary). (5) Good means of seed dispersal. (6) Capacity for rapid growth. (7) The ability to resist plant diseases. (8) Tolerance of shade (at least when young). (9) Tolerance of drought. (10) Tolerance of excessive water supply and lack of air in the soil. (11) The ability to resist the effects of dust in choking the stomata. (12) Capacity to thrive in poor soil. (13) Ability to retain vitality of seeds buried in the soil, sometimes from fifteen to twenty-five years. (14) Unpalatableness, offensive smell, prickles, or other disagreeable characteristics, which lessen the danger of being eaten by animals. Few if any weeds have all the above-named characteristics in a high degree, but many kinds of plants have the greater part of them. Which characteristics are common to many weeds of woodlands? of pastures? of lawns? of roadsides? of cornfields? of fields of the small grains? Name some of the weeds which you know that have the largest number of the qualifications (1)-(14). Can you name any plant that has both characteristics (9) and (10) ? 433. Effectiveness of weed equipment. In most instances it is easy to see how the characteristics listed in Sect. 432 enable weeds to persist. Evidently a plant which, like the Russian thistle, produces tens of thousands of seeds, or one which, like the dandelion, scatters seeds for miles with the wind, is likely to reproduce itself abundantly and to occupy any suit- able bit of vacant ground. But there are other most effec- tive qualifications which need a little explanation. If a sorrel plant 1 (Fig. 353) is dug up carefully, it will usually be found to have several others attached to it by the roots. This is rapidly becoming one of the worst weeds in the United States, 1 Rumex Acetosella. WEEDS 469 being especially abundant in slightly acid soils. Many other kinds of plants, from nettles to goldenrods, are joined in colonies by long underground stems. 1 The sorrel roots and the goldenrod rootstocks produce many buds, and each bud may grow into a new plant. If the rootstock is cut to pieces with a hoe, the process of reproduction is only urged on a little. Every tuber of some sunflowers (Fig. 67), the nut grass, and many other tuber-bearing plants may grow into a new individual. Purs- lane plants when hoed up and left on damp soil at once begin to grow, each bit forming a successful cutting. These are only a few of the hundreds of examples that might be given of vegetative reproduction among weeds. The way in which fox- tail grass maintains itself in grainfields, making slow growth while it is over- topped by the wheat, oats, or rye, and then pushes up rapidly, flowering and seeding among the stubble, is an excellent illustration of the importance to the plant of the power to tol- erate shade during the early period of growth. It must be remembered that any qualification that helps the weed in its struggle for existence is a good thing for the weed, even if it is discouraging from the point of view of the farmer. The survival of mullein and ironweed in pastures, and of dog fennel, smartweeds, and the offensive-smelling, poisonous Jimson weeds (Fig. 300) in barnyards, are only a few examples of the many that could be given to show how some weeds persist by being uneatable or positively offensive. 1 See Bulletin 76, Kansas Agr. Exp. Sta. FIG. 353. Portion of a plant of the com- mon sorrel The leaf is drawn about one half natural size. The running roots of a large specimen would be at least sixty times as long as the piece here shown 470 PRACTICAL BOTANY 434. How weeds injure the farm and garden. 1 Although some weeds are of use as food for man or the lower animals and a few have medicinal properties, their presence in the farm or garden is on the whole most harmful in the follow- ing ways : (1) Weeds take soil moisture needed by useful plants. (2) Weeds rob the soil of valuable salts, such as nitrates and potash compounds, and it is probable that they may add secretions that are injurious. (3) Weeds weaken other plants by shading them, thus hin- dering photosynthesis. (4) Parasitic weeds, like the flax dodder and the clover dodder (Fig. 351), rob their hosts of plant food. (5) Some weeds harbor parasitic fungi or insects injurious to useful plants. (6) Poisonous or intoxicating plants injure horses, cattle, and sheep. (7) Some spiny plants, such as the smaller cacti, and burs like the sand bur, may lame the feet of domestic animals. Thorny shrubs are very troublesome to woolgrowers, pulling out much wool, and burs greatly injure the quality of the fleece. (8) Certain weeds, when eaten by cows, render milk un- palatable or ill-scented. (9) Weed seeds injure the quality and affect the price of clover and other seeds that are raised for sale, and thus diminish the value of the grain with which they are mixed. The harm done by weeds in shading crops is most notice- able in the case of rapidly growing species which spring up among delicate seedlings such as flax and onions. In extreme cases the weeds may almost entirely prevent the growth of the crop. The most important example of fungi harbored by weeds is that of wheat rust on barberry bushes (Sect. 233). The potato beetle feeds on many plants of the Nightshade family, 1 See Bulletin 175, " A Second Weed Manual," Ohio Agr. Exp. Sta., for a fuller discussion. WEEDS 471 and then transfers itself to any neighboring potato plants that are not protected by applications of Paris green or of other poisons. A familiar example of a pasture weed poisonous to the lower animals is the common sheep laurel or lambkill. 1 There are a good many plants, such as some members of the Night- shade family, hemp, and some leguminous species, 2 which may produce symp- toms both of intoxication and of poisoning in horses, sheep, and cattle. Of the plants which give a bad taste to milk, field garlic or wild onion 3 is the most important. The bulblets of this weed may also impart an onion flavor to flour made from wheat grown in fields infested with it. As an instance of the extent to which weed seeds may contaminate commercial samples of useful seeds, the case of red clover may be cited. Inferior lots of clover seed may contain as much as 67 per cent of impurities, largely other seeds, 4 and the average of 84 samples examined at the Iowa station was 5 per cent, or 3 pounds to the bushel. In the red and mammoth clover seed examined at a single 1 Kalmia angustifolia. 2 The so-called "loco weeds," mostly species of Astragalus and Aragallus. 3 Allium. * See Bulletin 21, Iowa Agr. Coll. Exp. Sta. FIG. 354. Horse nettle (Solarium carolinense) A very troublesome weed of the Nightshade family, which has spread extensively from the southeastern states. One half natural size 472 PRACTICAL BOTANY agricultural experiment station there were found in all 87 species of other seeds, mostly those of noxious weeds, belong- ing to 23 different families of plants. 1 435. Other injuries caused by weeds. Aside from the dam- age inflicted by weeds upon growing crops and farm animals, much harm is done by them in less obvious ways. Roadside weeds of many species encroach upon roads of all kinds, from country byways to city boulevards. Among the weeds of waste ground there are many which disfigure the surface of vacant city lots, and the numerous burs among them load the passer with their clinging seeds or fruits. Railway rights of way, if left uncared for, soon become over- grown with weeds, which shade the ties and cause them to decay more rapidly. It is estimated that the expense of re- moving weeds from the railway tracks in the state of Ohio alone exceeds $500,000 a year. Streams, canals, and drainage or irrigation ditches are often infested by weeds, which may almost stop the current of water in them. The water weed, or ditch moss (Elodea), introduced into Europe from America, has become a nuisance there, choking small streams with its abundant growth. The so-called water hyacinth (Eiclihornia) from South America, often cultivated in aquaria and small ponds, has been introduced into Florida and other southern waters, where it greatly impedes navigation. 436. The origin and dissemination of weeds. One of the interesting facts with which the young botanist is first im- pressed on beginning to identify weeds and to trace their his- tory, is the extent to which they have immigrated from other countries. 2 No one can calculate with exactness the propor- tion of our weeds (that is, of individuals) which have been brought in from other countries. But it is not difficult to see how the numbers stand in comparing native and introduced 1 See Bulletin 175, Ohio Agr. Exp. Sta. 2 See the article, "Pertinacity and Predominance of Weeds," in the Scientific Papers of Asa Gray, selected by C. S. Sargent, Vol. II, Houghton Mifflin Company, Boston ; also Farm Weeds of Canada, Second Edition, Government Printing Bureau, Ottawa, Canada. WEEDS 473 species, if we look through a list of a hundred of the worst weeds over the continental area of the United States (exclud- ing Alaska), 1 it appears that almost exactly half of the num- ber are from Europe. Nine others are from tropical America or from India, so that a clear majority of these hundred nota- ble weeds are foreigners. It is rather difficult to give all the reasons why so many of our common weeds come from Europe, but it is certain that of the prevalent weeds on that con- tinent many represent the result of a gradual sifting- out process which has lasted for tens of cen- turies. Dur- ing all that long period the tilled lands of Eu- rope have gradually become populated by such European plants as proved able to live in cultivated ground in a temperate climate against human opposition. Together with these are found such other persistent species as may have found their way in from Asia and Africa. When the soil of temperate North America first began to be cultivated by the whites, it was inevitable that great numbers of European weeds should be brought in along with farm and garden seeds, in the ballast of vessels, and in other ways, and rapidly gain a foothold on the new continent. The history of the spread of many weeds has been preserved, and it forms a most interesting chapter of economic botany. 2 1 Farmers' Bulletin 28, U. S. Dept. Agr. 2 See the essay of Dr. Gray already cited ; also Farmers' Bulletin 28 and Bulletin 15, Division of Botany, U. S. Dept. Agr. Consult also all the attain- able weed reports of the state agricultural experiment stations. FIG. 355. Pokeweed, a common weed of waste ground A, a flowering branch ; B, flower ; C, fruit 474 PRACTICAL BOTANY It is a well-known fact that new weeds are particularly likely to be found in places where ballast from vessels is dumped, where cargoes of foreign grain are cleaned, and where foreign wool is scoured and cleaned from burs and other seeds. 1 Some very troublesome weeds, as the common carrot and the orange hawkweed, have been cultivated for use or ornament and escaped into fields, meadows, and pastures. 437. Weeds of various regions. Any two regions which differ widely in soil or climate are sure to differ also in the weeds which predominate there. Such tropical plants as the sensitive plant 2 and the rosy periwinkle, 3 not uncommon in our greenhouses and gardens, are troublesome weeds, the for- mer in tropical South America and the islands of the South Pacific, and the latter in the West Indies. But in our climate it requires care and protection to keep them alive. Even in the various climates afforded by the United States, there is range enough to make one weed troublesome in one portion of the country and another in another portion. The quack grass, or couch grass, 4 so injurious from its creeping rootstocks in fields and gardens from Maine to Minnesota, is replaced as a weed in the southern states by the Johnson grass, 5 which has still stronger and longer rootstocks. The wild gourd, 6 troublesome in the far Southwest, is not found as a weed northeast of California and New Mexico, and the cacti, 7 an- noying weeds in central and southern Kansas and westward and southward, are of no importance farther east. The amount of moisture in the soil is an important factor in the distribution of weeds. Such plants as the cacti just mentioned, some cinquefoils, St.-John's-worts, lambkill, some species of vervain, 8 the common mullein, rib grass, 9 and the 1 A curious case of distribution of a bur is that of the grass Andropogon acicularis. A buffalo with his hair filled with the needle-like fruits of this grass was sent as a present to the so-called king of Ternate, in the Malay Archi- pelago. From this one animal the grass soon spread over the whole island. 2 Mimosa pudica. 3 Vinca rosea. 4 Agropyron repens. 6 Sorghum halepense. 6 Cucurbita perennis. 7 Mamillaria, Opuntia, and other genera in the Southwest. 8 Verbena. 9 Plantago aristata and P. lanceolate. WEEDS 475 everlastings are especially frequent in dry pastures. A few ferns, such as the sensitive fern and the ostrich fern, 1 horse- tails, rushes, sedges, many worthless coarse grasses, smart- weeds, docks, some buttercups, mints, and the ironweeds are common only in moist fields, meadows, and pastures. 438. How to avoid weeds. The methods of destroying weeds are fully discussed in treatises on agriculture. A great deal can FIG. 356. Tumbleweeds (Cycloloma) drifted into heaps by the wind be done toward the prevention of weeds by taking pains not to use poor seed for the farm and garden, since the cheaper kinds often contain many weed seeds. Stable and barnyard manure frequently contains many seeds of the most objection- able weeds, and in caring for lawns it is often found cheaper to use ground bone or chemical fertilizers, such as superphos- phate of lime, than to spread over the grass fertilizers which may introduce multitudes of troublesome weeds. One of the most obvious means of keeping one's premises free from weeds is not to allow them any avoidable breeding 1 Onoclea. 476 PRACTICAL BOTANY places. All fence rows, hedges, clumps of blackberry and raspberry bushes, and similar lurking places for weeds, as well as grassland and tilled ground, should be kept as clean and as nearly weedless as possible. Weeds which have gone to seed should not be plowed or spaded under, but allowed to dry and then burned. It will be found well worth while to rake away from fences and burn all such accumulations of tumble- weeds as those shown in Fig. 356. Wild mustard, which is a very troublesome weed in fields of the small grains, is read- ily killed by spraying with a solution of copper sulphate or iron sulphate. Weedy lawns are sometimes improved by very careful salting, which does not injure the grass. Gravel walks may be cleared of weeds by watering them with a solution of sodium arsenate or of crude carbolic acid. CHAPTER XXVI ECOLOGICAL GROUPS; REGIONAL DISTRIBUTION OF PLANTS! 439. Ecology in earlier chapters. The term ecology has already been denned (Sect. 110). In the preceding chapters of this book the ecology of the plant has usually been some- what discussed along with the account of the plant itself and of its or- gans. For instance, much of what was said about the relations of the root to the soil (Chapter III), root-tubercle bac- teria (Chapters III and XXIV), mycorrhiza (Sect. 38), and the rela- tions of stem and leaf to light supply (Chapter FIG. 357. The duckweed, one of the simplest floating seed plants IV) is a part of plant ecology. So, too, is the treatment of pollination (Chapter VIII), of seed dispersal (Chapter IX), and much of the chapter on Weeds. The relation of parasites to their hosts and of symbionts to each other (Chapter XXI) consti- tutes a most important part of ecological botany. In the cases here referred to, however, the main emphasis was laid on the 1 See Warming, (Ecology of Plants (Clarendon Press, Oxford) ; Schimper, Plant Geography on a Physiological Basis (Clarendon Press, Oxford) ; and Coulter, Barnes, and Cowles, Textbook of Botany, Part II (American Book Company, New York). An excellent bibliography of the subject will be found in Warming's work, 477 478 PBACTICAL BOTANY FIG. 358. The pond lily, an aquatic with floating leaves and submerged stems FIG. 359. Free-floating aquatic plants in a pool Aquatics with aerial leaves, the most conspicuous of which is the arrowhead (Sagittaria) , grow in the mud about the pool. Photograph by Charles Gordon, ECOLOGICAL GROUPS 479 structure and mode of activity of the plant or organ under discussion. From the point of view of the ecologist the prin- cipal things to be considered are the relations (often very intricate) between the plant and other plants or animals, how the plant meets the conditions of soil and climate under which it exists, and why plants are distributed in the various regions of the earth's surface as they are. 440. Systematic groups not ecological. The way in which plants are classified according to their relationships has already been described (Chapter X). The systematic grouping into classes, orders, families, and so on, has no necessary relation to the life habits of the plant. The Heath order, for exam- ple, includes ordinary plants with the capacity for photosyn- thesis (Fig. 299), and also saprophytes (Figs. 307 and 308). Some of its members are sun-loving plants and some are shade- enduring, some can live in very dry soil and others occur only in swamps. One familiar genus of the Morning-glory family (Cuscuta, Fig. 351) is parasitic, while most of the genera of this family get their living in the ordinary way, from air and soil. Several genera of the Figwort family (such as the painted cup) are root parasites, while most are not. 441. Ecological groups. In classifying plants according to their ecological relations 'they are generally grouped with regard to their water requirements, as follows: (1) Water plants, those which usually live only in the water 1 or in marsh soil saturated with water 2 ; they may be unattached, like many algse (Chapters XII, XIII) and duckweed (Fig. 357) ; or rooted, like arrowhead (Fig. 359), cat-tails, pickerel weed, and pond lilies (Figs. 55 and 358). (2) Land plants, those which live in ordinary soil or on rocks, the bark of trees, and so on. The two main ecological divisions of land plants are as follows 3 : (a) Xerophytes, plants which can tolerate extremely dry conditions, as many lichens (Figs. 190-193), cacti (Fig. 68), 1 Hydrophytes, 2 Helophytes. 8 For halophytes see Sect. 452, 480 PRACTICAL BOTANY and in general plants which inhabit exposed or excessively dry regions. (6) Mesophytes, plants which require a moderate amount of moisture, such as most cultivated plants and our common- est deciduous trees and shrubs. FIG. 360. Cross section of stem of pond- weed (Potamogeton) showing air passages a, much magnified. After Green 442. Characteristics of water plants. Those water plants which live wholly sub- merged generally differ far more in their form and structure from land plants than do those which (like many grasses and sedges) grow in very wet soil. From the situation in which they grow, submerged plants are less > 3^1. A marsh P lant (Limnophila) familiar to us than common land plants ; The thread-like low- *T , er leaves are water but most people who know OUt-of-door leaves. There are things well, have seen pondweeds, water - at ' crowfoots, bladderworts (Fig. 362), mare's- ahove the middle, . ., -i , 7-17 7 N / ,i and the upper ones tail, water weed (Modea), or some of the are air leaves. About aquatic mosses. It is important to notice one half natural size. 11 11 PI i After Goebel how thoroughly most ot these are buoyed up and supported by the water. All such plants are soft and limp, without the distinct tough epidermis of land plants, and the leaves are often slender or thread-like. ECOLOGICAL GKOUPS 481 Definitely stated, some of the most noticeable characteristics often found in submerged aquatic seed plants are 1 : (1) Slight development of the root system. (2) Slight development of wood cells and vessels. (3) Stiffening structures scanty or lacking. (4) Air spaces large and abundant. (5) The epidermis thin and the cuticle very thin or wanting. (6) The leaves often dissected into thread-like divisions. What are probable reasons for character- istics (l)-(5) ? The thread-like divisions of the leaves mentioned in (6) are thought to favor exchange of gases between the water in which they are dissolved and the leaf interior and to offer little resistance to currents of water. 443. Characteristics of xerophytes. There are so many types of FlG - ^ 62> A free branch and two buds f , . ., a large, common bladderwort xerophytes that it is ... , . f After Beal not possible in a few words to sum them up or to give the student a comprehensive idea of their peculiarities of structure and of function. Per- haps the easiest way to suggest the leading characteristics of the group is to mention a few familiar representatives of the leading types as follows : (1) The olive (Fig. 51), the rubber tree (Ficus elasticci), and the wax plant (Hoya), not uncommon in greenhouses, are good examples of xerophytes with hard, thick-skinned leaves, which have a compact interior parenchyma, without the abun- dant air spaces shown in Fig. 11. 1 The student must not think of these characteristics as abnormal and of those of ordinary land plants as normal. It is possible that the earliest plants were aquatics and that the aquatics of to-day are more like primitive plants. But it is better to leave such reasoning for more advanced studies. 482 PEACTICAL BOTANY (2) The various kinds of heather, knotgrass (Polygonum aviculare), knawel (Scleranthus annuus), and the rushes are instances of xerophytes with small leaves, exposing compara- tively little surface to the sun and air. (3) Century plants (Fig. 62), houseleeks, and aloes are good examples of fleshy-leaved xerophytes. (4) Many xerophytes combine in their leaves some of the characteristics of groups (1), (2), and (3). The leaves of cedars, hemlocks, firs, and spruces have a thick epidermis and close interior struc- ture, like that shown in Fig. 249, and are also small, exposing little surface. The common purslane, the portu- laca, and the ice plants (Mesembryanthemum) have small and rather fleshy leaves. Many xerophytes have extraordinarily developed root systems, as in the case of the mesquite (Seel;. 27), and so can draw moisture from great depths in the earth. Others have extensive provisions for water storage (Sects. 34, 66, 67). Among these the cacti are notable for the amount of water which they can store in their succulent stems, which are often fluted, so as to expand and contract readily. This water has been rapidly absorbed by the spreading, shallow root system from the layer of earth (only an inch or two deep), which is moistened by the rare rains of the desert re- gions where many such cacti grow. Between rains the roots of these cacti serve only for anchorage. Xerophytes in general are so constituted as to transpire little at any time, or else to be able, in case of danger from excessive dryness, to reduce the amount of transpiration to a very low value. FIG. 363. Cross section of rolled-up leaf of crowberry (Empetrum nigrum) Magnified ECOLOGICAL GROUPS 483 In order to realize the extreme danger to which plants are exposed from dryness, one needs only to remember how often harvests in great part fail from the effects of drought. This may mean that the entire plants have been killed, or only that they have not borne much fruit or seed, or that the roots, stems, or leaves are stunted. Many wild plants are as sensitive to prolonged drought as are ordinary field crops, and irrigation of a desert region which has a rich soil helps the growth of weeds as much as it does that of the crops among which they spring up. 444. Means of limiting transpiration. Some of the principal means of limiting transpiration are as follows l : (1) Compact arrangement of the parenchyma cells in the interior of the leaf. (2) Development of a thick-walled epidermis (Figs. 249 and 364). (3) Situation of the sto- mata in pits or furrows (Figs. 249 and 364). (4) Inclosing the stomata in a sort of tubular cavity formed by the curving-in of the margins of the leaf (Fig. 363). (5) Presence of a coating of dead hairs, filled with air, on one or both surfaces of the leaf (Fig. 57). (6) Temporary reduction of the evaporating surface, as by rolling up leaves (Fig. 2), shedding leaves, reduction of living parts to a buried root, bulb, tuber, rootstock, or some combination of thickened roots and underground stems. 1 The subject is a very extensive one, fully treated in the writings of Warming, Schimper, Goebel, Volkens, and other ecologists. FIG. 364. Waterproof epidermis and protected stoma of the century plant c, cuticle ; cu, cutinized (waterproofed) layer of epidermis; ce, cellulose layer of epidermis ; pi, pit, at the bottom of which the stoma is situated; po, pore of the stoma. Magnified about 220 diameters. After Luerssen 484 PRACTICAL BOTANY (7) Reduction of leaf surface, as in the case of needle-shaped (Fig. 248), scale-like, or other small, narrow kinds of leaf. (8) Partial or complete absence of useful leaves, as in the " switch plants," such as Spartium, Casuarina (Fig. 365), and so on ; and iii asparagus, the cacti (Fig. 65), and some euphorbias (Fig. 366). 445. Discussion of xerophytic characters. The first four kinds of characters operate, as may be readily under- stood, greatly to limit the loss of water. Close- ly packed parenchyma cells in the leaf interior, with few air spaces, give little opportunity for the water in the interior cells to escape into the internal atmos- phere of the leaf and so gradually pass off into the air. When the epi- dermis is thick, espe- cially if it is covered with a heavy, water- proof cutinized layer (cu, Fig. 364), transpi- ration when the stomata are closed is very scanty. Stomata situated at the bottoms of microscopic pits or furrows are much protected from drafts of air and therefore give off vapor slowly. And when the stomata-bearing leaf surface, as in the FIG. 365. Casuarina, an Australian switch plant destitute of foliage leaves and depend- ing on the chlorophyll-containing cells of the bark for photosynthesis Photograph by Robert Cameron ECOLOGICAL GROUPS 485 crowberry (Fig. 363), forms the interior of a nearly closed tube, transpiration is still more hindered. Hairy leaves (5) are characteristic of plants of dry climates, as the Mediterranean region, and of dry exposed areas like FIG. 366. Part of a euphorbia stem, the branches showing considerable resemblance to those of some cacti the higher portions of the great Western plains in this country. Generally the hairs are relatively simple in their structure and do not completely cover the surface. But in many in- stances the hairs assume shield-like or other flattened forms, and they may overlap so as more than to cover the surface 486 PRACTICAL BOTANY on which they occur most abundantly (usually the lower one, Fig. 57, A). The same species or individual sometimes becomes more hairy when subjected to a drier atmosphere. Experiments show that shearing off the hairs from the surface of the living leaf increases the loss of water by transpiration, sometimes even doubling its amount. Rolled-up leaves (6) are familiar in the case of corn (Fig. 2). It would not be easy to perform a field experiment to prove exactly how much the loss of water is lessened in the rolled corn leaves, but it would seem that the surfaces are considr erably less freely exposed to the air in the roiled condition than when the blades are flat, and free exposure is a well- known factor in increasing transpiration. In some xerophytic grasses there is a complicated arrangement of folds in the leaves by means of which they can close up the transpir- ing surface (almost as in Fig. 363) or open it completely to the air. Shedding the leaves (6) is the principal means by which our deciduous trees and shrubs escape the dangers of dry winter weather when no moisture can be absorbed from the ground. It has been found that the larch (which sheds its leaves) is more resistant to such conditions than are most of the ever- green conifers. Some shrubs retain or shed their leaves in a rainless summer according to the amount of soil mois- ture with which they are supplied. The Euphorbia splendens (Fig. 292, A) is a commonly cultivated plant which well illus- trates this capacity to adjust the amount of leaf surface to a varying moisture supply. Plants with bulbs (6) are notably common in regions where there is a long rainless summer. To a botanist one of the most interesting sights of the Mediterranean coast region is the sudden blooming of many bulb-bearing plants toward the close of the summer. Most conspicuous of these is a mem- ber of the Lily family, Urginea Scilla, which sends up its stout flower stalk, almost as tall as a man, out of the earth baked hard by two or more months of hot weather almost without ECOLOGICAL GROUPS 487 rain. Since there are no living leaves at the base of the flower stalk it has the curious appearance of a blooming stem stuck upright in dry earth. Absolutely leafless plants (8) are not very numerous, but there are plants, like the common asparagus and most cacti, which have very small and short-lived leaves that are often nearly or quite functionless. In the common garden asparagus these may be seen as triangular scales on the fleshy shoots sent up in early spring. The green, bristle-like growths on the main branches of asparagus plants throughout the summer perform the offices of leaves but are stem-like in their origin. In the cacti the leaves often appear as awl-shaped, or rather stout, bristle-like organs, borne at the nodes, which soon wither and fall. In such plants the photosynthetic work all the year round is done by chlorophyll-bearing cells close under the epidermis of the stem. In some switch plants a crop of small leaves, borne only during two or three months of early spring, perform active photosynthesis while they last. 446. Characteristics of mesophytes. Since mesophytes do not live under such conditions as frequently to run the risk either of drowning or of drying up, they do not, as a rule, show extraordinary modifications of structure, such as would enable them to carry on exchange of gases under water or to prevent excessive transpiration in dangerously dry air. A large part of what has been said in the preceding chapters about the structure and. functions of seed plants has had reference to mesophytes, the average plants, and it is therefore unnecessary in this place to go into details in regard to their characteristics. In many respects these are midway between the characteristics of water plants and those of ex- treme xerophytes. In order to fix his knowledge of the sub- ject, the student, after doing what laboratory and field work he can upon the ecological groups discussed in Sects. 440- 446, should summarize his impressions by comparing three or more plants, each typical of one of the groups, in tabular form somewhat as follows : 488 PRACTICAL BOTANY A rooted hydrophyte (water milfoil or mare's-tail l ) A mesophyte (the common bean l ) A xerophyte (the houseleek l ) Root system General form of stem Relative amount of development of wood cells in stem Relative develop- ment of vessels in stem Development of ai r passages in stem General form of leaves Water storage in leaves Epidermis and cuticle Stomata Length of time plants can remain alive in air of room with roots in soil that is not watered 1 These plants are merely suggested. Pondweed (Potamogetori), water weed (Elodea), or one of the species of Banunculus with submerged, dis- sected leaves, will answer well as representative aquatics. There are hun- dreds of mesophytes from which to choose. Century plants (Agave), cacti, aloes, or echeverias are good examples of xerophytes. ECOLOGICAL GROUPS 489 Make a list of all the aquatic seed plants that you know, of some of the principal marsh plants, of several herbaceous and several woody mesophytes, of all the xerophytes you know, the xerophytes arranged somewhat in the order of their capacity to resist drought conditions. 447. Ecological groups based on light relations. Plants which prepare their food by photosynthesis evidently need FIG. 367. Spanish moss (Tillandsia) growing on branches of a tree Much reduced. Photograph by S. M. Tracy FIG. 368. Tufts of Spanish moss, with leaves of the magnolia on which it grew Reduced. Photograph by Florida Agri- cultural Experiment Station light as much as they do air or water; but there is great diversity in their demands as regards intensity of light. The practical forester soon becomes familiar with this fact, and the gardener and floriculturist know that while some plants, such as tulips, poppies, verbenas, and most composites, need all the sun they can get, other plants, as most ferns, lilies of the valley, spiderworts, many violets, many genera of the Pars- ley family and the Heath family, grow best in partial shade. 490 PKACTICAL BOTANY The various strata or stories of vegetation in a forest are usually arranged somewhat in the order of their light require- ments, the plants most tolerant of shade at the bottom and the most intolerant species at the top. Thus in an open forest composed mainly of white pines mixed with a few other conifers and some deciduous trees, in New England, we may find some such assemblage as this: close to the ground vari- ous species of mosses, the most conspicuous being the pigeon-wheat moss (Polyt- richum). Rising but little above the mosses are one or two species of " ground pine," or "Christmas ever- green" (Lycopodium, Fig. 245). Mingled with these are many herbaceous spe- cies, or very small under-, shrubs representing the seed plants, all shade-loving FIG. 369. An air plant ( TWandsia) of the . guch M rattlesnake Pineapple family , plantain, 1 " wild lily of the Living as an epiphyte, but having numerous r i i roots, it is intermediate in habit between valley, 2 chickweed, Wlll- the common pineapple (Fig. 283), which ter g reen 3 common wood grows rooted in the earth, and the Spanish & . . 9 . moss (Fig. 368), which is rootless and hangs SOrrel, 4 prince S pine, Shin- suspended from the bark of trees. Photo- | ea f 6 partridge berrv, 7 and graph by Robert Cameron ^ Q * .< rattlesnake-weed. 8 Above these, if the woods are young, grow such larger shrubs and small trees as Juneberry, 9 blueberry, 10 and gray birch. 11 Mixed with these are young spruces and perhaps hemlocks. Only 1 Goody era. 2 Maianihemum. 8 Trientalis. 4 Oxalis Acetosella. 6 Chimaphila. 6 Pyrola. 7 Mitchella. 8 Hieracium. 9 Amelanchier. 10 Vaccinium vacillans. ll Betula populifolia- ECOLOGICAL GROUPS 491 the tall pines which overtop all the other trees receive the sunlight in its full intensity ; under the densest shade of the pines the illumination, compared with that of the unshaded tree tops, may be only one fiftieth or less. 1 In a forest the number and character of the strata of vege- tation depend largely upon the kinds and density of the trees that compose the uppermost stratum. In an average deciduous forest such as is often found throughout the Central States the uppermost stratum consists of trees such as oaks, maple, beech, elm, hickory, and tulip (Fig. 319). In some regions one finds an almost pure beech or maple forest. The oak- maple or oak-maple-beech combination is not uncommon. If these trees grow closely crowded, the shade underneath is very dense and few shorter trees or shrubs are found. When the forest is more open a second stratum of young trees and tall shrubs is found. This stratum, in addition to the young trees, may contain the bladderwort (Stapliylea), the hop hornbeam (Ostrya), the ironwood (Carpinus), and many others. There may be a stratum of lower shrubs immediately below the tall- shrub stratum, and this lower-shrub stratum often is charac- terized by the blackberry, raspberry, and the greenbrier or cat claw. The next stratum usually is characterized by many tall ferns and many kinds of flowering plants that thrive in deep shade. Below the ferns and upon the soil or decaying vegeta- tion is the lowest stratum, which may include many kinds of toadstools and mushrooms and other fungi, mosses of many kinds, occasionally some of the leafy liverworts, and some of the soil lichens. In some forests in which there are but few strata of vegetation, during the greater part of the growing season the tall trees constitute almost the entire conspicuous flora. In early spring, however, such forests usually have a low stratum of early -flowering plants (spring beauty, blood- root, dogtooth violet or deer's-tongue, Dutchman's-breeches, etc.), which for a brief period carpet the forest floor. These 1 In the pine forests of the Tyrol, Wiesner found the illumination in entire shade only one sixtieth to one ninetieth of full sunlight. 492 PRACTICAL BOTANY plants flower at the expense of food material that was deposited in former seasons (Sects. 34 and 69), and do most of their vegetative work before the leaves of the trees are developed so as to shade them. As the season advances and the light intensity increases, these low plants may still work by means of the diffuse light that is filtered through the tree tops. Any local forested area will afford students interesting studies in the strata of forest vegetation. 448. Fractional part of total sunlight required by various plants. 1 The proportion of the full strength of sunlight re- quired by any given species is not the same in different lati- tudes ; for example, the common dandelion at Vienna (lat. 48.12) may grow in an illumination of one twelfth, but in northern Norway (lat. 70.33) the total light of the sun is needed to enable it to grow. The same individual often requires different amounts of light during different stages of its development. The English ivy (Hedera) will not bloom with a light intensity less than two ninths of total daylight, and therefore flowers are never seen on ivies grown as house plants. But the vegetative organs continue to grow with an illumination as low as one forty-eighth. Among the seed plants which can flourish in deep shade are many species of epiphytes and lianas. Good examples of the former are many tropical orchids ; of the latter, one of the most familiar is the common frost grape (Vitis cor dif olio), which can grow with an illumination as low as one seventieth. On the other hand, plants which live in the open and compara- tively unshaded, like all the larger prairie species, such as many kinds of Liatris, Coreopsis, sunflowers, rosinweeds, some iron- weeds and wormwoods, require high illuminations to thrive. 1 See Wiesner, Der Lichtgenuss derPflanzen (Engelmann, Leipzig). Great caution must be used in drawing conclusions on this head, since lack of soil water and salts may easily be responsible for part of the effects attributed to scanty light supply. ECOLOGICAL GKOUPS 493 449. Practical applications of the knowledge of light require- ments. A few words have already been said (Sect. 370) about the importance of recognizing the difference in the light re- quirement of trees. The farmer and the horticulturist often have need of considering the light requirements of cultivated plants. It is not infrequently desirable to grow some kind of crop in partial shade, as in a young orchard. In such situa- tions some of the plants which bear small fruits, as raspberries, blackberries, 1 and strawberries, will succeed fairly well. So also will common beans and broad or horse beans. Pumpkins and squashes grow well in cornfields. A good many useful grasses are tolerant of shade, and mixtures of grass seed suit- able for lawns under shade trees are sold by the principal seedsmen. Some of the grasses of more or less value for pasture or hay, which grow in moderate shade, are Kentucky blue grass, 2 Canada blue grass, 3 orchard grass, 4 rough-stalked meadow grass, 5 wood meadow grass, 6 crested dog's-tail, 7 and sheep's fescue. 8 Some crops, as sugar beets, are of inferior quality when grown in partial shade. In Austria-Hungary the beets grown in the sun were found by one observer to average rather more than three times the weight of those grown in the shade. Add to this the fact that the sun-grown beets contained about 1J per cent more sugar than the shade-grown ones, and the importance of full sunlight for the sugar-beet crop becomes very apparent. Certain crops depend for complete success upon a long series of days of the most brilliant sunshine. 1 The amount of shade which can be tolerated by plants of the same genus, natives of the same region, often differs widely. The black raspberry (Rubus occidentalis) has been found to flower freely but to mature hardly any fruit in a situation where the bushes were so shaded that during the earlier half of the day they received but one twelfth to one fifteenth of the total sunlight, although they had full sunlight during most of the after- noon. Mixed with these bushes were blackberries (perhaps a cultivated form of R. allegheniensis) which flowered and fruited abundantly. 2 Poa pratensis. 8 Poa compressa. 4 Dactylis glomerata. * Poa trivialis. 6 Poa nemoralis. 7 Cynosurus cristatus. 8 Festuca omna. 494 PRACTICAL BOTANY Corn is one of the most important of these crops, and the supremacy of the corn belt in the United States is perhaps as much due to the amount and intensity of its sunshine during the summer months as to its admirable soil. 1 In planting many kinds of crops (corn among others), atten- tion should be given to allowing light to enter freely between the plants ; otherwise the quantity and quality of the product from the field will suffer. Fruit trees should be pruned so that the lower limbs will not be prevented from developing by the shade, and should be planted far enough apart to pre- vent injury to the entire tree from the same cause. The in- tensity of sunlight in an orchard region has much to do with the amount of pruning necessary to make apple trees bear well-developed and ripened fruit. In the northeastern states the tops of the trees should be thinned out to not more than half the thickness allowable in the Middle West. The high color of apples from Colorado and other regions of intense sunlight is due to this abundant light supply, which brings about the coloration even in trees with dense tops. 450. Plant distribution. 2 The subject of the distribution of plants on the earth's surface was at first discussed almost wholly as a group of geographical facts. While travelers for thousands of years have known something of the diversity of the vegetation of the earth, it is only recently that careful attention has been given to the factors which determine the kinds of plant inhabitants of any given region. The vegetation of any portion of the earth is usually con- sidered either from the floristic or the ecological point of view. In the former case the student takes into account mainly the kinds of plants that is, the species, genera, families, and 1 See Warren, Elements of Agriculture, chap. vii. The Macmillan Com- pany, New York. 2 Within the limits of a chapter like the present one this subject can only be touched upon. Much information can be found in the larger physical geographies, in Schimper's Plant Geography on a Physiological Basis (see p. 477), and in the popular writings of naturalists like Humboldt, Darwin, J. D. Hooker, Wallace, Belt, Bates, Hudson, and others. REGIONAL DISTRIBUTION 495 higher groups with which the region is covered. In the latter case the student considers mainly the ecological groups which are present; that is, whether the plants are water or land forms, and in regard to the land plants whether they are xerophytes or mesophytes. In studying plant distribution from the floristic side a very important topic is the considera- tion of the history of the flora. This deals, for instance, with such questions as the investigation of the center or centers from which the plants were derived, the course which they took in migrating outward from those centers, and the time required to cover the territory which they now occupy. 451. Ecological plant geography. For most purposes the ecological characters of the principal floras of the earth are more important than their systematic relations; that is, we are especially concerned to know that arctic vegetation is scanty and of dwarf forms, that vast grassy meadows and prairies and extensive hard-wood forests, often of few spe- cies, are characteristic of temperate regions, and that tropical forests (in the rainy areas) are extremely dense, interwoven with lianas, and burdened with epiphytes. Such facts are of more general interest than the knowledge of the proportion of the floras of the different zones constituted by each family represented. The most important unit for beginners in ecological plant geography to consider is the association.^- In order to see what this term means it will be necessary to recall some of the things which most observing people already know without having studied botany. In a pond like that shown in Fig. 358 one is likely to find white pond lilies, yellow pond lilies, pick- erel weed, arrowhead, pondweed (Potamogetori), water smart- weeds, rushes, and perhaps a good many other flowering plants. Besides these there may be dozens of species of blue-green 1 The plant formation is a larger unit, made up of associations. Forma- tions may consist of many families, genera, and species, but must comprise such vegetation forms as are able to thrive in the habitat where the forma- tion occurs. 496 PRACTICAL BOTANY and green algae. Coniferous or hard-wood forests (Sect. 446) contain varied assemblages of herbs, shrubs, and trees. The plant life of the pond and that of the forest are good examples of associations. A plant association is a set of plants, usually con- sisting of several genera (perhaps comprising many species), of somewhat similar aspect, living together under essentially simi- lar conditions. It is important to notice that even a small area FIG. 370. A flowerless xerophyte (the lichen Usned) growing on conifers in the Maine woods may contain several associations. For instance, a rocky ledge in a meadow may have an entirely different plant population from that of the meadow around it. The aspect of an associa- tion depends largely upon the kind of vegetation forms (hy- drophytes, mesophytes, or xerophytes) which the station can support. It is also influenced by other circumstances, such as, in the case of aquatics, whether the plants are wholly or only partially submerged ; in the case of land plants, whether trees, shrubs, or herbs predominate. REGIONAL DISTRIBUTION 497 452. What determines the occurrence of vegetation forms. The ecological type of the plants which inhabit any kind of habitat depends usually on its soil (in the case of aquatics, the water), its climate, or both. If we find a region with FIG. 371. Mangroves, halophytes with aerial roots The young seedlings are rooting in the beach sand and the thicket is gradually pushing out toward the sea decidedly xerophytic vegetation, this fact may be due to any one of several causes, as follows : (1) A climate with very little annual rainfall. (2) A climate with considerable rainfall during the year but with long rainless periods. 498 PEACTICAL BOTANY (3) A soil or other root foothold which does not retain water, such as dry sand, bare rock surfaces, or the bark of trees. (4) A soil which contains a good deal of water, but is physiologically dry, that is, does not yield water freely for absorption by the roots. As regards (1) and (2), it is easy to see that regions like some of the Arizona deserts, with only about a half inch of rain during the entire year, can hardly support any perennial seed plants other than extreme xerophytes. Countries like those which border portions of the Mediterranean, with a total rainfall for the year of 30 to 40 inches, but one which for four months of summer sometimes falls as low as one half inch, with a maximum daily summer temperature in the sun of 130 F. and an intensely dry atmosphere, are better suited to support xerophytes than mesophytes. A plant under the conditions mentioned in (3) may be del- uged by violent rains during much of the year and yet in a few hours after each rain be wholly cut off from any water supply. Most lichens (Figs. 190-193 and 370) and many tropical epi- phytic seed plants (Fig. 20), as well as our own Spanish moss (Figs. 367 and 368), live under such conditions as these. It is difficult at first sight to recognize what is meant by physiologically dry soils, such as are mentioned in (4). Ordi- narily water cannot be absorbed from soils below a certain temperature, which varies in different kinds of plants. Hence soils in a frozen or nearly frozen condition are physiologically dry, although much water may be present in the form of ice. Soils (or waters) containing much of the humous acids derived from decaying vegetation are perhaps not physiologically dry, but the acids which they contain are injurious to most plants and it is necessary that species which are found in such sit- uations shall be able to live without absorbing much water. Hence many marsh plants, rooted in very wet mud, have xero- phytic leaves. Finally, soils containing much saline matter 1 are 1 As common salt, magnesium chloride, sodium carbonate, sodium sul- phate, magnesium sulphate, or mixtures of these salts. REGIONAL DISTRIBUTION 499 physiologically dry. On such soils the vegetation is composed of halophytes, or plants which tolerate a larger proportion of' mineral salts in the soil than can be endured by most plants. 1 One of the best-known halophytes is the common garden asparagus, which sometimes has its growth increased by the addition of common salt to the soil in which it is growing. FIG. 372. Plants taking possession of recently formed islands in a river Along the bank at the right are three zones of woody plants In many points of form and structure halophytes usually resemble ordinary xerophytes, and many of them are fleshy- stemmed or fleshy-leaved. Such plants abound in the salt marshes of the Atlantic coast and in some of the " alkali " tracts of the extreme Southwest. 1 For example, young seedlings of the saltwort (Salsola Kali, var. tenui- folia), a typical halophyte, live longer in a 5.5 per cent solution of common salt than most herbaceous mesophytes can in a 1.5 per cent solution. In other words, the tolerance of Salsola for common salt is at least four times as great as that of most herbs. 500 PRACTICAL BOTANY 453. Competition and emigration. A little has already been said (Sect. 137) about the severe competition among plants, which often allows only one seed among many thousands to grow into a new plant. This competition frequently tends to cause plants to nourish better in new territory. Other white pines would find it almost impossible to grow up from the seed under adult trees like those of Fig. 321, but seeds blown FIG. 373. A wooded river bank invaded by a moving sand dune In the foreground a young cottonwood is being covered by sand into neighboring clearings (Fig. 322) or among young birches or other deciduous trees (Fig. 323) may promptly begin their growth into forest trees. In this way there is a constant inva- sion of neighboring species into any territory not already occu- pied by those species or by others which they cannot crowd out of the way. A newly formed island in a river (Fig. 372), the recently drained bed of a lake or a bayou, is promptly populated by the plants which crowd in from adjacent terri- tory. The newcomers may arrive as seeds, or as cuttings, REGIONAL DISTRIBUTION 501 pieces of rootstocks, or even as entire plants washed down by the stream. Such immigration among plants is in accord- ance with the principle known as following the line of least resistance; that is, immigration occurs whenever and wher- ever a more densely populated area is in contact with one less densely populated, or when a set of plants of superior qualifications to occupy a given territory comes into contact with a set less well qualified. 454. Plants able to meet the conditions of their environment ; exceptions. A little observation and reading is enough to con- vince the student that the plants of a region usually meet fairly well the requirements of its soil and climate. That is to say, wild plants occur where they do, largely because of the fact that when they migrated into the area which they now occupy they were well equipped to contend with other plants and hold their own in this environment; or because, after immigrating, they developed characteristics which en- abled them to succeed. If a considerable piece of land with its flora could be transplanted bodily from the arctic regions to the most fertile part of the tropics, its vegetation would be promptly destroyed by the new climatic conditions or by the luxuriant growth which would invade it from every side. On the other hand, if a piece of ground covered with tropical vegetation were carried into arctic winter conditions, its plant life would perish of cold in a few hours. Exceptions to the rule that plants are found growing in the places that suit them fairly well are not uncommon. A little has already been said (Sect. 434) about the extraordinary way in which some plants multiply on first being brought into terri- tory new to them. Some of the most noteworthy instances of displacement of native plants by foreign species have oc- curred in New Zealand. There many large, robust plants, some of them very spiny and growing in masses impenetrable by cattle, have been replaced by European grasses and clovers. The sweetbrier destroys pastures and also drives out native shrubs; and the black locust, with its rapid growth and 502 PEACTICAL BOTANY numerous suckers from the roots, quickly gets a footing and holds its ground to the exclusion of most other vegetation. In 1855 only 44 species of foreign plants had become natural- ized in New Zealand, while in 1895 the number had increased to 500 or more. Evidently the newcomers have qualifications which enable them to succeed better than many native plants. 1 Botanists are coming to recognize more clearly than ever before that multitudes of plants grow under conditions which are really unfavorable for them. It is thought that they do so, occurring in abundance in uncongenial stations and infre- quently amid better surroundings, because the unfavorable conditions are so severe as largely to exclude the competition of other plants. For example, knotgrass, 2 knawel, 3 milk purs- lane, 4 and cudweed 5 do not grow in much-trodden paths be- cause they are benefited by being trampled and by having to root themselves in hard soil, but because in such paths they are not crowded and so overshadowed by taller weeds. Seed plants which usually grow on nearly bare rocks, as on cliff sides, generally flourish better (with an equally favorable light supply) in richer and moister soil. Desert plants, as many cacti, often grow more luxuriantly under conditions of soil and climate such as suit ordinary mesophytes. The com- mon groundsel, 6 which abounds on the clean sand of some Mediterranean beaches, blossoming and seeding with an un- branched stem only about an inch high, in fertile, fairly moist soil may grow to a height of 18 inches. It is not safe to assume of any species that the territory or station in which it most commonly grows is the best adapted to its needs. Such a statement could only be made with assurance 1 On the subject of the spread of species introduced into new territory see Darwin, Origin of Species, chap, iii ; Gray, essay on "The Pertinacity and Predominance of Weeds," in Scientific Papers of Asa Gray, edited by Sargent (Houghton Mifflin Company, Boston, 1889) ; also weed reports of the state agricultural experiment stations and of the United States Depart- ment of Agriculture. 2 Polygonum aviculare. 8 Scleranthus annuus. 4 Euphorbia maculata. 6 Gnaphalium uliginosum. 6 Senecio vulgaris. REGIONAL DISTRIBUTION 503 after careful endeavors to introduce the plant into all the kinds of environment in which it might have a fair chance of success. The student will find it most instructive to watch for instances of the occurrence of roadside weeds, such as knotgrass, wild peppergrass, Indian chickweed, and dog fennel, in deep, rich ground, or to plant these and similar tramp plants in good soil and observe how they succeed. 455. Plant geography of the United States. Briefly stated, the four great vegetation areas of the continuous territory of the United States 1 may be designated as follows : (1) The eastern and central forest region, occupying the east- ern and central portions of the country. It extends westward to an irregular boundary line, lying mostly to the east of the hundredth meridian. The easternmost portions of this bound- ary run considerably east of the Mississippi River, while the westernmost extend at least 500 miles west of the river. (2) The Plains region, stretching westward from the forest region to the Rocky Mountain plateau. (3) The Rocky Mountain region, including the Rocky Moun- tains, the Sierra Nevada, and the plateaus between them. (4) The Pacific slope, extending from the Cascade Range and the Sierra Nevada to the Pacific coast. It must be understood that the same species of plant may occur in several or even in all of these regions. Compare the temperature requirements of the white pine and bald cypress (as far as shown by the maps on page 504). Do the ranges of the two anywhere overlap ? If so, where ? Consult Fig. 380 and compare the moisture requirements of the two trees (as far as shown by the maps). Which species avoids the Appalachian highlands? What two reasons may be given for this ? In using the maps shown in Figs. 374 and 375 it should be kept in mind that they are not drawn to exactly the same scale. 1 That is, excluding Alaska, Porto Rico, the Hawaiian Islands, and the Philippines. FIG. 374. Map of distribution of white pine Modified after R. B. Hough. " Handbook of the Trees of the Northern States and Canada " FIG. 375. Map of distribution of bald cypress Modified after R. B. Hough 604 REGIONAL DISTRIBUTION 505 456. The eastern and central forest region. This region con- tains more species of useful hard woods than any similar area within the temperate zones. The oaks are the leading timber trees, but others, as the hickory, the tulip tree, and the sassa- fras, are of especial interest to botanists as characteristic Amer- ican species. The northeasterly part of the forest region, while it contains many hard-wood genera, such as beeches, elms, and maples, is notable for its conifers. Chief among these are the pines (Fig. 321), spruces, hemlocks, and white cedars (Thuja). In the southerly part are several species of conifers, such as bald cypress (Fig. 19) and long-leaf pine (Fig. 260), together with such hard woods as walnuts, hickories, beeches, chest- nuts, oaks, elms, magnolias, sycamores, and ashes. These are deciduous mesophytes, but there are some water-loving trees, such as the water hickory, the sweet bay, and the anise tree, in the moister parts of the South, which may fairly be ranked as hydrophytes. Some trees, as the bald cypress, may grow either as hydrophytes or mesophytes. The forest region has always contained extensive treeless areas. The earliest settlers found " openings " in the hard- wood forests, and extensive prairies, marshes, and heaths, all nearly or quite destitute of trees. Of course the tendency under cultivation has been greatly to decrease the tree-cov- ered area, and it is now very unusual to find bits of primeval forest like those shown in Figs. 319 and 320. Since the forest region extends more than 1500 miles north and south, it contains plants ranging all the way from sub- arctic species, such as the dwarf herbaceous willow, saxifrages, and crowberry, to sub-tropical ones, such as palms and ma- hoganies. 457. The Plains region. The prairies of the Middle West merge imperceptibly into the Great Plains, which terminate, at an elevation of 5000 feet or more, in the beginnings of the Rocky Mountain system. The prairies of western Kansas, western Iowa, Minnesota, Nebraska, and South Dakota have less than 20 per cent of wooded surface, and the high plains 506 PRACTICAL BOTANY are bare of trees except where they have been planted or occur naturally in belts along the streams. Some of the principal reasons that have been given for the treeless condition of the prairies and the plains are the frequency with which prairie fires were set by the Indians, the scanty rainfall, and the de- structive effect of violent dry winter winds, acting on the trees when they can get no water from the frozen soil. Ex- cessive evaporation, due to exposure to high winds at all seasons, seems to be a cause of prairies. Such winds are particularly fa- tal to seedling trees which are not yet deeply rooted. Large areas also have never been reforested since their vegetation was swept away by great geological changes in the Mississippi Basin. 1 The prairies in their nat- ural condition were rather closely covered by coarse grasses, forming a very tough sod. This, when turned over by the break- ing plow, was firm and durable enough to be used by the early settlers for the walls of sod houses. Among the prairie grasses are found several plants of the Pea family, such as the lead plant or shoe strings, 2 prairie clover, 3 ground plum, 4 and some others. Composites are very abundant and characteristic, among them being goldenrods and asters, the blazing star, 5 the cone flower, 6 and several species of tickseed. 7 Some sunflowers 8 1 See Pound and Clements, Phytogeography of Nebraska, Vol. I, pp. 67-70. 2 Amorpha canescens. 8 Petalostemum. 4 Astragalus. 6 Liatris. Budbeckia. 7 Coreopsis. 8 Helianthus. FIG. 376. Occurrence of trees above the ordinary timber line, in sheltered valleys and ravines, Rocky Mountains REGIONAL DISTRIBUTION 507 and rosinweeds 1 are among our largest herbaceous prairie plants, reaching a height of ten or more feet and forming a striking feature in most prairie landscapes in late summer and autumn. In their eastern portion the treeless areas of the high plains are largely covered by close mats of short xerophytic grasses known as buffalo grass 2 and grama grass. 3 Some prickly- pear cacti, 4 milkweeds, 5 and thistles 6 are also found. In early July the grasses dry up, and then hardly any vegetation remains alive aboveground except the succulent cacti. The western portion of the high treeless plains is the beginning of the foot- hill region, of high, rather barren table-lands, extend- ing from Montana to New Mexico inclusive, with an altitude in many portions of 5000 feet above sea level. FlG ' 377 ne - sided g wth of trees near timber line due to severe winds Among the most character- f rom one direction. Rocky Mountains istic woody plants of the region are several wormwoods, especially the sagebrush, 7 and (in " alkali " soils) the greasewood. 8 The sagebrush (Fig. 378) is highly xerophytic, with deep roots, small leaf area, and hairy surface. 458. The Rocky Mountain region. The Rocky Mountain region includes the most diverse formations, ranging from coniferous forest to alpine meadow Characteristic conifers are several true spruces, the Douglas spruce, 9 and a considerable 1 Silphium. 2 Bulbilis, 8 Bouteloua, 4 Opuntia, 5 Asclepias* 6 Cirsium. 7 Artemisia tridentatGr 3 fiarvobatus vermiculatus 9 Pseudotsuga* 508 PKACTICAL BOTANY FIG. 378. A twig of sagebrush Modified after Schimper number of pines. The alpine flora, occurring on the mountains toward the timber line and above it, comprises many beautiful herbaceous and shrubby species. The "alkali" regions, with a highly saline soil, abound in such hal- ophytes as the salty sage, 1 the greasewood, 2 the glasswort, 3 and the Western blite. 4 The best known of these saline areas is the Great Basin, covering an extensive area to the east of the Sierra Nevada, extending nearly to the Great Salt Lake. It is desolate, treeless, and without grass. The less saline valleys and the foothills are covered with sagebrush, while the lower and more "alkaline" valleys are tenanted by such decided halophytes as those just named. In the southern part of the region of the Rocky Mountain system and to the south- west are found some of the principal deserts of the United States, such as the Mohave Des- ert, the Ralston Desert, and in southern Cali- fornia the Colorado Desert. In some of these the temperature for long periods in the sum- mer ranges as high as 118 F., and the total annual rainfall may be less than an inch. Ex- treme xerophytes, such as cacti, a few palms, and tree yuccas (Fig. 379), abound. 459. The Pacific slope. The summer and the winter climate of the Pacific coast region differ in temperature much less than do por- tions of the Atlantic coast in the same lati- tude. In the southern part of the region the most striking difference between seasons is the contrast between their amount of rainfall. 1 Atriplex. 2 Sarcobatus vermiculatus* 3 Salicornia. * Suceda. REGIONAL DISTRIBUTION 509 FIG. 379. Tree yucca in the Mohave Desert Redrawn from a photograph by Coville At Stanford University, thirty miles south of San Francisco, the rainy season usually begins in October and lasts until April. June, July, August, and September are usually rain- less. At San Diego the dry season begins in April and lasts for seven months. Vegetation begins with the autumn rains 510 REGIONAL DISTRIBUTION 511 and is merely accelerated by the coming of warm weather in the spring. Most herbaceous plants cease to grow soon after the summer drought has set in, so that the face of the country is parched and in places seems almost lifeless. The northern portion of the Pacific slope, through the states of Washington and Oregon, is divided by the Cascade Mountains into a comparatively moist western region and a FIG. 381. Annual rainfall of the United States Darkest shade, over 80 inches ; lighter vertical lines, from 40 inches to 80 inches ; horizontal lines, from 20 inches to 40 inches ; blank, from 10 inches to 20 inches ; dotted, less than 10 inches. After W. M. Davis, " Physical Geography " much drier (sometimes semi-desert) eastern region. This is due to the fact that the Cascade Range, running in a general north-and-south direction, causes the precipitation, in the form of rain or snow, of most of the moisture brought from the Pacific by the southwest winds. These mountains are heav- ily timbered, especially along their western slope, and the dense forests abound in such valuable coniferous trees as the western white pine, 1 several species of true fir, 2 and the west- ern hemlock. 3 West of the Cascades three of the principal 1 Pinus monticola. 2 Abies. 8 Tsuga heterophylla. 512 PRACTICAL BOTANY conifers are the giant cedar, 1 red fir, 2 and Sitka spruce. 3 In the bottom lands of Washington, especially along rivers, there are found, besides some conifers, groves of poplar, maple, and ash. In the wettest of these lands occur dense thickets of willows, Western cornel, crab apple, and vine maple. Much of eastern Washington has an annual rainfall of not more than ten inches, and is generally covered with sage- brush and with other semi-desert vegetation, although the soil when irrigated is extremely fertile. Southeastern Oregon is in great part a rocky, sterile plateau of volcanic origin, with vegetation consisting largely of sagebrush, dwarf pine, and juniper. From the forty-first to the thirty-fifth parallel (beginning a little to the south of the Oregon line) the southern portion of the Pacific slope is characterized by the California ever- green conifers, the sugar pine 4 of the coast region, the yellow pine, 5 and others. Two redwoods are notable among the moun- tain flora, the smaller 6 a very important source of lumber, the larger 7 (big tree or giant redwood) the greatest and most imposing of all trees (Figs. 250 and 260). Among the characteristic members of the California flora are many xerophytic shrubs and small trees, in appearance not unlike the abundant thickets of some parts of the Medi- terranean coast region. The California thickets, known as chaparral, contain many leathery-leaved evergreen dicotyle- dons, among them members of the Oak, the Rose, the Sumach, the Heath, the Buckthorn, and the Composite families. On account of the long and severe dry season, southern California abounds in deep-rooted and in bulb-bearing plants, many of the latter belonging to the Lily family ; and in and about the deserts are many cacti and other succulent plants, together with numerous xerophytic shrubs which are not succulent. 1 Thuja plicata. 2 Pseudotsuga mucronata. 8 Picea sitchensis. 4 Pinus Lambertiana. 6 P. ponderosa. 6 Sequoia sempervirens. 7 S. Washinytoniana, REGIONAL DISTRIBUTION 513 460. Influence of rainfall on forest distribution. Plant forma- tions in general, and forest ones among the rest, have their boundaries determined largely by the amount and seasonal distribution of the annual rainfall of the region. A careful comparison of the forest map of the United States (Fig. 380) with the rainfall map (Fig. 381) shows that the arid and semi- arid regions are treeless. By far the greater portion of the immense area lying to the west of an irregular line extending from the Red River of the North to the junction of the Pecos with the Rio Grande, has an annual rainfall ranging from twenty inches down to almost nothing. Over this great ter- ritory there are few extensive forests except those covered with xerophytic conifers, and these occur mostly in the moun- tains where the rainfall is somewhat greater. Our true deserts are treeless except for scattered individuals of such extreme xerophytes as the tree yucca (Fig. 379). The Pacific slope, in its northern portion, has an annual rainfall of thirty-seven inches, and is covered with such luxuriant forests as are shown in Fig. 262. The southern portion has an average annual rain- fall of ten inches, and (except on the mountains) has no con- siderable forests but only a scanty growth of trees and xerophytic shrubs (chaparral). APPENDIX INFLORESCENCE The manner in which flowers are arranged on the floral axis or flower-bearing portion of the stem is called inflorescence. Some- times the flower clusters themselves are also called inflorescences. Each flower, like a vegetative branch, usually arises from the axil of a leaf (Fig. 1, -4), but leaves along the floral axis are often minute, sometimes even scale-like in appearance (Fig.l,.B; Fig. 4, ). All such reduced leaves are known as bracts, and when they arise from branches of the main axis, as in Fig. 6, A, they are called bractlets. There are two main types of inflorescence which are distin- guished by the relative development of the main axis and of the lateral axes. In the racemose type of inflorescence the main axis is more strongly developed than the lateral ones and overtops them, while in the cymose type the lateral axes extend beyond the main one. Some of the principal kinds of flower clusters are shown in the figures which follow. CLUSTERS OF THE RACEMOSE TYPE (INDETERMINATE INFLORESCENCE) FIG. 1. A, axillary and solitary flowers of pimpernel ; red currant p, peduncle; p', pedicel; 6r, bract 515 , raceme of common 516 PRACTICAL BOTANY A B I II FIG. 2. I, simple umbel of cherry ; II, catkins of willow A, staminate flowers ; B, pistillate flowers FIG. 3. A, spike of plantain ; B, head of red clover APPENDIX 517 ch B FIG. 4. Head of yarrow A, top view (magnified); B, lengthwise section (magnified), re, receptacle; i, involucre; r, ray flowers; d, disk flowers; c, corolla; s, stigma; ch, chaff or bracts of receptacle A B FIG. 5. A, panicle of oat ; B, compound umbel of carrot 518 PEACTICAL BOTANY \ p A BCD FIG. 6. Diagrams of inflorescence panicle ; B, raceme ; C, spike ; Z), head ; E, umbel CLUSTERS OF THE CYMOSE TYPE (DETERMINATE INFLORESCENCE) FIG. 7 Compound cyme of mouse-ear chickweed t, the terminal (oldest) flower APPENDIX 519 SUMMARY OF PRINCIPAL KINDS OF FLOWER CLUSTERS A. Indeterminate inflorescence. Order of blossoming from below up- ward, or from without inward 1. Axillary flowers. Flowers growing in the axils of ordinary leaves. 2. Raceme. Flowers with flower stalks, called pedicels, arranged along the peduncle or stem in the axils of special (usually pretty small) leaves called tracts. 3. Corymb. Flowers arranged as in the raceme, but with the lower pedicels so lengthened as to make the flower cluster flat or nearly so (as in the hawthorn or the yarrow). 4. Umbel. Flowers with pedicels of nearly equal length, all appear- ing to spring from a common point, like the ribs of an um- brella. An involucre of bracts usually surrounds the bases of the pedicels. 5. Spike. Flowers as in the raceme, but sessile ; that is, without pedicels. 6. Head. Flowers as in the spike, but the cluster nearly globular. 7. Panicle. Flowers as in the raceme, but the cluster made com- pound by the branching of the peduncle. B. Determinate inflorescence. Order of blossoming from within outward. 1. Flower terminal. One flower borne at the summit of the stem. 2. Cyme. Flowers much as in the umbel, but the innermost blos- soming first. GLOSSARY Abortive. Imperfectly developed, as in abortive stamens. Absorption. Act of taking in substances through the tissues. Accessory fruits. Fruits reenforced by ripening of stem or other struc- tures together with ordinary fruits, as in strawberry, apple, pear, quince. Adventitious buds. Buds that spring from various parts of the root or stem, not from nodes. Aerial roots. Roots that develop in the air. Akene. A small, dry, one-seeded fruit in which the ovary wall adheres to the seed, as in sunflower, dandelion, and grains of common cereals. Albuminous seeds. Seeds that, when ripe, contain endosperm. Aleurone. Grains of definite structure containing protein food; aleu- rone grains are often found in a single layer of regular cells just within the seed coat. Alternation of generations. Alternating of a sexual and a sexless gen- eration in the life cycle of a plant. Ament. The flower cluster of trees and shrubs, such as oak, willow, etc. Anabolism. Building-up processes ; making and assimilating food materials. Anaerobes. Plants that cannot carry on their life processes in presence of ordinary air. Anatropous (turned up). Applied to ovules or seeds that grow in an inverted position. Androecium (male household). Stamens of a flower collectively ; this name was given when stamens were thought to be male sex organs. Anemophilous flowers (wind-loving flowers). Those whose fertiliza- tion is effected by means of the wind. Angiosperms (inclosed seeds). One of the two groups of spermato phytes (seed plants). Annulus (a ring). The elastic ring of cells around the sporangium in ferns. Anther. The pollen-bearing part of the stamen. Antheridiophores. Stalks upon which antheridia are borne. Antheridium ; pi. antheridia. The male sex organ in the lower groups of plants. Antherozoid. See Sperm. 620 GLOSSARY 521 Antipodal (against the foot). Applied to a group of cells at the en4 of the eirbryo sac farthest from the micropyle. Apetalcns. Without petals. Apical. At the apex or tip. Apocarpous (without carpels). Applied to flowers in which the car- pels are entirely free from one another. Appressed. Lying flat throughout its length, as appressed bracts. Association. An ecological unit group smaller than a plant forma- tion, of which the latter is sometimes made up. Awl-shaped. Narrow, tapering to a point, as awl-shaped leaves. Awned. Having bristle-like appendages, as in heads of many kinds of wheat. Basidium (club) ; pi. basidia. The specialized club-shaped cells on which the spores of some fungi are borne. Bast. The phloem portion of a fibrovascular bundle. It may be fibrous (hard bast), or composed of sieve tubes (soft bast). Bilabiate (two-lipped). Applied to the form of corolla in certain di-' cotyledonous plants. Bract (a thin plate). The small, scale-like, modified leaves which sometimes are found at the base of the flower cluster. Calyptra (a cover). In mosses, the hood that covers the tip of the capsule. Calyx (a cup). All the sepals, which together form the outer enve- lope of a flower. Cambium. The meristem cells of a fibrovascular bundle lying be- tween the phloem and xyleni, and having the power of division, so as to produce new phloem and xylem. Capitate (relating to head). (1) Rounded, as the head of the stigma of the primrose ; or (2) growing in heads. Capsule (a small box). A dry, dehiscent seed vessel (formed of more than one carpel). Carpel (fruit). The megasporophyll ; hence either a simple pistil or one of the parts of a compound pistil. Carpellary. Relating to a carpel. Catkins. See Ament. Caulicle (a small stem). The initial stem in an embryo. Cell. The morphological or anatomical unit of plant and animal structure. Cellulose (pertaining to a cell). The primary substance of the cell wall. Central cylinder. The stele, or portion of the root or stem which is inclosed by the primary cortex. Chaff. Small dry scales usually found in connection with the seeds of plants, as in grasses and Composites. 522 PRACTICAL BOTANY Chalaza. The base of an ovule where integuments and nucellus are one common tissue. Chlorophyll (green leaf). The green coloring matter of plants. Chloroplast. One of the special bodies that contain chlorophyll. Choripetalous (separate petals). With the petals separate, not united. Chromatophore (color-bearing). A general term for all bodies in plants containing coloring matter. Cilium (eyelash) ; pi. cilia. Marginal hairs ; motile protoplasmic fila- ments, as those of sperms. Cleistogamous. With close fertilization, occurring in flowers before they open. Closed bundle. A fibrovascular bundle containing no cambium ; growth is closed. Coenocyte. A number of nucleated masses of cytoplasm (cells) in- closed by a common wall. Collateral (sides together). Side by side, as in a fibrovascular bundle in which the xylem and phloem are side by side in a radial direction. Columella (a small column). The persistent axis of certain spore cases, as in mosses. Concentric (center together). Technically used of a fibrovascular bundle whose tissues are arranged so as to surround one another. Conidiophore (conidium-bearer). Stalk upon which conidia are borne. Conidium ; pi. conidia. The asexual spore of some fungi, as in potato blight and grape mildew. Conjugation (joined together). The sexual union of similar gametes. Connate. Applied to leaves that appear united or grown together at their bases. Connective. The portion of the stamen connecting the parts of the anther. Cordate. Heart-shaped. Corm. The fleshy stem or base of a stem ; a bulb-like structure, as on the underground part of jack-in-the-pulpit. Corolla (a small crown). The inner envelope of a flower within the calyx, composed of petals. Cortex. Rind or bark. Cortical. Relating to cortex. Cotyledon. A primary embryo leaf borne by the hypocotyl (caulicle) of the embryo plant. Cryptogams (hidden marriage). A term used to include thallophytes, bryophytes, and pteridophytes. Cupule (a little cup). The gemma cup of liverworts. Cuticle (skin). The outermost layer of epidermis, differing chemically from the remainder of the cell wall. GLOSSARY 523 Cutinization. The transformation of the outer layer of the epidermis into cutin, a substance which is nearly waterproof and not easily pene- trated by gases. Cyclic. An arrangement of leaves or floral organs in such a way that two or more appear upon the axis at the same level, thus forming a cycle or whorl. Cytoplasm. The jelly-like living material of the cell. Deciduous. Applied to plants which lose their leaves at regular intervals. Dehiscence (gaping). The opening of an organ to discharge its con- tents, as in case of anthers, sporangia, and capsules. Dermatogen (skin-producer). The layer of young epidermis in grow- ing points. Dichogamous. With stamens and pistils not maturing together, as in many plantains. Dichotomous (cutting in two). Forked regularly in pairs. Dicotyledonous (cotyledons double). Having two cotyledons or seed leaves. Dimorphism (two structures). Having two different forms. Long- styled and short-styled flowers of the same species are dimorphous. Dioecious (two households). Having the two kinds of reproductive organs borne by separate individuals Dorsiventral. Having the two surfaces differentiated so that one is upper and one lower. Drupe. A stone fruit with a fleshy outer and a hard inner layer of the pericarp, as in the walnut, peach, plum, etc. Ecology. The study of the relations between the plant and its envi- ronment, including the other living beings with which it has to do. Egg or oosphere. The female gamete. Egg apparatus. A group of three cells, consisting of the egg and two synergids, one at each side. Found in angiosperms. Embryo. The young plantlet within the seed. Embryo sac. The cavity within which the embryo develops. Endodermis (within the skin). The layer of cells inclosing the fibro- vascular bundle ; the bundle sheath. Endogenous (produced within). Originating from internal tissues. Endosperm (within the seed). A tissue containing reserve materials developed within the embryo sac. Endosperm nucleus. The nucleus of the angiosperm embryo sac from which the endosperm of the embryo sac develops. Enzyme. One of the plant secretions which digest substances ex- ternal to the plant, as in carnivorous plants, or reserve materials, as in seeds. 524 PRACTICAL BOTANY Epiphyte. A plant which grows upon other plants. Fertilization. The act of uniting an egg and a sperm. Fibrovascular bundles (fiber vessels). The strands that make up the framework of higher plants. Filament (a thread). The stalk of the stamen that supports the anther ; also the individual threads of algae or fungi. Filiform. Thread-like. Fission (splitting). Cell division resulting in division into halves. Fleshy. Thick, succulent. Flowering glume. In grasses, the bract that subtends each flower, sometimes called lower palet. Formation. An ecological group. It signifies a well-defined assem- blage of plants characteristic of some kind of station. Frond (a leaf). A name given to the leaf of ferns. Fruit. The ripened ovary and its contents. Funiculus (a slender rope). The stalk of an ovule or seed. Gametangium (gamete vessel). The specialized organ for production of gametes. Gamete. A reproductive cell which ordinarily becomes functional only upon union with another. As a result of this union a sexual spore is formed. Gametophyte (gamete plant). The sexual stage of an alternating plant. Gemma (a bud) ; pi. gemmae. In bryophytes, many-celled buds special- ized for vegetative propagation. Generative cell. The cell within the male gametophyte of spermato- phytes (usually within the microspore wall) which divides to form the two male cells. Geotropism (turning toward the earth). The tendency of organs or portions of organs to go downward. Glaucous (pale green, gray). Whitened with a bloom, like that on a cabbage leaf. Glume (a husk). A chaff-like bract belonging to the inflorescence of grasses; the outer glumes subtend the spikelet; the flowering glume is the bract of the flower. . Gluten (glue). A term used for the glue-like products of plants, especially of seeds. Grain. A seed-like fruit, like those of grasses, with pericarp grown fast to the seed ; also any small, rounded body, as of starch. Growing point. The group of meristem cells at the growing tip of an organ, from which the various tissues arise. Guard cells. The cells (usually two) which Open and close a stoma. Gymnosperms (naked seeds). One of the two groups of spermato- phytes (seed plants). GLOSSARY 525 Gynaecium (female household). The pistil, or collectively the pistils, of a flower. Halophyte. A plant which can thrive in saline soil, as that of "alkali" lands or salt marshes. Haustorium (drinking organs) ; pi. haustoria. The absorbing organs of some parasites. Heliotropism (turning to light). Tendency of plants to turn toward the sun. Heterogamy (unlike gametes). The condition of plants whose pairing gametes are dissimilar. Heterogamous. Pertaining to heterogamy. Heterospory (unlike spores). The condition in plants which produce two kinds of asexual spores. Heterosporous. Pertaining to heterospory. Homospory (similar spores). The condition in plants which produce but one kind of asexual spore. Homosporous. Pertaining to homospory. Host. The plant upon or within which parasitic plants or animals develop, and from which they obtain nourishment. Hybrid. A plant which is the offspring of an egg of one species fer- tilized by the pollen of another species. The term is also used for crosses between two varieties of plants. Hydrophyte (water plant). A plant thriving only in water or marshes. Hygroscopic (moisture seeking). Having an avidity for water. Hymenium (a membrane). In fungi, a surface layer of interwoven filaments from which the spore-bearing filaments arise. Hypha (a web) ; pi. hyphse. The slender vegetative filaments of fungi which may or may not be woven into a mat (mycelium) or a definitely organized plant. Hypocotyl. The short stem of an embryo seed plant. Hypodermis (under the skin). The tissues which lie immediately beneath the epidermis and which serve to strengthen it. Hypogynous (being under the ovary). Applied to those flowers whose stamens and floral envelopes are at the base of the ovary. Indehiscent. Not dehiscent, or not splitting regularly. Indusium (covering) ; pi. indusia. In ferns, a cellular outgrowth of the leaf covering the clusters of sporangia (son). Inflorescence (flowering). The arrangement of flowers ; or the flower- ing portion of a plant. Integument (covering). The covering of the ovule. Intercellular. Between or among the cells. Internode. The part of a stem between two nodes or joints. Intine (on the inside). The inner coat of a pollen grain. 526 PRACTICAL BOTANY Involucre (rolled within). The leaf-like or bract-like sheath that in- closes a cluster of flowers. Irritability. The capacity which protoplasm possesses of respond- ing to stimuli, such as light, heat, gravity, and contact with chemical reagents. Isogamous (equal gametes). Applied to those plants whose pairing- gametes are similar. Lamina (a layer). The blade or expanded part of a leaf. Leaf trace. The fibrovascular bundles from the leaf which blend with- in the stem with its fibrovascular cylinder. Xenticel. A round, oval, or lens-shaped opening on the exterior surface of the bark. Leucoplast (white molded). A minute colorless body within a cell. When exposed to light, leucoplasts may develop into chloroplasts. Liana. A climbing plant. Ligule (a small tongue). In grasses a thin appendage at the junction of leaf blade and sheath. Medullary. Relating to the pith ; medullary rays are the pith rays which radiate to the bark between the fibrovascular bundles. Megasporangium (large spore vessel). The sporangium that produces the megaspores. Megaspore (great or large spore). The larger one of the two kinds of asexual spores produced by certain pteridophytes and all spermatophytes. Megasporophyll (large spore leaf). The leaf upon which the mega- sporangium develops. Meristem (dividing tissue). Tissues with the cells all nearly alike and still capable of subdividing. Mesophyll (middle leaf). The green or soft tissue of the inner part of the leaf. Mesophytes (middle plants). Normal land plants such as grow in an average soil and under a moderate climate. Metabolism. Chemical transformations of matter carried on by plants in the production and utilization of their food supply, and disposition of waste products. Micropyle (small gate). The opening left by the integuments of the ovule, and which leads to the nucellus. Microsporangium (small spore vessel). The sporangium that produces the microspore. Microspore (small spore). The smaller spore of the two kinds pro- duced by certain pteridophytes and all spermatophytes. Microsporophyll (small spore leaf). The leaf upon which the micro- sporangium is borne. Midrib. The central or main rib of a leaf or thallus. GLOSSARY 527 Monoecious (one household). Applied to those plants upon one of which both kinds of gametes are borne. Strictly speaking, the term applies only to the gametophyte stage of plants. A monoecious seed plant bears both staminate and pistillate flowers. Monopodial (having one foot). Said of a stem consisting of a single and continuous axis (footstalk). Mother cell. A cell that produces new cells (usually) by internal division. Mutualism. A symbiotic relationship in which the organisms are mutually helpful. Mycelium (fungous growth). The filamentous vegetative growth of fungi, composed of hyphre. Naked. Wanting some usual covering. Nascent. Developing or growing. Nastic movements. Movements produced by all-round stimuli, as heat. The opening and closing of the flowers of crocuses and tulips are thermonastic movements. Nectary. The structure in which nectar is secreted. Nerve. A simple vein or rib. Node (a joint). That part of a stem which normally bears leaves. Nucellus (a little kernel). The mass of the ovule within the in- teguments. Nucleolus (diminutive of nucleus). The sharply defined rounded part often seen in the nucleus. Nucleus (a kernel). The usually roundish mass found in the proto- plasm of most active cells, and differing from the rest of the protoplasm in its greater density. Oogonium; pi. oogonia. The female reproductive organ of thallophytes. Oosphere (egg sphere). The egg cell; the mass of protoplasm pre- pared for fertilization. 06'spore (egg spore). The egg cell after fertilization. Open bundle. A fibrovascular bundle which contains cambium. Operculum (a cover or lid) ; pi. opercula. In mosses the terminal lid of the capsule, just beneath the calyptra. Osmosis. The interchange of liquids through a membrane. Ovary (egg-keeper). That part of the carpel in which the ovules are formed. Ovule (an egg). The body which becomes a seed after fertilization and maturation ; formerly thought to be an egg. Palet (chaff). In grasses, the inner bract of the flower. Palisade cells. The elongated parenchyma cells of a leaf, which stand at right angles to its surface and are often confined to the upper part of the leaf. 528 PRACTICAL BOTANY Palmate (pertaining to the hand). Radiating like the fingers; said of the veins or divisions of some leaves. Panicle (a tuft). A loose and irregularly branching flower cluster, as in many grasses. Pappus (down). The modified calyx of the composites. Paraphysis (accompanying organs) ; pi. paraphyses. Sterile bodies, usually hairs, which are found mingled with the reproductive organs of various lower plants. Parasite. An organism that obtains its food from the living tissues or the secretions of other organisms. Parenchyma. Ordinary or typical cellular tissue, i.e. of thin-walled cells nearly equal in all their dimensions. Parthenogenesis. The formation, without fertilization, of a spore which is functionally the same as a sexual spore. In general it means that the fe- male gamete becomes a spore directly, and may grow without fertilization. Pedicel (a little foot). The stalk upon which a structure is borne. Peduncle (a little foot). The flower stalk. Pentacyclic (five cycles). Applied to flowers whose four kinds of floral organs are in five cycles. Perianth (around the flower). The floral envelopes or leaves of a flower, taken collectively; and an analogous envelope of the sporogo- nium of certain liverworts. Periblem (a cloak). A name given to that part of the meristem at the growing point of the plant axis, which lies just beneath the epider- mis and develops into the cortex. Pericambium (surrounding growing tissue). In roots, the external layer of the fibrovascular cylinder. Pericarp (around the fruit). The wall of the ovary, developed into a part of the fruit. Perigynous (around the ovary). Applied to those flowers whose sta- mens and perianth arise from around the wall of the ovary. Peristome (around the mouth). In mosses, usually bristle-like or tooth-like structures surrounding the orifice of the capsule. Petal (a leaf). A corolla leaf. Petiole (a little foot). The stalk of a leaf. Phanerogamia (evident marriage). A primary division (the highest) of plants, named, from their mode of reproduction, the seed-producing plants. Phanerogam is the English equivalent. Phloem (the inner bark). The bark or bast portion of a fibrovas- cular bundle. Photosynthesis (light construction). The name applied to the process by which chloroplasts under the influence of sunlight manufacture such carbohydrates as sugar and starch from water and carbon dioxide. GLOSSARY 529 Phycocyanin (seaweed blue). A bluish coloring matter found within certain algae. Phyllotaxy. Leaf arrangement. Pinna (a feather) ; pi. pinnae. One of the primary divisions of a pin- nate leaf, as in ferns. Pinnate. Having the veins or the divisions of the leaf arranged in rows on each side of the midrib, as in black locust (Robinia). Pinnule (a little feather). One of the divisions of a pinna. Pistil (a pestle). A simple or compound carpel in spermatophytes. Placenta ; pi. placentae. That portion of the ovary which bears the ovules. Plerome (that which fills). A name given to that part of the meri- stem, near the growing points of the plant axis, which forms a central shaft or cylinder and develops into the axial tissues. Plumule (a little feather). The terminal bud of the embryo above the cotyledons. Pod. A dry, several-seeded, dehiscent fruit. Pollen. The spores developed in the anther. Pollen tube. The structure that develops from the wall of the micro- spore of spermatophytes and carries male cells to the egg. Pollination. The transfer of pollen to the stigma. Polypetalous (many petals). Applied to flowers that have their petals free from one another. Prosenchyma. Tissue composed of elongated cells, with tapering ends which overlap. Prothallium (a forerunning shoot) ; pi. prothallia. The small, usually short-lived plant which develops from the spore and bears the sex organs. Protonema (that which is first sent out) ; pi. protonemata. In mosses, the filamentous growth which is produced by the spores, and from which the leafy moss plant is developed. Protoplasm (that which is first formed). The living matter of cells. Pubescent. Downy, with fine hairs. Pyrenoid (kernel formed). Minute colorless bodies embedded in the chlorophyll structures of some lower plants. Receptacle. That portion of an axis or pedicel (usually broadened) which forms a common support for a cluster of organs, either sex organs or sporophylls. Respiration. The series of processes by which plants obtain energy through breaking down of protoplasm or food. Usually oxygen is used and carbon dioxide is formed as a result of the process. Reticulated (net-like). Having a net-like appearance. Rhizoid. Root-like ; a name applied to the root-like hairs found in bryophytes and pteridophytes. 530 PRACTICAL BOTANY Rhizome. See Rootstock. Rootstock. A horizontal, more or less thickened, root-like stem, either on the ground or underground. Saprophyte. An organism that obtains its food from dead or decay- ing organisms. Scalariform (ladder form). A name applied to ducts with piths hori-. zontally elongated, and so placed that the intervening thickening ridges appear like the rounds of a ladder. Scale (a flight of steps). Any thin scarious body, as a degenerated leaf, or flat hair. Sclerenchyma. A tissue composed of cells that are thick-walled, often extremely so. Seed. The matured ovule. Sepal. A calyx leaf. Seta ; pi. setae. A bristle, or bristle-shaped body ; in mosses, the stalk of the capsule. Sexual spore. One formed by the union of cells. Sheath. A thin enveloping part, as of a filament, leaf, or resin duct. Sieve cells. Cells belonging to the phloem, and characterized by the presence of perforated plates in the wall. Sorus (a heap) ; pi. sori. In ferns, the groups of sporangia, constitut- ing the so-called " fruit dots " ; in parasitic fungi, well-defined groups of spores, breaking through the epidermis of the host. Sperm, or Spermatozoid (animal-like sperm). The male gamete. Spermatophytes (seed plants). The highest great group of plants, of which a characteristic structure is the seed. Spike. A flower cluster, having its flowers sessile on an elongated axis. Spikelet (diminutive of spike). A secondary spike; in grasses, the ultimate flower cluster, consisting of one or more flowers subtended by a common pair of glumes. Sporangium (spore vessel) ; pi. sporangia. The spore-producing structure. Spore (seed). Originally used as the analogue of seed in flowerless plants ; now applied to any one-celled or few-celled body which is sepa- rated from the parent for the purpose of reproduction, whether sexually or asexually produced ; the different methods of its production are in- dicated by suitable prefixes. Sporogonium (spore offspring) ; pi. sporogonia. The whole structure of the spore-bearing stage of bryophytes. Sporophyll. A leaf that bears sporangia. Sporophyte (spore plant). The asexual or spore-producing stage of an alternating plant GLOSSARY 531 Stamen. The microsporophyll in spermatophytes." Stigma. That portion of the surface of a pistil (without epidermis) which receives the pollen. Stigmatic. Relating to the stigma, or stigma-like. Stoma (a mouth) ; pi. stomata. Epidermal structures which serve for facilitating gaseous interchanges with the external air, and for transpi- ration of moisture. They are often incorrectly called w breathing pores." Strobilus. A cone-like cluster of sporophylls. Style. The usually attenuated portion of the pistil which bears the stigma. Succulent. Thick and fleshy. Suspensor. A chain of cells which develops early from the oospore, and serves to push the embryo cell deep within the embryo sac. Symbiont. One of the organisms that has entered into a symbiotic relationship. Symbiosis (living together). Applied to a condition in which two or more organisms are living in an intimate relationship. Sympetalous. Having the petals apparently all united, as if grown together by their edges. Syncarpous (carpels united). Applied to those conditions in which the carpels have united into a compound pistil. Synergids (helpers). The two nucleated bodies which accompany the oosphere in the embryo sac, and together with it form the egg apparatus. Testa (a shell). The outer seed coat. Tetracyclic (four cycles). Applied to those flowers in which there are four cycles of floral organs. Tetradynamous (four strong). Said of a stamen cluster in which there are four long and two shorter stamens. Thalloid. Thallus-like. Thallus (a young shoot). The body of lower plants, which exhibits no differentiation of stem, leaf, and root. Tissue. A texture built up of mutually dependent cells of similar origin and character, as the cambium layer. Tracheid. A long, slender cell, with closed ends and its walls thick- ened after the cell has attained its full size, as in the pitted cells of coniferous wood. Transpiration. The loss of water derived from the interior of the plant body in the form of vapor. The term is not generally used with reference to plants of low organization. Trichome (a hair). A general name for a slender outgrowth from the epidermis, usually arising from a single cell. Turgidity. The normal swollen condition of active cells which results from the distension brought about by absorption of water. 532 PRACTICAL BOTANY Unisexual. Having only male or only female reproductive organs. Vein. One of the fibrovascular bundles of leaves or of any flat organ of plants. Venation. The mode of vein distribution. Xerophyte. A plant capable of thriving under conditions of strongest transpiration and with scanty water supply. Xylem (wood). The wood (inner) portion of the fibrovascular bundle. Zoospore (animal spore). A motile asexual spore. Zygomorphic. Said of a flower which can be bisected by only one plane into similar halves, bilaterally symmetrical. Zygospore (yoke spore). The spore formed by conjugation of similar gametes. INDEX (References to illustrations are indicated by asterisks accompanying page num- bers. When an asterisk precedes the citation of a group of pages it means that several illustrations are included.) Absorption of carbon dioxide, 15, 16 Absorption of water by roots, 7-9 Acacia, flower of, 353* Acacia, leaf of, 66* Accessory buds, 92, 93* Acorns, sprouting, 403* Actinomorphic, 108, 109* Adventitious buds, 92 Aerial roots, 30, 31*, 32* Agaricus, 249 Agave, 75, 76*, 77* Agriculture, 3, 159, 167, 434-459. See also under Plant Breeding and Weeds Ailanthus fruit, 150* Air, relation to germination, 139, 140 Air chamber, 14* Air passages, 29, 30 Air plants, 31*, 32, 33, 381, 382, 489* Air roots, 30, 31*, 32*, 33 Air storage, 76 Akene, 328 Albugo, 223 Albuminous substances. See Proteins Alfalfa, nitrogen production by, 37 Alga-fungi, *213~225 Alga-fungi, summary of, 223, 224 Algae, 159, * 180-212 Algae, classification of, 212 Alsophila, 276 Alternate leaves, 65, 56* Alternation of generations, 263-265 Ament. See Catkin Angiosperm, life history of, 328, 329 Angiosperm flower, 20, 21, 104-114, *322-328 Angiosperms, 158, *321-334 Angiosperms, summary of life cycle, 329 Animal food, plant sources of , 2, 1 7, 82 Annual growth, definite, 95, 304 Annual growth, indefinite, 95 Annual ring, 12, 60*, 61, 304 Annuals, 12, 33, 34 Anther, 20*, 21, 110*, 323 Anther, modes of opening, 111* Antheridium, 201, 261*, 269*, 284* Anthoceros, 272*, 273, 285 Anthrax, 165, 171 Antipodal cells, 21*, 117*, 325 Antitoxins, 172, 173 Apetalous, 106* Apple, leaf arrangement of, 66* Apples, 454*, 459, 460, 494 Aquatic plants, *479-481 Arbor vitse, 310*, 312 Archegonium, 260*, 270*, 285*, 306* Aristolochia stem, cross section of, 45* Arrangement of leaves, *55-60 Arrowhead, 478* Ascocarp, 230*, 231 Ascomycetes, *226-234 Ascophyllum, 207 Ascospores, 228 Ascus, 228, 230* Asexual generation, 264 Asexual reproduction, 194 Asparagus flower, 109* Asparagus rust, 245 Associations, plant, 455, 495, 496 Avens, fruit of, 164* Axil, 92* Axillary bud, 92* Axillary inflorescence, 515* Bacteria, 36, 37, 161-179, 162* Bacteria, classification of, 179 Bacteriology, 159 Bald cypress, distribution map, 504* Balsam, wild, flowers of, 130* Balsam, wild, fruits of, 163* Bamboo, 337 Banana, 349*, 360 Barberry, 245 Bark, 46, 50* Barley, 465, 457 Basidia fungi, 226, 240 633 534 PRACTICAL BOTANY Basidiomycetes, 226, *240-256 Bast, hard, 47* Bast, soft (sieve tubes), 80 Batrachospermum, 209* Bean seed, 22*, 136* Bean seeds and pod, development of, 22* Beech, one-sided pruning of, 42* Beech seedlings, 23* Bees, 123 Begonia, flowers of, 108* Begonia, leaf mosaic of, 59* Berries, 460, 461 Biennial, 33, 34 Big tree, 304*, 311*, 313* Bilaterally symmetrical flowers, 108, 109* Birch, flowers and flower clusters of, 351* Bird pollination, 130 Bisexual, 131 Black knot, 234 Black walnut, buds of, 90* Blackberry, 430, 461 Bladderwort, 481* Blade of leaf, 10*, 13*, *55-71 Bleeding, 9 Blueberry, 364 Blue-green algae, *180~187 Blue-green algse, classification of, 187 Bluets, flowers of, 133* Bordeaux mixture, 222. See Spray ing Botany, economic, definition of, 159 Botany, systematic, definition of, 159 Botrychium, 288*, 290 Box elder, buds of, 93* Bract, 515* Branches, origin of, 52*, 53* Branching and leaf arrangement, 56 Breeding, plant, *412-433 Brown algse, *206-209 Brown rot, 227, 228 Bryophytes, 158, 257, 273 Bryophytes, classification of, 273 Bryophytes, evolution of plants, 330, 334 Bryophytes, summary of, 272, 273 Buckeye, bud of, 91* Buckwheat, flower of, 106*, 124* Budding, 87*, 88 Buds, *90-102 Buds, adventitious, 92 Buds, naked, 90 Buds, opening of, 99, 100 Buds, position of, 92 Buds, structure of, 91*, 95*, 96* Bud-scale scar, 92*, 98*, 100*, 102* Bud-scales, 90, 91*, 95*, 96* Bulb, 73, 74*, 83 Bundles, fibrovascular, 11*, 12 Burbank, Luther, 430 Burs, 146*, 154* Cacao, 359, 360 Cactus, 81*, 482 Calcium, 448 Calyx, 20*, 104* Cambium, 45*, 304 Cambium layer, 45*, 46 Camembert cheese, 231 Camphor tree, 362* Cancer root, 383* Canna, leaf of, 336* Canning, 169 Capsule, 153* Caraway, flower and fruit of, 359* Carbohydrates, 16 Carbon, 16 Carbon dioxide, 15, 16, 19 Carbon dioxide, absorption of, 15-17 Carboniferous Period, 296 Carnation rust, 245 Carnivorous plants, 381, *385-388 Carpel, 105*, 111 Carrot fruit, 359* Cascade Range, 511 Cassava, 356, 357 Cassia, flower of, 353* Casuarina, 484* Catalpa, hardy, 405* Catkin, 106*, 107*, 516* Cattleya, 31* Cedar, 312*, 313 Cedar apples, 246*, 247* Cell, 8* Cell turgor, 9, 10 Cell wall, 8* Central cylinder, 24* Central placenta, 112* Century plant, 75, 76*, 77*, 482 Century plant, section of leaf of, 483* Cereals, 339, 340*, 455-458 Cetraria, 239 Channels for carrying plant food, 80, 81 Chaparral, 512 Chara, 204, 205, 207* INDEX 535 Cherries, 462 Cherry, wild black, fruits of, 155* Chestnut sprouts, 404* Chlorophycese, * 188-206, 212 Chlorophyll, 14, 181 Chlorophyll bodies, 14* Chloroplast, 14*, 189 Chocolate, 359, 360 Choripetalous, 110 Choripetalous dicotyledons, *350- 362 Chorisepalous, 110 Cilium, 190 Citrous fruits, 430, 431, 462, 463 Cladonia, 237*, 238* Cladophora, 194-197 Cladophyll, 41* Classification, 156, 158 Clavaria, 252* Claviceps, 233* Clay, 435 Cleistogamous flowers, 133, 134* Clerodendron, flowers of, 132* Climbing plants, 41/60*, 61*, 62*, 63*, 380, 381 Climbing stems, 45*, 49, *60-63 Closed bundles, 54 Clover, nitrogen-fixing by, 37. *374- 377, 449 Clover leaf, 64* Clover seed, 471, 472 Club moss, 293, 294* Coal, 297, 298 Coal-forming periods, 291, 296, 297 Cocklebur, 467* Coco palm, 340*, 341*, 343 Ccenocyte, 195, 199, 215 Coffee, 367*, 368* Coleochaete, 204, 206* Collenchyma, 47*, 49* Colors of flowers, 125, 126 Columella, 216* Coming true from the seed, 413, 417, 425 Comparison of great groups, 330- 334 Compass plants, 64 Competition, 148-151 Composite family, *368-370 Compound cyme, 518* Compound pistil, 112* Compound umbel, 517* Cone, 292, 294, 301* Cones of gymnosperms, 310*, 311* Confervas, 204 Conidia, 221 Coniferales, 311, 320 Coniferous forest, 314*, 315* Coniferous woods, 316, 390* Conifers, industrial importance of, 313, 316 Conjugation, 194 Coppice, 403, 404* Coprinus, 253 Cork, 46 Corn, cultivation of, 37, 448, 456, 457 Corn, fibrovascular bundles of, 11* Corn, grain of, 419* Corn, root system of, 7* Corn breeding, *419-424 Corn cockle, 467* Corn smut, 242*, 373 Corn stem, structure of, 11*, 12, 54* Corolla, 20*, 104* Cortex, 12*, 45*, 49*, 54* Cotton, 458, 459 Cotton wilt, 234 Cottonwood branches destroyed by sleet, 43* Cottonwood buds, development of, 98*, 99* Cottonwood leaf, network of veins, 10* Cotyledon, 136*, 137*, 139*, 142*, 143*, 144 Cover (operculum), 262 Cranberry, 363* Cranberry-gall fungus, 223 Cranesbill, fruit of , 153* Cratsegus bud, section of, 96* Cross pollination, 122, 422*, 423 Crowberry, rolled-up leaf of, 482* Cruciferae, diseases of, 223 Cryptogams, 323 Cup (cupule) of Marchantia, 268* Cuticle, 483* Cutinized, 484* Cyanophyceae, *180-187 Cycadales, 311, *316-318 Cycads, *316-318 Cycas, 317 Cycloloma, 475* Cyme, 518* Cypress, 29*, 312 Cypripedium, 346*, 347* Cystopteris, 286* Cystopus, 223 Cytology, 159 Cytoplasm, 8, 181, 189 536 PRACTICAL BOTANY Dahlia, thickened roots of, 34* Daily movements of leaves, *64-66 Damping off, 223 Dandelion, 27 Dandelion, fruits of, 147* Darwin, Charles, 148 Dasya, 211* Date palm, 344 Decay, 166, 167 Deciduous, 19, 66, 68, 302 Definite annual growth, 95 Dehiscence, 323 Denitrification, 377 Dependent habit, 213 Dependent plants, *371-388 Desert plants, 35, 156, 508, 509* Deserts of United States, 508 Desmids, 204* Desmodium, 355* Desmodium, fruits of, 154* Determinate inflorescence, 519 Diadelphous, 111 Diagrams, floral, 114* Diastase, 145 Dichogamy, 131*, 132* Diclinous, 106* Dicotyledonous stem, cross section of, 12*, 45*, 49*, 50* Dicotyledonous stem, gross structure of, 12*, *48-53 Dicotyledonous stem, minute struc- ture of, *44-48 Dicotyledonous stem, rise of water in, 11 Dicotyledons, 12, 327 Dicotyledons, families of, *350-370 Diffuse porous wood, 392* Diffusion, 79, 80 Dimorphous flowers, 132, 133* Dioecious, 106*, 107* Dionsea, 387* Diphtheria, 172, 173 Disease, 171, 172, 173, 174, 176 Disk flowers, 369* Distribution of plants, 1, *494-513 Distribution of seeds, *146-155 Diurnal position, *64-66 Dodder, 36, 383, 384, 466* Dogtooth violet, 83*, 345 Double fertilization, *324, 326 Douglas fir, 315* Downy mildew, 219*, 222 Dragon root, 342* Drainage, 436, 437-439 Draparnaldia, 204* Dry fruits, 151 Dry-land farming, 440 Duckweed, 477* Duct. See Vessels Dunes, 500* Earth star, 254 Earthworms, 437 Eastern and central forest region *503-505 Ecological groups, 479, 480 Ecology, plant, definition of, 118, 119, 159 Ecology, summary of, *477-513 Economic botany, 159 Ectocarpus, 208 Edible seeds, dispersal of, 155 Egg apparatus, 21*, 117*, *324 Egg cell, 117*, 201 Elater, 270, 292* Elder stem, structure of, 49* Elementary species, 417 Elm, flowers and flower clusters of, 352* Elm buds, 96*, 97* Elm fruit, 150* Embryo, 118, *136-139, 284, 309*, 327* Embryo sac, 21*, 117* Endosperm, 118, *136-139, 325* Endosperm nucleus, 117*, 325* Energy, source of, in plants, 19 Enzymes, 116, 144, 145 Epidermis, 14*, 24*, 45*, 46, 483*, 484 Epigynous, 114 Epiphytes, 381, 382 Equisetineae, 291 Equisetum, *291-293 Ergot, 233, 234 Erosion, 28, 407, 408, *441-446 Eryngium flower stalk, structure of, 49* Esparto, 337 Euphorbia, 356*, 485* Evening primrose, flowers of, 113* Evening primrose, fruits of, 153* Evening primrose, rosettes of, 57* Evergreen, 302 Evolution of plants, 330, 334 Evolution of sex, 197 Excretion of water, 18 Excretions, 166, 167, 172 Existence, struggle for, 148-151 Explosive fruits, 153* INDEX 537 Fairy ring toadstool, 249, 250* Fall of the leaf, 19, 66, 68 Family, 158 Fermentation, 145, 232, 233 Ferments, 36 Fern gametophyte, 282*, 283* Fern leaflets, 280* Ferns, *274-291 Fertilization, 201, 325*, 326 Fertilization, in angiosperms, 116*, 117*, 118 Fertilizers, 209 Fibers, 47*, 48* Fibers, commercial, 348, 361 Fibrovascular bundles, 11*, 12, 46*, 54* Filament, 110, 111* Filicineae, 274 Fission plants, 159 Fleshy fruits, uses of, 155* Fleshy roots, 34*, 35 Floating seeds, 154 Floral diagrams, 114* Floral organs, 20* Flower, 20*, 21, *104-114, 322 Flower, definition of, 104 Flower, morphology of, 104, *323~327 Flower, organs of, 20*, 21, *104-112 Flower, plan of, 105*, 106*, 114* Flower, symmetry of, 108, 109* Flower buds, 94*, 95, 96 Flowering plants, 156 Flowers, ecology of, .*! 18-135 Flytrap, Venus, 387* Food, raw materials for, 15, 447, 448 Food, storage of, in root, 33, 34*, 35 Food, storage of, in stem, 77-79 Food, transportation of, in plant, 78-81 Food cycle, 15-17 Food in embryo, *137-139 Food manufacture, 15-17 Forest, strata of vegetation in, 490- 492 Forest fires, 409, 441, 443 Forest map of United States, 510* Forestry, *398-411 Forests, pure and mixed, 399 Formations, plant, 495 Fossil plants, 295-297, 318, 319 Foxglove, leaf of, 336* Fruit, *1 50-155 Fruit bud, 94*, 95, 96 Fruit scars, 101 Fruit spurs, 94*, 95, 96 Fruits, edible, *348-350, 351 Frullania, *271 Fucus, 207, 208 Fuel value of wood, 395 Funaria, 265 Fungi, 159,*213-256 Fungi, classification of, 225, 256 Fungi, origin of, 215 Funiculus, 139 Fusarium, 432 Gamete, 194 Gametophyte, 263-265 Gamopetalous, 110 Garnosepalous, 110 Garden vegetables, 464 Gardening, 167, 451, 464 Geaster, 254 Gelatinous foods, 209 Generations, alternation of, 263-265 Generative cells in pollen tube, 116* Generative nucleus, 116* Genus, 156 Geography, plant, of the United States, *503-513 Geranium (Pelargonium) cutting, 5* Geranium leaf, section of, 14* Geranium leaf, surface view of, 13*, 70* Geranium (Pelargonium) stem, cross section of, 12* Germ diseases, 161-179 Germination, chemical changes dur- ing, 144, 145 Germination, conditions for, 139, 140 Germination, preparation for, 140, 141 Gigartina, 210* Gills, 248*, 249* Ginger, wild, 58* Ginkgo, 318* Ginkgoales, 311, 318* Ginseng, 358* Glceocapsa, 180, 181, 182 Glceotrichia, 186, 187 Gnetales, 311, 318 Gourd family, 370 Grafting, 87, 88*, 89, 462 Grain, 138*, 139* Grape mildew, *219-222 Grapefruit, 462 Grapes, 463, 464 Grass family, *336-340 Grasses, *336-340 Grasses, culture of, 458 538 PRACTICAL BOTANY Great Basin, 508 Green algae, * 188-207 Green felt. See Vaucheria Green slime, 188 Groups of plants, 156, 158 Growing point, 52* Guard cells, 13*, 14 - Gymnosperm, life history of, 299-311 Gymnosperm cones, 310*, 311* Gymnosperms, 158, *299-320 Gymnosperms, classification of, 320 Gymnosperms of past ages, 318, 319 Gymnosporangium, 246*, 247* Gynecoeum, 111 Gypsy moth, destruction caused by, 411 Hairs, root, 7, 8*, 9 Hairs on leaves, 70*, 71, 485, 486 Half -inferior ovary, 113 Halophytes, 497*, 499 Hard bast, 47* Hard woods, *391-393 Hardwoqd trees, 350, 351 Haustoria, 36, 221*, 230, 384 Hay, 458 Hays, W. M., 417 Head, 516*, 517* Heartwood, 51 Heath family, 363*, 364 Helophytes, 479 Helotism, 373 Helotists, 213 Hemlock, 310*, 312, 313 Hepaticae, 257, 273 Herbs, 35, 90 Heredity. See Coming true Heterocyst, 183 Heterospory, 295 Hevea, 357* Hickory, buds of, 92* Hilum, 136* Holdfast, 196*, 202*, 206, 208*, 210* Holly wood, section of, 392* Honeybee, leg of, 123* Hop, twining of, 60* Hopkins, C. G., 420 Horse nettle, 471* Horse-chestnut buds, 100*, 101* Horsetails, *291-293 Horticulture, 434, 451-455 Host, 35, 36 Humus, 382, 435, 436 Hyacinth, bulb of, 74* Hybrid blackberries, 430 Hybrid plums, 430* Hybridizing, *426-431 Hybrids, 426, 428*, 429*, 430, 431 Hydnum, 252 Hydrangea, 11 Hydrogen, 16 Hydrophytes, 479. See also Water plants Hypha, 214* Hypocotyl, 136*, 137*, 143* Hypogynous, 114 Iceland moss, 239 Immigration of plants, 500-503 Immune, 172, 432 Imperfect fungi, 234 Indefinite annual growth, 95 Independent plants, 371 Indeterminate inflorescence, 519 Indian corn, kernel of, 419*, 420 Indian corn, light requirement of. 494 Indian corn, structure of stem of. 11*, 54* Indian corn breeding, *4l 7-424 Indian corn culture, 456, 457 Indian pipe, 381* Indusium, 279*, 280*, 286* Industries, plants in, 2, 3. See also under Agriculture, Horticulture, Fuel, Fibers, Timber Inferior ovary, 113* Inflorescence, *515-519 Inflorescence, determinate, 519 Inflorescence, diagrams of, 518* Inflorescence, indeterminate, 519 Insect pollination, *123-129 Insectivorous plants. See Carnivo- rous plants Insects, pollen-carrying apparatus of, 123*, 129* Insects, sense of smell of, 124, 125 Insects, vision of, 125, 126 Integuments, 324* Intercellular spaces, 14*, 479* Internode, 100*, 101* Invasion, 501, 502 Involucre, 519 Iodine test for starch, 78, 79 Irish moss, 212 Iron, 15, 448 Ironweed, fruits of, 152* Irrigation, 440, 441 Irritability in plants, nature and occurrence of, 388, 389 INDEX 539 Irritability of tendrils, 62 Ivy, aerial roots of, 63* Ivy, relations of, to light, 63* Jimson weed, 365* Jordan, E. 0., 162, 164, 165, 173 Juniper, 311*, 313 Kelps, 208* Kerner, Anton, 71 Knees, of cypress, 29* Knots, 53* Laminaria, 208* Land plants, 480 Lateral buds, 92* Leaf, *13-20, *55-69, 89 Leaf, fall of, 19, 66, 68 Leaf, member of plant body, 39 Leaf arrangement, 55*, 56* Leaf blade, 10*, 13 Leaf buds, 91 Leaf mosaics, 59*, 60 Leaf movements, 57, *63-66 Leaf scars, 92*, 100*, 101* Leaf sections, 14* Leaf tendril, 62 Leafstalk, 10*, 13 Leafy liverworts, 271*, 272 Leaves, compound, 13 Leaves, functions of, 15-20, *76-79, 89 Leaves, simple, 13 Leaves, structure of, 14* Leaves, submerged, 481* Legume, 353, 354* Leguminous plants, 36, 37, *374-377 Lemon, 462 Lenticels, 102*, 103* Leucoplasts, 79 Lianas. See Climbing plants Lichens, 226, *235-239 Lichens, nature of, 235-239 Lichens, uses of, 237-239 Lichens and soil formation, 235, 236, 238 Liebig, Justus von, 26 Light, exposure to, 55*, 57*, 59* Light, movements caused by, 63* Light requirements, 489-494 Lilac mildew, 229*, 230* Lily family, 345*, 346 Lime, 37 Limnophila, 480* Linden, fruit cluster of, 161* Litmus, 239 Liverworts, 158, 257, *266-272 Locules, 112* Locust, black, 65, 501, 502 Lycoperdon, 253* Lycopodineae, 293 Lycopodium, *293-295 Macrocystis, 208 Madder family, 367*, 368* Magnesium, 448 Male cells of pollen tube, 116*, 326 Male nuclei of pollen tube, 116* Mallows, pollination in, 121*, 131* Malting, 145 Mangrove, 497* Maple fruit, 150* Maple sugar, 82 Marchantia, *266-271 Marl, 205 Marsilia, 290*, 291 May apple, 72* Mechanics of stem and root, 48, 49*, 50 Medullary ray, 50*, 81 Megasporangium, 295, 306 Megaspore, 295, 306, 325 Mendel's law, 426 Mesocarpus, 204* Mesophytes, 480, 487, 488 Mesquite, root system of, 27 Messmates, 35 Micropyle, 21*, 117*, 324 Microsphsera, 229*, 230* Microsporangium, 295, 306 Microspore, 295, 306, 325 Microsporophyll, 295, 307* Migula, W., 162 Mildews, *219-222 Milk supply, 169, 175, 177 Mineral constituents of plants, 15, 448 Mint family, 364 Mississippi River, delta of, 28 Mississippi River, silt carried by, 28 Mistletoe, 36, 384* Mixed buds, 91, 94* Molds, 166, 178, *214-219, 231 Monadelphous, 111 Monocotyledonous stems, *53-55 Monocotyledonous stems, growth of, in thickness, 54, 55 Monocotyledons, 12, 327, 335 Monocotyledons, families of, *335- 360 540 PRACTICAL BOTANY Monoecious, 107, 108* Morchella, 229* Morel, 229* Morning-glory, fruits of, 153* Morphology, 159 Morphology of the flower, 104*, *323- 327 Mosaics, leaf, 59*, 60 Moss, life history of, 257*-265 Mosses, 158, *257~265 Mucor, 214-217 Muehlenbeckia, 40* Musci, 273 Mushroom, 240, *247~252 Mustard seedling, root hairs of, 8* Mutations, 412 Mutualists, 35-38*, 213 Mycelium, 214 Mycorrhiza, 38* Myrsiphyllum, 41* Myxomycetes, 224*, 225 Naked buds, 90 Nectar, 124 Nectar glands, 124* Nectaries, 124 Nest fungi, 255* Netted veining, 336* New Zealand, displacement of na- tive plants in, 501, 502 Nightshade, leaf mosaic of, 59* Nightshade family, *364-367 Nilsson, Hjalmar, 417 Nitrification, 36, 37, 374, 377 Nitrogen, 15, 17, 374-378, 448, 449 Nitrogen-fixing bacteria, 374-378, 448 Nocturnal position, *64-66 Nostoc, 182*, 183, 184 Nucellus, 117* Nucleus, 8* Nutrient substances, 15 Nutrition of plants, 15-17, 36-38, 39, 40, *77-81, 160, *371-388, 447-451 Oak leaves and acorns, 157* Oak tracheids, 48* Oak trees, 410* Oak wood, cross section of, 50* Oat, root system of, 26 Oat smut, 240*-242 Oats, 455, 457 Odors of flowers, 124, 125 03dogonium, 201*, 202* Oil, 138, 144 Oleander leaf, 76 Olive, vertical leaves of, 64* Olive family, 370 Onion, seed and seedling of, 137* Onoclea, 289* Oogonium, 201*, 203* Oospore, 201, 203*, 221*, 222*, 261, 270, 284, 309, 326 Open bundles, 54 Opposite leaves, 55* Orange, 431, 462 Orchid, 31*, 382 Orchis family, *346-348 Order, 158 Origin of sex, 197 Orobanche, 383* Oscillatoria, 184, 185*, 186 Osmosis, 79 Osmunda, 287* Ovary, 112*, 324*, 324 Ovule, 112*, 306, 324* Ovule, structure of, 21*, 306*, 324* Oxygen, 17*, 19 Palisade cells, 14* Palm family, 341 Palms, *340-343 Panicle, 517* Parallel veining, 336* Parasites, 35-37, 156, 213, 218, 219, 222, 223, 226, 229, 234, 240, 241, 372, 381, 383*, 384* Parasitic bacteria, 378, 379 Parasitic roots, 35, 36 Parasitism, 372 Parenchyma, 14* Parsley family, 357, 358, 359* Parsnip fruit, 359* Parthenogenesis, 219 Pasteur, Louis, 165, 178, 233 Pathology, 159 Pea family, *353-355 Pea seedling, mutilated, 144* Peach flower, prepared for hybridi- zation, 427* Peach mildew, 234 Peach rot, 228 Peaches, 461, 462 Peanut seedling, 22* Peanuts, crop of, 354 Pears, 460 Peat, 264*, 265 Peat bogs, 265 Peat moss, 264*, 266 Pedicel, 519 Peduncle, 619 INDEX 541 Penicillium, 223, 231* Perennial, 12, 33, 35 Perianth, 109 Perigynous, 114 Perisperm, 136 "Peronospora, 223 Petal, 20*, 105* Petiole, 13 Peziza, 226, 227 Pfeffer, W., 389 Phseophycese, 206 Phallus, 254* Phanerogams, 323 Phloem, see Bast Phosphorus, 15, 448 Photosynthesis, 15-17, 39, 40, 181 Phycomycetes, *213-225 Phylloxera, 463, 464 Physiology, 159 Phytopathology, 159 Phytophthora, 222, 223 Pine forests, 299 Pine needle, 300, 302*, 303* Pine seed, 309* Pine stem, growth of, 44, 51, 52 Pine wood, section, 390* Pineapples, 348* Pmesap, 382* Pi mis, *299-309, 314 Pistil, 20*, 21*, 111, 112* Pistillate flower, 106*, 108* Pitcher plants, 386, 387* Pith, 11, 12* Placenta, 112* Plains region, 505-507 Plant associations, 495, 496 Plant breeding, *412-433 Plant cell, 7, 8 Plant fibers, 47*, 48* Plant food for domestic animals, 2 Plant formations, 495 Plant geography, *495~513 Plant industries, *434-464 Plant lice, 372, 373 Plantain, flowers of, 131* Plants as fertilizers, 36, 37 Plasmopara, *219-222 Plastid, 14* Pleurococcus, 188, 189*, 190 Plowrightia, 234 Plum, black knot, 234 Plums, 430*, 462 Plumule, 136* Poison ivy, 60* Pokeweed, 473* Pollen, 115*, 307, 325 Pollen, discharge of, 111* Pollen chamber, 110* Pollen grain, germination of, 115 116*, 117*, 308, 325, 326* Pollen sac, 110*, 111, 307* Pollen tubes, 116*, 117*, 308*, 326* Pollen-carrying apparatus, 123*, 129* Pollination, *115-135, 307, 326 Pollution of water supply, 169, 174, 177, 205, 206 Polyporus, *251-253 Polytrichum, 265 Pome fruits, 459, 460 Pond lily, 67*, 478* Pondweed, section of stem of, 479* Poplar bud, section of, 96* Position of buds, 92* Postelsia, 208 Potassium, 15, 448 Potato, 365, 366, 413*, 453* Potato blight, 222, 453* Prairies, 506, 507 Preservation of fruits, 168, 169 Prickly-pear cactus, 81* Pronuba, 128*, 129* Propagation by cuttings, 86 Propagation by roots, 33* Propagation of seed plants, 33*, *82- 89, *139-144 Proteins, 17, 35, 77, 80, 138, 144, 419- 421 Protonema, 257, 259 Protoplasm, 8*, 181 Protoplasm, structure of, 181 Pruning, 451-453 Pruning, due to shade, 42* Pteridophytes, 158, *274-298 Pteridophytes, classification of, 298 Pteridophytes, evolution of plants, 330, 334 Pteridophytes, summary of, 297, 298 Pteris, 275* Ptomaines, 170 Public health, 161-179, 169, 174, 177, 205, 206 Puccinia, *243-246 Puffball, 240, 253, 254 Pulvinus, 65 Pythium, 223 Quercus, 157*, 158 Quince, 460 542 PRACTICAL BOTANY Raceme, 615* Radial symmetry, 108, 109* Rafflesia, 384 Rainfall, 437 Rainfall map of United States, 511* Ray, medullary, 50* Ray flowers, 369* Receptacle, 105 Red algae, 209 Red clover, leaf of, 64* Redwood, 313*, 512 Regions of vegetation in United States, *503-513 Reindeer moss, 239 Reproduction, 160, 194 Reproduction, sexual, in flowering plants, 21*, 22*, * 115-1 18 Reproduction by leaves, 89 Reproduction by portions of stem, 82, *83-89 Resin duct, 303* Respiration, 19, 76 Response, 389 Resting buds, 90* Rhizoids, 214, 215* Rhizopus, *214-217 Rhododendron, 69* Rhodophycese, *209-212 Riccia, 266, 267 Ricciocarpus, 266* Rice, 339, 340*, 455, 458 Ring, annual, 50*, 51 Ring-porous wood, 391* Rise of water in steins, 11, 80 Rockweeds, 207* Rocky Mountain region, *506~508 Root, *5-10, *24-38 Root, dicotyledonous, section of, 24* Root, fleshy, 34* Root absorption, 7-9 Root climbers, 61, 63* Root hair, 7, 8*, 9 Root pressure, 9 Root rot, 234 Root system, 6*, 7*, 26, 27 Root tubercle bacteria, 374-378, 449 Root-tubercles. 36, 37 Roots, aerial, 30, 31* Roots, air requirements of, 29 Roots, anchorage by, 5, 6*, 25 Roots, earth, 25, 26 Roots, effects of, on soil, 28 Roots, parasitic, 35, 36 Roots, pull of, 27 Roots, reproduction by, 33* Roots, storage of food and water in, 33, 34, 35 Roots, structure of, 24*, 49* Roots, water, 30 Roots, water-lifting by, 9 Rootstock, 72*, 73*, 275*, 276, 277 Roquefort cheese, 231 Rose family, 352*, 353 Rose family, fruits of, 459-462 Rose mildew, 234 Rosette plants, 57*, 58 Rosin, 316 Russian thistle, 148 Rusts, 240 Rye, 455, 457 Sac fungi, *226-234 Saccharomycetes, 232*, 233 Sagebrush, 508* Sago palm, 317 Salt marsh plants. See Halophytes Salts, 498, 499 Saltwort, 499 Salvinia, 291* Sap, movements of, 9, 11, 80 Saprolegnia, 217*, 218* Saprophytes, 213, 218, 372, 381*, 382* Saprophytic bacteria, 374 Saprophytism, 372 Sapwood, 51 Sargasso seas, 207 Sargassum, 207 Sassafras wood, section, 391* Scaly buds, *90~96 Schizomycetes, 161, 179 Scion, 88* Sclerenchyma, 303* Sclerotinia, *226-228 Scouring rush, 291*, 293 Scramblers, 61 Scutellum, 139* Sea lettuce, 204 ' Seed, 21-23, *136-141, 309 Seed, definition of, 22, 23, 147, 148 Seed coats, 138, 139 Seed distribution, *146~155 Seed leaf, 136*, 137* Seed plants, *5-155, 299, 321 Seedlings, 22*, 23*, 137*, *141-145 Seedlings, mutilated, growth of, 144* Seedlings, types of, *1 41-1 43 Selaginella, 293-295 Selection by plant breeder, 412, 415, 416, 421-425, 432 INDEX 543 Self-pollination, 120, 121* Self-pruning, 66, 93~95 Sepal, 20*, 105* Sequoia, 304*, 311*, 313* Sex, origin of, 197 Sexual reproduction in angiosperms, *115-118 Sexual spore, 194 Shade plants, 489-492 Shepherd's-purse, ovule and embryo, 327* Shoot, 39 Short-stemmed plants, 58* Sieve tubes, 45*, 80 Simple pistil, 105*, 112 Slime molds, 224*, 225 Smilax. See Myrsiphyllum Smilax, 62* Smuts, *240-242, 454 Snail pollination, 130 Snapdragon, flowers of, 126* Soft bast (sieve tubes), 45*, 80 Soil, 434-451 Soil bacteria, 374-378, 449 Soil fertility, 447-451 Solomon's seal, rootstock of, 73* Solomon's seal, leaf of, 336* Sorrel, 467* Sorus, 280 Spanish moss, 381, 382, 489* Spanish needles, fruits of, 146* Species, 156, 158 Sperm, 201, 202*, 219, 261*, 269*, 283,308,318 Spermatophytes, 158 Sperinatophytes, evolution of plants, 330,334 Sphagnum, 264*, 265 Spiderwort, 343* Spike, 516* Spiral vessel, 46* Spirogyra, *191-193 Spongy parenchyma of leaf, 14* Sporangiophore, 216 Sporangium, 279*, 281* Spore, 190 Sporidia, 245 Sporophyll, 290 Sporophyte, 263-265 Spraying, 222, 453*, 454, 455 Spruce, Douglas, 315* Spruce trees, 6*, 257, 312 Spur, fruit, 94*, 95, 96 Spurge family, 356*, 357* Squash seed, section of, 136* Stamen, 20*, 104*, 105*, 110*, 111*, 307, 323 Staminate flower, 106*, 108* Starch, 15-17, 35, 77-80, 82, 138, 145 Starch in leaves, 78, 79 Starch-making, 16 Stem, 11*, 12*, *39-55, 74-77, *80- 103 Stem, dicotyledonous, minute struc- ture of, 44, 45*, 46*, 47*, 48*, 49* Stem, early history of, 52*, 142*, 143* Stem, functions of, 39-42 Stem, monocotyledonous, 53, 54*, 55 Stem, rate of growth of, 44 Stem, structure of, 11*, 12*, *44-54 Stemless plants, 58* Steins, climbing, *60~64 Stems, storage of food in, 77 Stems, twining, 60*, 61 Stems, underground, 72*, 73*, 74* Sterilization, 169 Stiffening, mechanics for, 48, 49* Stigma, 112*, 324 Stimulation, responses to, 389 Stipe, 249 Stipules, 91* Stomata, 13*, 14, 303*, 483* Stone fruits, 461, 462 Stonecrop, flower of, 105* Stonewort, 205, 207* Storage of food in root, 33, 34*, 35 Storage of food in the seed, *137-139 Storage of food in the stem, 77 Strawberries, 460, 461 Strengthening tissue, arrangement of, 48, 49* Strobilus, 292*, 294* Struggle for existence, 148-151 Style, 112*, 324 Submerged leaves, 480*, 481* Sugar, 15-17, 337, 424 Sugar, formed during germination, 145 Sugar beet, light requirement of, 493 Sugar-beet breeding, 424, 425 Sugar cane, 337, 339* Sulphur, 15, 448 Sumach, 361 Summer-deciduous trees and shrubs, 70, 486 Sun plants, 489, 492, 493, 494 Sundew, 385*, 386* Sunflower stem, cross section of, 45* 544 PEACTICAL BOTANY Superior ovary, 113 Suspensor, 327* Swamp lands, 436, 438 Sweet pea, flower of, 109*, 354* Sweet pea, fruit of, 354* Sweet potato, sprouting of, 33* Switch plants, 39 Sycamore wood, section of, 392* Symbiosis, 35-37, *372-375 Symmetry, 108, 109* Sympetalous, 110 Sympetalous dicotyledons, *363- 370 Synergids, 325 Synsepalous, 110 Syringa (Philadelphus) leaves, ar- rangement of, 55* Systematic botany, 159 Taproot, 143* Tar, 316 Taxodium, 29* Taxonomy, definition of, 159 Tea, 360* Teleutospores, 243 Temperature and germination, 139, 140 Tendril, 61*, 62* Tendril climbers, 61*, 62* Terminal bud, 92* Terminal flowers, 518*, 519 Terrace farming, 444, 446 Testa, 136* Thallophytes, classification of, 187, 212, 225, 256 Thallophytes, evolution of plants, 159, 330, 334 Thickening of stems, 50*, 51, 52 Thistle, Russian, 148 Thuja, 310*, 313* Tillage, 439 Tillandsia, 489*, 490* Timber, *390-397 Timber line, 506*, 507* Timber supply, 396, 397 Timothy, pistil of, 119* Timothy, variation in, 413 Tissue, 11, 12 Toadstool, 240, 247-252 Tobacco, 366 Tolerant and intolerant trees, 399, 400 Tomato, 366 Toxins, 172 Tracheids, 48*, 390* Transition from stamens to petals, 105* Transpiration, 18, *482-487 Transpiration, amount of, 18 Transplanting, 452 Transportation by water, 155 Tree ferns, 276* Tree planting, *403-405 Trees, 6*, 26, 29*, 32*, 42*, 43*, 44, 51-53. See also Forestry Trillium, 344* Trypsins, 145 Tube nucleus, 116* Tuber, 73 Tubercles on roots, 36, 37 Tuberculos's, 162, 171, 174, 175, 176 Tumbleweeds, 475* Turgidity, 9-11 Turgor, 9-11 Turpentine, 314*, 316 Twigs, fall of, 66 Twiners, 60*, 61 Typhoid, 162, 164, 172, 174, 177 Ulothrix, 196*, 197 Ulva, 204 Umbel, 516* Umbellet, 517* Underground stems, *72~77 Union of carpels, 112 Union of stamens, 110, 111 Unisexual flowers, 106*, 107* United States, plant geography of, *503-513 Uredospores, 243 Usnea, 236, 237, 496* Ustilago, 240 Vaccination, 172 Vacuole, 189 Variation, 412-414, *417-421, 425, *428-430 Variety, 412 Vaucheria, 195, *198-201, 215 Vegetative reproduction, 33*, *82- 89, 187 Vein, 10* Venus' s-fly trap, 387* Vernal grass, 337*, 338* Vessel, 46* Victoria, 67* Vilmorin, Louis, 424 Violets, cleistogamous flowers of, . 134* Virginia creeper, 61*, 380 INDEX 545 Water, absorption by roots, 7-9 Water, amount transpired, 18 Water, movement of, 9, 11, 80 Water ferns, 290*, 291* Water lily, flower of, 105* Water molds, *21 7-219 Water plants, *479-481 Water plants, leaves of, 67*, 68 Water roots, 30 Water storage, 74, 75 Water supply, 169, 174, 177, 205, 206 Water supply in soils, 439-441 Webber, H. J., 430 Weeds, *465-476 Weeds, aquatic, 471 Weeds, classes of, 465, 466 Weeds, dissemination of, 472-474 Weeds, injuries caused by, 470-472 Weeds, origin of, 473 Weeds, prevention of, 475, 476 Weeds, success of, 466-468 Wheat, hybridizing of, 428*, 429* Wheat breeding, 413-417 Wheat culture, 457 Wheat grain, section of, 138*, 139* Wheat rust, *242-245 White pine, distribution map, 504* Wild ginger, 58* Williams, C. G., 423 Willow, flowers of, 106*, 107* Wilting of corn leaves, 6*, 20 Wind pollination, 120 Winged fruits and seeds, 150*, 151* Winter buds, 90* Winter spores of wheat, rust, *243- 245 Wood, coniferous, 304, 390* Wood, fuel value of, 395 Wood, physical properties of, 392- 395 Wood, structural advantages of, 394, 395 Wood, structure of, 45*, 46*, 48*, *50-53 Wood, tracheids of, 48*, 391 Wood fibers, 48 Wood sections, 50*, 53*, *390-392 Wood sorrel, leaf positions of, 65* Woodbine, 61* Xerophytes, 480, *481-487 Yarrow, head and flower of, 369* Yeast, 232*, 233 Yellow fever, 163 Yellow pond lily, transitions between petals and stamens of, 105* Yucca, 509* Yucca, pollination of, 127, 128*, 129* Zamia, 317 Zoospores, 191 Zygnema, 204* Zygomorphic, 108, 109* Zygospore, 194 ANNOUNCEMENTS BERGEN AND CALDWELL BOTANIES By JOSEPH Y. BERGEN and OTIS W. CALDWELL, The University of Chicago INTRODUCTION TO BOTANY 368 pages, illustrated With Key and Flora PRACTICAL BOTANY 545 pages, illustrated THE Bergen and Caldwell Botanies have been received with enthusiasm by teachers the country over. They meet modern teaching conditions, placing the emphasis on those aspects of plant life that are particularly worth while for general knowledge. They give definite treatment to plant diseases, bacteria and their relation to gardening and to sanitation, forestry, plant breeding, and the application of botanical facts to agriculture, horticul- ture, and other industries. At the same time they furnish a thor- ough and well-proportioned grounding in the science of botany. The text is written for beginning students and is always clear and interesting. Technical terms are used sparingly and when used are carefully explained. Throughout the authors empha- size the dynamic side of botany. They do not treat the plant primarily as a subject for dissection or for making preserved specimens, but as an organism with a living to make under con- ditions sometimes favorable and sometimes unfavorable. The illustrations are numerous, pertinent, and of unusual technical and artistic excellence. They are from original draw- ings and photographs prepared by naturalist-artists expressly for these books. " Introduction to Botany" offers a distinctly elementary pres- entation for shorter courses. " Practical Botany " contains an abundance of material for a full year's work. GINN AND COMPANY PUBLISHERS TEXTBOOKS IN BIOLOGY FOR HIGH SCHOOLS AND COLLEGES BOTANY Bergen : Botanies (For list see High-School and College Catalogue) Bergen and Caldwell : Introduction to Botany With or without Key and Flora Bergen and Caldwell : Practical Botany Clute: Agronomy Clute : Laboratory Botany Clute : Laboratory Manual and Notebook in Botany Densmore : General Botany Duggar : Fungous Diseases of Plants Eikenberry : Problems in Botany Frye and Rigg : Laboratory Exercises in Elementary Botany Gruenberg : Elementary Biology Hodge and Dawson : Civic Biology Meier : Herbarium and Plant Description Meier : Plant Study (Revised Edition) Penhallow : Manual ,of North American Gymnosperms Roth: First Book of Forestry . _. BACTERIOLOGY Conn : Bacteria, Yeasts, and Molds in the Home (Rev. Ed.) Reed : Manual of Bacteriology ZOOLOGY Linville and Kelly : Laboratory and Field Work in Zoology Linville antl Kelly : Textbook in General Zoology Meier : Animal Study Pratt: Course in Invertebrate Zoology (Rev. Ed.) Pratt : Course in Vertebrate Zoplogy Sanderson and Jackson : Elementary Entomology PHYSIOLOGY Blaisdell : Life and Health Blaisdell: Practical Physiology Brown : Physiology for the Laboratory Bussey : A Manual of Personal Hygiene v Hough and Sedgwick : The Human Mechanism (Rev. Ed.) Jewett : The Next Generation GINN AND COMPANY PUBLISHERS HIGH-SCHOOL BIOLOGY ELEMENTARY BIOLOGY By BENJAMIN CHARLES GRUENBERG, Head of the Biology Department, Julia Richman High School, New York. 8vo, cloth, x+ 528 pages, illustrated. MANUAL OF SUGGESTIONS FOR TEACHERS to accompany " Elemen- tary Biology." J2mo, cloth, 95 pages, illustrated. HITHERTO the knowledge of biology has been regarded as an end in itself. Here it is considered as a weapon by means of which man may conquer his surroundings. The student learns not only what biology is, but how it can be used. Application of the principles learned is immediate and practical. The problems presented and suggested are such as affect the welfare of individual, community, and race. In method the book is inductive. Pupils learn rather to observe what plants and animals do and how they do it than to memorize lists of organisms and their functions. CIVIC BIOLOGY By CLIFTON F. HODGE, General Extension Division, University of Florida, and JEAN DAWSON, recently head of the Department of Biology, Cleveland Normal School. 8vo, cloth, viii + 381 pages, illustrated. THIS book provides a well-organized course in high-school biology that places the emphasis on the practical applications of the subject, particularly to community problems. The keynote of the whole argu- ment is united effort to prevent the enormous losses in destruc- tion of natural resources, in unfruitful labor, in damage to property, in preventable disease now common because of insufficient civic organization and to preserve valuable species from extermination. i66a GINN AND COMPANY PUBLISHERS BOOKS IN BOTANY PLANT STUDY (REVISED EDITION) By W. H. D. MEIER, Head of the Department of Natural Science in the State Normal School, Framingham, Mass. Portfolio containing 36 plant studies, with space for drawings, 18 sheets ruled on both sides for notes, and 10 sheets for description and preservation of specimens. In Biflex Binder. Plant Study Sheets (pages 1-36). OFFERS a laboratory and field course in botany admirably designed for students who desire to make it their final course, as well as for those who intend to do higher work. The material presented is ample for stu- dents who take the examination offered by the College Entrance Exam- ination Board, and the special examinations in botany given by Harvard University and other leading schools. The general facts of structure and function, starting with seeds and ending with fruits, are first studied; then the life history of plants, beginning with the lowest forms. A sufficient number of plant-description sheets are given to enable the student to become familiar with the leading groups of flowering plants. LABORATORY MANUAL AND NOTEBOOK IN BOTANY By WILLARD N. CLUTE, Flower Technical High School for Girls, Chicago. 65+42 blank pages A COMPREHENSIVE laboratory manual of botany on the loose-leaf plan. Designed for the first half-year in botany in the high school, it deals with the structure and life processes of the flowering plants, with a brief survey of the lower forms of vegetation, such as mosses, ferns, and fungi. The course is inductive, and is so arranged that the pupil must see and reason for himself, working out his answers from the study of easily obtained material. LABORATORY BOTANY By WILLARD N. CLUTE, Flower Technical High School for Girls, Chicago. xiv + 177 pages FOR the teacher who is crowded for time or the student who de- sires to do independent work, Clute's " Laboratory Botany " will be found invaluable. It is made up of clear and accurate outlines of spe- cific subjects, such as root, stem, flower, fungi, bryophytes, gymno- sperms, etc. ; directions for examining ; and lists of definite questions which will bring out all the different points of the student's investi- gation. It can be condensed or extended at will. GINN AND COMPANY PUBLISHERS RETURN _ l TO* <5D -Pglt'CJl. LOAN PERIOD 1 2 3 4 5 6 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS DUE AS STAMPED BELOW DUENRLF JAN1 ?1986 UNIVERSITY OF CALIFORNIA, BERKELEY FORM NO. DDO, 5m, 12/80 BERKELEY, CA 94720 36061 I/ &^L UNIVERSITY OF CALIFORNIA LIBRARY