A/W/J T QL C65 TV thi.s.- reserved fur *|nviul ref- 1C, may l.i- ki-pt for wri'k ;ml uv.l fur tin- NMIII,. time. This book is .1 'rurn.-.l ,n, the last -latr stani|>-,| l,,>lo\v. \ fin.- of li\.- .-nits will In- clun-^,.,1 fur ,. ; ,i-h da v JAH 521915. MAfi 1 2 '5' TEXT-BOOKS IN BOTANY By John M. Coulter, Ph.D. HEAD OP DEPARTMENT OF BOTANY IN THE UNIVERSITY OF CHICAGO Text-Book of Botany. 12mo. Illustrated. Cloth $1.25 Plant Studies. An Elementary Botany. 12mo. Cloth $1.25 Plant Relations. A First Book of Botany. 12mo. Cloth $1.10 Plant Structures. A Second Book of Bot- any. 12mo. Cloth $1.20 Plants. The two foregoing in one volume. For Normal Schools and Colleges. 12mo. Cloth $1.80 In the Twentieth Century Series of Text-Books D. Appleton and Company, New York TWENTIETH CENTURY TEXT-BOOKS A TEXT-BOOK OF BOTANY FOR SECONDARY SCHOOLS BY JOHN M. COULTER, A.M., PH.D. HEAD OF DEPARTMENT OF BOTANY, THE UNIVERSITY OF CHICAGO NEW YORK D. APPLETON AND COMPANY 1909 COPYRIGHT, 1905, BY D. APPLETON AND COMPANY PREFACE THE several editions of. Plant Studies, designed for use in secondary schools, were combined abridgments of Plant Relations and Plant Structures. Although this arrangement involved a certain amount of repetition and lack of conti- nuity, it was felt that these faults would be corrected by the competent teacher, whose chief desire would be to secure points of view in reference to botanical material. During the five years that have elapsed since the publi- cation of the first edition of Plant Studies, the opinions of many experienced teachers have been obtained. These opinions have been based upon repeated use of the book, and have been of the greatest possible service in develop- ing definite ideas as to the adjustment of the subject to the needs of the schools. The natural outgrowth of this co- operation between author and teachers has been the prep- aration of the present Text-Book of Botany, which seeks to express their combined judgment. There has been substan- tial agreement as to the nature of the material and the points of view, the only differences of opinion being such minor ones of presentation as must always be found among equally competent teachers. There has been no attempt to treat the various divisions T 310808 vi PREFACE of Botany separately, but rather to develop them all in their most natural relationships; and yet morphology, physiology, and ecology have been kept so distinct that the teacher will have no difficulty in calling attention to these divisions, if it is thought desirable. In the first five chapters the structure, function, and rela- tionships of the most obvious plant organs are considered. The purpose has been to use the most easily observed ma- terial to give preliminary training in observation and some conception of the activities of plants. The following thirteen chapters present an outline of the plant kingdom in the simplest possible form to be at all ade- quate. In these chapters the morphological point of view necessarily dominates, but not to the exclusion of the phys- iological and ecological. In this presentation of the great groups, which is also an outline of classification, there have been included special accounts of forms of economic interest ; not only because such forms as well as any others may illustrate groups, but chiefly because there is a growing con- viction that Botany in the schools must relate pupils to their common experiences, as well as train them in science. For the same general reason the brief chapters on plant-breeding and forestry have been introduced. The four closing chapters include a very brief account of plant associations, the most inclusive view of plants. This subject is merely introduced rather than developed. It cannot be repeated too often that this book will not serve its purpose unless it is used as a supplement to the teacher, to the laboratory, and to field-work. Furthermore it must be insisted that the sequence of the book need not be PREFACE vii the sequence used by the teacher. For example, work on leaves, stems, roots, and seeds may come in any order, and may well differ according to the availability of material or the conviction of the teacher. It so happens that the book begins with leaves, but those teachers who prefer to begin with seeds should do so. In the matter of illustrations, there have been many im- provements, eliminations, and additions. All of this work has been done or directed by my assistant, Dr. W. J. G. Land, whose skill in photography has been made use of freely and whose cooperation has added much to the value of the book. Unless otherwise credited, all illustrations have been prepared for this volume or those previously mentioned. JOHN M. COULTER. THE UNIVERSITY OP CHICAGO, September, 1905. CONTENTS CHAPTER PAGE. I. INTRODUCTION 1 II. LEAVES 5 III. STEMS II IV. ROOTS 71 V. GERMINATION OF Si 84 VI. ALG^ .98 VII. FUNGI 129 VIII. LIVERWORTS 165 IX. MOSSES 175 X . -FERNS 183 XI. IlnlfSKTAILS AND CLUK-MI .s ..... 197 XII. GYMNOSPERMS 207 XIII. ANGIOSPERMS 220 XIV. FLOWERS AND INSECTS 212 XV. SEED DISPERSAL ........ -'>"> XVI. MONOCOTYLEDONS -<>- XVII. DICOTYLEDONS: ARCHICHLAMYDE.E .... 282 XVIII. DICOTYLEDONS : SYMPETAL.E 302 XIX. PLANT-BREEDING 316 XX FORESTRY 320 X X I. PLANT ASSOCIATIONS ....... 324 XXII. HYDROPHYTES 328 XXIII. XEROPHYTES 337 XXIV. MESOPHYTES 345 INDEX . 357 A TEXT-BOOK OF BOTANY FOR SECONDARY SCHOOLS CHAPTER I INTRODUCTION 1. Occurrence of plants. Plants form the natural cover- ing of the earth's surface. So generally is this true that a land surface without plants seems remarkable. Not only do plants cover the land, but they abound in waters as well, both fresh and salt waters. One of the most noticeable facts in regard to the occurrence of plants is that they do not form a monotonous covering for the earth's surface, but that there are forests in one place, meadows in another, swamp growths in another, etc. In this way the general appearance of vegetation is exceedingly varied, and each appearance tells of certain conditions of living. 2. Plants as living things. It is very important to begin the study of plants with the knowledge that they are alive and at work. It must not be thought that animals are alive and plants are not. There is a common impression that to be alive means to have the power of locomotion, but this is far from true; and in fact some plants have the power of locomotion and some animals do not. Both plants and animals are living forms, and the law r s of living that animals obey must be obeyed also by plants. Of course there are differences in detail, but the general principles of living are the same in all living forms. To begin with the 1 2 A TEXT-BOOK OP BOTANY thought that plants are alive and at work is important because this fact gives meaning to their forms and structures and positions. For example, the structure of a leaf has no meaning until it is discovered how its structure enables the leaf to do its work. 3. The plant body. Every plant has a body, which may be alike throughout or may be made up of a number of different parts. If one part of the body does not differ from another, the plant is said to be simple; but the most con- spicuous plants, those with which every one is best ac- quainted, are made up of dissimilar parts, such as root, stem, and leaf, and such plants are said to be complex. Simple and complex plants do the same work; but in the simple plant the whole body does every kind of work, while in the complex plant different kinds of work are done by different regions of the body, and these regions come to look unlike when different shapes are better suited to different kinds of work, as in the case of leaf and root. 4. Plant organs. The different regions of the plant body thus set apart for special purposes are called organs; and complex plants have several kinds of organs, just as the human body has hands, feet, eyes, etc. The advantage of this to the plant becomes plain by using the common illus- tration of the difference between a tribe of savages and a civilized community. The savages all do the same things, and each savage does everything. In the civilized com- munity some of the members are farmers, others bakers, others tailors, others butchers, etc. This is known as "division of labor," and one great advantage it has is that every kind of work is better done. Several kinds of organs in a plant mean to the plant just what division of labor means to the community; it results in better work and more work. 5. Plant work. Although many different kinds of work are being carried on by plants, all the work may be put INTRODUCTION 3 under two heads: nutrition and reproduction. This means that every plant must care for two things: (1) the support of its own body (nutrition) and (2) the production of other plants like itself (reproduction). To the great work of nutrition many kinds of work contribute, and the same is true of reproduction. In a complex plant, therefore, there are nutritive organs and reproductive organs; and this means that there are certain organs which specially con- tribute to the work of nutrition, and others which are specially concerned with the work of reproduction. It must not be supposed that an organ is necessarily limited to one kind of work. Its form and structure fit it for a particular kind of work, which may be called its specialty; but it is not excluded from other kinds of work, just as a man who is specially trained to be a carpenter may do other things also. 6. Life-relations. In all of its work a plant is very de- pendent upon its surroundings. For example, it must receive material from the outside and get rid of waste material. Therefore, organs must establish certain definite relations with things outside of themselves before they can work effectively; and these necessary relations are known as life-relations. For example, green leaves are definitely related to light they cannot do their peculiar work without it; many roots must be related to the soil; certain plants are related to abundant water; some plants are re- lated to other plants, as parasites, etc. It is evident that a plant with several organs may hold a great variety of life- relations, and it is a very complex problem for such a plant to adjust all of its parts properly to their most effective relations. It must not be supposed that even a single organ holds a perfectly simple life-relation, for it is affected by a great variety of things. For example, a root is affected by gravity, moisture, soil material, contact, etc. Each organ, therefore, must become adjusted to a complex set of rela- 4 A TEXT-BOOK OF BOTANY tions; and a plant with several organs has so many delicate adjustments to care for that it is impossible, as yet, for us to explain why all of its parts are placed just as they are. 7. Some conspicuous organs. The prominent plants, which are spoken of as herbs, shrubs, and trees, have three conspicuous organs, root, stem, and leaf, which are con- cerned with nutrition; and most of these plants have at some time also another structure, the flower, which is con- cerned with reproduction. Our first attention will be given to these three great nutritive organs. A tree, for example, has its roots extending more or less widely through the soil; from the roots a stem rises into the air and branches more or less extensively; and upon this stem or its branches leaves are borne. Such is the general plan of the more complex plants; and our first purpose will be to discover what these organs are doing, and why they are so related to one another and to their surroundings. CHAPTER II LEAVES 8. Arrangement. Leaves appear upon the stems at definite regions called nodes (joints); and this jointed structure of the stem is one of its characteristic features, although it is much more conspicuous in some plants than FIG. 1. Leaf arrangement: A, spiral or alternate .eaves; B, opposite (cyclic) leaves; C, whorled (cyclic) leaves. After GRAY. in others. In certain plants only one leaf appears at each node; and if an imaginary line be drawn connecting the points on the nodes at which successive leaves appear, it 5 6 A TEXT-BOOK OF BOTANY will form a spiral winding about the stem (Fig. 1, ^4). As a consequence, leaves with this arrangement are said to be spiral, though they are still often called alternate. On account of this spiral arrangement, two successive leaves are in different vertical planes, and the danger of the upper leaf shading the lower is reduced. In other plants two or more leaves appear at each node; and as an imaginary line con- necting their points of origin forms a circle about the stem, the arrangement is called cyclic. Very commonly, however, when two leaves appear at a node they are said to be opposite (Fig. 1, B); and when more than two appear they are described as whorled (Fig. 1, C). The cycle of leaves at one node does not stand directly over the cycle at the node below, but over the spaces between the lower leaves, the danger of shading being reduced as in the case of the spiral arrangement. In fact, the cyclic arrangement differs from the spiral only in having two or more parallel spirals. 9. Regions. The conspicuous part of a leaf is the ex- panded portion known as the blade, and often the leaf is all blade. In many cases the leaf has a stalk (petiole) which bears the blade more or less away from the stem; and in certain groups of plants a third region is evident, usually consisting of a pair of more or less blade-like appendages (stipules) on the petiole where it joins the stem (Fig. 2, A). As might be expected, the essential part of the leaf is the blade, and ordinarily when the word leaf is used it refers to the blade. 10. Venation. Upon examining an ordinary leaf, the blade is seen to consist of a green substance through which a network of veins is variously distributed The larger veins that enter the blade send off smaller branches, and these send off still smaller ones, until the smallest veinlets are invisible. This is plainly shown by a skeleton leaf; that is, one which has been so treated that all the green substance has disappeared, and only the network of veins LEAVES 7 remains. The vein-system or venation of leaves is ex- ceedingly diverse, but all forms can be referred to a few general plans. In some leaves a single very prominent vein runs through the middle of the blade, and is called the midrib. From this all the minor veins arise as branches, and such a leaf is said to be pinnately veined (Fig. 2, A, and Fig. 9). In other leaves several large veins (ribs) of equal prominence enter the blade and diverge, each giving rise to smaller branches. FIG. 2. Venation: A, pinnately veined leaf of quince, showing blade, petiole, and stipules ; /?, palmately veined leaf of geranium ; C, parallel-veined leaf of lily-of-the-valley. After GRAY. Such a leaf is said to be palmately veined (Fig. 2, B, and Fig. 16). In still other leaves all the visible veins run ap- proximately parallel from the base of the blade to its apex, such leaves being parallel-veined (Fig. 2, C), as distinct from the two preceding, which are both net-veined. 1 1 . Form. The forms of leaves are exceedingly varied and are related to their venation. Palmately veined leaves 8 A TEXT-BOOK OF BOTANY incline to broader forms than leaves pinnately veined or parallel-veined. Names have been given to the various leaf forms, as linear, lanceolate, ovate, orbicular, etc., but they can be learned as they are needed. In the net- veined leaves the margin of the blade may be more or less deeply toothed br lobed (Fig. 2, B) ; but in the parallel-veined leaves the margin is not at all toothed, in which case the leaf is said to be en- tire (Fig. 2, C). It is quite common also for net-veined leaves to branch, when they are said to be compound. In this case the leaf- blade is broken up into a number of small blades, sometimes very many of them, called leaflets. A branching pinnate leaf is said to be pinnately compound (Fig. 3, A); and a branching palmateleaf, palmately compound (Fig. 3,5). 12. Exposure to light. The special work of leaves is ex- ceedingly important, and this work cannot be done unless the leaf is exposed to light. This fact explains many things in connection with the position and arrangement of leaves. Leaves must be arranged to receive as much light as possible to help in their work, but too intense light is dangerous; hence the adjustment to light is a delicate one. The exact position any particular leaf holds in relation to light, therefore, depends upon many circumstances, and FIG. 3. Compound leaves: .4, pinnately com- pound leaf of black locust ; B, palmately com- pound leaf of red clover, with three leaflets, also showing stipules. LEAVES cannot be covered by a general rule, except that it seeks to get all the light it can without danger. How leaves seek the light will be first considered, and later how they protect themselves against it. (1) Horizontal position. The ordinary position of the leaf is more or less horizontal. This enables it to receive the direct rays of light upon its upper surface, and more rays strike it than if it stood obliquely or on edge. Most leaves when fully grown are in a fixed position and cannot change it, however unfavorable it may become; but there FIG. 4. Geranium leave- *-\|.if>il first to vertical (A) and then to oblique (B) rays of light. are leaves so constructed that they can shift their position as the direction of the light changes, or the stem bearing the leaves may shift its position so that a better relation to light is secured (Fig. 4). If a garden nasturtium growing in a window be observed, its leaves will be seen facing the 10 A TEXT-BOOK OF BOTANY light; but if it be turned around so as to bring the other side of the plant to the light, the leaves will become adjusted gradually to the new direction. Many plants have more or less power to direct their leaves, and it would be in- teresting to observe what common plants of any region possess it. ^ (2) Problem of shading. It is evident that leaves of the same plant are in danger of shading one another; and while it cannot always be pre- vented, there are ways by which the danger is dimin- "**** """^SSBI ished. The problem of the ttl^^TKPxL plant is to develop as much leaf surface as possible and to place it in the most fa- vorable position for work. The spiral arrangement of leaves prevents two suc- cessive leaves standing in the same plane, and results in vertical rows of leaves distributed about the stem. The narrower the leaves, the more numerous may be the vertical rows; and the broader the leaves, the fewer the vertical rows (Fig. 5). In many herbs whose leaves are rather large and close together, FIG. 5. A broad-leaved plant, showing the petioles of the lower few vertical rows, and variously directed leaves are USUally longer leaves. than those above, and thus their blades are thrust beyond the shadow. The same result is obtained when the lowest leaves of a plant LEAVES 11 are the largest, and the upper leaves gradually diminish in size. (3) Rosette-habit. An extreme case of crowding is shown by plants with the rosette-habit : that is, those which produce FIG. 6. Rosette-habit shown by mullein (4) and evening-primrose (5). a cluster or rosette of leaves at the base of the stem (Figs. and 7). Often this rosette, frequently lying flat upon the ground or upon the rocks, includes all the leaves the plant produces. This close overlapping of leaves is a poor adjustment to light at best, but there is evident an adjustment to se- cure the most light possible under the circumstances. The lowest leaves of the rosette are the long- est, and the upper ones become gradually shorter, so that each leaf has at least a part of its surface exposed to light. 12 LEAVES 13 The overlapped base is not expanded so much as the ex- posed apex, and hence such leaves are usually narrow toward the base and broad toward the apex. This nar- rowing at the base is sometimes carried so far that most of the overlapped part is only a petiole. (4) Leaf-mosaics. All leaf adjustments (including the spiral arrangement, elongation of lower petioles, etc.) that have to do with fitting leaf-blades together, so that the greatest amount of leaf surface may be exposed to direct illumination, may be regarded as concerned in the con- Fin. 9. Leaves of Fittonia showing mosaic arrangement. st ruction of a leaf-mosaic. A general mosaic arrangement of leaves may be observed in connection with almost every broad-leaved plant (Figs. 8 and 9) ; and even when the leaves are separated along an erect stem, a view from above, 14 LEAVES 15 in which all the leaves are referred to a single plane, shows the mosaic. In many trees in dense forests, notably in the tropics, the leaves appear chiefly and sometimes ex- clusively at the extremities of the branches, often producing a magnificent dome-like mosaic. In the case of stem- exposed to direct light only on one side, as the horizontal branches of trees, stems prostrate on the ground, and stems against a support (as climbers and twiners), the leaf-i>lades must be brought to the light side so far as possible, and those that belong to the shaded side must be fitted into the spaces left by those that belong to the illuminated side. This is brought about in various ways, as by the twisting of the stem, the twisting and elongation of the petiole, the bending of the blade on the petiole, etc. Looking up into a tree in full foliage, one will notice that the horizontal branches are comparatively bare beneath, the leaf-blades being displayed on the upper side as a mosaic. The most complete leaf-mosaic is shown by certain ivies, involving such an amount of twisting, dis- placement, elongation of petioles, etc., as to give ample evidence of the importance of securing for leaves an ex- posure to light (Fig. 10). 13. Structure. Before considering the work of the leaf it will be necessary to know something of its minute structure. To see this structure, not merely surface views must be obtained, but also good clear sections through the leaf (cross-sections) must be made; and for this purpose a relatively thick spongy leaf, like that of the hyacinth or the lily, gives the least trouble. (1) Epidermis. It is possible to peel off from the sur- face of such a leaf a delicate transparent skin (epidermis}. This epidermis completely covers the leaf, and generally shows no green color. Examined under the compound microscope it is seen to be made up of small units of structure known as cells (Fig. 11). Each cell is bounded 16 A TEXT-BOOK OF BOTANY by a wall, and in the epidermis these cells fit closely to- gether, sometimes dovetailing with one another. Characteristic openings in the epidermis also will be dis- covered, sometimes in very great numbers. Guarding each slit-like opening are two crescent-shaped epidermal cells, called guard-cells (Fig. 11). The whole apparatus is known as a stoma (plural stomata), which really means "mouth," of which the guard-cells might be thought of as the lips. One important fact about stomata is that the guard-cells can change their shape, and so vary the size of the opening. These numerous openings are passageways into the interior of the leaf, putting the internal cells into communication with the air out- side, and so fa- cilitating the in- terchange of gases that will be de- scribed later in connection with the work of the leaf. In horizon- tal leaves the sto- mata are chiefly and sometimes ex- clusively on the lower surface, a fair average number being about 100 to each square milli- meter of surface (about 62,500 to the square inch) ; although in some cases the number may reach 700 to the square milli- meter (almost 450,000 to the square inch). In leaves exposed alike on both sides to the light, as in the erect leaves of the common flag, the stomata are equally dis- tributed on both surfaces. In floating leaves, as those of water-lilies, the stomata are all on the upper surface; and in submerged leaves there are no stomata. From this dis- FIG. 11. Surface view of the epidermis of a hyacinth leaf: A, epidermal cells and four stomata with their guard-cells ; B, enlarged view of a single stoma. LEAVES 17 tribution it is evident that stomata are definitely related to air; and that where there is difference of illumination on the two surfaces they occur chiefly on the less illuminated sur- face. Stomata are not peculiar to the epidermis of leaves; for they are found in the epidermis of any green part, as young stems, fruit, etc., and even on the colored parts of flowers. (2) Mesophyll. A cross-section of a leaf such as that of the lily shows the single layer of epidermal cells bounding the section above and below, pierced here and there by stomata, recognized by their guard-cells (Fig. 12). An en- larged view of a sec- tion of a single sto- ma may be seen in Fig. 20. Between these two epidermal layers is the mass of green tissue mak- ing up the body of the leaf, and known as mesophylL This comprises cells con- taining the numer- ous small green bodies (chloroplasts) that give color to the whole leaf. Usually the mesophyll cells are arranged differently in the upper and lower regions of the horizontal leaf. In the upper region the cells just beneath the epidermis are elongated at right angles to the surface of the leaf, and stand in close contact, forming the palisade tissue. In the lower region of the leaf the cells FIG. 12. Cross-section of a lily leaf, showing epi- dermal layers <>> with stomata () ; mesophyll made up of palisade tissue (p) and spongy tissue (p) with air-spaces (a), and containing chloro- plasts ; and sections of veinlets (r) 18 A TEXT-BOOK OF BOTANY are irregular in form, and so loosely arranged as to leave air-spaces between the cells, the whole region forming the spongy tissue (Fig. 12). The air-spaces communicate with one another, thus forming a labyrinthine system of air- chambers throughout the spongy mesophyll. It is into this system of air-chambers that the stomata open, and thus what may be called an internal atmosphere is in con- tact with all the green working cells, and this internal atmosphere is in free communication through the stomata with the external atmosphere. The significance of the palisade arrangement will be considered under the head of leaf protection. (3) Veins. In the cross-section of the leaf there will be seen also here and there, embedded in the mesophyll, the cross-sections of veins and veinlets, that constitute the supporting framework of the leaf and conduct material to and from the green working cells (Fig. 12). 14. Photosynthesis. The peculiar work of green plants or green parts of plants is to manufacture the kind of food best known as sugars and starch, such foods being called carbohydrates. This manufacture is exceedingly important, for all life is dependent upon it. If green plants should stop the manufacture of carbohydrates, the food supply of the world would soon be exhausted. All other forms of food are derived from carbohydrates in some way, and only green plants can add to the stock that is being drawn upon con- tinually. This means that green plants must manufacture carbohydrates not only for their own use, but also for the use of animals and of plants that are not green. Since leaves are chiefly expansions of green tissue, they are con- spicuous in the manufacture of carbohydrates; but it must be remembered that the manufacture goes on wherever there is green tissue, whether it is found in leaves or not. A very conspicuous fact about this manufacture is that it cannot go on unless the green tissue is exposed to light. LEA VMS J9 This explains why leaves arv trd in go many ways to obtain light, as described in 12. It also gives name to the process, photosynthesis, the name indicating that the work is done in the presence of light. The process demands that carbohydrates shall be made from raw materials common in nature and easily obtained by plants, and in photosynthesis two such substances are used. One of these is water, which in the plants com- monly thought of is absorbed by the roots from the soil, passes up through the stem, and reaches the green working cells of the leaves through the veins. The other substance is carbon dioxide, a gas present in small proportion in the air (really in the form of carbonic acid gas), but one which is being constantly renewed as it is used, so that it is always available. Water is made up of one part of oxygen and two parts of hydrogen; while carbon dioxide consists of two parts of oxygen and one part of carbon. These are just the elements that enter into the structure of a carbohydrate. In photosynthesis the elements of water and carbon dioxide are separated and recombined to form a carbo- hydrate, and when this has been accomplished it is found that some oxygen has been left over. That is, in the process oxygen is a waste product and is given off by the working cells. Therefore, in the sunlight a leaf is absorbing carbon dioxide and giving off oxygen; and this gas exchange is the superficial indication that photosynthesis is going on. It is very easy to discover that oxygen is being given off by a leaf exposed to light, and that the amount given off (and hence the amount of work) depends upon the intensity of the light. If an actively growing water-plant, submerged in water in a glass vessel, be exposed to bright light, bubbles may be seen coming from the plant and rising through the water (Figs. 13 and 14). Shading the vessel diminishes the number of bubbles. That the gas being given off is mainly oxygen may be proved by invert- 20 LEAVES 21 ing over the plants a large funnel and leading the bubbles into a test tube, in which the presence of oxygen can then be tested. It has been noted that photo- synthesis is associated not mere- ly with light but also with green tissue ; and in examining the structure of the leaf it was dis- covered (13) that the green color is due to the presence of chloroplasts in the mesophyll cells. It is these chloroplasts that manufacture the carbo- hydrates, and they obtain irom the light the power (energy) to do it. The first visible product of photosynthesis is starch, and when the working cells are very active starch may be observed to accumulate in them ; but when the process becomes slower or stops, as during the night, this starch disappears, the food being carried away for use (Figs. 15 and 16).* A summarized statement of photosynthesis is as follows: It is the manufacture of carbohydrates by chloroplasts in the presence of FIG. 16. A geranium leaf, one- n ght, water and carbon dioxide half of which has been cov- being used, and oxygen beinsr ered ; the test shows absence * of starch in the covered half. given OH as a Waste product. * Experiments should be devised to test for the accumulation of starch in leaves that have been exposed for some time to a strong light, and to show that this accumulation does not take place in the dark. In the experiments illustrated by Figs. 15 and 16, the test for starch was FIG. 15. A bean leaf whose termi- nal leaflet has been covered and whose lateral leaflets have been exposed to light ; the test shows an absence of starch in the former and an abundance of it in the latter. 22 A TEXT-BOOK OF BOTANY 15. Transpiration. Water is being evaporated con- stantly from the surface of a living plant exposed to the air. This loss of water by the plant has been called transpiration. Since leaves are especially exposed to the air, their transpira- tion is conspicuous. Although the epidermis impedes trans- piration, we have seen ( 13) that the leaf has in its system of air-spaces an internal atmosphere, which is in communica- tion with the external atmosphere through the stomata. Hence, water vapor is constantly passing from the working cells into the internal atmosphere and diffusing through the stomata into the external atmosphere. Although a certain amount of transpiration takes place directly through the epi- dermal cells, much the larger part of the water vapor passes out by way of the stomata. If the stomata are closed by the guard-cells, the internal atmosphere becomes saturated with water vapor and transpiration ceases. It is evident that the larger the air-spaces in the leaf, that is, the looser the leaf is in texture, the greater is the amount of internal atmosphere, and the more rapid is transpiration. Hence the amount of transpiration from a leaf depends more upon its structure than upon the extent of its exposed surface. If a glass vessel (bell jar) be placed over a small active plant, the moisture is seen to condense on the glass, and even to trickle down the sides (Eig. 17).* When the as follows : After the exposure to light, the leaves were placed in alcohol to extract the green coloring matter (chlorophyll). When this was accomplished, they were rinsed thoroughly, to remove the alcohol, and placed in a water solution of iodine. In this solution the starch-con- taining portion becomes dark blue, the other portion remaining colorless. The water solution of iodine is obtained by dissolving potassium iodide in water and adding scales of iodine. * Some such experiment should be performed to demonstrate the fact of transpiration. Care must be taken to shut off the evaporation from the pot or soil, since it is to be demonstrated that water is coming from the plant. Rubber cloth or a coating of paraffin or wax may be used for sealing up all sources of moisture except the plant (Fig. 17). LEAVES 23 amount of water given off by a few leaves is noted, some vague idea may be formed as to the amount given off by a great mass of vegetation, such as a meadow or a forest. One observer has stated that a single stalk of corn during its life (173 days) transpired about four gallons of water; and that a single hemp plant (140 days) transpired nearly eight gallons. An- other observer esti- mated that a sun- flower, whose leaf surface was approxi- mately nine square yards, gave off near- ly one quart of wa- ter in a single day. 16. Growth. In very young leaves growth takes place , i ' | . FIG. 17. Transpiration experiment: a potted gera- at the apex, but tlllS nium sealed with a rubber cloth and covered with a bell jar; the mist and droplets of water on the glass more or less obscure the plant. may cease early. The subsequent growth often occurs at the base of the blade, in a special growing region, as may be seen in long and narrow leaves such as those of grasses. To discover these special regions of growth in leaves, some rapidly growing plants (such as the gourds) should be cultivated in pots. When the young leaves first appear, a scale should be marked off in India ink with a pointed camel's hair brush on the petiole (if there be one) and the midrib. The scale should be made 3 24 A TEXT-BOOK OF BOTANY with definitely spaced lines, preferably five millimeters apart.* As the leaf continues to grow, the most active growing region will be indicated by the lines that draw farthest apart. 17. Protection. Such an important organ as the leaf, with its delicate active cells necessarily in communication with the air, is exposed to numerous dangers. Conspicu- ous among these dangers are drought, intense light, and cold. Many ways of meeting these dangers have been developed by plants, but the subject is too large and com- plex to be presented with any completeness. The best that can be done is to select a few striking illustrations of protection that seem to be definite. Perhaps the most common danger to most plants is an excessive loss of water, and when a drought prevails the problem of checking trans- piration is a most serious one. As the leaves are the prominent transpiring organs, the chief methods of protec- tion concern them. A B FIG. 18. Sections through leaves of the same plant, showing the effect of exposure to light upon the structure of the mesophyll : A, leaf exposed to intense sun- light ; B, leaf grown in the shade. After STAHL. (1) The epidermis may be regarded as an ever-present check against transpiration (Fig. 12), for without it the * Such scales on stem and root are seen in Figs. 57 and 75. LEAVES active mesophyll cells would soon lose all their water. In some plants of very dry regions, what may be regarded as several epidermal layers appear. (2) The palisade layer of the mesophyll ( 13) also is very commonly present and tends to diminish transpira- FIG. 19. Section througn a small portion of yew leaf, showing the epidermal layer (e) with its cuticle (c), and the upper portion of the palisade layer (j>). tion, exposing only the ends of elongated cells, which stand so close together that there is no drying air between them (Fig. 12). It is very characteristic of alpine and desert plants to form two or three layers of palisade cells, apparently as a protection against unusual danger from drought and intensity of light. The accompanying figure (Fig. 18) shows in a striking way the effect of light intensity upon the structure of mesophyll, by contrasting leaves of the same plant exposed to ex- treme conditions of light and shade. Tne intense light is dangerous to the chloroplasts, and it has FIG. 20. Section through a small portion of carnation leaf, showing the epider- mal cells (e) with their heavy cuticle (c); a single stoma in the epidermal layer, opening without into a broad passageway through the cuticle, and within into an air-chamber ; and the upper portion of palisade cells (p) con- taining chloroplasts. been observed that they are able to assume various positions, in very intense light mov- ing to the more shaded depths of the palisade cells, and in less intense light moving to the more external regions of the cell. A TEXT-BOOK OP BOTANY FIG. 21. Section through the leaf of bush clover, showing upper and lower epidermis, palisade cells, and cells of the spongy tissue; the lower epidermis produces numerous simple hairs that bend sharply and lie along the surface of the leaf. (3) The cuticle, which is often developed upon the epidermis, is one of the best protections against loss of water. It is developed by the exposed walls of the epi- dermal cells, and being constantly renewed from beneath it may become very thick and many-layered (Fig. 19). Some- times the cuticle be- comes so thick that the passageways through it to the stomata re- semble tubes (Fig. 20) . In dry regions, or in any much exposed place, the cuticle is a very constant feature of plants. (4) Hairs in great variety are developed upon leaf surfaces, being outgrowths from the epidermal cells. They may form only a slightly downy covering (Fig. 21), or the leaf may be covered by a woolly or felt-like mass so that the epi- dermis is entirely concealed, as in the common mullein (Fig. 22). In dry or cold regions the hairy covering of leaves is very notice- able, often giving them a brilliant silky white or bronze look. Some- times instead of hairs the epi- dermis develops scales of various patterns (Fig. 23), often overlap- ping and forming a complete covering. The great variety of these hairs and scales, and the ease with which they may be ex- amined, make them an attractive study. At the same time, just how they protect the leaves is by no means FIG. 22. Branching hair of mullein. LEAVES 27 clear; and doubtless they may serve other purposes also, or sometimes may even be of no use whatever to the plant. It has been suggested that in re- gions of intense light a covering of hairs is an effective sun - screen. The explanation is that being dead struc- tures, containing air, they reflect the light, thus diminishing the amount that reaches the working cells. As is well known, hairs are by no means re- stricted to leaves, but occur on all parts of plants. (5) Small leaves are characteristic of dry regions, in this way each leaf exposing a small surface to the drying air and intense light. That this reduction in size holds a direct relation to the dry conditions is evident from the fact that the same plant often produces small leaves in a dry region and larger ones in moist condi- tions. In the case of the cactus, a large group in the dry regions of the Southwest, the leaves have become so colorless water storage tissue ine. ing horizontally from it (Fig. 42); while in other trees, as the oak and the elm (Figs. 43 and 44), the main stem soon divides into large branches. In the former case the 44 A TEXT-BOOK OF BOTANY tree has a general conical outline; in the latter case it has a spreading top or crown. It is an excellent plan to become FIG. 43. An. oak in winter condition. acquainted with the common trees of a neighborhood and to learn to recognize them by their habits. Trees are also an excellent illustration of the fact that while the main stem of a plant may be erect, the branches may be di- STEMS 45 reeled at any angle, often horizontal, and sometimes even descending. (2) Prostrate stems. In many plants the main stem or certain branches lie prostrate on the ground or nearly so, Fn;. 44. An elm in f ullage. sometimes spreading in all directions and becoming inter- woven into a mat or carpet (Fig. 45). They are found 46 A TEXT-BOOK OF BOTANY especially on sterile and exposed soil, and there may be an important relation between this fact and their habit. In such stems there is a distinct disadvantage in the display FIG. 45. Prostrate stem of Potentilla. of leaves as compared with erect stems; for instead of being free to spread out leaves on all sides, one side is against the ground, and the free space for them is diminished at least one-half. All the leaves such a stem bears are necessarily directed toward the free side. FIG. 46. A strawberry-plant, showing a runner that has developed a new plant, which in turn has sent out an- other runner. After SEUBERT. We may not know all the reasons why so unfavorable a position for leaf display is assumed ; but among the results are protection in exposed situations in some cases, and the STEMS 47 multiplication of plants in others. In many plants, as the prostrate stem advances over the ground, roots develop from the nodes and enter the soil, leaves are formed, and a new plant is started, which may become independent by the death of the older parts. In this way a plant may spread over the ground, multiplying itself indefinitely. So effective is this method of multiplication that plants with erect stems often make use of it, sending out from near the base special prostrate branches which advance over the ground and start new plants. A very familiar illustration is furnished by the strawberry-plant, which sends out peculiar leafless runners to strike root at the tip and start new plants, which become independent by the death of the runners (Fig. 46). These various prostrate stems illustrate the fact that nodes can produce not only leaves and branches, but also roots, if placed in suitable conditions. Advantage is taken of this fact in the common process of layering, in which such stems as those of blackberries and raspberries are bent down to the ground and covered with soil, when the nodes strike root and new plants are started. (3) Climbing stems. A great many plants have developed the ability to sus- tain themselves by using supports. Al- though not able to stand alone, by using these supports they may attain great length and display their leaves to light even in a dense forest. This climbing is effected in a variety of ways. In some cases, as the morning-glory, bean, and hop-vine, the stem twines about the support, such plants often being distinguished as twiners (Fig. 47); bean twining about support. A TEXT-BOOK OF BOTANY in other cases, as the grape-vine and star-cucumber, tendrils are formed, which twine or hook about the supports (Fig. 48) ; in still other cases, as the woodbine, the tendrils pro- duce suckers that act as holdfasts and enable the plant to cling to trees or walls (Figs. 49 and 50). It is in the dense forests of the tropics that climb- ing plants become espe- cially conspicuous. There great woody vines fairly interlace the vegetation, and are known as lianas or lianes. If a young morning- glory or twining bean be watched, it will be dis- FIG. 48.-Branch of star-cucumber, with its covere d that the elonga- tendrils in various conditions. ting stem is unable to stand upright, and that, as it bends over, the inclined part begins to swing through a horizontal curve, which may bring the stem in contact with a suitable support. If this hap- pens, the stem, continuing to swing in a curve and growing in length at the same time, winds itself about the support. This movement of the portion of the stem which is in a hori- zontal position is thought to be brought about by a peculiar response of the plant to gravity. The influence of gravity in directing plant organs will be considered later. Tendrils are illustrations of plant structures that are unusually sensitive to contact. When the tip of a tendril in moving about touches a suitable support, the side touched becomes concave and the tendril hooks or coils about the support. This is only the first response of the tendril to contact, for presently the rest of it begins to curve a move- STEMS 1 i<;. 49. Woodbine in a deciduous forest. ment which results in spiral coils, since the tendril is fastened at both ends (Fig. 48). This curving and twist- ing of the tendril between its fastened extremities naturally results in two spiral coils run- ning in opposite directions. In this way the stem is fastened to its support by numerous spiral springs. All of these movements and their results may be observed by cultiva- ting a plant such as the star- cucumber, which growls rapidly and has conspicuous and very sensitive tendrils. In the case of the ordinary climbing wood- bine and certain species of ivy, J ' FIG. 50. Woodbine clinging to a wall Which cling tO Walls Or tree . by means of tendril suckers. 50 A TEXT-BOOK OF BOTANY trunks, the tip of the tendril when it comes into contact with a support is stimulated into developing the sucker- like disk which acts as a holdfast (Fig. 50). * 24. Internal structure. As the stems of seed-plants show two distinct types of structure, it will be necessary to point out the great groups of seed-plants, so that the types of structure may be referred to them. The Gymnosperms include the pines and their allies, the common evergreens; the Monocotyledons include such plants as grasses, lilies, and palms; the Dicotyledons, much the largest group, include the common deciduous trees, such as oak, maple, hickory, poplar, beech, etc., as well as the great majority of common herbs. In stem structure the Gymnosperms. and the Dicotyledons show the same general plan, while the other type of structure is exhibited by the Monocotyle- dons. (1) Gymnosperms and Dicotyledons. If an active twig of an ordinary woody plant be cut across, it will be seen that it is made up of four general regions (Fig. 51): ~. W an outer Protecting lay- er which may be stripped 'P off as a thin skin, the epi- c dermis; (2) within this a zone of spongy tissue, usu- ally green, the cortex; (3) then a relatively broad zone of firm wood, the vascular cylinder; and (4) in the cen- ter the pith. The special feature of this arrangement is that the wood occurs as a hollow cylinder, enclosing the pith and surrounded by the cortex. In the older parts of stems the pith often dis- appears, leaving a hollow stem. The cortex is the active. W FIG. 51. Cross-section of a branch of box elder one year old : e, epidermis ; c, cortex ; w, vascular cylinder ; p, pith. STEMS 51 working region of the stem: since it is green it is able to manufacture carbohydrates as do the leaves ( 14); and it is also concerned in other work connected with nutri- tion. The vascular cylinder, on the other hand, is the great conducting region, as well as one that gives rigidity to the stem. This work of conduction will be considered later. If the vascular cylinder be examined closely, it will be seen that it is broken up into segments by plates of cells that traverse it from the pith to the cortex, these radiating plates of cells being the pith rays (Fig. 51). The cylinder is thus made up of a number of segments which are called vascular bundles. The peculiarity of the structure of the stem in Gymnosperms and Dicotyledons, therefore, can be described as the arrangement of the vascular bundles so as FIG. 52. Cross-section of vascular bundle from pine stem, showing xylem (i), cambium (c), and phloem (p) ; on each side of the single row of cambium cells there are young xylem and phloem cells that pass gradually into the mature condition. to form a hollow cylinder. In woody stems the bundles are very close together in the cylinder, forming a compact cylinder with narrow pith rays; but in the stems of herbs the bundles are well separated, leaving broad pith rays. If the cross-section of an individual vascular bundle be examined under the microscope, two regions will be recognized (Fig. 52) : the inner one, toward the pith, being called wood (xylem), and the outer one being called bast 52 A TEXT-BOOK OF BOTANY (phloem)* A vascular bundle, therefore, is made up of wood and bast, which differ from one another in the work of conduction, the wood chiefly conducting the water that enters the plants by the roots and is passing to the leaves, and the bast chiefly conducting prepared food. The cells of the wood that conduct water are called tracheary vessels. They are more or less elongated and have very thick walls, upon which there appear markings of various kinds. These markings may be seen in a B FIG. 53. Vessels : spiral (A) and annular (5) vessels ; dotted vessel (C) ; sieve vessel (D) and sieve plate (E) from pumpkin. A and B after BONNIER and SABLON ; C after DE BARY ; D after STRASBURGER. longitudinal section through the wood. Some of the vessels are marked by a spiral band that extends from end to end, and are called spiral vessels (Fig. 53, A); others show a series of thickened rings, and are called annular vessels (Fig. 53, B); while others, and among them the largest, * If a cross-section of a pine twig be stained first with safranin and afterward with Delafield's haematoxylon, the xylem will become bright red and the phloem rich violet. STEMS 53 have numerous thin spots in their walls which look like dots of various sizes, and these are the dotted or pitted vessels (Fig. 53, C), often called dotted ducts. These pitted vessels are often very large, their openings being visible to the naked eye in the cross-section of oak wood. The cells of the bast that conduct prepared food are called sieve vessels (Fig. 53, D), because in their walls, usually the end walls, there appear areas full of perfora- tions, like the lid of a pepper-box, these areas being called sieve-plates (Fig. 53, E). The veins of leaves are vascular bundles that are continuous with those of the stem. If the relative positions of wood and bast in the stem be remembered, it will be seen that when a bundle turns out into a leaf, the wood with its tracheary vessels is toward the upper side of the leaf, and the bast with its sieve vessels toward the lower side. A prominent feature of such stems is that they can increase in diameter. If the stem lasts only one growing season, that is, if it is an annual, the increase in diameter does not occur; but if it lasts through several seasons, that is, if it is a perennial, it increases in diameter from year to year. Naturally annual stems belong to herbs and perennial stems to shrubs and trees. Taking the tree as an illustra- tion, the increase in diameter occurs as follows: Between the wood and the bast of each bundle is a layer of very active cells called the cambium (Fig. 52, c), which soon extends across the intervening pith rays, and so forms a complete cylinder of cambium. This cambium has the power of adding new wood cells to the outer surface of the wood, and new bast cells to the inner surface of the bast, as well as adding to the pith rays where it traverses them. In this way a new layer of wood is laid down on the outside of the old wood; and usually these layers, added year after year, are so distinct that a section of wood shows a series A TEXT-BOOK OB" BOTANY of concentric rings (Fig. 54). Ordinarily one such layer is added each year, and hence the layers are called annual rings. The age of a tree is usually estimated by counting these rings, but occasion- ally more than one ring may be added during a single year. The new layers added to the bast are not persistent; but the wood accumulates year after year, until in an ordinary tree the stem is a great mass of wood covered with thin layers of bast and cor- tex. It is this mass of wood that supplies our lumber. This annual increase in diameter enables the tree to put out an in- creased number of branches, and hence leaves, each suc- ceeding year, so that its capacity for leaf work becomes greater year after year. A reason for this is that since the wood is conducting water to the leaves, for food manufac- ture, the new layers enable it to conduct more water, and more leaves can be supplied. When a stem increases in diameter it is very seldom that the epidermis grows in proportion. Hence it is usu- ally sloughed off and a new protective covering is de- veloped by the cortex. Either the outermost layer of the cortex or some deeper one becomes a cambium, which means that it is able to form new cells. This cambium is called the cork cambium, since it forms at its outer surface layer after layer of cork cells, which are peculiarly resistant FIG. 54. Cross-section of a branch of box elder three years old, showing three an- nual rings in the vascular cylinder; the radiating lines (TO) which cross the vascu- lar ring (w;) represent the pith rays, the principal ones extending from pith to cor- tex (c). STEMS 55 to water. If the cork cambium is formed deep in the cortex, all the cells outside of it die, since they are cut off from the water supply in the plant. The cork cambium is often renewed year after year, and two prominent kinds of bark are formed. In some cases the successive cork cambiums form zones completely about the stem, and the cork is then deposited in concentric layers, forming the ringed bark. Such bark often becomes very thick, and the surface becomes seamed or furrowed. In the cork oak there is a very great accumulation of cork, which is stripped off in sheets, from which corks of commerce are made. In other cases the successive cork cambiums, instead of passing completely around the stem, run into the next outer one, thus cutting out segments which presently loosen and flake off, forming scaly bark, as in hickory, apple, etc. The layers of cork and other cells that may lie outside of the cork cambium form the outer bark, which is dead and dry. The tissues between the cork cambium and the cambium of the vascular cylinder, that is more or less cortex and the bast, form the inner bark, which contains some living cells. To remove the outer bark does not injure a tree; but removing the inner bark kills it, because it interrupts the work of conduction carried on by the sieve vessels. In the process known as girdling, not only is the bark cut through, but the young wood is cut into. This interferes with the movement of water up the stem as well as with conduction by the sieve vessels. If a small portion of the bark is removed, the incision extending only to the wood, as in the making of inscriptions on trees, the wound is healed, unless too large, by the growth of tissue from all sides until it is closed over. In this new tissue a cork cambium is developed, and presently there may be no surface indication of the wound. But if the wound has gone deeper and entered the wood, the record of it may always be found m the wood by removing the 56 A TEXT-BOOK OF BOTANY bark. In this way old inscriptions have often been un- covered. The well-known operation of grafting depends upon the ability of plants to heal wounds. The plant upon which the operation is performed is called the 4 t stock, and the twig graft- M I ed into it the scion. An % m ordinary method, called i cleft-grafting, is to cut off E M the stem or a branch of the stock, split the stump, insert into the cleft the wedge-shaped end of the scion, and seal up the wound with wax or clay. The cambiums of the stock and the scion must be put into contact at some point; and hence it is usual to insert a scion in each side of the cleft, since the cambium of the stock is comparatively near the surface (Fig. 55). The cambium of stock and scion unite, the wound heals, and the scion becomes as closely related to the activities of the stock plant as are the ordinary branches. The scions are usually cut in the fall, after the leaves have fallen, are kept through the winter in moist soil or sand, and the grafting is done in the spring. A number of important things are secured by grafting, but chief among them is the perpetuation of useful varieties with certainty and at a great saving of time. (2) Monocotyledons. In this great group of plants tne vascular bundles of the stem are not arranged so as to form A B FIG. 55. Cleft-grafting showing scions in place (A) and the wound sealed with clay or wax (B). STEMS 57 Fio. 56. A corn-stalk, show- ing in cross - section and longitudinal section the scattered vascular bundles. a hollow cylinder, but are more or less irregularly scattered, as may be seen in a cross-section of a corn-stalk (Fig. 56). As a consequence, there is no en- closing of a definite pith, nor is there any distinctly bounded cor- tex. In the bundles there is no cambium, and therefore new wood and bast cannot be added to the old, so that in the trees there is no annual increase in diameter; and this means that there is no branch- ing and no increased foliage from year to year. A palm well illus- trates this habit, with its columnar, unbranching trunk, and its crown of leaves, which continue about the same in number each year. 25. Ascent of sap. The water entering the plant by the roots and .moving upward through the stem is usually called sap. It is not pure water, but contains certain soil substances dissolved in it. In low plants, as most annuals, the ascent of sap requires no special explanation; but in plants such as trees, in which the crown of leaves is many feet above the soil, the case is very different. Several explanations of the ascent of sap in trees have been sug- gested, and all have been disproved, so that we are as yet entirely in the dark as to the method. That the path of ascent is through the vessels of the wood, and not through cortex or bast or pith, may be demonstrated by a simple experiment. A stem of corn or sunflower or balsam is cut off and placed in water for an hour. Then it is transferred to a vessel containing water stained with cheap red ink (a solution of eosin), and exposed to diffuse light. A few hours later, sections of the stem will show the wood vessels stained red, the 58 A TEXT-BOOK OF BOTANY ascending water having stained its path. Of course the stain may spread somewhat into adjacent cells. In most trees, as the mass of wood increases in diameter, the ascending sap abandons the inner (older) wood and moves only through the newer wood. This results in a different appearance of the two regions, the old centra! wood, abandoned by the sap, becoming darker and often characteristically colored (heart wood); and the younger outer wood, used by the sap, being lighter colored (sap wood). Trees vary greatly in the relative thickness of the sap wood; for example, in the beech it is a thick zone, while in the oak it is a narrow one. In successful girdling this must be taken into account, since an incision which would cut off the water supply of an oak sufficiently to kill it would not kill a beech. The rate of movement of the ascending sap of course varies with different plants and different conditions. In the pumpkin-vine, in which the movement is very rapid, it has been found to reach about twenty feet an hour. It is estimated that in ordinary broad-leaved trees the rate is probably three to six feet an hour. If certain stems are cut off near the ground, it is ob- served that after a short time the sap begins to ooze out a phenomenon that is often called bleeding. In some woody plants, as grape-vines and birches, the sap flows out with considerable force, indicating some pressure be- low, which is called root-pressure. While root-pressure may force the sap into the stem, it is entirely inadequate to force it to the top of a tree. The so-called maple sap obtained from the sugar- maple is an interesting illustration of the use of sap that accumulates in a woody stem in the spring. At that time the water has no opportunity to escape through leaf trans- piration; so the wood becomes gorged with sap, which can be drawn off by boring into the wood and inserting spiles. STEMS 59 The characteristic sugar has been obtained by the sap from food stored in the stem, notably in the older wood. 26. Growth in length. Growth in length begins at the tip of the stem by the formation of new cells, which are organized into alternating nodes and internodes. When these regions are first formed the internodes are very short, and their subsequent elonga- tion, separating the nodes, is the chief cause of the lengthening of the stem. Internodes are able to elongate for only a certain time, so that the elon- gating portion of a stem does not often extend more than ten to twenty inches below the tip. Seedlings such as those of the bean should be cultivated, and the region of growth, the region of greatest growth, and the rate of growth determined. The same method may be used as was used with the leaf ( 16), in this case each internode being marked with equally spaced lines in India ink. Measuring these spaces at intervals of one or two days will determine the facts referred to above (Fig. 57). 27. Special forms of stems. Usu- ally branches resemble the stem from which they arise, but occasionally they differ in a striking way. That these different structures are really branches is usually evident to external observation from the fact that they stand in the position of branches, that is, in the axils of leaves ( 22). The three following forms illustrate axillary structures that do not resemble ordinary branches. FIG. 57. Scarlet runner bean marked with a scale of five millimeter intervals and photo- graphed after forty- eight hours ; the lines closest together show the original spacing. 60 A TEXT-BOOK OP BOTANY / (1) Cladophylls. If the greenhouse smilax, often called wedding smilax, be examined, the apparent leaves will be discovered to be branches modified so as to assume the form and work of leaves, each one of these leaf-like branches standing in the axil of a minute scale-like leaf (Fig. 58, A). Such branches are called cladophylls, which means " leaf-like B FIG. 58. Cladophylls: A, wedding smilax (the apparent leaves are the modified branches, and the real leaves are the minute scales that subtend them); B, Phyllocladus. branches." In the Australian region a group of evergreens is characterized by bearing cladophylls; and the young plantlet shows the gradual change of true green leaves into little scales, and of branches into cladophylls (Fig. 58, B). In the common garden asparagus the apparent slender, needle-like leaves are all cladophylls doing leaf work. (2) Tendrils. It was shown ( 20) that leaves or parts of leaves may develop as tendrils, and this is true also of STEMS 61 branches, as observed in the passion-flower, whose long and very sensitive tendrils appear in the axils of the leaves (Fig. 59). Whether tendrils replace leaves or branches FIG. 59. Plants of passion-flower showing axillary tendrils. makes no difference as to their structure and activity, but it is of interest to note that different organs may thus be replaced by the same organ. 62 A TEXT-BOOK OF BOTANY (3) Thorns. Branches, as well as leaves ( 20), may develop as thorns; an excellent illustration of a branching thorn being seen in the honey locust (Fig. 60, A), and of a simple thorn in hawthorn (Fig. 60, B). In dry regions, ' A V. B FIG. 60. Thorns: A, honey locust; B, hawthorn. such as may be found along the Mexican border, thorns and spiny branches are very common; and since in some cases these spiny branches develop into ordinary branches when the plant has a sufficient supply of water, it is thought that such thorns and spines are results of unfavorable conditions for growth. The same statement applies, of course, to those cases in which thorns have replaced leaves. The most common modifications of the stem are those which arise when it is an underground structure. Although it is natural to think of all underground structures as roots, this is far from being true. Since the stem is primarily a STEMS 63 leaf-bearing structure, it continues to bear leaves when under ground; but often these leaves are much modified, either reduced in size so as to be mere rudiments, or used for some other purpose. The fact that a subterranean structure bears leaves of some kind indicates that it is a stem and not a root. Since both the stem and its leaves must be considered in connection with the underground habit, the shoot (21) will be considered rather than the stem alone. In general the subterranean shoot is con- spicuously a region of food storage. The three following types are the most common. (4) Rhizomes. This is probably the most common form of subterranean stem. It is usually horizontal, more or less elongated, and much thickened for food storage, and is often called the rootstock (Fig. 61). It advances through the soil year after year, often branching, sending out roots be- neath and leaf-bearing branches into the air. As it continues to grow at the apex, it gradually dies behind, thus isolating branches in the case of branching rhi- zomes. It is a very efficient method for the ^ I0< 61- Rootstock f a f ern (common brake), bearing young leaves. spreading of plants and is extensively used by grasses in covering areas and forming turf. The persistent continuance of some weeds, especially certain grasses and sedges that infest lawns and meadows, is due to this habit (Fig. 62). It is \ A TEXT-BOOK OF BOTANY impossible to remove from the soil all of the indefinitely branching rhizomes, and any nodes that remain are able to send up fresh crops of aerial branches. In many cases FIG. 62. Rootstock of a Juncus, showing how it advances beneath the ground and sends up a succession of branches; the breaking up of such a rootstock only results in separate individuals. only a single aerial branch is sent up each year, as in wild ginger, Solomon's seal (Fig. 63), iris, bloodroot, etc.; in others, leaves and flowers may be sent up separately by the rhizome. In the com- mon ferns, it FIG. 63. Rootstock of Solomon's seal, showing terminal Will be noted, bud, the base of this year's aerial branch, and scars of the branches of three preceding years. After GRAY. ^Jjg QQ _ called fronds are sim- ply large leaves developed directly by the rhizome. Per- haps even more familiar is the extensive rhizome system STEMS 65 of the water-lilies, from which arise the leaves with large floating blades (pads). Therefore, a rhizome does not nec- essarily bear only scale leaves, but may develop also leaves that become aerial; and in that case they are usually large. It is evident that in plants possessing rhizomes the subterranean stems are perennial, while the aerial parts may be annual. (5) Tubers. In some plants the ends of underground stems become very much enlarged for food storage. These enlargements are called tubers, the best-known illustration being the common potato (Fig. 64). That it is a stem structure is evident from the fact that it bears very much Flo. 64. Potato tuber showing eyes (scale leaves and axillary buds). reduced leaves, in the axils of which are buds, the so-called "eyes." Abnormally developed potatoes often show the shoot character of the tuber very plainly, and in the case of potatoes sprouting it is evident that the eyes have de- veloped into branches. In planting potatoes, advantage is taken of the fact that any node placed in proper conditions may strike root and put out a branch. Since the eyes are branch buds standing at nodes, and any piece of the potato containing a bud is able to produce a new plant, it is customary to cut the potato into pieces, being careful that each piece contains one or more eyes. Heaping up the soil (hilling up) about the base of the potato plant induces the formation of more of the subterranean, tuber-bearing 66 A TEXT r BOOK OF BOTANY branches. In the tuber called Jerusalem artichoke, which is developed by the subterranean stems of a kind of sunflower, the nodes of the stem and the buds of branches are more conspicuous than in the potato. Fleshy roots, such as those of the sweet potato, should not be confused with tubers. (6) Bulbs. In some plants the main stem is very short and is covered by numerous thickened, overlapping leaves or leaf bases (usually called scales), the whole structure being a bulb. Bulbs such as those of the lily, hyacinth, tulip, and onion are very familiar. In this case the food storage is chiefly in the scales. Scaly bulbs are those in which the scales overlap, but are not broad enough to enwrap those within, as the lily bulb (Fig. 65); coated bulbs are those in which the broad scales com- pletely enwrap those within, as the bulbs of onions and tulips. Small bulbs, called bulblets, are borne by some plants on parts above ground; as, for example, the bulblets that ap- pear in the axils of the leaves of the tiger-lily and those that replace flower-buds in the common onion. These bulblets, when planted, have the power of producing new plants, as do the subterranean bulbs. The above subterranean shoots, with their storage of reserve food, enable plants to put out their aerial parts with remarkable promptness and develop them with great rapidity. As an illustration of a situation in which this FIG. 65. Scaly bulb of white lily: A, exte- rior view; B, longitudinal section, showing short stem and overlapping scales. After BAILLON STEMS 67 ability is of great advantage to plants, the vernal habit may be mentioned. It is a matter of common observation that the rich display of spring flowers occurs in forests and wooded glens before the trees come into full foliage. The working season of these spring plants is between the begin- ning of the growing season and the full forest foliage, and the subterranean shoots enable them to send up branches or leaves with great rapidity. After the forest leaves are fully developed, the available light for work beneath the forest crown diminishes, the spring flowers disappear, and the short period of activity does not return until the next season. It has been observed that many of these underground structures gradually become more and more deeply buried, .and it appears that some process of self-burial is going on. For example, it has been observed that if the tuberous underground stem of Jack-in-the-pulpit, often called In- dian turnip, be planted in a flower-pot near the surface of the soil, it will be found six inches deeper within a week. This is probably an illustration of exceedingly rapid burial, but enough has been observed of the habits of such plants to indicate that such gradual self-burial of underground parts is very common. Experiments have indicated that this self-burial is not continued indefinitely, but that for each kind of plant there is a normal depth reached by the underground stems. If such stems are planted below their normal depth, the experiments show that there are various methods of ascending to the proper depth. BUDS .28.. Mature of buds. A bud is an undeveloped shoot, whose internodes have not elongated, so that the leaves overlap, forming a more or less compact structure (Fig. 66). It resembles a bulb or bulblet in general structure, except that the overlapping leaves are not thickened as food reservoirs. The outer (older) leaves of the bud protect the 68 A TEXT-BOOK OF BOTANY inner (younger) ones, and all the leaves protect the delicate growing apex of the stem or the branch. There are what are called leaf-buds and flower-buds, but only the former will be considered here. 29. Position of buds. In shrubs and trees the growth of stem and branches is not continuous, but is interrupted during the winter. Preparatory to this interruption a bud is formed at the end of each growing axis, and is called the termi- nal bud (Fig. 66). When it opens the fol- lowing season it continues the growth of the stem or branch. Buds are formed also in the axils of leaves, usually one bud in an axil, and hence they are called axil- lary buds (Fig. 66). When they develop they form new branches. When the ter- minal buds are stronger than the axillary buds, the main stem or branches continue to elongate year after year; but if the axillary buds are stronger, the growth of the new branches may replace that of the stem from which they arise. For exam- ple, in the common lilac the two buds in the axils of the uppermost opposite leaves develop branches, the terminal bud be- tween them not continuing the growth of the axis, and often not even being formed. Hence the lilac bush is charac- terized by its forked branching, each axis appearing to end in a pair of branches. Axillary buds do not all develop into branches by any means, but any of them may do so under certain conditions. If the terminal bud is injured or is fee- ble, the axillary bud or buds nearest to it will be more likely to develop branches; and if the upper axillary buds are injured, the next lower ones will develop, and so on FIG. 66. Scaly buds of hickory; termi- nal one strongest; lateral ones axil- lary as shown by the leaf scars. After GRAY, STEMS 69 down the axis. Axillary buds may exist for several years without any opportunity to develop, and they may even be overlaid by the growth of the stem on which they stand. 30. Scaly buds. The most conspicuous buds are the so-called scaly buds, in which the outermost leaves develop as dry and often hard scales, entirely unlike the true leaves (Fig. 66). These overlapping scales protect the delicate leaves within and the growing apex of the stem from sudden changes of temperature and from moisture, and are often made still more effective against moisture by becoming covered with a sort of varnish or balsam, as in the horse- chestnut and balsam-poplar. The inside of the scales or the young leaves within are often covered with wool, as a further protection against sudden changes of temperature. It is evident that scaly buds are especially adapted to protect delicate structures during the winter and early spring, and hence are characteristic of the shrubs and trees of temperate regions. In the spring, such buds first swell and then open, the young branch emerging by the lengthening of its inter- nodes, and gradually spreading its leaves. During the opening the scales usually drop off, leaving more or less complete rings of scars about the stem, thus permanently marking the position of the bud. If a branch continues to elongate for a number of years, its age and the amount of growth each year can be determined by the successive sets of bud scars. 31. Naked buds. Buds in which no protective scales are developed, or any other special coverings, are called naked buds, and are characteristic of tropical plants, although not entirely lacking in plants of the temperate regions. 32. Accessory buds. In some plants more than one bud may appear in the axil of a leaf, as in the maples, in which three buds occur side by side (Fig. 67). As these buds are most conspicuous in the early spring, the position 70 A TEXT-BOOK OF BOTANY of the leaf is indicated by the leaf scar, immediately above which the three buds appear. In the common bush honey- suckle, three to six buds appear in each axil. In all such cases the extra buds are called accessory buds. 33. Adventitious buds. Since the tips of stems or branches and the axils of leaves are the usual places for buds, those which occur in other positions are called adventitious buds. Such buds appear on stems (on the inter- nodes), roots, and even leaves, and very commonly they arise as a result of injury. On the trunks of trees, even at the base, wounds often result in the formation of buds and the development of vigorous young branches, usually called suckers or water sprouts. Often from a stump young shoots arise, and the process of pollarding consists in cutting off the crowns of trees that new branches may be developed in connection with the wound. In the willows, for example, the production of such shoots is so prompt FIG. 67. Branch of maple, show- ing terminal, lateral, and ac- and they are so vigorous and pliable that twigs for basket-work are obtained from them cessory buds. After GRAY. in this way. In propagating plants by root- cuttings, as can be done with blackberries and raspberries, advantage is taken of the fact that some roots can produce buds. In propagating by stem-cuttings it is the axillary buds that develop the new shoots; but in root-cuttings the new shoots arise from adventitious buds. That leaves also may produce adventitious buds is shown in connection with the practise of propagating begonias by leaf-cuttings. It is evident, therefore, that while plants ordinarily produce terminal and axillary buds, under certain con- ditions buds may be developed and shoots arise at any place. CHAPTER IV ROOTS 34. General character. In general, roots are organized to work in the soil, but this is not true of all of them. The soil roots, however, will be considered first, as being the most common and as exhibiting most clearly the structure FIG. 68. Roots: .A , dandelion with tap-root; B. grass with cluster of fibrous roots. 6 71 A TEXT-BOOK OF BOTANY and work of roots. One of the most obvious contrasts with the stem in external appearance is that roots bear no leaves or scales, and are not made up of nodes and inter- nodes. The root that comes from the seed, including all of its subsequent branches, is the primary root. In some cases the primary root develops a single prominent vertically descending axis, called the tap-root, which gives off small branches, as in the dandelion (Fig. 68, A); in other cases the primary root breaks up at once into a cluster of branches, as in many grasses (Fig. 68, B). In many cases the tap- root becomes conspicuously thickened for food storage, as illustrated by such common vegetables as radish (Fig. 69, A), turnip, and parsnip. In some cases where there is no FIG. ). Fleshy roots: A, radish with fleshy tap-root; B, dahlia with cluster of fleshy roots tap-root, the branches become thickened, forming such clusters of thickened roots as those of the dahlia (Fig. 69, B} and of the sweet potato. Roots that arise from the stem or the leaves are secondary roots. For example, a subterranean stem or a creeping stem strikes root from the ROOTS 73 nodes, and such secondary roots may be the only roots of many plants (Fig. 46). In propagating plants by layering ( 23) or by cuttings, the roots are necessarily all secondary roots. Even erect stems sometimes send down secondary roots into the soil from the lower joints (Fig. 77), as is very com- mon in corn. 35. Root-cap. The growing tip of each root and rootlet is protected by a cap of cells called the root-cap (Fig. 70). This root-cap consists of several layers of cells, the outer ones gradually dying or being worn away as the tip of the root pushes through the soil, and being replaced by new layers which are continually forming be- neath. In some plants the root-cap is very easily seen as a conical thickening at the tip of the root; in others it can only by examining un- der the microscope lon- gitudinal sections through the root-tip. The presence of such a protective cap in the root is in strong contrast with the stem, whose growing tips are protected by overlapping leaves. i j i FIG. 70. Longitudinal section through root- be demonstrated tip of 8piderwortt showing central vascular axis (pi), cortex (p), epidermis (e), and root-cap (c). 74 A TEXT-BOOK OF BOTANY 36. Root-hairs. A short distance behind the root-cap the surface of the root becomes covered by a more or less dense growth of hairs, known as root-hairs (Fig. 71). These hairs are outgrowths, some- times very long ones, from the superficial cells, a single cell producing a single root-hair. In fact the root-hair is only an extended part of the superfi- cial cell. The root absorbs water and materials dissolved in it from the soil, and the root-hairs enormously increase the absorbing surface. Gen- erally root-hairs do not last very long; but new hairs are being put out by the elonga- ting root as the old ones behind root-hairs and their position in ref- <}i e> so that there is always a erence to the growing tip: A, grown in soil (higher up the hairs become much more abundant and longer); B, grown in moist air. FIG. 71. Root-tips of corn, showing zone of active root-hairs near the tip, but none on the older parts of the root. 37. Internal structure. A cross-section of a young root shows two prominent regions (Fig. 73). In the center is a solid" vascular cylinder, often called the central axis. It will be remembered that in the stems of Dicotyledons and Gymnosperms ( 24) the vascular cylinder is hollow, en- closing pith. Investing the solid vascular cylinder of the root is the cortex, which often can be stripped from the central axis like a spongy bark. If the section has passed through the zone of root-hairs, they can be seen coming from the superficial cells. A longitudinal section of a root- tip, in which these regions are very young, is shown in Fig. 70. The wood (xylem) and the bast (phloem) of the vascular ROOTS 75 cylinder do not hold the same relation to each other as in the stem ( 24). The vascular cylinder, instead of being made up of vascular bundles with wood toward the center and bast toward the outside, as in stems, is made up of wood and bast strands alter- nating with each other around the center (Fig. 72). The wood strands radiate from the center like the spokes of a wheel, and the bast strands are between these spokes near their outer ends. This ar- rangement of wood and bast is peculiar to roots. When roots increase in diameter, a cambium soon begins to form new wood and bast, as in the stems that increase FIG. 72. Diagrammatic cross-section of a young root, showing the innermost layer of the cortex (c) and the vascu- lar cylinder (t>) containing alternating regions of xylem (z~) and phloem (p). B A FIG. 73. Diagram showing the method of thickening the vascular cylinder of a root : A represents the cross-section of a young root in which four phloem strands (p) alternate with four xylem strands (x), the whole bundle region being enveloped by the thick cortex ; B represents an older root in which there is a continuous zone of cambium (c), which is forming on the outside new phloem (np) in contact with the old Op), and on the inside new xylem (nz) alternating with the old (x) 76 A TEXT-BOOK OF BOTANY in diameter ( 24). The new wood, however, is not formed in connection with the old wood, but just within the bast, that is, farther in between the " spokes" of old wood, resulting in bundles like those of the stem (Fig. 73). In this way a thickening vascular cylinder is formed, like that of stems that increase in diameter; and presently the cross- section of the root resembles that of the stem. It is evident (Fig. 73) that the principal pith rays separating the vas- cular bundles of such a root extend inward to the original radiating strands of wood that alternate with the original strands of bast. The vas- cular bundles of the root connect with those of the stem, and these in turn with those of the leaves, so that throughout the whole plant there is a continuous vascular system. The origin of the branches of roots is very different from that of stems. In a stem the branch begins at the outer part of the cortex, but in the root it begins at the sur- face of the vascular cylinder and breaks through the cortex (Fig. 74). If the cor- tex of a root be stripped off, the branches will be found attached to the central axis, and the perforations made by the branches through the cortex can be seen. 38. Growth in length. The elongating region of the root is much more restricted than that of the stem. It was stated ( 26) that the elongating region of a stem may extend ten to twenty inches from the tip, or even more; but the elongating region of a root is hardly ever more than two-fifths of an inch, and often not more than half of that. The region of elongation and of greatest elongation should be determined by using such seedlings as those of peas, beans, and corn. When the young roots have become a FIG. 74. Longitu- dinal section of root of arrow- leaf, showing the branches start- ing from the central axis and penetrating the cortex. ROOTS 77 FIG. 75. Roots of scarlet - runner bean marked with lines one millimeter apart and photographed after forty -eight hours. half to one inch long, mark as delicately as possible in India ink with a soft camePs-hair brush a series of equally spaced lines, beginning at the tip. Observations at the end of twenty-four to forty-eight hours will discover the region of elongation and of greatest elongation (Fig. 75). 39. The soil. Before absorption by roots is con- sidered, it is necessary to know something of the structure of soil. Soil is finely divided rock ma- terial, which may be mixed with a greater or less amount of material (called organic material) derived from the broken-down bodies or waste products of plants and animals. However fine the particles of soil may be, they never fit together in close contact, so that there are open spaces everywhere among them. Immediately after a soaking rain these spaces are full of water, but if the soil is one that drains easily, the water gradually disappears from the spaces, and the larger ones are occupied by air. In addition to this occasional water, each particle of soil is invested by a thin film of water, which adheres to it closely, and which never entirely disappears even in the driest soil. The soil water is never absolutely pure, but contains dissolved in it cer- tain materials obtained from the soil. As types of soil, sand, clay, and humus may be con- sidered. Humus is a soil in which there is intermixed a large amount of decayed plant material; and it is frequently called vegetable mold, or leaf mold, the best illustration being the upper soil of forests. Aside from certain materials 78 A TEXT-BOOK OF BOTANY that the different soils may supply to the plant, they are especially characterized by their relation to water. The power of a soil to receive and to retain water is a very important consideration in connection with plants. For example, it is evident that the receptive power of sand is high, and its retentive power is low; while in the case of clay the reverse is true. One of the great advantages of humus is that its receptive and retentive powers are better balanced than in sand and clay. It is easy to devise a series of experiments that will show in a rough way the comparative receptive and retentive powers of these three types of soil. It has been shown also that for any given soil, the more finely the particles are divided the better it is for plants. When the soil is turned up with plow or spade, it is dried by the air and pulverized and so put in better condition for plants. It is evident that in considering the relation of the soil to plants, not only the surface soil must be considered, but also the soil beneath (subsoil). For example, if humus rests on sand, the water will drain away much more rapidly than if humus rests on clay. The whole subject of the soil in its relation to plants is one of extreme complexity and is as yet little understood. 40. Absorption of water. To obtain water from the soil, the root not only often branches profusely, but also develops the root-hairs described above ( 36). Only in the younger portions of the root, that is, in the general re- gion of the root-hairs, is absorption of water effected. The root-hairs push out among the soil particles and come into very close contact with them, the particles sometimes be- coming embedded in the wall of the hair (Fig. 76). In this way the films of water adhering to each soil particle are closely applied to the hair, and water passes from them through the wall of the hair into its cavity, and so into the plant. The process by which the water passes in is known ROOTS 79 as osmosis. As water is absorbed from the films they become thinner, and this loss is supplied from neighboring films. In this way a flow from regions of the soil deeper and more distant than those to which the root reaches is set up toward the films losing water. The water supply may not be able to make good such loss indefinitely; and if so, the films gradually become thinner, until a point is reached when the root-hair can obtain no more water, the film holding tenaciously to its particle of soil. After the roots have obtained all the water they can from the soil, and it seems perfectly dry, it still contains two to twelve per cent of water in the form of films. The water thus obtained by the root-hairs passes inward through the cortex and enters the wood of the vascular cylinder, and then is free to ascend to the wood of the stem, and so to the leaves. It should be understood that the water does not carry into the plant the soil substances dissolved in it; but each dissolved substance, although it must be in solution in order to enter the plant, is turned back or enters upon con- ditions that belong to itself alone. Certain dissolved substances may not be able to enter at all, and in con- sequence of this the root has been said to possess a selective power; while other substances may enter with greater or less rapidity at different times, or may even be turned back at certain times. All this diversity of behavior is dependent upon definite laws of physics. FIG. 76. Root-hair of wheat, which is shown to be an out- growth from an epidermal cell, in close contact with soil particles. 80 A TEXT-BOOK OF BOTANY 41. Special forms of roots. Roots in the soil serve the double purpose of anchoring the plant and absorbing wa- ter, but certain roots hold other relations and need special mention. (1) Prop roots. In certain plants roots are sent out from the stem or the branches, and finally reaching the ground establish the usual soil relations. Since these roots resemble braces or props, the name prop roots has been ap- .plied to them (Fig. 77). A very common illustration is that of the corn-stalk, which sends out such roots from the lower nodes of the stem. More striking illustrations, how- ever, are furnished by the banyan and the mangrove. The banyan sends down from its wide-spreading branches prop roots, which are sometimes very numerous. When they enter the soil they often grow into large trunk-like sup- ports, enabling the branches to extend over an extraordi- nary area. There is record of a banyan cultivated in Ceylon with 350 large and 3,000 small prop roots, and able to cover a village of one hundred huts. The man- grove is found along tropical and subtropical seacoasts, and gradually advances into the shallow water by drop- ping prop roots from its branches and entangling the detritus (Fig. 307). (2) Water roots. If a stem is floating, clusters of whitisli thread-like rootlets usually put out from it and dangle in the water. Plants which ordinarily develop soil roots, if brought into proper water relations, may develop water roots. For instance, willows or other stream-bank plants may be so close to the water that some of the root system enters it. In such cases the numerous clustered roots show their water character. Sometimes root systems developing in the soil may enter tile drains, when water roots will develop in such clusters as to choke the drains. The same bunching of water roots may be noticed when a hyacinth bulb is grown in a vessel of water. It is evident ROOTS 81 that contact with abundant water modifies the formation of roots, both as to number and character. (3) Clinging roots. Such roots are developed to fasten the plant body to some support, and may be regarded as A TEXT-BOOK OF BOTANY roots serving as tendrils. In the trumpet-creeper and poison-ivy these tendril-like roots cling to various supports, such as stone walls and tree trunks, by sending minute branches into the crevices. In such cases, however, the plant has also true soil roots. (4) Air roots. Some plants have no soil connection at alL In the rainy tropics,, where it is possible to obtain sufficient moisture from the air, there are many such plants, notable among which are the orchids, to be ob- served in almost any greenhouse. Clinging to the trunks of trees, usu- ally imitated in the greenhouse by nests of sticks, they send out long roots which dangle in the moist air (Fig. 78). Such plants are called epiphytes, the name indi- cating that they perch upon other plants and have no con- nection with the soil (Fig. 79). A very common epiphyte of our Southern States is the common long moss or black moss (although it is by no means a moss) that hangs in stringy masses from the branches of live-oaks and other trees (Fig. 80). FIG. 78. An orchid with aerial roots. FIG. 79. A group of aerial plants (epiphyte^ in a tropical forest. After KARSTEN and Si IIKNCK. FIG. 80. Live-oaks covered with long "moss. 1 83 < CHAPTER V GERMINATION OP SEEDS 42. Introductory. In the preceding chapters the struc- ture and the work of the three great nutritive organs (leaf, stem, and root) of the higher plants were considered. In studying the germination of seeds, these organs may be observed assuming their various positions and relations, and the student may be introduced to certain important facts. FIG. 81. Section of bean; removing one cotyledon, and showing the testa, the remaining cotyledon, the hypocotyl (its tip in position to emerge), and the plumule. Perhaps the most common seed used in class study of seed germination is the garden bean, although other seeds should be germinated in the laboratory, and, when possible, studies of germination should be extended beyond the laboratory. 43. General structure of the seed. It is very common to study even the surface of the seed in great detail, but 84 GERMINATION OF SEEDS 85 only such features as have an evident bearing upon its germination will be considered here. The seed is invested by a hard coat (testa), which in some seeds is extremely hard, and is evidently a protective structure during the more or less prolonged period of rest. Within the testa the young plantlet is packed, at this stage called the embryo (Fig. 81). The process of germination is the escape of this plantlet from the testa. If the embryo of the bean be removed from the testa better FIG. 81a. Section of violet seed, showing embryo, endosperm, and testa. FIG. 82. Seedling of bean: A, embryo removed from testa; B, young seedling showing hypocotyl, cotyle- dons, and plumule; C, older seedling showing the first internode and leaves of the stem. After GRAY. done after soaking in water for some time and straightened out, it will be found to consist of three distinct parts (Fig. 82). The most conspicuous of these is the two "halves" of the bean, which are the seed-leaves (cotyledons) gorged with reserve food. These cotyledons stand upon a minute stem, which in the seed is curved up against them, and which is called the hypocotyl, a name applied to the peculiar stem of an embryo. Between the cotyledons, and arising from the top 86 A TEXT-BOOK OF BOTANY of the hypocotyl is a bud, called the plumule, from which the future leafy stem is to develop. In many seeds the reserve food is not stored in the cotyledons, but in a spe- cial tissue surrounding the embryo, which in general may be called endosperm. In the violet seed, for example, within the testa is the endosperm, and embedded in the endosperm lies the embryo (Fig. 8 la). 44. Conditions for germination. The length of time seeds may retain their vitality varies with different plants. In nature they are expected to germinate in the growing season following their maturity; but many are known to re- tain the power of germination for several years if kept in proper conditions, chief among which, apparently, is dry- ness. The stories of the germination of wheat and corn ob- tained from the wrappings of mummies have proved to be myths. The conditions required for germination are abundant moisture, suitable temperature, and a supply of oxygen (which means access of air). Seeds vary greatly in the amount of heat necessary for germination, as may be inferred from the fact that some seeds germinate in early spring or even on the melting snow-fields of alpine and arctic regions, while others need the heat of the tropics. 45. Absorption of water. When a seed has been placed in the proper conditions for germination, the first visible result is its swelling through the absorption of water. The amount and force of this swelling may be observed by plac- ing a quantity of seeds in a tumbler of water and putting various weights on the mass. It is entirely clear also that oxygen has been passing in, for the seed gives off carbon dioxide and heat. That heat is given off by a germinating seed is made very plain in the process of malting, in which a large mass of barley is put in germinating conditions in a confined space, and the combined heat from all the seeds becomes very evident. GERMINATION OF SEEDS 87 46. Respiration. The escape of carbon dioxide, which follows the taking in of oxygen, is the superficial indication that the very important process called respiration is going on a process that is essential not only to every living animal and plant, but also to every living cell. Just what happens in respiration is very uncertain ; but it involves a series of changes in the living substance (protoplasm) itself changes which are made possible by the presence of oxygen, and among whose results are the liberation of carbon dioxide as a waste product, and of energy for plant work, such as growth and movement. A plant, therefore, cannot work without respiration; and if it cannot work it ceases to live. The contrast between photosynthesis ( 14) and res- piration should be kept distinctly in mind, as the former process so masks the latter in green plants exposed to light that the occurrence and the importance of respiration in them is not always fully appreciated. It was once custom- ary to contrast plants and animals by stating that the form- er take in carbon dioxide and give out oxygen (photosyn- thesis), and the latter take in oxygen and give out carbon dioxide (respiration). It is evident that all living things, whether plants or animals, are dependent upon respiration; while green plants when exposed to light can also do the work of photosynthesis. The contrast between the two processes may be made still more evident by the following statement: photosynthesis occurs only in green cells, re- quires light, uses carbon dioxide, liberates oxygen, makes organic material, and accumulates energy; while respiration occurs in every living cell, does not require light, uses oxygen, liberates carbon dioxide, uses organic material, and liberates energy. 47. Digestion. Before any growth of the embryo can take place the reserve food must be changed. Most fre- quently in seeds the storage form is starch, but starch is insoluble and therefore cannot move out of the cells in 7 88 A TEXT-BOOK OF BOTANY which it is stored. Accordingly it must be changed into a soluble form; and this work is commonly done by a sub- stance called an enzyme, which is produced by the living substance (protoplasm) of the cell. There are numerous enzymes, which act upon different substances; but the one most frequently found in seeds is that called diastase, which has the power of converting starch into one of the soluble sugars. This process of converting insoluble food into a soluble form is digestion, and in ordinary seeds the starch is digested and becomes sugar. All of this work preparatory to growth accounts for the activity noted in the two preced- ing sections. The food being in the form of a soluble sugar can leave the storage cells and pass to the regions where growth occurs. 48. Assimilation. In a germinating seed the soluble sugar produced by digestion passes in solution from cell to cell, according to the laws of osmosis, until it reaches cells where growth is taking place; that is, where the protoplasm is forming new cells by dividing those already formed, and enlarging the new ones until each one is as large as the cell of which it was a division. This cell division and cell growth are going on very actively in the hypocotyl and plumule of the germinating seed; and when the sugar in solution reaches the active cells, it is used in building up the active protoplasm, which is being broken down by its activity. This transformation of food into protoplasm, by numerous intermediate steps, is assimilation. 49. Proteids. Thus far we have considered only carbo- hydrate foods, but in building up protoplasm the carbo- hydrates are first used in the manufacture of proteids. Just how proteids are formed is very uncertain, but they are more complex than carbohydrates; and in addition to the carbon, hydrogen, and oxygen of the carbohydrates, proteids contain other elements, notable among which are nitrogen, sulphur, and phosphorus, and these enter the GERMINATION OF SEEDS plant in various compounds found in the soil. The white of an egg is an illustration of a proteid; and meat in general is a proteid food, as contrasted with bread, which is a car- bohydrate food. In many seeds proteid food is stored in the form of alcurone grains. For example, a section of a wheat grain, or the grain of any common cereal, shows aleurone grains in the outer layer of endosperm cells, just inside of the testa; while the other endosperm cells contain starch grains. 50. Fats. In addition to carbohydrates and proteids, some plants form fats, the third kind of organic food; and these fats are sometimes stored in the seeds in liquid form (in small drops), as in the castor-bean, flaxseed, etc. Fats contain carbon, hydrogen, and oxygen as do the carbo- hydrates; but while in the carbohydrates the hydrogen and oxygen occur in the proportion of two to one (H 2 O), in the fats the proportion of oxygen is much less. In ad- dition to the oil obtained from the seeds mentioned above, olive oil and cotton-seed oil may be mentioned as plant fats of commercial importance. 51. Escape of the hypocotyl. The first part of the seedling to push out of the testa is the tip of the hy- pocotyl, which is to develop the root. It is soon evident that this elon- gating tip di- rects its growth downward, that is, toward the earth, even if it has to curve about the seed to do so (Fig. 83). It is exceedingly FIG. 83. Germinating beans: the bean to the left has not been moved; the one to the right was turned 90 after it had reached the stage of the other ' sensitive to surrounding influ- 90 A TEXT-BOOK OF BOTANY ences, a condition that is called irritability. The outside influences that affect irritable organs are called stimuli; for example, among animals light is a stimulus to the eye. 52. Geotropism. The young root, developing at the end of the hypocotyl, is very sensitive to gravity, a con- dition that is called geotropism, the root being said to be geotropic. The word means "directed by the influence of the earth," what is commonly called gravity acting as a stimulus. If the root-tip, when it pushes out of the testa, is directed upward or horizontally, gravity acts as a stimulus and the irritable root responds by developing a curvature that directs it downward (Fig. 83). This is only one way of responding to the stimulus of gravity; and since this way directs the organ toward the source of the stimulus, the organ is said to be positively geotropic. If the same stimulus and response that directs the root-tip toward the soil continues to direct it within the soil, it continues-to grow directly downward and becomes a tap- root (Figs. 68 and 89). When such a root, having en- tered the soil, begins to send out branches, these do not respond to the stimulus of gravity as does the tap-root, for they extend through the soil in every direction, and are evidently not positively geotropic. 53. Hydrotropism. The root is very sensitive also to the presence of moisture, a condition that is called hydrotropism, the root being said to be hydrotropic. The word means "directed by the influence of moisture/' the moisture acting as a stimulus, and the root being positively hydrotropic. Since ordinarily the stimuli of moisture and gravity act from the same general direction upon the root, the responses are not contradictory. It is of interest, therefore, to arrange an experiment that will make them contradictory. An erect support, shaped as shown in Fig. 84, is covered with bibulous paper which is kept moist. GERMINATION OF SEEDS 91 To the inward sloping surface is pinned a seedling whose root has well started. The photograph (Fig. 84) shows that the root, con- tinuing to grow, has turned from the ver- tical direction under the stimulus of the moisture in the bibu- lous paper, and is pursuing a general di- rection that is a re- sultant between the two stimuli. A more detailed observation of such an experi- ment shows that the root - tip sometimes turns toward and sometimes away from the moist paper. 54. Escape of the cotyledons and the plumule. After the root with its branches has anchored the plantlet to the soil, the hypocotyl begins to elongate rapidly; and since the cotyledons are still within the testa this elongation results in the development of an arch, the hypocotyl arch (Fig. 85). As the arch constantly seeks to straighten itself, the upward pull on the cotyledons finally draws them out of the testa and the hypocotyl straightens. The cotyledons, however, have done their work, and although they may become green and persist for some time, in the bean they are of no further importance. It is the escape of the FIG. 84. A bean seedling showing the response of the root when the stimulus of gravity is from one direction and that of moisture from another. 92 A TEXT-BOOK OF BOTANY plumule that is especially significant, for it develops the shoot (Fig. 85). FIG. 85. A series in the germination of the garden bean, showing the hypocotyl arch, the pulling out of the cotyledons and the plumule, and the straightening of the hypocotyl. With the establishment of roots in the soil and the exposure of green leaves to the light and air, germination is over; for the plant is able to make its own food. 55. Phototropism. The stem is sensitive to the direc- tion of rays of light, a condition that is called phototrop- FIG. 86. A bean seedling that was placed in a horizontal position and after two hours photographed. ism, the stem being said to be phototropic. The word means "directed by the influence of light," the same stem GERMINATION OF SEEDS 93 appearing in the word "photograph." The term helio- tropism is often used, meaning "directed by the influence of the sun "; but while the sun is the usual source of light, it is not the only one. It should be noted that it is not light in general that acts as the stimulus, but the direction of the rays of light. The response of the stem to this stimulus is to turn directly toward the source of the light rays; that is, the stem is positively phototropic. Fig/ 86 shows a bean seedling that was placed in a horizontal position and two hours afterward photographed. Fig. 87 shows the same plant completely inverted, allowed to grow for two days, and then photographed. In both cases the strong curvature developed in response to the stimu- lus of light is very evident, the tip of the stem in both experiments being directed toward the source of light. It should be remembered that these stimuli that influence direc- tion call forth a response only when the organ is out of line, and the response or reaction is a curve that brings it back into line. It is also important to note that the sensi- tive or irritable region of an organ is not necessarily the region in which the reaction occurs; and this means that the stimulus has been transmitted in some way from the irritable cells to those that respond, for example, by developing a curvature. Nor does the reac- tion follow the stimulation immediately; for there is an FIG. 87. The same seedling shown in Fig. 86, com- pletely inverted, and after two days photographed. 94 A TEXT-BOOK OF BOTANY interval, known as reaction time, which is generally much longer in plants than in animals. The reaction time may be several hours, but the movement of the leaves of the sensitive-plant (17) and the snapping shut of the leaves of Dioncea ( 20) follow the stimulation with remarkable prompt- ness. The main stem in most cases is positively phototropic, as shown before (Figs. 86 and 87); but it is also negatively geotropic. The branches, jf - however, may respond to these FIG. ss.-A seedling of stimuli in a veI T different way, usu- white mustard grown in ally extending in a more or less hori- water and exposed to .L i j- j.' 11- i weak light, showing the zontal direction, and being mainly positive phototropism transversely aeotromc. of the stem and the The leaves, negative" phototropism also, are usually neither positively of the root; the arrows nor ne g a tively phototropic, but are indicate the direction of J XT the rays of light. directed horizontally, being trans- FIG. 89. A series in the germination of the scarlet runner bean. GERMINATION OF SEEDS 95 FIG. 89. First stage of the series shown in Fig. 89; one cotyledon removed to show the relation of parts, and the arch developed by the first internode. phototropism. It is interesting to note that a tap-root be- ing positively geo- tropic, positively hy- drotropic, and nega- tively phototropic, all of its responses under ordinary conditions combine to direct it into the soil. 56. Other seeds. It must not be sup- versely phototropic. The adjust- ment of the leaf-blades to the new direction of the light may be seen in Fig. 87. The root also is phototropic, turning directly away from the source of light; that is, it is negatively phototropic. Fig. 88 shows a seedling of white mus- tard so arranged that both stem and root are exposed only to weak light, the former showing positive, the latter negative FIG. 90. Seedling of castor-bean, showing large and green cotyledons. 96 A TEXT-BOOK OF BOTANY posed that all of the details of germination given for the garden bean are found in the germination of all seeds. The conditions for germination, and such life processes as res- piration, digestion, etc., belong to the germination of all seeds; but the relations of parts to one another and the details of the es- cape of the young plantlet vary wide- ly, and should be examined in as many plants as possible. For ex- ample, in the scar- let-runner bean the cotyledons are not usually freed from the testa, the first internode of the stem developing the arch and free- ing the leaves, as may be seen in the series shown in Figs. 89 and 89a which is completed by Fig. 57. Seeds such as peas, castor-bean, squash, and corn also should be ger- minated, as they show important variations. For exam- ple, in the pea and the acorn the cotyledons, so gorged with food as to have lost all power of acting as leaves, are never extricated from the testa; but the plumule is pushed out by the elongation of the cotyledons at their FIG. 91. Seedling of corn at several stages, showing the superficial position of the embryo, the unfold- ing leaves, and the roots; the single cotyledon is not seen, remaining in close contact with the endo- sperm. GERMINATION OF SEEDS 97 bases into short or sometimes long stalks. In the castor- bean and the squash, the cotyledons not only escape from the testa, but become green and work like ordinary leaves (Fig. 90). In corn, as in all the cereals, the embryo lies close against one side of the seed so that it is completely exposed by the splitting of the thin skin that covers it. In this case the single cotyledon is never freely expanded, but remains as an absorbing organ in contact with the starch-containing endosperm, while the root grows in one direction, and the stem, with its succession of unsheathing leaves, grows in the other direction (Fig. 91). CHAPTER VI 57. General characters. Algae are the simplest green plants, and it is thought that the higher plants have been derived from them. They grow in the water, and hence their habits are adapted to a water environment. They are often called seaweeds, but although they are very abundant along seacoasts they are also abundant in fresh waters. Some of them are so small that the individual bodies are visible only under the microscope, and there is every grada- tion in size from this to the bulky bodies of certain marine forms. Although all Algae contain chlorophyll, and hence are able to make their own food ( 14), they do not all appear green; for in many of them the chlorophyll is obscured by other coloring matters. The four great groups of Algae are named from the general color of their bodies, although it must be remembered that they all contain chlorophyll, which makes them independent. Some representatives of each group are selected for description, but they or others like them must be examined before any real knowledge of them can be obtained. 1. BLUE-GREEN ALG^E (Cyanophycece) 58. Gloeocapsa. These plants form blue-green or olive- green patches on damp tree trunks, rocks, walls, etc. By means of the microscope these patches are seen to be com- ALGJE 99 posed of multitudes of spherical cells, each cell representing a complete Gloeocapsa body. One of the peculiarities of the plant is that the outer part of the cell wall becomes mucilaginous, swells, and forms a jelly-like sheath. Among the cells examined there will be found some that are dividing, a wall extend- ing across the spherical cell and di- viding it into hemispheres. Each hemisphere is a new plant which FIG. 92. Glceocapsa: show- ing single cells, and small groups that have been formed by division and are held together by the enveloping mucilage. grows as large as the parent cell .and then divides in turn. The mucilaginous walls hold the cells together, and so they are found in groups of various sizes (Fig. 92). This method of reproduction by cell- division is the simplest kind of reproduction. > 59. Nostoc. These plants occur in jelly- like masses in damp places. If the jelly be examined, it will be found to contain em- bedded in it numerous IFic. 93. 4, Nostoc: showing the chain-like fila- ment and a heterocyst (a) ; B. Glceotrir/nn: showing mucilage sheath, basal heterocyst. and tapering apex. 100 A TEXT-BOOK OF BOTANY cells like those of Glceocapsa, but they are strung together so as to form chains of varying lengths (Fig. 93, A). The jelly in which these chains are embedded is formed from the cell walls, as in Glceocapsa, but it is much more abun- dant. One notable fact in Nostoc is that the cells of a chain are not all alike, for at irregular intervals there occur larger colorless cells, called heterocysts (Fig. 93, A, a), a name which means simply "other cells." It is observed that when the chain breaks up into fragments, each fragment is composed of the cells between two heterocysts. The fragments wriggle out of the jelly matrix and start new colonies or chains, each cell dividing to increase the length of the chain. A common plant related to Nostoc shows still more differentiation in the cells of the filament, the heterocyst being at the base, and the end cells forming a tapering and sometimes whip-like termination (Fig. 93, B). That each cell of Nostoc is an individual is evident from the fact that a single cell separated from the chain continues to live and divides; and therefore the chain is a colony of individuals, each one reproducing by cell-division. 60. Oscillatoria. These plants are found as bluish- green slippery masses on wet rocks, or on damp soil, or freely floating. They are simple filaments composed of very short flattened cells (Fig. 94), and the name refers to the fact that the filaments exhibit a peculiar oscillating move- ment. A filament is really a row of independent cells packed in a mucilaginous sheath, like coins in a coin-case. The cells are evidently flattened by mutual pressure, for the free face of the terminal cell is rounded (Fig. 94, B); and if a filament is broken, and a new cell surface exposed, it at once bulges out. If a single cell of the filament is free from all the rest, both flattened faces become rounded, and the cell becomes spherical. It is evident that pressure within the cell distends the elastic wall whenever it is free. Each cell is able to divide, forming new cells and thus 101 lengthening the filament, which may break up into frag- ments, each fragment forming a new filament. Although Oscillatoria is regarded as a filamentous colony of individuals, the peculiar waving and gliding movements of the filament show the cells working to- gether. The transition from a colony of one-celled independent individuals to an individual of many interdependent cells is insensible and indefinite. 61. Conclusions. These three forms of blue-green Algae will serve to illustrate the general features of the whole group. The name of the group refers to the fact that in addition to the chlorophyll the cells contain a characteristic blue color- ing matter which does not mask the green, but combined with it gives a bluish-green tint to the plants when seen in masses. Not all the blue-green Algae are bluish-green in tint, however; for the presence of other substances may disguise it, and the color may be yellow, or brown, or even reddish. For example, the largest of all the blue-green Algae has given name to the Red Sea. The group is sometimes called the green slimes on ac- count of the characteristic slimy, mucilaginous walls. They are very simple, being one-celled plants, the cells occurring singly or in chains and filaments. The reproduction is exclusively by means of cell-division; and since the cells that divide are ordinary working cells, this method of re- production is usually called vegetative multiplication. In plants whose bodies are many-celled, cell-division usually results in the growth of the individual rather than in the formation of new individuals. The power of motion is * marked in certain forms, and there is also a tendency Fio. 94. Oscillatoria: A, group of filaments; B, a single filament more enlarged. 102 A TEXT-BOOK OF BOTANY shown by the cells of a colony to work together. Different forms of cells are exhibited by Nostoc ; and this condition, spoken of as the differentiation of cells, implies also a differ- entiation of work. 62. Presence in water reservoirs. Until recently the Algae were thought to be of no importance to man; but it is now known that the offensive odor and taste too often observed in drinking water are due almost entirely to them, and chief among the polluting forms are the blue-green Algae. This pollution of water becomes very conspicuous when it occurs in city reservoirs or in ponds, and various methods of purification have been suggested. Of these none had proved satisfactory, until in 1904 the Department of Agriculture at Washington announced that an effective method of destroying the Algae or preventing their appear- ance had been discovered. It consists in introducing into the water a solution of copper sulphate so dilute that it is tasteless and harmless to man; but the warning is given that each reservoir or pond must be studied before the proper amount of the solution can be known. 2. GREEN ALG.E (Chlorophyceoe) V 63. Pleurococcus. These plants are exceedingly com- mon, occurring in masses, especially on the north side of tree trunks, old fences, etc., and looking like a green stain. After a few damp days the green of the masses becomes more vivid and noticeable. These finely granular green masses are found to consist of multitudes of spherical cells, resembling those of Gloeocapsa, except that there is no blue with the chlorophyll, and the cells are not embedded in a jelly-like substance derived from the walls. The cells may be solitary, or they may cling together in groups of various sizes (Fig. 95). Cells that have just divided may be observed easily, the evidence being that the ALG^E 103 two daughter cells have not yet rounded off or separated, so that they appear as two halves of the parent cell. Even before they sepa- rate they may di- vide again, and thus a group of cells may be formed. Pleuro- coccus, therefore, is another illustra- tion of an extreme- ly simple plant, in that it consists of one cell and repro- Flo> ^ pleurococcui: A > * h adult plant, with its nucleus ; B-E, various stages of division in pro- duceS^by Cell;jdiyi- ducing new cells; F, colonies of cells that have 'ned in contact. It woiilcLea-^e^imagine a simpler plant, and the pTanTTdngdom can be thought of as beginning with individ- uals consisting of one green cell and reproducing by divi- sion. This one cell, however, absorbs material, makes food, assimilates it, conducts respiration, etc.; in fact, does all the work of living carried on by plants with roots, stems, and leaves, although they may contain millions of cells. 64. The plant cell. Pleurococcus may be used to illus- trate the conspicuous features of a living plant cell. Bound- ing the cell there is a thin, elastic cell-wall, composed of a substance called cellulose. The cell- wall, therefore, con- stitutes a delicate sac, which contains the living substance known as protoplasm. It is the protoplasm that has formed the wall about itself, in the same sense that a snail deposits the shell about its body. The protoplasm is organized into various structures which are called organs of the cell. One of the most conspicuous protoplasmic organs is the nucleus, a comparatively compact and usually spherical body, and generally centrally placed within the cell (Fig. 95, A). 104 A TEXT-BOOK OF BOTANY C' In the great majority of cells there is a single nucleus, and all about it, filling the general cavity within the cell- wall, is a mass of much less dense protoplasm, known as cytoplasm. The cytoplasm seems to form the general background or matrix of the cell, and the nucleus lies embedded within it. Another protoplasmic organ of the cell is the plastid. Plastids are relatively compact bodies, and variable in form and num- ber. The most common kind of plastid is the one that contains chlorophyll, and hence is known as the chloroplastid or chloroplast. An ordinary cell of an alga, therefore, consists of a cell-wall, within which the protoplasm is organized into cytoplasm, nu- cleus, and chloroplasts. With proper staining the nucleus and the chloroplasts of Pleurococcus can be seen; but these structures may be seen more distinctly and with much less trouble in the cells of a moss leaf (Fig. 96). The cell-wall is elastic, so that the cell can be compressed or inflated. The single cell of Pleurococcus, unless pressed upon by neighboring cells, retains a spherical form as long as it is alive, a fact which shows that there is constant and uniform pressure on the wall from, within the cell. It is found that this pressure is due to the absorption of water in sufficient amount to stretch the wall, this distended con- dition of the cell being called turgor, a name indicating that the cell is turgid. Pleurococcus retains its spherical form, 4'heref ore, because it is turgid; and the bulging of free walls of Oscillatoria ( 60) is due to the turgor of the cells. FIG. 96. Cells of a moss leaf, show- ing chloroplasts (a), nucleus (6), and cytoplasm (c). 105 65. Ulothrix. These are bright green, thread-like plants found in the shallow, moving water of streams or lake margins, where they are anchored to sticks or stones. Each plant is a simple (unbranched) filament, composed of a single row of cells; and the cells are all alike excepting that the lowest one is usually colorless, and is elongated and more or less modified to act as a holdfast, anchoring the filament to its support (Fig. 97, A). With the possi- FIG. 97. Ulothrix: A, base of filament, showing holdfast cell and five vegetative cells, each with a single conspicuous cylindrical chloroplast (seen in section) surrounding a nucleus; B, four cells containing swimming spores; C, one cell containing four swimming spores (a), a free swimming spore (6), a cell (c) from which most of the gametes have escaped, pairing gametes (rf), and the resulting oospores (e); D, young filament from a swimming spore; E, oospore growing after rest; F, oospore producing swimming spores. E and F, after DODEL-PORT. ble exception of the holdfast cell, in each cell there may be seen a nucleus and a single chloroplast of peculiaAMrn, being a thick cylinder investing the rest of the cell-conBits. As seen under the microscope in optical section, thej^lin- 106 A TEXT-BOOK OF BOTANY drical chloroplast appears as a thick green mass on each side of the central nucleus (Fig. 97, A). Each cell is able to divide, and so the filament grows in length; or frag- ments of old filaments may develop new ones, resulting in vegetative multiplication. Although each cell of the filament is an ordinary nutri- tive cell, under certain conditions one or more of these cells contain other cells, that have been formed by what is called the internal division of the older one (Fig. 97, B). In ordinary cell-division the wall of the old cell forms a part of the walls of the two new cells; but in internal division the wall of the old cell is only a case which encloses the new ones, and from which they escape. When these cells formed by internal division escape from the mother-cell into the water, it is discovered that they are able to swim about by the lashing movements of four cilia that appear in a cluster at the pointed end (Fig. 97, C, b). After a time these swimming cells settle down, lose their cilia, and by division begin the development of new filaments like those from which they came (Fig. 97, D). It is evident that the swimming cells have introduced a new method of reproduc- tion a method that involves the formation of a special cell for reproduction, quite distinct from the ordinary nutritive cells. A special cell thus set apart for reproduction is called a spore, and spores that swim are distinguished as swim- ming spores. A very important fact about Ulothrix, there- fore, is that it reproduces not only by vegetative multipli- cation, but also by swimming spores. In other cells of the same filaments, or in cells of fila- ments under different conditions, the same formation of cells by internal division may be observed; but the con- tained cells are smaller and more numerous (Fig. 97, C, c). When they escape, it is discovered that they also are ciliated swimming cells; but since they do not produce new fila- ments, it is evident that they are not swimming spores. ALG.E 107 It has been observed that these small swimming cells come together in pairs and fuse (Fig. 97, C, d), each pair thus forming one new cell (Fig. 97, C, e). The cell thus formed passes through a resting period (usually during winter), then begins to grow (Fig. 97, ), and finally produces four swimming spores (Fig. .97, F), each of which is able to pro- duce a new filament of Ulothrix. Here is evidently a third method of reproduction, which is peculiar in the fact that two special cells unite to form the spore that produces the new plant. These two special cells are gametes (sexual cells); their act of fusion is fertilization; the spore thus formed is the oospore (egg-spore); and this kind of re- production is called sexual reproduction.* It should be observed that the swimming spores and the oospores of Ulothrix do not differ in what they are able to do, but in the method of their formation, one being formed by cell- division and the other by cell-fusion; but to distinguish re- production by spores from sexual reproduction by oospores, the former is called asexual reproduction, and the spores are often spoken of as asexual spores; although when the word "spore "is used it generally implies an asexual spore. The three methods of reproduction found in Ulothrix may be summarized in the following graphic way: (1) Vegetative multiplication is indicated by P P P P , in which P stands for the plant, there being a succession of plants arising directly one from the other without the interposition of any special cells. (2) Reproduction by asexual spores is indicated by P o P o P o P , indicating that new plants are not produced directly from the old ones, but that between the successive generations there is the asexual spore. * It does not seem wise to multiply terms at this point, and hence the more general terms "fertilization" and "oospore" are used as in- cluding the more special terms "conjugation" and "zygospore." 108 A TEXT-BOOK OF BOTANY (3) Sexual reproduction is indicated by >-Mi:>Hl>-^ indicating that two special cells (gametes) are produced by the plant, that these two fuse to form one (oospore) , which then produces a new plant. 66. Cladophora. This plant is found attached to sticks and stones at the edge of ponds or lakes, and is often so abundant as to form thick mats of long anchored filaments. It is easily distinguished from Ulothrix, for it is a much coarser plant and branches freely (Fig. 98). It is mentioned here both because it is common and be- cause it illustrates a branching filamentous body. Just as in Ulothrix, reproduction in Clado- phora is carried on by means of swimming spores, and also by the fusion of swimming gametes to form oospores. 67. CEdogonium. The fila- ments of CEdogonium are long and simple, the lowest cell act- ing as a holdfast, as in Ulothrix and Cladophora. In each cell a nucleus may be seen (Fig. 99), and apparently several chloroplasts; but really there is only one large complex chloroplast. Any one of these cells may produce within itself a single large swimming spore, which escapes from the mother-cell into the water (Fig. 99, C). At its more pointed clear end there is a little crown of cilia, by means of which it swims about rapidly. These spores finally anchor themselves, and each one produces a new filament (Fig. 99, D and #). FIG. 98. Cladophora: a branch- ing filament, each of whose cells contains several nuclei. ALG^E 109 Certain cells of the filament become very different from the ordinary cells, enlarging and becoming globular (Fig. 99, A and B). In each one of these spherical cells there is FIG. 99.(Edogonium: A, portion of filament showing vegetative cell with its nucleus (rf).an oogonium (a) filled by a large egg packed with food, a second oogonium (c) containing an oospore, as shown by heavy wall, and two antheridia (6), each containing two sperms; B, portion of filament showing antheridia (a), from which two sperms (6) have escaped, a vegetative cell with its nucleus, and an oogonium which a sperm has entered (c), and whose egg nucleus (d) may be seen; C, swimming spore; D and E, young filaments developing from swimming spores. 110 A TEXT-BOOK OF BOTANY formed a single large gamete, which remains in the cell that produces it. This large gamete, which remains passive, is the female gamete or egg, and the globular cell that produces it is the oogonium (egg-case). In the figure (Fig. 99, A and B] these large eggs are seen packed with roundish masses of reserve food. Other cells, either in the same filament or in some other filament, differ from the ordinary cells in being much shorter (Fig. 99, A, b, and B, a). In each of them one or two gametes are formed and are set free, swimming about like small swimming spores (Fig. 99, B, 6). These active gametes are the male gametes or sperms, and the short cell that produces them is the antheridium. The sperms swim actively about in the vicinity of an oogonium, and sooner or later one enters through an open- ing in the oogonium wall and fuses with the egg (Fig. 99, B, c). As a result of this act of fertilization an oospore is formed that soon organizes a firm wall about itself (Fig. 99, A, c). This firm wall indicates that the oospore is not to germinate immediately, but is to be protected through an unfavorable season, such as failure of food supply, cold, or drought. It is evident, therefore, that although both the swimming spores and the oospores are able to produce new plants, the former germinate immediately and enable the plant to spread during the growing season, while the latter last through the winter when the parent plants have perished, and form new plants in the new growing season. The most important fact illustrated by (Edogonium is that the gametes are not alike, as in Ulothrix and Clad- ophora, but have become very unlike. One of them (the egg) is relatively large and passive; the other (the sperm) is relatively small and active. In this case, therefore, the two sexes are apparent, and we recognize male and female gametes. 111 68. Vaucheria. This is one of the most common of the green Algae, occurring in felt-like masses of coarse filaments in shallow water and on muddy banks, and also commonly found on the damp earth and pots of greenhouses. It is often called green felt. The filament is very long and usually branches exten- sively; but its great pe- culiarity is that there is FIG. 100. Vaucheria: showing the large, branching, cceno- cytic, filamentous body, con- taining numerous chloro- plasts and nuclei. no partition wall in the whole body, which forms one long con- tinuous cavity. This cavity is full of cyto- plasm, and embedded in the cytoplasm are very numerous chloro- plasts and also numer- ous nuclei (Fig. 100). Such a body, contain- ing nuclei not sepa- rated from each other by cell-walls, is called a cwnocyte (common cell), or it is said to be ccenocytic. FIG. 101. Vaucheria: showing the formation of the lirge spore (A), its discharge (B), and the beginning of a new filament (C). 112 A TEXT-BOOK OF BOTANY Vaucheria produces very large asexual spores. The tip of a branch becomes separated from the rest of the body by a wall (Fig. 101, A). In this improvised chamber the whole of the contents form a single large spore. It escapes into the water through an opening in the wall, (Fig. 101, B) and finally develops a new filament (Fig. 101, C). Sex organs (antheridia and oogonia) are also developed. In a common form of Vaucheria they appear separately on the side of the large coenocytic body, and are separated from the general cavity by walls. The oogonium is a globular cell (Fig. 102, 6), usually with a perforated beak for the entrance of sperms (Fig. 102, /), and contains a single FIG. 102. Sexual reproduction in Vaucheria: A, a single antheridial branch with an empty antheridium (a) at its tip, and also an oogonium (6) containing a heavy-walled oospore (c) and showing the beak (/) through which the sperm passed; B, another species, in which a single branch bears several oogonia, and a terminal coiled antheridium. large egg. The antheridium is a much smaller cell, on the end of a branch (Fig. 102, a), within which numerous very small sperms are formed. The usual escape into the water and entrance into the oogonium is followed by fertilization (one sperm fusing with the egg), which results in an oospore. The oospore develops a thick wall and is thus protected until the next growing season (Fig. 102, c). In another species, ALGLE 113 often more abundant, a single branch from the main body bears several lateral oogonia and a terminal coiled anther- idium (Fig. 102, B). The two important facts illustrated by Vaucheria are the coenocytic body and the development of special cells to act as sex organs. FIG. 103. Spirogyra: one complete cell, showing the spiral, band-like chloroplasts, with embedded pyrenoids, and a nucleus (near the center) swung by radiating strands of cytoplasm. * 69. Spirogyra. This is one of the most common of the pond scums, occurring in slippery and often frothy masses of deli- cate filaments floating in still water or about springs. The filaments are simple, and are not anchored by a special basal cell. The cells contain re- markable chloroplasts, which are bands pass- ing spirally about with- in the cell-wall (Figs. 103 and 104). These bands may be solitary Or Several in a Cell, and FlG - 104. Sptnw/ra: A-C, various stages in the development of sexual tubes; D, a completed form very striking and 114 A TEXT-BOOK OF BOTANY conspicuous objects. The band is not flat, and to deter- mine its form is an excellent exercise for a student learn- ing to reconstruct objects under the microscope. Embed- ded in the chlorophyll band nodule-like bodies (pyrenoids) are seen, around which a granular zone of starch grains is often visible. In favorable material, notably cells with a single band, the nucleus may be seen, surrounded by a zone of cytoplasm that is connected by radiating strands with the cytoplasm against the wall (Fig. 103). Spirogyra is peculiar in producing no swimming spores, or asexual spores of any kind. Its method of sexual re- FIG. 105. Spirogyra, showing some common exceptions: A , two connected cells- that have formed oospores without fusion, and a second cell that has attempted to connect with one of them; B, cells of three filaments, the cells of the cen- tral one having connected with both the others. production also is peculiar. Cells of two adjacent fila- ments put out protuberances toward one another; and where they come in contact an opening is formed, the result being that there is a continuous passageway connecting a cell of one filament with a cell of the other (Figs. 104 and 105). When many of the cells of two parallel filaments become thus united, the appearance is that of a ladder, with the filaments as the side pieces and the connecting tubes as the ALGJE 115 rounds. In each cell thus connected with another a single large gamete is formed, and one of them passes through the connecting tube to the other. The gametes are similar, and their fusion results in a heavy- walled oospore (Fig. 104, D), which endures through the winter and germinates during the following season. Plasmolysis. Spirogyra is a very favorable form for demonstrating plasmolysis, which means the shrinkage of protoplasm from loss of water. The cytoplasm of an active cell is full of water, which often col- lects in droplets of vary- ing size, called vacuoles. - There is always a layer of cytoplasm in close con- B tact with the cell-wall, but the interior of the cell may be one large vacuole traversed by strands of cytoplasm, as in Spirogyra. The turgor of the cell ( 64) keeps the elastic wall distended; but if the cell be put in a solution of sugar, water will be withdrawn. The vacuoles thus beginning to lose their water, the cytoplasm shrinks; and if the loss continues, the vacuoles are obliterated, and the layer of cytoplasm in contact with the wall separates from it, all the cytoplasm of the cell contracting into a compact mass (Fig. 106). The name plasmolysis really means the " loosen- ing" of the "plasma" (protoplasm) from the wall. Any- thing that withdraws water from a cell plasmolyzes it, and the filamentous Algae are favorable forms for experiments to show this. 70. Conclusions. The green Algae are so named because the green of the chloroplasts is neither modified nor obscured FIG. 106. Plasmolysis: A, a cell of Spirogyra before plasmolysis; B, the same cell after plasmolysis with a ten per cent solution of salt. 116 A TEXT-BOOK OF BOTANY by other colors, and tne plants have a characteristic grass- green color. As indicated by the illustrations given above, they include simple one-celled forms which reproduce only by cell-division (vegetative multiplication), .and simple or branching filamentous forms which also reproduce by swimming spores and cospores. Such filamentous forms as Ulothrix, Cladophora, and (Edogonium are representa- tives of a group known as the Conferva forms, having bodies of many cells and swimming spores. Vaucheria represents the large group of Siphon forms, characterized by their crenocytic bodies. Spirogyra represents the Con- jugate forms, the name meaning "yoked together," and referring to the connecting of the filaments for fertilization; the group is characterized also by the absence of swimming spores and the peculiar chloroplasts, not all of which are spiral bands. The bodies of green Algae are not all single cells or filaments, the marine sea-lettuces, belonging with the Conferva forms, having broad, flat, leaf-like bodies that have suggested the common name. Some of the green Algae are associated with the blue-green Algae in the pol- lution of water reservoirs referred to in 62. 3. BROWN ALG.E (Phceophycece). 71. General characters. The two preceding groups are the most common Algae of the fresh waters, but the brown Algae are almost all of them marine. The association of a brown coloring matter with the chlorophyll has given name to the group, and the plant bodies display various shades of yellow, brown, or olive. In size the brown Algae range from forms that are microscopic to those that are hundreds of feet long. They belong chiefly to the colder waters of the globe, reaching their greatest development in the arctic and antarctic regions. The greatest displays of huge bodies 117 along our own coasts are to be found on the rocky shores of the North Atlantic and the North Pacific, the display on the latter coast being especially rich in forms. They are all anchored plants, the strong holdfasts and leathery bodies enabling them to live exposed to strong waves and cur- rents. The largest forms are the kelps (Laminarias), the general habit of body being a stem fastened to the rocks by a cluster FIG. 107. A common kelp, showing root- like holdfast, stalk, and blade. Alter SAUNDERS. of strong, root-like holdfasts, and ending in a blade-like expansion (Fig. 107). The giant kelps of the Pacific Coast are the most notable forms. One of these has a stem about FIG. 108. A kelp with very long and rope- like stem bearing numerous leaves. After BENNETT and MURRAY. as large as a clothes-line, reported as sometimes reaching a length of 900 feet, and bearing numerous leaves (Fig. 108). The bladder kelp has a very long flexible stem (120 to 150 us A TEXT-BOOK OF BOTANY feet) that swells at the end into a large globular float, to which are attached leaves often ten or twelve feet long (Fig. 109). The sea-palm has a thick erect stem that bears a crown of large drooping leaves (Fig. 110). FlG. 109. A bladder kelp. After POSTELS and RUPRECHT. Another group of brown Algae is represented .by the rock- weeds (called also wrack) and the gulfweeds. The former (mostly Fucus) cover the rocks between tide-marks, being ribbon-like forms repeatedly forking at the swollen tips ALG.E 119 and often bearing air-bladders to assist in floating (Fig. 111). The most complex body is that of the gulf weed (Sargassum), in which there are slender branching sterna FIG. 110. A sea-palm. After Ru- Fio. 111. Fragment of Fucut, showing PRECHT. forked branching, reproductive tips, and air-bladders. After LUERSSEN. bearing numerous leaves like ordinary foliage, and stalked air-bladders that resemble berries (Fig. 112). The gulf- weeds occur in warmer waters than do the other large forms, and are often torn from their anchorage and carried away from the coast by currents, collecting in the great sea eddies produced by oceanic currents and forming the so-called Sargasso seas. Some of the gulfweeds forming these masses 9 120 A TEXT-BOOK OF BOTANY of vegetation floating in mid-ocean continue to grow luxu- riantly, especially in warmer parts of the Atlantic. From the ashes of kelps and rockweeds the chief supply of iodine is obtained; and these great masses of vegetation, FIG. 112. Fragment of Sargassum, showing differentiation of the thallus into stem-like and leaf-like portions, and also the bladder-like floats. After BENNETT and MURRAY. thrown up or left exposed by the tides, are used for enriching farm lands. 72. Ectocarpus. The two principal groups of brown Algae are distinguished from each other by their re- production. By far the larger group includes the kelps, whose method of reproduction is very simple, although many ALG^E 121 of their bodies are huge. Ectocarpus may be used to illustrate the essential features of the group. Its body is filamentous (Fig. 113), suggesting the body of some of the Conferva forms among the green Algae. Certain cells of the filament (Fig. 113, A), or the end cells of special short branches, become enlarged and produce numerous swimming spores. The swim- ming spores of brown Algae are peculiar in usu- ally bearing the two cilia on one side of the body rather than at one end, and hence they are described as laterally bicili- ate (Fig. 115, G). The cell that produces swimming spores was sometimes spoken of among the green Algae as a mother- cell, but a mother-cell may not al- ways produce spores. Hence it is well to use ~ a term that implies the product of the mother- cell, and in this case the term is sporangium (spore-case). A sporan- gium, therefore, is an or- gan that produces spores; and among the Algae de- scribed thus far it con- sists of one cell. In addition to the one- celled sporangia, other organs in similar posi- tions may occur; but they differ from the spo- rangia in being many-celled (Fig. 113, B). In -each cell usually one body is formed, which when discharged is seen B FIG. 113. Ectocarpus: a filamentous, branch- ing form: A. filament bearing one-celled sporangia (); B, filament bearing many- celled gametangia (#). 122 A TEXT-BOOK OF BOTANY to resemble the swimming spores. However, it fuses with another cell of the same kind, and this behavior and the result show that it is a gamete. As a result of this act of fertilization an oospore is formed, as in the case of Ulothrix ( 65). This kind of sexual reproduction is regarded as simple because the pairing gametes are alike, and have not become distinguished as egg and sperm, as in (Edogonium ( 67) and Vaucheria ( 68). In those plants separate names were given to the organs producing eggs (oogonia) and those producing sperms (antheridia). In Ulothrix and Ectocarpus, on the other hand, no such distinction can be made, and hence the organ producing gametes is called a gametangium (gamete-case). Of course oogonia and an- theridia are gametangia, but the latter name is generally used only when the gametes are alike. In Ectocarpus, therefore, many-celled gametan- gia are produced (Fig. 113, B), in addition to one - celled sporangia (Fig. 113, A). This great group of brown Algae, of which Ectocarpus is here used as a representative, is distinguished, there- fore, by its swimming spores and its similar gametes. 73. Fucus. The smaller group of brown Algae comprises the rockweeds (Fucus) and the gulf weeds (Sargassum), the former of which may be used to illustrate the group. 7U- FIG. 114. Fucus: showing a section of the cavity (conceptacle) containing the sex-organs, in this case only oogonia. After THURETO ALG.E 123 In the swollen and forked tips (Fig. Ill) of the rib- bon-like body of Fucus numerous flask-shaped cavities oc- cur, each of which communicates with the surface by a FIG. 115. Fucus: showing eggs in the oogonium (A) and after discharge (E), anther- idium containing sperms (C), the discharged laterally biciliate sperms (G),aud eggs surrounded by swarming sperms (F and H). After STRASBUHGER. 124: A TEXT-BOOK OF BOTANY small, pore-like opening (Fig. 114). On the walls of these cavities oogonia and antheridia are produced. The oogo- nium is peculiar in that it usually produces eight eggs, which are discharged and float free in the water (Fig. 115, A and E). About these eggs the sperms swim in great numbers, often striking against them and setting them rotating (Fig. 115, F and H). Finally, a single sperm fuses with an egg and an oospore is formed, which later produces a new Fucus plant. This group of brown Alga3, therefore, differs from the other one in producing no swimming spores, and in its dissimilar gametes (eggs and sperms). 4. RED ALG.E (Rhodophycece) . 74. General characters. The red Algae are mostly marine forms, and receive their name from the fact that FIG. 116. One of the red Algae. a red coloring matter completely masks the chlorophyll. As a consequence, the plants are various shades of red, ALGJE 125 violet, dark purple, and reddish-brown, often beautifully tinted. In general, the bodies are much more graceful and delicate than those of the brown Algae. There is the FIG. 117. One of the red Algae. greatest variety of forms, branching filaments, ribbons, and filmy plates prevailing; and often profuse branching occurs, the plants resembling mosses of delicate texture (Figs. 116 and 117). One remarkable group, chiefly displayed on tropical and surf-beaten coasts, contains such a deposit of lime in the cell-walls that the forms resemble branching corals or coral-like incrustations; and for this reason they are called corallines. Red Algae are all anchored forms, and are chiefly dis- played in temperate and tropical waters. While not re- 126 A TEXT-BOOK OF BOTANY stricted to any special depth, they are characteristic of the deeper waters in which Algae grow. The red Algae are very little used by man, probably the most conspicuous article of commerce obtained from them being Irish moss, used in jelly-like preparations, which is the dried bodies of certain forms abundant in the North Sea. 75. Reproduction. The reproduction of the red Algae is very peculiar, being entirely unlike that of the other Algae. No swimming spores are produced, but sporan- gia occur that produce and discharge spores without cilia and hence without the ability to swim. Since each sporangium usually pro- duces four such spores, they are called tetraspores (Fig. 118). Floating about in the water instead of actively swimming, they FIG. 118. The sporangium (.4) and dis- finally germinate and pro- charged tetraspores (B) of one of the , , 1,1 redAi ge .-AfterTHURET. duce new plants, as do the swimming spores, The sexual reproduction, however, is most remarkable, but is too complex to be presented in any detail in an elementary text. The sperms, like the tetraspores, are without cilia and simply float into contact with the oogo- nium, whose form is like that of a flask with a long narrow neck (Fig. 119, A). In the bulbous base of the oogonium the egg is developed. In a very simple ease the floating sperm comes in contact with the long neck, the two walls become perforated at the point of contact, the contents of the sperm enters and passes to the egg, and thus fertili- zation is accomplished. As a result of fertilization there appears on the plant a spore-containing structure like a B ALG^E 127 little fruit (Fig. 119, B and C, and Fig. 120). The spores it contains produce the alga plants again. Such a life-history is more complex than any thus far given. During the growing season the tetraspores multiply the plant; and the life-history may be indicated as follows, P designating the ordinary plant body : P tetraspore P tetraspore P tetraspore, etc. Such a series, however, does not continue indefinitely; for it is stopped by the coming of an unfavorable period, such a period as winter represents to many plants. In the life-history of our red alga this unfavorable period is bridged by the fruit-like body, just as in the other Algae it is bridged by the heavy- walled oospore. Such FIG. 119. One of the red Algae: A, sexual branches, showing antheridia (a), odgonium (o) with its long neck (0 to which are attached two sperms (); B and C, development of the fruit-like body. After KNY. Fio. 120. A branch of one of the red Algae showing a mature fruit-ljke body (e), with escaping spores (a). 128 A TEXT-BOOK OF BOTANY a life-history may be indicated as follows, a formula in which the fruit-like body is designated by F: P\ - Spera >-spore-P j - Sperm >-spore-P,etc. I egg / I -egg / The formula shows an alternation of the ordinary plant body and the fruit-like body; the latter always resulting from the act of fertilization, and the former coming from an asexual spore. This alternation becomes a conspicuous feature of higher plants. CHAPTER VII FUNOI ^ 76. General characters. The Fungi do not contain chlorophyll, and this fact forms the sharpest contrast be- tween them and the Algae. The presence of chlorophyll enables the Alga3 to be independent of any other organism, since they can manufacture their food out of carbon dioxide and water ( 14). The absence of chlorophyll compels the Fungi to be dependent upon other organisms for their food. This food is obtained in two general ways: either (1) directly from living plants and animals, or (2) from organic waste products or dead bodies. In case a living body is attacked, the attacking fungus is called a parasite; and the plant or animal attacked, the host. In case the food is obtained in the other way, the fungus is called a sapro- phyte. For example, the rust that attacks wheat is a parasite, and the wheat is the host; while the mold which often develops on stale bread is a saprophyte. In case parasites attack valuable plants or animals they may be very harmful, giving rise to destructive diseases. The United States Government has expended a great deal of money in studying such Fungi, trying to discover some method of destroying them or of preventing their attacks. There is an interesting selective power exhibited by many parasites, that restrict themselves to certain plants and animals, or even to certain organs. Many, however, are more general in their attacks; and some can live as para- sites or saprophytes as occasion demands. It must not be 129 130 A TEXT-BOOK OF BOTANY supposed that all parasites are harmful to man or even destructive to their host. In the case of saprophytes, dead bodies or body products are attacked, and sooner or later all organic matter is attacked and decomposed by them. Were it not for them "the whole surface of the earth would be covered with a thick deposit of the animal and plant remains of the past thousands of years.'' The parasitic andsaprophytic habits are not restricted to the Fungi, for they have been developed also by some of the higher plants; but by far the largest display of these habits is that given by the Fungi. It is thought that Fungi have been derived from Algae; that is, that Fungi are simply Algse that have learned the parasitic or saprophytic habit. Some of them resemble certain Algse so closely that the connection seems very plain; but others have become so modified that they have lost all likeness to the Algse. No attempt will be made to present even an outline of the classification of this vast and perplexing group. A few illustrations will be seized from the best-known forms, especially those of importance to man. 77. Bacteria. Bacteria include the smallest known living forms, some of which are spherical cells only 5 > 1 inch in diameter. It is estimated that 1,500 of certain rod-shaped forms, placed end to end, would about stretch across the head of an ordinary pin. Even to distinguish ordinary bacteria, therefore, the highest powers of the microscope are necessary; and to study them is too difficult for the untrained student. However, they are so very im- portant to man, on account of their useful and destructive operations, that every student should have some informa- tion about them. Public attention has been drawn to them chiefly on account of the part they play in many infectious diseases, in which connection they are often referred to as "microbes" or "germs." FUNGI 131 Bacteria are found almost everywhere in the air, in the water, in the soil, in most foods, and in the bodies of plants and animals, as regular inhabitants. Many of them are entirely harmless, some are useful, and others are very dangerous. A laboratory near Paris, arranged for studying bacteria in the air, has found that the average number of bacteria in every quart of air in that locality is eighty. The highest numbers were found during the autumn, and the lowest during the winter; while a wind from the city increased the numbers very much. The "pure" water of springs and wells contains abundant bacteria, while in stagnant water and sewer water they swarm in immense numbers. The slimy deposits usually observed about "iron" and "sulphur" springs, or in the pipes leading from them, are due to the presence of the peculiar bacteria liv- ing in such waters. The presence of dangerous bacteria in drinking water is probably the most common cause of epidemics of infectious diseases, and warnings as to the dangerous condition of a city water-supply should always be heeded. It is very evident that no sewage should find its way into such water-supply. It is important to know something about the structure and the habits of bacteria, before considering some of their important relations to man. They are one-celled and occur in three general forms: (1) spherical cells, usually grouped in various ways, and including the minutest forms (Fig. 121, B}} (2) rod-shaped cells, that is, longer than broad, the cells remaining separate or attached end to end and forming filaments (Fig. 121, F and <7);(3) elongated cells, more or less curved, from short curved forms resem- bling a comma to long spirals (Fig. 121, J-Af). Many bacteria swim more or less actively by means of cilia; and this fact first gave the impression that they are minute animals an impression that is still prevalent outside of laboratories (Fig. 121). A TEXT-BOOK OF BOTANY Reproduction is by cell-division, as among the blue- green Algae ( 58-60), a group which the bacteria resemble FIG. 121. A group of bacteria of various kinds, mostly ciliated; F is the bac- terium of typhoid fever, and H that of cholera. After EXGLER and PRAXTL. in many ways. This cell-division is remarkably rapid in bacteria, resulting in such a prodigious multiplication of in- FUNGI 133 dividuals in a comparatively short time that it is impossible to imagine what would happen if bacteria were left free to reproduce to their full capacity. Bacteria have been observed to reproduce themselves in fifteen to forty minutes after their formation; that is, a single generation of such bacteria is that length of time. It would be interesting to determine the number of progeny from a single bacterium at the end of twenty-four hours, if such a rate were main- tained. When nutrition fails, many bacteria have the power of passing into a protected condition, a portion of the protoplasm within the cell separating from the rest and becoming surrounded by a thick membrane (Fig. 122). The rest of the cell finally disorganizes and this internally formed cell persists. It has received the name of "spore/* but is not to be regarded as a spore in the usual sense. A single bacterium produces only one such spore, and when this spore again encounters favorable conditions it produces in turn only a single bacterium. This "spore," therefore, is only an inactive and protected condition of the bacterium. It is of great importance to determine the power of resistance of bacteria and of their more resistant "spores," and there is great variation in this regard. Drying and cold kill many, but not all. For example, it is known that the bacterium of typhoid fever (Fig. 121, F) can endure freezing in a block of ice for months and become active again when the ice melts; and for this reason the source of ice used in drinking water should be considered as carefully as the source of the water itself. Moist heat, however, as boiling or steaming, has been found to be most efficient in killing bacteria; and so the boiling of water and the cooking of food are usually ample safeguards against them. The so-called disinfectants are chemicals that destroy bacteria. It is the knowledge of such facts that has developed what is called antiseptic surgery, which is the use of various means to exclude bacteria and so prevent inflammation and decay. 134 A TEXT-BOOK OF BOTANY The most important relations of bacteria to man may be grouped under the following three heads: (1) those that induce fermentation; (2) those that induce disease; (3) and those that fix nitrogen. (1) Bacteria that induce fermentation. In general, fer- mentation is the decomposition of carbohydrates and proteids by the action of living forms directly or by the enzymes ( 47) which they produce, and conspicuous among these forms are bacteria. When proteids (meat, etc.) con- taining nitrogen and sulphur are decomposed in this way, offensive gases are liberated, such decomposition being often called putrefaction. When the word fermentation is ordinarily used it refers to the decomposition of sugars in A B C FIG. 122. Certain bacteria of fermentation and disease: bacteria of souring milk (A), of vinegar (B), of diphtheria (C), of tetanus or lockjaw (Z>); C and D show the formation of the so-called " spore." After FISCHER. solution, as in various fruit juices, which breaks them up into alcohol and carbon dioxide, the latter rising as bubbles through the solution, which is then said to be working. Such fermentations are produced chiefly by yeasts, which are considered in the next section; but bacteria are con- cerned in the souring of milk and of fruit juices and in the manufacture of vinegar (Fig. 122). These saprophytic bacteria that induce fermentation and putrefaction are of much service as scavengers, being the chief agents in the destruction of dead bodies. The various processes for FUXGI 135 preserving food are attempts to exclude bacteria that would induce fermentation or decay. (2) Bacteria that induce disease. Fortunately most bacteria are harmless, for they are constantly present in the nostrils and mouth and alimentary tract. Even those that are dangerous may be resisted successfully and fail to develop any symptoms of disease. When the resistance has been ineffectual and the disease has developed, the bacteria may produce local effects, as in diphtheria (Fig. 122, C) and in typhoid fever (Fig. 121, F); but the most general effect is from the production of poisons (toxins) which are distributed by the blood, leading to fever, de- lirium, etc. These poisons are different for each disease, so that a successful antidote (antitoxin) for the diphtheria poison has no effect on the poison of the bacterium of typhoid fever. It is hoped that antitoxins will be discov- ered for all such bacterial diseases, among which are not only diphtheria and typhoid fever, but also cholera (Fig. 121, //), tuberculosis, and pneumonia. Such eruptive dis- eases as measles and scarlet fever have not yet been proved to be due to bacteria. Among plants also certain bacterial diseases occasion great loss, as pear blight and peach yel- lows, and as yet have baffled those seeking for remedies. (3) Bacteria that fix nitrogen. It will be remembered that green plants manufacture carbohydrates from carbon dioxide and water ( 14); but that in the manufacture of proteids from carbohydrates nitrogen is necessary. Al- though free nitrogen constitutes nearly eight-tenths of the air, plants cannot use it in that form, but must obtain it through their roots from certain compounds existing in the soil. As crops are removed, the nitrogen supply in the soil is diminished, and presently the soil becomes so impover- ished that it is said to be exhausted. To restore the fertility of the soil, the farmer has learned to use nitrogen- containing fertilizers. Through the removal of crops and 10 136 A TEXT-BOOK OF BOTANY in various other ways the loss of available nitrogen for plants is enormous; and to meet this loss is one of the most important problems, for the known sources of suitable fertilizers cannot yield them for very many years. Since an endless supply of free nitrogen exists in the air, it is natural to turn to this source of nitrogen supply for plants. This means that the free nitrogen of the air must be "fixed " in some combination that can be used by plants. It is just here that bacteria of the soil play a very important part. Not only do those bacteria that produce fermenta- tion and decay lay hold of plant and animal bodies and produce the necessary nitrogen-containing substances in the soil, but certain other bacteria of the soil have the power of fixing the free nitrogen of the air into compounds, and hence they are called "nitrogen-fixing bacteria." If worn-out land lies fallow for a few years there will be a slow accumulation of nitrogen salts through the activity of these bacteria. They have been cultivated artificially, and it is hoped that such cultures will be obtained that it may be possible to use them to inoculate impoverished land with nitrogen-fixing bacteria and so hasten its restoration. A peculiar group of soil bacteria penetrates the roots of certain leguminous plants, as clover, alfalfa, peas, beans, etc., and produces little wart-like outgrowths known as root-tubercles (Fig. 123). The cells of the tubercles swarm with bacteria, which are found to have the power of fixing the free nitrogen of the air circulating in the soil. As a con- sequence, such plants can live and thrive in a soil exhausted of its nitrogen salts, and can be used in restoring the soil. After an ordinary crop, such as wheat, has exhausted the soil, a crop of clover or of alfalfa plowed under will restore such an amount of nitrogen salts to the soil that it can be used again for wheat, often with a surprising yield. This indicates the significance of what is called rotation of crops. It is a very interesting and important fact that these FUNGI 137 root-tubercle bacteria have been cultivated artificially at the United States Department of Agriculture in such a way r FIG. 123. Root-tuber feet clover. that they can be shipped anywhere at small cost and used to inoculate soils that are deficient in tubercle-forming bac- teria. This deficiency may be discovered either by the ab- 138 A TEXT-BOOK OF BOTANY sence of tubercles on the roots of leguminous plants or by the failure of such plants to grow at all. 78. Yeasts. Yeasts are one-celled plants that reproduce by budding. This curious method consists in a cell's putting out one or more projections which gradually enlarge and finally become pinched off. Often the cells thus pro- duced cling together in short irregu- lar chains (Fig. 124). The chief in- terest in connection with yeasts is the important part they play in the fermentation of sugar solutions, " split- ting" the sugar into alcohol and car- bon dioxide, a process also induced by certain bacteria ( 77), but chiefly by the yeasts. Fermentation by yeasts FIG. 124. Yeast-ceils, re- is employed on a large scale in the producing by budding, manufacture of beer, wine, and spirits. and forming chains. * and in the making of bread. In the last-named process, the dough is inoculated with yeast plants and placed in a sufficiently warm temperature to induce rapid growth. The plants begin to reproduce act- ively by budding; the sugar in the dough is split into alcohol and carbon dioxide ; and the latter, being a gas, ex- pands and puffs up the dough, making it light and porous, that is, causing it to "rise." The yeasts commonly used have been cultivated for centuries and are not known in the wild state. There are also "wild yeasts" of many kinds, and many spores of the higher Fungi behave like the yeasts in budding and induc- ing fermentation. The " working " of yeast may be demon- strated by introducing some of the yeast preparations into a solution of sugar or sirup and setting it in a warm place. After a few hours the bubbles of carbon dioxide should be seen rising through the liquid. FUNGI 139 79. Mucor. One of the most common of the Mucors, or black molds, forms white furry growths on damp bread, preserved fruits, manure heaps, etc. It may be grown easily FIG. 125. Diagram of Mucor, showing the profusely branching mycelium and three sporophores, sporangia forming on b and c. After ZOPF. FIG. 126. Diagram showing mycelium and sporophores of Mucor. 140 A TEXT-BOOK OF BOTANY B FIG. 127. Developing sporangia of Mucor: A, swollen tip of sporophore; B, wall separating sporangium from the rest of the body. by keeping a piece of moist bread in a warm room un- der a glass vessel. The sources of its food supply indicate that it is a sapro- phyte. The body of Mucor is a good illustration of the bodies of ordinary Fungi. The principal part of the body consists of colorless branching threads, either isolated or more often in- terwoven, and is called the mycelium (Fig. 125). The interweaving may be very loose, the mycelium look- ing like a delicate cobweb; or it may be close and FIG. 128. Mature sporangium of Mucor, showing wall (a), numerous spores (c), and partition wall pushed up into the cavity of the sporangium (6). FIG. 129. Burst sporangium of Mucor, the ruptured wall not being shown, the loose spores adhering to the con- vex partition wall (see Fig. 128). FUNGI compact, forming a felt-like mass, as may be seen some- times in connection with preserved fruits. The mycelium is in contact with its source of food-supply, which is called the substratum. From the prostrate mycelium numerous erect branches arise, each branch bearing at its tip a large globular cell FIG. 130. Sexual reproduction ol Mucar, showing tips of sexual branches in con- tact (A), the two gametangia cut off by partition walls (B), and the heavy- walled oospore (C); B and C are more or less diagrammatic as to cell contents. containing spores (Figs. 126, 127, 128). The globular cell, therefore, is a sporangium, and the erect branch is a sporo- phore (spore-bearer). The sporangium wall bursts (Fig. 129), the light spores are scattered by the wind, and fall- 1*2 A TEXT-BOOK OF BOTANY ing upon a suitable substratum germinate and produce new mycelia. These spores, although asexual, are evidently not swimming spores, as there is no w r ater medium for them to use. This method of transfer being impossible, the spores are scattered by currents of air, and must be correspond- ingly light and powdery. It is interesting to note that cer- tain molds that grow in the water develop swimming spores. While the ordinary method of reproduction through the growing season is by means of these rapidly germinating spores, in certain conditions sexual reproduction also occurs. Branches put forth from two contiguous mycelial threads, the tips of the branches being in contact (Fig. 130, A). Partition walls separate the tips from the main body of the plant (Fig. 130, B}, the walls in contact become perforated, the contents of the two tips fuse, and a heavy-walled oospore is the result (Fig. 130, C).* This sexual process suggests that of Spirogyra ( 69). 80. Peronospora. These are the downy mildews, very common parasites on the leaves of seed-plants. The mycelium is entire- ly internal, branch- ing among the tis- sues of the leaf, and piercing the living cells with sucker-like branches that rap- idly absorb their contents (Fig. 131). The presence of the parasite is made known by discolored and finally deadened spots on the leaves, where the tissues have been killed. * It is not easy to induce Mucor to perform the sexual process, and in fact such a process may not often occur in nature. FIG. 131. Branch of mycelium of Peronospora in contact with two cells of a host plant, and send- ing into them absorbing branches. After DE BARY. FUNGI From this internal mycelium numerous sporophores arise and reach the surface of the leaf; and many of them rising above the surface close together, they form little velvety patches sug- gesting the name downy mildew. These sporophores, after rising above the surface of the leaf, branch freely and produce spores (Fig. 132). The spores are scattered by the wind, fall upon other leaves, and start new my- celiu, which penetrate into the tissues of the leaf and begin their ravages. In this way the parasite spreads with great rapidity, often producing seri- ous epidemics among plants. In certain conditions special branch- es arise from the mycelium which bear antheridia and oogonia that remain within the host (Fig. 133). The oogo- nium develops a single egg. The an- theridium comes into contact with it, puts out a tube that pierces the oogo- nium wall, and discharges its contents (Fig. 133, B). As a result of this act FIG. 132. Sporophores of a Peronospara form ris- ing through the stomata of the host-leaf (potato), branching, and bear- ing spores; this form causes potato-rot. Aft- er STRASBURGER. B FIG. 133. Peronospora: A, oogonium (o) with antheridium (a) in contact; B, tube from antheridium penetrating oogonium; C, oogonium containing oospore. After DEBARY. 144 A TEXT-BOOK OP BOTANY of fertilization, a heavy- walled oospore is formed within the oogonium (Fig. 133, C). The infected leaves containing the oospores fall and gradually decay, thus liberating the oospores, which are free to germinate during the next spring and infect new leaves. The downy mildews include some very destructive par- asites, attacking potatoes (potato-rot), grape-vines, lima beans, lettuce, onions, cucumbers, melons, radishes, etc. Various means have been discovered for holding these dis- eases in check. 81. Alga-like Fungi. Mucor and Peronospora are repre- sentatives of a large group (Phycomycetes) of Fungi that most resemble Alga3, and suggest clearly that they are Algae that have become parasitic or saprophytic. In the whole group the filaments of the mycelium are coenocytic, as are the bodies of the group of green Algse to which Vaucheria belongs ( 68). They reproduce by spores, which are usu- ally scattered by the wind, and also produce oospores. Some of them, represented by Mucor, have similar gametes, that are brought together in a way that suggests the Spiro- gyra group among the green Algae ( 69) ; while the others, represented by Peronospora, produce eggs and sperms, as in the case of Vaucheria, though, since there is no water connection, the sperm reaches the egg through a tube. Mucor also illustrates the saprophytes, and Peronospora the internal and destructive parasites. 82. Mildews. The true mildews are very common parasites on leaves and other parts of seed-plants, the mycelium spreading over the surface like a cobweb. They are often called powdery mildews in contrast with the downy mildews ( 80), since in most cases they look like patches of whitish powder on the leaves. A very com- mon form occurs on lilac leaves (Fig. 134), which nearly always show the whitish patches from early summer until fall. Other common mildews attack such valuable plants FUNGI 145 as apple, pear, cherry, rose, hop, grape, wheat, gooseberry, cucumber, pea, verbena, sunflower, aster, etc. In fact, very few seed-plants seem to escape their attacks. Being exter- nal parasites, mildews are not necessarily destructive ; but they often cause the death of the host. An examination of the my- celium shows that its filaments have partition walls; and hence the body is not coenocytic, as in Mucor and Peronospora, but made up of a row of cells as in the Conferva forms among the green Algae. Small disk-like outgrowths are sent into the epidermal cells of the host, anchoring the mycelium and absorbing the cell contents. During the summer, numer- ous sporophores arise from the mycelium, not bearing sporan- gia, as in Mucor ( 79), but forming spores in a peculiar way. The end of the sporophore rounds off, almost separat- ing itself from the part below, and becomes a spore. Below this another organizes in the same way, then another, until a chain of spores is developed (Fig. 135, A), easily broken apart and scattered by the wind. Falling upon other suit- able leaves, these spores germinate and produce new my- celia, enabling the parasite to spread with great rapidity. The mycelium produces also minute antheridia and oogonia, which come in contact with one another as do those of Peronospora ( 80), but it is not worth while for the untrained student to try to observe them. As a result of FIG. 134. Lilac leaf covered -with mildew, the shaded regions repre- senting the mycelium, and the black dots the spore-cases. 146 A TEXT-BOOK OF BOTANY fertilization, however, a structure called the spore-fruit is developed. These spore-fruits appear on infected leaves as minute dark dots (Fig. 134), each one being a sphere of heavy- walled cells (Fig. 135, B), which usually bear hair- like appendages of various forms. In fact, the spore- fruit is a heavy protecting case for spores, and carries mildews through the winter or the dry season. The ap- pearance of a many-celled spore-case as the result of fertilization, rather than a new mycelium, suggests the similar result of fertilization among the red Algse ( 75). By bursting the wall of this Spore-fruit, One Or more jv uiJJ vi delicate bladder-like SaCS are FIG. 135. Reproduction of mildew: A, chain of spores developed by a sporophore; B, spore-case burst, and showing the extruded sac extruded, and through the (ascus) with its spores. After TULASNE. transparent wall of each sac several spoies may be seen (Fig. 135, B). The delicate sacs are called asci (singular, ascus), & word meaning "sacs," and hence the great group of Fungi represented here by the mildews is named the Ascomycetes, which means "sac Fungi." In the life-history of the mildews it is evident that there are two kinds of asexual spores: those produced in chains by the sporophores, and those produced in the sacs of the spore-fruit. Both produce new mycelia, the latter starting the first mycelia of the growing season, and the former multiplying mycelia throughout the growing season. 83. Other Sac Fungi. The group of sac Fungi is a very large one, containing many forms that are well known and FUNGI some that are important. All of them, at some period of the life-history, produce spores in sacs, and the sacs are usually contained in a spore- fruit. The spore-fruit is of three general kinds: (1) a hollow sphere, completely enclosing the sacs; (2) a flask-like structure with a small open neck; and (3) a cup-like or saucer-like structure which is lined by a layer of sacs. The first kind of spore-fruit is illustrated by the mildews just described. It is of interest to know that truffles are such closed spore-fruits, having be- come large and edible. The truffle Fungi are saprophytic, the mycelium being found espe- cially in forests under decaying leaves. The truffles of commerce are obtained chiefly from France and Italy. The sac Fungi with flask-like spore-fruits are illustrated by many forms growing on dead wood or as parasites under the bark of trees and shrubs, and forming upon the surface of the bark black, wart-like growths that include the spore-fruits, in plum- and cherry-trees produc- ing the disease known as black knot. An important member of this group is the fungus that produces the ergot of medi- cine. It is parasitic upon the young heads of rye and FIG. 136. Head of rye attacked by ergot fungus, conspicuous growths replacing the grains of rye. After TULASNE. 14S A TEXT-BOOK OP BOTANY other grasses, distorting them and producing the excrescent growths from which the ergot is obtained (Fig. 136). FIG. 137. Two kinds of cup-fungus. After LINDAU. Flo. 138. A cup-fungus growing on a spruce. After RKHM. Most attractive, however, is the group of sac Fungi with spore-fruits shaped like saucers, cups, funnels, flat disks, etc.; for the lining, made up of a layer of the spore - containing sacs, is often some brilliant shade of red, yellow, or brown (Figs. 137 and 138). The scarlet-lined cups of certain forms are often seen on decaying logs, stumps, etc.; and in the morels the spore-fruits get so large and fleshy that they are used as one of the most delicate of the edible mushrooms, although they FIG. 139. The common edible morel, the depressions in the surface being lined by a layer of asci. After GIBSON. are not mushrooms at all (Fig. 139). FUNGI 1 '. 84. Rusts. Rusts are destructive parasites that attack almost all seed-plants, but those that attack the cereals arc of -perial importance. Wheat, oats, rye, and barley all have their rusts; and in the United States there is a yearly loss of several million dollars on account of the ravnu' < >f the wheat -rust alone, scarcely a field being en- tirely free from the pest. Naturally these parasites have been investigated persistently; but while very much has been learned about their life-histories and behavior, no remedy has been discovered. It has been found that certain varieties of wheat resist the rust better than others, and that varieties ripening early escape serious injury; and these facts may lead to the breeding of resistant and early races. The life-history of a rust is usually very complex, since there are several phases in the history, and all the phases may not occur on the same host plant. Since wheat-rusts are better known than any other, one of them may be used to illus- trate the life-history. While the leaves and the stems of wheat are growing, tn(l mycelium of the parasite is burrowing among the tissues of infected plants. About the time of harvest, numerous sporo- phores arise from the mycelium and reach the surface of leaves and st.-tns, each sporophore producing at its tip a reddish spore (Fig. 140). These are the summer spores, and they occur in such great numbers that they form rusty-looking lines and spots, giving name to the disease. The summer spores are scat- tered freely by the wind; and those falling upon other plants germinate immediately, the new mycelium pene- trating the host plant, and lie^inning its ravages. By Fio. 140. The summer spores of wheat-rust. 150 A TEXT-BOOK OF BOTANY FIG. 141. The winter spores of wheat-rust. means of these summer spores the rust may spread through a field of wheat and into adjoining fields with great rapidity. Later in the season, on the stubble and on plants not removed in the har- vesting, black lines and dots appear, which are masses of a very different kind of spore sent to the surface by the myce- lium (Fig. 141). This spore, which is two- celled and has a very heavy wall, is the winter spore; for it is in this form that the rust usually endures the winter. In the spring the winter spores, lying where the plants on which they were produced have decayed, begin to ger- minate, each one of the two cells send- ing out a short filament. This filament is not a parasite, but a saprophyte, and usually consists of four cells, each one of which sends out a little branch, at the tip of which a small spore is pro- duced (Fig. 142). These may be called early spring spores. These early spring spores are scat- tered by the wind; and those falling upon barberry leaves germinate, the new mycelia entering and spreading through the leaves. In this phase the rust is parasitic upon an entirely dif- ferent host, and one that holds no relation to wheat. The mycelium in the barberry leaves sends to the leaf surface, FIG. 142. A winter spore of wheat - rust germinating, each fila- ment producing four cells, each of which sends out 'a branch that produces at its tip a spore (early spring spore). After Tu- LASNE. FUNGI 151 Fio. 143. A cluster-cup (on barberry) of wheat-rust containing chains of spring spores. After STRAS- BURGER. usually the under one, groups of sporophores, each group surrounded by a cup-like structure; and hence these cup- like clusters have been called cluster-cups. In these cluster- cups the spores oc- cur in long chains, and may be called spring spores or clus- ter-cup spores (Fig. 143). These spring spores on the bar- berry leaves are scattered by the wind and infect young wheat plants; that is, germinate and produce myce- lia which penetrate them. These new mycelia later put forth the summer spores, and in this way the life cycle has returned to the point with which this account began. It will be noted that in this life-history there are four kinds of spores: (1) the early spring spores, produced by a simple saprophytic filament, and infecting barberry leaves; (2) the spring or cluster-cup spores, produced by a mycelium parasitic on the barberry, and infecting young wheat plants; (3) the summer spores, produced by a mycelium parasitic on wheat, and infecting other wheat plants; (4) the winter spores, produced by the same mycelium, and in spring producing the saprophytic filaments. In the United States the barberry is not widely distributed enough to play so important a part in the life-history of wheat-rust, and other seed-plants have been found to be used as hosts for the cluster-cup stage of certain forms of rust. It is also stated that the cluster-cup stage may be omitted, in that 11 152 A TEXT-BOOK OF BOTANY case the early spring spores infecting wheat plants rather than barberry leaves; and recently it has been shown that often the summer spores survive the severest winter and infect young wheat plants of the next season. Another well-known rust is that which attacks apple- trees and their relatives, the wild crab, hawthorn, etc. The stage on the apple-tree is the clus- ter-cup stage, the cluster-cups occurring on the under surface of the leaves; the mycelium also attacks and ruins the fruit, the cluster-cups being seen in connection with the diseased parts. The cluster-cup spores infect the cedars, producing swellings half an inch or more in diame- ter and known as cedar- apples (Fig. 144). In the spring these cedar-apples become conspicuous, espe- cially after a rain, when the jelly-like masses con- taining the orange-colored spores swell. These spores are blown about and in- fect the apples. Attempts are made to check the ap- ple-rust by destroying the cedar-trees and by spray- ing the apple-trees, when they are putting out their leaves, with a liquid that kills such Fungi. Although rusts possess several kinds of ordinary (asex- ual) spores, no oospores (sexually formed spores) have been observed; but a process in the life-history representing a sexual act has been discovered in some forms. FIG. 144. A cedar-apple. FUN(JI 153 85. Mushrooms. This name is a very indefinite one; sometimes applying to any of the fleshy Fungi of the umbrella form, and sometimes including among such forms only those that are edible, the poisonous ones being spoken of as toadstools. For our pur- pose, no exact definition of the word is necessary, it being used as the com- mon name of a group of forms with which the stu- dent should be somewhat familiar. The life-history of the Fio. 145. Mycelium of a mushroom produo- Ordinary edible mushroom ing sporophores (buttons) .After SACHS. FIG. 146. A common edible mushroom (Lepiota). 154: A TEXT-BOOK OF BOTANY of the markets will serve as an illustration. The myce- lium of white branching threads spreads extensively through the substratum of decaying organic material, and by those who grow mush- rooms is called spawn. This my- celium, although the least conspicu- ous part of the mushroom, is, of course, the real vegetative body. Upon this under- ground mycelium little knob-like pro- tuberances arise (buttons), growing larger and larger (Fig. 145) until they develop into the umbrella - like structures common- ly spoken of as mushrooms (Fig. 146). This um- brella-like struc- ture, however, cor- responds to the sporophores that arise from the my- celia of other groups of Fungi, except that it includes a large number of sporophores organized into a single large body. Therefore, the real mushroom body is a subterranean mycelium, upon which the struc- Fio. 147. Sections through the gills of a common mushroom: A, gills hanging from the pileus; B, single gill showing the basidium layer; C. much enlarged view, showing the basidia-bearing spores. After SACHS. FUNGI 155 tures commonly called mushrooms are the spore-bearing branches. In pulling up a mushroom, fragments of the mycelium may often be seen attached to it, looking like small rootlets. In the following description, however, the word mushroom will be used in its ordinary sense. The mushroom has a stalk-like portion (stipe} and an expanded umbrella-like top (pileus). On the under side of the pileus there are found thin, radiating, knife-blade-like plates (gills} (Fig. 147, A). The surface of the gills consists of a layer of peculiar club-shaped cells called basidia (Fig. 147, B). From the broad end of each basidium usually four delicate branches arise, each producing at its tip a minute spore (Fig. 147, C). The ripe spores shower down from the gill surfaces, germinate, and produce new mycelia. The most common edi- ble mushrooms grow in fields and pastures; but there are numerous mush- rooms in the deep woods, in fact wherever there is decaying organic material. It has been found impos- sible to give directions for distinguishing edible and poisonous forms that can be used by those who are not familiar with mushrooms. It is exceedingly unsafe for an inexperienced person to gather wild mushrooms for eat- ing, for some of the deadliest forms resemble in a general way those commonly eaten. The mushrooms with gills form a very large group, FIG. 148. A common pore-fungus. After GIBSON. 156 A TEXT-BOOK OF BOTANY but numerous forms display the spore-producing layer in other ways. For example, the pore Fungi are so named because they have pore-like depressions or tubes lined by the basidium-layer, instead of gills. In addition to umbrella- like forms among the pore Fungi (Fig. 148), there are the numerous bracket Fungi, which appear as hard hoof-like outgrowths on tree trunks (Fig. 149), stumps, etc. Some 149. A bracket-fungus (pore-fungus) growing on red oak. of these bracket Fungi are perennial, showing annual lay- ers of growth, as the common touchwood or punk. Other * mushrooms have the umbrella-like bodies, but instead of either gills or pores, there are spine-like processes coated by the spore-forming layer (Fig. 150); others appear as FUNGI 157 gelatinous, dark-brown, shell-shaped masses, resembling ears; still others resemble fleshy branching corals (Fig. 151), and hence are called coral Fungi. In general, mushrooms are harmless and often useful saprophytes, but there are also destructive parasitic forms FIG. 150. Mushroom with spine-like processes instead of gills. After GIBSON. Fio. 151. The common edible coral fungus. After GIBSON. that attack forest-trees. The mycelium usually spreads between the bark and the wood, sending special absorbing branches into the wood, often even into the heart wood, causing decay and weakening of the stem. The spore- bearing structures are sent to the surface, and appear as toadstools, bracket Fungi, etc. Spores are produced in great profusion and infect other trees, the new mycelium using wounds to effect its entrance. Some mycelia spread through the soil, inoculating trees through their roots; while 158 A TEXT-BOOK OF BOTANY in other cases the spores are scattered by the wind and the infection starts in the tree tops. Almost all full-grown trees are diseased at some point. 86. Puffballs. The puffballs are fleshy Fungi that differ from the mushrooms in having the spores enclosed until they are ripe (Fig. 152). There is a subterranean mycelium, as in the mush- rooms; but the spore- bearing structure is a fleshy, globular body, con- taining irregular cham- bers lined with the spore- producing layer. When young, this body is solid and white; but as the spores mature, it becomes yellowish and brownish, gradually dries up, and finally is only a brown parchment-like shell con- taining innumerable, ex- ceedingly small spores that are discharged by the breaking of the shell. Some of the puffballs become very large, reaching a diameter of twelve to eighteen inches. 87. The highest group of Fungi. The rusts, mushrooms, and puffballs represent the highest and most extensive group of Fungi, characterized by producing spores by means of a basidium, and hence called Basidiomycetes, which means "basidium Fungi." The peculiarity of the basidium is that it sends out branches, each of which produces a spore at its tip (Fig. 147, C). The layers of basidia (spore-pro- ducing cells) were noted in the mushrooms and the puff- FIG. 152. Puffballs. After GIBSON. FUNGI 159 balls: but it is thought that a basidium is represented also in the life-history of the rusts, and hence they are now included among the Basidiomycetes. This supposed ba- sidium of the rust is the little filament produced by the winter spore, which sends out branches that bear the small early spring spores ( 84). 88. Mycorhiza. This name means root-fungus, and refers to an association that exists between certain Fungi of the soil and the roots of higher plants. It was thought once that this association of fungus and root occurred only in connection with a limited number of higher plants, such as orchids, oaks, heath plants, etc.; but more recent study indicates that probably the large majority of vascular plants, that is, plants with true roots, have developed this relation to a soil fungus, the water-plants being excepted. It has been found that the humus soil of forests is in large part "a living mass of innumerable filamentous Fungi." It is of advantage to roots to relate themselves to this great network of filaments, which are already in the best relations for absorption; and those plants which are unable to do this are at a disadvantage in the competition for the nutrient materials of the forest soil. It is doubtful whether many vascular green plants can absorb from the soil enough for their needs with- out this assistance; and if this is true, the mycorhiza Fungi become FIG. 153. Mycorhiza : the tip of a beech rootlet enmeshed of vital importance in the nutri- by a soil fungus. After FRANK. tion of such plants. The delicate branching filaments of the mycelium either enwrap the rootlets with a jacket of interwoven threads (Fig. 153), or occur within the cortical cells of the root. 160 A TEXT-BOOK OF BOTANY 89. Lichens. Lichens are abundant everywhere, form- ing splotches of various colors on tree trunks, rocks, old FIG. 154. A common lichen growing on bark; the numerous dark disks are lined by a layer of asci. boards, etc., and growing also upon the ground (Figs. 154 and 155). They have a general greenish-gray color, but brighter colors also may be observed. The great interest connected with lichens is that they FIG. 155. A common foliose lichen growing upon a board. FUNGI 161 are not single plants, but that each lichen is formed of a fungus and an alga living together so inti- mately as to appear like a single plant. In other words, a lichen is not an individual but a firm of two individuals, very un- like one another. If a lichen be sectioned, the relation between the two constituent plants may be seen (Fig. 156). The fun- gus makes the bulk of the body with its interwoven mycelial threads, in the meshes of which lie the Algae, sometimes scattered, sometimes massed. It is these enmeshed Algae, showing through the transparent my- celium, that give the greenish tint to the lichen. Fio. 156. Cross-section of a lichen, show- ing the interwoven mycelium of the fungus (TO) and the enmeshed alga (g). After SACHS. Fio. 157. Section of one of the cup-like bodies of a lichen, showing the stalk of the cup (m), the masses of Algae (g), and the lining layer of asci (A). After SACHS. 162 A TEXT-BOOK OF BOTANY It has been found that the lichen-alga can live quite independently of the lichen-fungus. In fact, the enmeshed Algae are often recognized as identical with forms living independently, the forms usually being certain blue-green FIG. 158. Much enlarged section of portion of lining layer, showing the asci (1, 2, 3, 4) with their contained spores. After SACHS. Algae and some of the simpler green Algae. On the other hand, it has been found that the lichen-fungus is com- pletely dependent upon the Algae; for the germinating spores of the fungus do not develop far unless the young FUNGI 163 mycelium can lay hold of suitable Algae. Artificial lich- ens also have been made by bringing together wild Algae and lichen-fungi. Lichens, therefore, are really combina- tions of a parasitic fungus and its host, the parasitism being peculiar in that the host is not injured. The fungus lives upon the food made by the alga, and the relation suggested is that the alga is enslaved by the fungus. At certain times cup-like or disk-like bodies appear upon the surface of the lichen, with brown or black or more brightly colored lining (Fig. 154). A section through these FIG. 159. Fruticose lichens: -4, a simple form; B. reindeer moss; C, & common hanging lichen. A and B after STRASBURGER; C, after SACHS. bodies shows that the colored lining is largely made up of delicate sacs containing spores (Figs. 157 and 158). It is evident, therefore, that such a lichen-fungus is one of the Ascomycetes ( 82), and it is this group of Fungi that 164 A TEXT-BOOK OF BOTANY is chiefly concerned in forming lichens. Some Basidio- mycetes also have learned to form lichens. Various forms of lichens can be distinguished as fol- lows: (1) crustaceous lichens, in which the body resembles an incrustation upon its substratum of rock, soil, etc.; (2) foliose lichens, with flattened, leaf-like, lobed bodies, attached only at the middle or irregularly to the substra- tum (Fig. 155); (3) fruticose lichens, with slender bodies branching like shrubs, either erect, hanging, or prostrate (Fig. 159). Lichens are often very important in starting a humus formation on bare rocks and sterile soil. In such exposed situations Algae could not endure alone, and of course Fungi could not exist alone in any situation. The lichen combination can exist, however, since the fungus obtains its food from the Algae, while the latter are protected against drying out by the enveloping meshwork of the fungus. As the lichens grow and decay, enough humus is collected for higher forms of plant life to start; and these in turn con- tribute to a more rapid accumulation of humus, until presently a respectable soil may be the result. CHAPTER VIII LIVERWORTS 90. Summary. As an introduction to liverworts it is well to state the most important facts in reference to the Algse and Fungi. The Algae and Fungi together consti- tute the first great division of the plant kingdom, known as Thallophytes. The name means "thallus plants," and "thallus" means a body usually prostrate and having no special vegetative organs as leaves and roots. Such a definition cannot be very rigid, for some Algae cannot be said to have strictly thallus bodies, and in the higher groups thallus bodies also occur; but the name is a convenient one to apply to all plants below the liverworts. As the study of the higher plants is begun, the important progress made by the Thallophytes must be kept clearly in mind, for the liverworts start with this progress behind them. The important progress may be stated as follows: (1) Increasing complexity of the plant body. Beginning with single isolated cells, the plant body reaches con- siderable complexity among the Thallophytes, in the form of simple or branching filaments, plates of cells, and masses of cells. (2) Appearance of spores. Beginning with reproduction by vegetative multiplication, the Thallophytes soon develop special cells for reproduction (spores) , and produce them not only in abundance but in a variety of methods and forms. (3) Appearance of sexual cells. After ordinary spores appear, the Thalloph-ytes also introduce a third form of 165 166 A TEXT-BOOK OF BOTANY reproduction by producing sexual cells (gametes), which by fusing in pairs (fertilization) form oospores. At first the pairing gametes are alike, but later they become very different, and are called sperms and eggs. The organ pro- ducing sperms is called the antheridium, and that pro- ducing an egg the oogonium; and among the Thallophytes each of these organs consists of a single cell. (4) Algce the independent line. This means not only that the Fungi have probably been derived from the Alga? by losing the ability to make their own food, but also that the higher plants have been derived from the Algae. Accord- ingly the liverworts, about to be studied, are believed to have developed from the Algae. 91. General character of Liverworts. Liverworts are found in a variety of conditions, some floating, many in damp places, and many on the bark of trees. They seem to be plants that have barely learned to live on land, and this change from the water to the land is one of the greatest and most important in the history of plants. Although in general they are moisture-loving, some can endure great FIG. 160. Ricciocarpus: showing thallose body, forked branching, rhizoids on the under surface, and spore-cases along the main axes (showing position of archegonia). dryness, so that the land habit can be said to have become well-established among the liverworts. LIVERWORTS 167 The plant body is flat and compact, lying prostrate upon its substratum, and is often a thallus; that is, it shows no distinction of stem and leaves, the whole body appearing leaf-like (Fig. 160). The upper surface of the body is freely exposed to the light, but the lower surface is against the substratum and puts out hair-like processes (rhizoids) for anchorage. If the body is thin, all the cells contain chloroplasts; but if the body is so thick that the light cannot penetrate it, the under layers of cells are not green. 92. Marchantia. Marchantia is one of the most com- mon and conspicuous liverworts. The body is a thick chl FIG. 161. Marchantia, cross-section of thallus: showing lower epidermis (from which, in other parts of the thallus, rhizoids are developed), two layers of colorless cells (p), and one large air-chamber (, a, the bounding walls) contain- ing cells with chloroplasts (chl) and pierced by a chimney -like air-pore (p). After GOEBEL. thallus that forks repeatedly, giving the appearance of notches of greater or less depth (general habit as in Fig. 160). The central axis of the thallus, or of a branch, ends in the terminal notch, in the bottom of which, therefore, is the growing tip. The upper surface of the Marchantia body is blocked off into small rhombic areas, in the center of each one of which is a minute opening (Fig. 162). A section through this body shows its general structure (Fig. 161). Beginning with the lower side, there is seen first the layer of cells forming the epidermis, from which the rhizoids and certain other appendages arise; above this 12 168 A TEXT-BOOK OF BOTANY epidermis there are several layers of colorless cells; above these there is a series of large air-chambers into which project the curious cells containing the chloroplasts; and forming the dome-like roof of each air-chamber is the upper epidermis, pierced by a single air-pore in the center of the roof of each cham- ber. Each air-pore resembles a little chimney, built up with several tiers of cells. The rhombic areas seen on the surface of the body are the outlines of the air-chambers, and the minute open- ing in the center of each is the air-pore no. iv.-Marchantia: && 162 ) This arrangement of cells rhombic areas on up- containing chloroplasts exposed in air- ^rfTctou^iine^li"- chambers that communicate freely chambers), each one through pierced by an air- pore After SACHS, air-pores suggests the same general mechan- ism for plant work as that B described for leaves, with their internal atmosphere and stomata (13). A remarkable fact con- nected with the Marchantia body, as contrasted with that of the Thallophytes, is that it produces no spores. However, provi- sion for rapid multiplica- FIG 163 ,_ Marchantia: A , thallus bear- tion is made by the pro- ing little cups containing reproduc- , . tive bodies, and an antheridial branch auction ot peculiar repro- ^^ its d i sk) as we ii a s some very ductive bodies that are young antheridial branches; B, section through antheridial disk, showing the developed in little CUpS O11 sunken antheridia. After KNY. LIVERWORTS 169 the back of the thallus (Fig. 163). These bodies are round and flat (biscuit-shaped) and many-celled, and falling out of the cup they start new thallus bodies. Although the thallus body produces no spores, it does produce sex-organs. In Marchantia, long, erect, stem-like branches arise from the thallus, bearing at their summits conspicuous disks that contain the sex-organs. The disks containing antheridia are lobed or scalloped (Fig. 163); while those containing the egg-producing organs are star- shaped (Fig. 165). The two kinds of disks are not found on the same plant. 93. The antheridium. The sperm-producing organ is called an antheridium, but it is very different from the antheridia of the Thallophytes. Instead of be- ing a single cell, it is a stalked, club-shaped or globular, many- celled structure (Fig. 164). A single layer of cells forms the covering, and within it there is a closely packed mass of small cells, each one of which pro- duces a sperm. The sperm is a very small cell with two long cilia, and these small biciliate sperms are one of the distinguishing features of the liverworts and their allies. 94. The archegonium. The egg-producing organ is called the archegonium, and it is very different from the oogonium of the Thallophytes. Instead of being a single cell, it is a many-celled structure, shaped like a flask with a long neck, and within the bulbous base the single egg is formed (Fig. 165, B, and Fig. 166). To this neck the swimming sperms are attracted; they enter and pass down FIG. 164. Marchantia: antheridi- um and two sperms. After SACHS. 170 A TEXT-BOOK OF BOTANY it, one of them fuses with the egg, and an oospore is formed. It is evident that fertilization can take place only in the presence of moisture. A B FIG. 165. Marchantia: A, thallus bearing archegonial branches of various ages; B, section through portion of archegonial disk, showing pendant archegonia. After KNY. FIG. 166. Marchan- tia: archegonium, containing an egg; sperms seen at the mouth of the neck. After KNY. 95. The spore-case. it begins to germinate; B FIG. 167. Marchantia: A, spo- rophyte formed within the enlarged archegonium, show- ing the spore-bearing (a) and sterile (6) regions; B, spore- case discharging spores, the sterile region of the sporo- phyte having developed into a stalk. After KNY. As soon as the oospore is formed but instead of forming a new Mar- chantia thallus, it produces a very different structure. The oospore germinates just where it was formed, that is, in the bulbous base of the archegonium; and there the new structure grows. When it is fully developed it is seen to consist of a terminal spore-case full of spores, and a sterile base (Fig. 167, A). While growing, this spore-case be- comes anchored in the Marchantia body (that is, in the archegonium- bearing disk) by the sterile base, LIVERWORTS 171 and absorbs the necessary nourishment from it. When ripe, the spore-case is ruptured (Fig. 167, B), and the light spores are scattered; and when they germinate they pro- duce new thallus bodies. 96. Alternation of generations. The life-history of Mar- chantia shows a distinct alternation of generations, and since this is a feature of all the higher plants it is necessary to understand it clearly. The thallus body produces no spores, but produces sperms and eggs; that is, it produces gametes, and hence is called a gametophyte, which means a "gamete plant." The gametes produce an oospore; but the oospore does not produce a new thallus plant, producing instead a spore-case. This structure, called the spore-case, does not produce gametes, but produces spores; and hence it is called a sporophyte, which means a "spore plant." Thus in the life-history of Marchantia and of all higher plants, there is an alternation of gametophyte and sporo- phyte. It is evident that in this alternation of generations the gametophyte is the sexual and the sporophyte is the sexless generation. Therefore, oospores are produced by the gametophyte, and ordinary spores by the sporophyte; but the oospores always produce sporophytes, and the ordinary spores always produce gametophytes. These relations may be indicated clearly by the following formula, in which G and S are used for gametophyte and sporophyte respec- tively: G I ~ OS > S o G \ ~~^;oSoG, etc. ( o / ( o/ The formula indicates that the gametophyte produces two gametes, which fuse to form an oospore, which produces the sporophyte, which produces an ordinary spore, which produces a gametophyte, etc. It will be remembered that a similar alternation of generations was noted in the red Algae ( 75) and in the mildews ( 82) among the Thallo- 172 A TEXT-BOOK OP BOTANY phytes, but it is not definite and universal until the liver- worts are reached. It is important to note that in this life-history the pro- tected stage of the plant, that is, the stage which can endure the winter, is not a heavy-walled oospore, as is common among the Thallophytes, but the spore-case or sporophyte. 97. Other Marchantia forms. Associated with Marchan- tia are other liverworts that are much simpler, and which are really better to study if they are available. They differ in having thallus bodies thinner, and hence simpler, in structure; in having the sex-organs directly upon the thallus or embedded in it; and in having simpler and more easily observed spore-cases or sporophytes.* 98. Jungermannia forms. These are commonly called the leafy liverworts, and they are by far the largest group of liverworts. They grow in damp places; or in drier situations on rocks, ground, logs, or tree trunks; or in the tropics on the leaves of forest plants. They are general- ly delicate plants, and resemble small mosses, many of them being com- monly mistaken for mosses. The common name of the group suggests one of its principal features. The lowest forms have a very simple thallus body (Fig. 168, A); but in most of the forms the body consists of a central stem-like axis bearing two rows FIG. 168. Jungermannia forms: A, thallose form; B, leafy form. * In case either Ricdocarpus or Riccia can be obtained, it should be studied rather than Marchantia. LIVERWORTS 173 of small, often crowded leaves (Fig. 168, B). There are really three rows of leaves, but the third is against the substratum and is usually so much changed in appearance as not to resemble the other rows. There is, of co.urse, the same alternation of generations as in the Marchantia forms, but the sporophyte is more than a spore-case. It develops a distinct stalk or stem that bears a spore-case at its summit, and therefore the sporo- phyte has become more complex. Besides, the spore-case does not burst open somewhat irregularly, as in the Mar- chantia forms, but splits into four pieces that spread apart and expose the spores. 99. Anthoceros forms. This group contains compara- tively few forms; but they are of great interest, since many suppose that they are the liverworts that approach most nearly the higher plants. The thallus body is very simple, not becoming so thick as are the Marchantia bodies, nor becoming leafy bodies as are those of the leafy liverworts. The important feature of the group is the sporophyte. At the "fruiting" period the thallus be- comes more or less covered by structures that look like small, erect grass-blades (Fig. 169). Each of these blade-like bodies is a sporophyte that has devel- oped from an oospore lying ^ m within an archegonium. The sporophyte has a large bulbous base embedded in the simple thallus, and above this base there arises a long pod-like spore-case. The cells forming the wall of this spore-case contain chloro- plasts, so that the sporophyte is able to make food for itself, FIG. 1 69. A rdhoce- ros: A , thallus with spore - cases (spor- ophytes); B, a sin- gle spore-case, hav- ing split for the dis- charge of spores. 174 A TEXT-BOOK OF BOTANY in addition to absorbing food from the thallus through the bulbous base. In the other liverworts the sporophyte is entirely dependent upon the gametophyte for its food; but in the Anthoceros forms the sporophyte, by developing green tissue, has begun to be somewhat independent. Another important feature of the sporophyte of this group is that it continues to increase in length like a stem, but the growth takes place at the bottom of the spore-case. As the pod-like spore-case splits into two valves, beginning at the top, the ripe spores above are first exposed and scat- tered; as the splitting becomes deeper the region of the younger spores is reached; and so on until the capsule has become completely split, and all the spores have been ex- posed (Fig. 169, B). It is evident that the Anthoceros forms have the most complex sporophytes among liverworts. In addition to producing spores, these sporophytes have a bulbous absorb- ing base and develop green tissue for the manufacture of food. CHAPTER IX MOSSES 100. General character. Mosses are very abundant and ^amiliar plants that occur almost everywhere. They grow in all conditions of moisture, from submerged to very dry. Many of them can endure drying out wonderfully; and hence they can grow in very much exposed situations, as do many lichens. In fact, lichens and mosses, being able to grow in the most exposed situations, are the first plants to appear upon bare rocks and ground, and are the last plants one sees in climbing high mountains or in going into very high latitudes. Mosses have great power of vegetative multiplication, new leafy branches putting out from old ones indefinitely, thus forming thick carpets and masses. Bog mosses often completely fill up bogs or small ponds and lakes with a dense growth, which dies below and continues to grow above so long as the conditions are favorable. These quaking bogs or "mosses/' as they are sometimes called, furnish very treacherous footing unless rendered firmer by other plants. 101. Peat. In moss-filled bogs the water and the dense vegetation shut off the lower strata of moss from complete decay; and they become modified into a coaly substance called peat, which may accumulate to considerable thickness by the continued upward growth of the mass of moss. Other marsh plants are associated with mosses in the formation of peat, and often the preservation of these plants is remarkable. In fact, the water of peat-bogs is 175 176 A TEXT-BOOK OF BOTANY antiseptic, and in such bogs there are often found almost perfectly preserved specimens of ancient trees or their parts and sometimes of mired animals. Peat is extensively used for fuel, being cut into bricks and allowed to dry. The less decomposed peat is brown, and the more completely decomposed is nearly black. It is not formed to any large extent in warm countries, probably on account of the rapid decay of vegetation; but in the cooler parts of the globe it has been formed in very large masses. All through northern Asia and Europe, and in the northern United States and Canada, there are millions of acres of peat; but little use has been made of it yet in the United States. Its ex- tensive use in Ireland is well known, but there it is more apt to be called turf than peat. 102. Life-history of a Moss. The conspicuous part of an ordinary moss plant consists of a more or less erect and usually branching stem bearing numerous delicate leaves (Fig. 170, A). This plant is evidently able to make its own food, and it is anchored to its substra- tum by hair-like rhi- zoids. Its power of vege- tative propagation has been described, but it produces no spores. At certain times, however, there usually appears at the end of the main stem or at the end of a branch a rosette of FIG. 170. An ordinary moss plant, showing the leafy stem (A) with its rhizoids, and a rosette (B) containing sex-organs. MOSSES 177 leaves (Fig. 170, 5), often called the moss flower. In the center of this rosette there is a group of antheridia and archegonia, sometimes both kinds of organs in a single rosette, sometimes only one kind. The antheridia are club-shaped organs containing nu- merous biciliate sperms (Fig. 171,4); and the archegonia FIG. 171. Sex-organs of a moss: A, an antheridium discharging a mass of mother- cells (a) containing sperms, and also a single enlarged mother-cell (fc) and sperm (c); B, a group of archegonia within a rosette of leaves; C, an archegonium. After SACHS. are flask-shaped organs usually with very long necks, and containing a single egg in the bulbous base (Fig. 171, B and C). These sex-organs are exactly like those described for liverworts (93 and 94). It is evident that this leafy 178 A TEXT-BOOK OF BOTANY moss plant, which does not produce spores, but which does produce sex-organs, is the gametophyte generation in the life-history. It is plain that the ciliated sperms are organ- ized for swimming, and that fertili- zation can take place only when there is sufficient moisture for this purpose. FIG. 172. Developing sporophyte of a moss: A , young sporophyte developed from egg in archegonium; B and C, more advanced stages, in which the sporophyte is elongating and becoming anchored in the leafy plant. After GOEBEL. FIG. 173. A common moss- bearing mature sporo- phytes, which are long- stalked spore - cases. After SCHENCK. MOSSES 179 It must be remembered, however, that the sperms are very small and can swim in such a film of water as may be left on the plant by a heavy dew or rain. Since many mosses grow in very dry places, fertilization with them must be very in- frequent. When the sperms are free to swim they are attracted toward the necks of the arche- gonia, pass down them, reach the egg, and fertili- zation is accomplished. The oospore thus formed within the archegonium at once begins to germinate (Fig. 172), and forms the spore- producing structure, which in mosses is much more than a FIG. 174. Spore-cases of a moss, from which the lids have fallen, displaying the teeth. After KERNER. IIG. 175. Filamentous growth of the young moss: A, very young filament coming from a spore (); B, older filament, showing branching habit, remains of old spore (), rhizoids (r), and buds (6) which develop the erect leafy branches. After MUELLER-THURGAU. 180 A TEXT-BOOK OF BOTANY spore-case. It has a long slender stalk, which becomes anchored in the stem of the leafy plant (Fig. 172); and the stalk bears an elaborate and usually urn-shaped spore-case full of spores (Fig. 173). This spore-case opens by means of a lid, which drops off; and often at the mouth of the urn thus opened there may be seen a set of delicate teeth extending from the margin of the rim and meeting in the center (Fig. 174). These teeth bend inward and outward as they are dry or moist, and help discharge the spores. It is evident that this -spore-case with its anchored stalk is the sporophyte generation in the life-history. When the spores fajl in suitable situations they germi- nate, and each one produces a green branching filament that looks like one of the filamentous green Algae (Fig. 175). This branching filamentous growth spreads over the substratum, and presently there appear upon it buds (Fig. 175, B, b), each of which develops an erect leafy stem, which is recognized as a new leafy moss plant, the form with which this account of the life-history was begun. 103. Alternation of generations* In the life-history just given, it is evident that the prostrate green filament and the erect leafy stems are two parts of the gametophyte; for the leafy stems simply arise as erect branches from the prostrate filament. It is strictly true, therefore, that the so-called moss plant, the conspicuous part of the moss, is a leafy branch of the gametophyte. These leafy branches become independent of the filament by sending out rhizoids into the substratum, so that it is only by actually germina- ting the spores that the filaments are seen. Not only does this branch bear leaves, and hence perform the chief work of food manufacture, but it also bears the sex-organs. The sporophyte, on the other hand, is dependent upon this leafy branch for its food-supply, and in that sense may be said to be parasitic upon it. Its only work is to produce spores; while the gametophyte does the chlorophyll work MOSSES 181 and also produces the sex-organs. The life-history, with its alternating generations, may be indicated as follows: etc. 104. The great groups of Mosses. There are two great groups of mosses, knowj^uni, lllU tog^nosses and the true mosses. The bog m^SS^^apge^k/flj^ailkd mosses found abundantly in bo^s^id marshy ground, arm are the most conspicuous peapformers. They.dtffef-fro'mjhe true mosses in structure inunafn^'ways that need rwpbe mentioned, but one contrastHcchrato^ttention. When the spore of a bog mSStf^ggjaaBiee&s^it, does not produce a branching green filament, but a flat compact thallus body like that of the liverworts. On this thallus body the erect leafy branches arise, just as they do from the fila- mentous body in true mosses. This is interesting, because in the bog mosses the thallus body of the liverworts is continued, and also because it indicates that the prostrate filamentous body of the true mosses is probably a modified thallus body. The true mosses are much more numerous than the bog mosses, and live in a far greater variety of situations. Some of them are also peat formers, but most of them have become established in much drier situations. 105. The erect leafy axis. The lowest green plants live in the water or in very moist places, but the liverworts begin to occupy the land. In this new position they are better exposed to light, which is an advantage in food manufacture; but they are in danger of being dried out by the air. In consequence of these dangers, various protect- ive structures have been developed, one of the first being a compact body with an epidermis. An exposure of more green tissue to the light is secured by the leafy liverworts in their development of leaves, but their bodies are prostrate 182 A TEXT-BOOK OF BOTANY and the best exposure is not obtained. The mosses have made still further progress in developing an erect branch upon which leaves are spread out to the light and air freely in all directions. All this advance has been made by the gametophyte, which in the mosses has reached the best position for leaves and hence for food manufacture. How progress in this direction is carried further by the higher plants will be seen in subsequent chapters. CHAPTER X FERNS 106. Summary. Before studying the ferns, it is well to note the progress that has been made by* the plants previ- ously considered. It has been said that the Alga? and Fungi together form the first great division of the plant kingdom, the Thallophytes. The liverworts and mosses together form the second great division, called the Bryo- phytes, a name meaning "moss plants. " The ferns intro- duce the third great division, called the Pteridophytes, which means "fern plants." A summary of the contributions made by the Bryophytes to the progress of plants is as follows: (1) The land habit. The Bryophytes establish green plants upon the land, and as a consequence begin to develop those structures that the new conditions demand. (2) Alternation of generations. A life-history consisting of alternating sexual (gametophyte) and sexless (sporo- phyte) generations is finally established, although it is in- dicated in the life-histories of certain Thallophytes. (3) Gametophyte the chlorophyll generation. In the alter- nation the gametophyte generation develops the chloro- plasts for food manufacture, and on this account is the con- spicuous generation. When a moss or a liverwort is spoken of, therefore, the gametophyte is usually referred to. (4) Sporophyte dependent. The sporophyte in the Bry- ophytes is dependent upon the gametophyte for food, and hence remains attached to it. Only by the Anthoceros forms has a partial independence of the sporophyte been attained. 13 183 184 A TEXT-BOOK OF BOTANY (5) Appearance of leaves. Among the Bryophytes very simple leaves are developed by the gametophyte, and the mosses produce leaves upon an erect stem. (6) Many-celled sex-organs. The many-celled antheridia and flask-shaped archegonia are very characteristic of Bryo- phytes, and distinguish even the thallose forms from any Thallophytes. 107. General characters of Ferns. The ferns are well- known plants, and the ordinary forms are easily recognized FIG. 176. Shield ferns. (Fig. 176). In fact, the general appearance of the large compound leaves is so characteristic that when a leaf is said to be fern-like a particular appearance is suggested. Al- i 185 186 A TEXT-BOOK OF BOTANY though ferns are found in considerable numbers in temper- ate regions, their chief display is in the tropics, where they form a striking and characteristic feature of the vegetation. In the tropics not only are great masses of the low forms to be seen, from those with delicate and filmy moss-like leaves to those with huge leaves, but also tree forms with FIG. 178. The staghorn fern, which is an epiphyte. cylindrical trunks encased by the rough remnants of fallen leaves and sometimes rising to a height of thirty-five to forty-five feet, with a crown of great leaves fifteen to twenty feet long (Fig. 177). There are also air forms (Fig. 178), that is, ferns that perch upon other plants but FERNS 1ST derive no nourishment from them ( 41). This habit be- longs chiefly to the moist tropics, where plants may obtain sufficient moisture from the air without sending roots into the soil. 108. Sporophytes. If an ordinary fern be examined, it will be discovered that it has a horizontal underground stem or rootstock ( 27), which sends out roots into the soil, and one or more large leaves into the air (Fig. 179). These leaves, appearing to come directly from the soil, were once supposed to be different from ordinary leaves and were called fronds ; but al- though the name is still used in connection with fern leaves, it is neither nec- essary nor ac- curate. These leaves are usu- ally compourd, branchingeith- er pmnately or i. 179. The habit of an ordinary fern showing the horizontal rootstock sending out roots and rpi leaves, and also the peculiar rolled tip of the developing leaves. two peculiari- ties about fern leaves that should be noted. One is that in expanding the leaves seem to unroll from the base, as though they had been rolled from the apex downward, the apex being in the center of the roll. When unrolling, this gives the leaves a crozier-like tip (Fig. 179). The other peculiarity is that the veins fork repeatedly (Fig. 180). This combination of unrolling leaves and forking veins is very characteristic of ferns. Probably the most important fact about the fern body 188 A TEXT-BOOK OF BOTANY is that it contains a vascular system ( 24) (Fig. 181). The appearance of this system marks some such epoch in the 'evolution of plants as is marked among animals by the appearance of the backbone. As animals are often grouped as vertebrates and invertebrates, so plants are often grouped as vascular plants and non-vascular plants, the latter being the Thallophytes and the Bryophytes, the for- mer the ferns and the seed-plants. The presence of this vascular system means a special conducting system, and in connection with it there are developed the first roots FIG. 180. Portion of the leaf of maidenhair fern, showing the forking veins. and the first complex leaves. Such a plant body, with its vascular system and roots and complex leaves, is so dif- ferent from any plant body among Bryophytes that the greatest gap in the whole series of plants, from lowest to FERNS 189 highest, is felt to be the one between Bryophytes and Pteridophytes. On account of the vascular system and other resistant structures, the remains of ferns have been FIG. 181. Cross-section of the stem (rootstock) of a fern, showing the peculiar vascular axis, the large xylem vessels being completely surrounded by the phloem. preserved in great abundance in the rocks. These records show that the ferns are a very ancient group, occurring in special abundance during the Coal-measures. Another striking fact about this leafy body of the ferns is that it never produces sex-organs, but does produce spores abundantly. This means that it is the sporophyte in the life-history of the fern, and when it is contrasted with the sporophyte of Bryophytes the differences are remarkable. Among the liverworts and the mosses the sporophyte is a leafless structure attached to the gameto- phyte and dependent on it, while the gametophyte is the leafy body doing chlorophyll work. Among the ferns, however, the sporophyte is an elaborate leafy structure and entirely independent. Therefore, when one ordinarily 190 A TEXT -BOOK OF BOTANY speaks of a moss and a fern, the gametophyte is referred to in the former case and the sporophyte in the latter. This means that, in passing from mosses to ferns, plants have transferred the chief work of food manufacture from the gametophyte to the sporophyte, which has thus become the conspicuous generation. The leaves of mosses, there- fore, are gametophyte leaves; while the leaves of ferns are the first sporophyte leaves. A common and brief statement of the contrast between the two groups is that mosses have a leafless and ferns a leafy sporophyte. How the leafless sporophyte has become a leafy one is an interesting but un- A B FIG. 182. Sporangia of ferns: .A, elongated sori, with pocket-like indusia; B, round sori, with shield-like indusia. FERNS 191 answered question. The great interest of the Anthoceros forms ( 99) is due to the fact that their sporophytes are green and do chlorophyll work; and this has suggested the thought that from such green tissue leaves have been de- veloped, and thus a leafy sporophyte has been started. 109. Sporangia. Upon the under surface of fern leaves dark dots or lines are often seen (Fig. 182). These arc groups of sporangia, usu- ally occurring along the veins of the under surface, but some- times in long lines along the edge, the margin of the leaf rolling in and protecting them, as iii maidenhair fern and com- mon brake (Fig. 183). In ferns having the groups of sporangia away from the margin, each group (sorus) is usually pro- tected by. a delicate flap (indu- fiium) growing out from the epi- dermis, sometimes forming a pocket (Fig. 182, ^4.) and some- times an umbrella-like or shield- like covering (as in shield ferns) (Fig. 182, ). The position and the shape of the sorus and the character of the indusium furnish useful characters in the classification of ferns. Most fern leaves do chlorophyll work and produce sporangia, two very distinct kinds of work. In some ferns, however, some of the leaves are sterile, that is, do not produce sporangia, the other leaves doing both kinds of work; while in other ferns certain leaves or leaf branches are set apart to produce sporangia and do no chlorophyll work, and vice versa, the two kinds of work thus being divided among the leaves or leaf branches. Such a FIG. 183. Sporangia of ferns, show- ing marginal lines of sporangia protected by the inrolled margin of the leaf: A , the common brake; B, maidenhair fern. 192 A TEXT-BOOK OF BOTANY division of work occurs in the royal fern, climbing fern, ostrich fern, sensitive fern, moonwort (Fig. 184), adder's tongue, etc. The sporangium of an ordinary fern consists of a spore- case with a slender stalk (Fig. 185). The case has a del- icate wall formed of a single layer of cells; and, extending around it from the stalk and nearly to the stalk again, like a meridian line about a globe, is a row of peculiar cells FIG. 185. Section through the sorus of a shield fern, showing in- dusium and sporangia. After ENGLER and PRANTL. with thick walls, forming a heavy ring. This ring is like a bent spring; and when the delicate wall begins to yield, the spring straightens violently, the wall is torn, and FIG. 184 Am - as ^ e s P rm g rebounds the spores are hurled wort, showing with considerable force, like a handful of pebbles thrown forward from the hand. branches of a leaf. This discharge of spores may be seen by After STRAS- BURGER. placing some mature sporangia upon a moist FERNS 193 slide, and under a low power watching them as they dry and burst. 110. Gametophytes. In continuing the life-history of a fern, the spores when discharged, as just described, begin to germinate, provided they have reached suitable con- ditions. Each germinating spore produces a green thallose body that resembles a very small delicate liverwort (Fig. 186). It is deeply notched, having a general heart- shaped outline, and is usually less than one-fifth of an inch in diame- ter. This thallus is so thin that all its cells contain chloroplasts, and rhizoids from the under surface an- chor it to .the soil. It is evident that it is an indepen- dent plant, al- though a very small one. Upon this minute plant the sex-organs are produced, and therefore it is the garnet ophyte in the life- history. This fern gametophyte, because it is a thallus body which precedes the appearance of the large sporo- phyte, has been called the prothallium (or prothallus), and this name has come to be very commonly used for gametophyte among all the higher plants. At the bottom of the conspicuous notch of the prothallium is the grow- ing point, representing the apex of the plant. The antheridia and the archegonia are produced on the FIG. 186. Gametophyte (prothallium) of a fern: A, under surface showing rhizoids (rA). antheridia (an), and archegonia (ar); B, under surface of an older gametophyte, showing the young sporophyte, with root (w) and leaf (6). After SCHENCK. 194 A TEXT-BOOK OF BOTANY under surface of the prothallium in the region of the central axis. When the prothallia are very young, the antheridia begin to appear; and if the prothallia are poorly nourished and stunted only antheridia appear. In mature, well- nourished prothallia, however, archegonia also appear. In consequence of their late appearance, the group of archego- nia is near the notch, that is, near the growing point, while the group of antheridia is farther back, on the older part of the prothallium (Fig. 186, A). The antheridia and the archegonia are not free and pro- jecting organs, as among the Bryophytes, but they are more or less sunken in the tissue of the prothallium and open on its surface. In the case of the archegonium only FIG. 187. Archegonium of a fern containing an egg (e), the neck being curved back- ward toward the antheridia. the neck projects, and this is usually bent backward to- ward the antheridia (Fig. 187). The egg resembles those of all other archegonium-bearing plants; but the sperms are very different from those of Bryophytes, having large FERNS 195 spirally coiled bodies, blunt behind and tapering to a beak in front, the beak bearing numerous cilia (Fig. 188). The fern sperm, therefore, is a large, spirally coiled, multiciliate Fro. 188. Two antheridia of a fern (A), one containing sperms, the other discharg- ing them; also a single sperm much enlarged (B). sperm, as compared with the small biciliate sperm of Bry- ophytes. With a ciliated sperm, fertilization can be effected only in the presence of moisture, and if prothallia are kept dry fertilization does not occur. In nature, however, the pro- thallia lying prostrate on the substratum are in a favor- able position for moisture; and when there is a film of mois- ture between the prothallium and the substratum the sperms can swim to the archegonia. The oospore which is produced germinates at once and forms the leafy sporophyte (Fig. 186, B}. The young stem and the root remain under the soil, but the young leaf is seen curving upward through the notch of the prothallium and growing up into the air and light. For a short time the young plantlet absorbs nourishment from the prothallium, but with its own root system and leaves it soon becomes 196 A TEXT-BOOK OF BOTANY independent. In fact, the prothallium is so small, and the leafy sporophyte becomes relatively so large, that the dependence of the latter upon the former is a very small item in the life-history. 111. Alternation of generations. The contrast between the alternating generations of mosses and the same genera- tions in ferns is striking. In mosses the gametophyte is the conspicuous phase in the life-history, with its prostrate filaments and leafy branches; while in ferns the gameto- phyte (prothallium) is a very inconspicuous phase in the life-history, being seen only by those who know what to look for, and resembling a very small simple liverwort. In the mosses the sporophyte is at most only a stalked spore-case, attached to the gametophyte and dependent upon it for nourishment; while in ferns the sporophyte is a large, independent, leafy plant, with vascular system and roots. The formula for the life-history of a fern may be written as follows: G(prothallium) > O (leafy plant) O GrH%> O S O G, etc. CHAPTER XI HORSETAILS AND CLUB-MOSSES HORSETAILS 112. General characters. The horsetails or equisetums are represented to- day by only twenty- five species ; but during the Coal- measures the spe- cies were very nu- merous, and some of them were great trees, forming a conspicuous part of the forest vegeta- tion. They grow in moist or dry ground, sometimes in great abun- dance, and have such a character- istic appearance that they cannot be mistaken. The stem is slen- der and conspicu- ously jointed, the joints Separating FIG. 189. Equisetum: showing the jointed and fluted .. ._,. 1 QO\ stem, the sheath of minute leaves at each joint, easily (r Ig. 189) . strobili in various stages, and some young branches, 197 198 A TEXT-BOOK OF BOTANY It is also green, and fluted with small longitudinal ridges; and there is such an abundant deposit of silica in the epi- dermis that the plants feel rough. This last property sug- gested formerly its use in scouring, and the name " scouring rush." At each joint there is a sheath of minute leaves, more or less coalesced, the individual leaves sometimes being indicated only by minute teeth. This arrangement of leaves in a circle about the joint is the cyclic ar- rangement, the leaves be- ing said to be whorled (8). These leaves contain no chlorophyll and have evi- dently abandoned food manufacture, which is car- ried on by the green stem; hence they are scales rather than foliage leaves. The aerial stem, which arises from an elongated root- stock, is either simple or profusely branched. In some cases the aerial stems early in the season are simple, usually not green, and bear the sporangia (Fig. 190); while the later branches from the same rootstock are sterile, profusely branched, and green (Fig. 191). 113. Strobilus. At the apex of the aerial stem there may be found a more or less conspicuous cone-like structure, called the strobilus, meaning "pine cone," whrch it resem- bles in general outline (Fig. 190). The strobilus is a com- FIG. 190. Early fertile shoots of Equise- tum, which are not green, have con- spicuous leaf -sheaths at the joints, and bear conspicuous strobili; beginnings of the later sterile shoots also seen. HORSETAILS AND CLUB-MOSSES 199 pact group of modified leaves bearing sporangia. Just as in some ferns certain leaves are set apart to do chloro- phyll work and others to bear sporangia, so in the Equisetum the same division of work oc- curs; but the notable thing is that the spo- rangium-bearing leaves are massed together in a cluster that is quite distinct from the rest of the plant. Leaves set apart for bearing spo- rangia are called spo- rophylls, which means "spore leaves.'' A strobilus, therefore, is a group of sporophylls that form a more or less distinct cluster, dis- tinct from the rest of the plant. In Equisetum each sporophyll consists of a stalk-like portion and a shield-like top, be- neath which the several sporangia hang (Fig. 192, A). The spores have a very peculiar outer wall. It consists of two spiral bands wound about the spore and fastened to it only at the point where they intersect (Fig. 192, ). When dry, the bands 14 FIG. 191. Later sterile shoots of the species shown in Fig. 190, and photographed a month later. 200 A TEXT-BOOK OF BOTANY B loosen and uncoil; when moistened, they close around the spore. The coiling and uncoiling movements of these bands as they are wet or dry entan- gle the spores, and they fall in clumps, a num- ber of them thus germinat- ing close to- FIG. 192. A, a sporophyll of Equisetum, bearing sporangia pother beneath the shield-like top; B and C, spores, showing the unwinding of the two bands forming the outer coat. 114. GametO- phyte. When the spores of an Equisetum germinate they give rise to gametophytes that in all general features resemble those of the ferns; that is, they are small, green thallus bodies pro- ducing antheridia and archegonia. From the oospores pro- duced in the archegonia the large sporophyte arises, with its roots, xootstock, branches, leaves, and strobili. It is evident that, although an Equisetum does not seem to resemble a fern in the least, the life-history and the character of the alternating generations are the same. CLUB-MOSSES 115. General characters. The club-mosses often look like coarse mosses, as the name suggests. Some of the larger ones are called also ground pines, because of a cer- tain resemblance to miniature pines. They are slender branching plants, with the prostrate or erect stems com- pletely clothed with small leaves (Fig. 193). The larger and coarser forms are abundant in the Northern woods, the prostrate stems often trailing extensively and giving rise to erect branches. The more delicate forms are abundant in the tropics, and are very common in greenhouses as decorative plants. HORSETAILS AND CLUB-MOSSES 201 During the Coal-measures the club-mosses occurred in great abundance, and among them were large trees of vari- ous kinds, forming a very prominent part of the forest B FIG. 193.Lycopodium: A, the whole plant, showing the horizontal stem giving rise to roots and erect branches bearing strobili; B, a. single sporophyll with its sporangium; C, spores much magnified. After WOSSIDLO. vegetation. As in the case of the equisetums, therefore, the club-mosses, or Lycopods as they are called, were once 202 A TEXT-BOOK OF BOTANY far more conspicuous plants than they are now, and only the smaller forms have persisted to the present time. 116. Strobili. One of the conspicuous features of the lycopods is the cylindrical strobilus, which usually termi- nates the erect branches, and is the "club" that enters into the name club-moss (Fig. 193, A). Sometimes the strobilus is quite distinct from the rest of the stem; and sometimes it cannot be distinguished from it, so that there is no external indication where leafy stem ends and strobilus begins. The leaves of the strobilus resemble the ordinary fo- liage leaves; but each one is a sporophyll, bearing a single large sporangium on its upper surface at the base (Fig. 193, B), so that the sporangium ap- pears in the axil of the sporo- phyll. Among the ferns the spo- rangia are numerous on the under side of leaves; among equisetums they are several on the under side of sporophylls; among lycopods they are solitary on the upper side of sporophylls. 117. Lycopodium. The Lyco- podium forms are chiefly the coarse club-mosses of temperate regions, and are mostly spoken of as the large club-mosses. The strobili are often conspicuous and very distinct from the rest of the plant. This leafy, branching plant with its strobili is, of course, the sporophyte (Fig. 193, A). When its spores germinate they rkrnr | nr o-arnAf nrJiirf AC Vmf fVi^GA P F< 3 gametOpnyteS, t instead of being sou. After BRUCHMANN. green, prostrate, thallose bodies, FIG. 194. Subterranean gam- etophytes of Lycopodium, showing their irregular, tu- berous form; the dotted line frametophvtes represents the surface of the * HORSETAILS AXD CLUB-MOSSES 203 as are the gametophytes (prothallia) of ferns and equi- setums, are subterranean tuberous bodies with no chloro- phyll, on which the antheridia and archegonia appear (Fig. 194). In some forms of Lycopodium the tuberous prothal- lium develops an aerial portion that is green and bears the sex-organs. This strange subterranean and saprophytic prothallium is in marked contrast with the prothallia of ferns in its habits and appearance.* 118. Selaginella.- The Selaginella forms are much more numer- ous than the Lyco- podium forms, being especially abundant in the tropics, and are often called the little club-mosses on ac- count of their smaller size and more delicate texture. It is these forms that are com- mon in greenhouses as decorative plants. There are often no strobili very distinct from the leafy stem, the solitary sporangia occurring in the axils of the upper leaves (Fig. 195). The most important fact in connection with Selaginella is that all the sporangia in a strobilus do not produce the * The gametophytes of Lycopodium are so rarely found that it is not expected that they will be seen by the student. FIG. 195. Branch of Selaginella bearing strobili. A TEXT-BOOK OF BOTANY same kind of spores. For example, certain sporangia (usu- ally the lower ones) may each contain four large spores (Fig. 196, C and D), while the other sporangia contain very numerous and very much smaller spores (Fig. 196, A and B). There may be no differ- ence in the appearance of the sporangia. A plant that produces two kinds of spores, differing in size, is said to be he- terosporous (spores dif- ferent). The appear- ance of this condition is a very important fact, for it is an intro- duction to the appear- ance of the higher plants. Difference in the size of spores does not seem important; but when this is accompanied by difference in the gameto- phytes produced, it is very important. When the small spore germi- nates, it produces a few- celled gametophyte, so small that it is contained entirely within the old spore wall. This gametophyte produces one antheridium, and this antheridium forms the bulk of the whole body. Therefore, the small spore produces a very small male gametophyte. When the large spore ger- minates, it produces a many-celled gametophyte, which bursts through the spore wall and becomes partly ex- FIG. 196. Sporophylls of Selaginella: A, spo- rophyll bearing sporangium that produces numerous small spores (B); C, sporophyll bearing sporangium that produces few large spores (Z)). HORSETAILS AND CLUB-MOSSES posed. In this exposed part archegonia appear, and therefore the large spore produces a female gametophyte (Fig. 197). In Selaginella, there- fore, the two kinds of sex-organs are produced by different plants, and we speak of male and female gametophytes. The connection of these two kinds of gameto- phytes with the two kinds of spores must be kept clear. The small spore (microspore) pro- duces the male gameto- phyte, and the large spore (megaspore) pro- duces the female ga- metophyte. It must be remembered, also, that with this change the gametophytes have become much smaller than they were before, and are no longer indepen- dent, in the sense of doing chlorophyll work. It follows that in the life-history of Selaginella there is an alternation of the sporophyte with two gametophytes. How this contrasts with the life-history of an ordinary fern may be indicated as follows: Fern: Gn>o S o G~>o S o Gn>o S, etc, Selaginella: g~g> o S~~g~~c~g> o S~~g~~g~g> o, etc. 119. Coal. The ferns, equisetums, and lycopods were associated together during the Coal-measures, and were the most conspicuous plants in the formation of coal. The formation of peat, already referred to ( 101), indicates the FIG. 197. Female gametophyte of Selaginella, having burst through the wall of the mega- spore (m), and bearing archegonia (a) and rhizoids (r) upon its exposed part; somewhat diagrammatic. 206 A TEXT-BOOK OF BOTANY first stages in coal-formation. During the Coal-measures there were very extensive areas of swampy land covered with a luxuriant vegetation, consisting principally of ferns, equisetums, and lycopods. The dead bodies of these plants accumulated in immense deposits in the swamp waters; and when a sinking of the land brought it under water, sediments were deposited upon the accumulated vegetation and it was gradually changed into coal. Suc- cessive risings and sinkings of the 'land surface brought about an alternation of vegetation and sediments, and so the coal lies in beds of varying thickness. The ferns, equisetums, and lycopods are often spoken of as peculiarly useless plants; but when one considers the part they played in coal-formation, and the importance of coal in our civilization, it is evident that no plants have done more for human welfare. The different kinds of coal depend upon the amount and kind of changes in this old buried vegetation. For example, hard coal (anthracite) has been changed most, containing eighty-five per cent or more of carbon; while soft (bitumi- nous) coal contains only fifty to seventy-five per cent of carbon. It will be remembered that green plants take carbon dioxide from the air and use the carbon in building their bodies ( 14). Therefore, the enormous amount of carbon contained in coal deposits was in the main drawn from the air by plants. When coal is burned now there is made a tardy return of carbon dioxide to the air for that which was taken from it millions of years ago. The coal-fields of the United States are the greatest in the world that are now being worked; but the coal-fields of China are probably even greater. The coal of the United States is all soft coal, except in the mountain region of Pennsylvania, where the bituminous coal has been changed into anthracite. CHAPTER XII GYMNOSPERMS 120. Summary. The ferns, equisetums, and lyco- pods are representatives of the third great division of the plant kingdom, the Pteridophytes (fern plants). Their con- tributions to the progress of plants are very important and may be summarized as follows: (1) Leafy sporophytes. All Pteridophytes have leafy sporophytes, and all Bryophytes have leafless ones, so that this change is not only great, but also complete. The leafy sporophyte means also a vascular system and roots, and therefore these structures are introduced by the Pterido- phytes. (2) Sporophylls. The setting apart of certain leaves to bear sporangia makes a division of work between foliage leaves and sporophylls, and the arrangement of the sporo- phylls into the distinct cluster known as the strobilus marks another advance. (3) Heterospory. The occasional appearance of hetero- sporous plants among Pteridophytes, as Selaginella and a few other forms, is noteworthy, because all the plants of the next and highest group are heterosporous. Associated with heterospory is a great reduction in the size of the two gametophytes, which are so small that they project little if at all from the spores which produce them. 121. The four great plant groups. Three of the great divisions of the plant kingdom have been considered. The 207 208 A TEXT-BOOK OF BOTANY fourth differs from them all in producing seeds, and hence is called Spermatophytes or seed-plants. It may be well to give certain prominent characters that will serve to dis- tinguish these four primary groups. It must not be sup- posed that these are the only characters, or even the most important ones in every case, but they are convenient for our purpose. (1) Thallophytes. Thallus. body, but no archegonia. (2) Bryophytes. Archegonia, but no vascular system. (3) Pteridophytes. Vascular system, but no seeds. (4) Spermatophytes. Seeds. It will be noticed that for each of the first three groups two characters are given, one a positive character that belongs to it, the -5^, ffilHHHI other a negative character that dis- tinguishes it from the group above, and becomes the positive charac- ter of that group. For example, thal- lus bodies are found among Bryo- phytes, and the pro- thallium of a Fern is a thallus body; but plants whose thallus bodies do not bear arche- gonia are Thallo- phytes. Also, arch- egonia are produced by Pteridophytes as well as by Bryophytes, but archegonium-bearing plants without a vascular system can be only Bryophytes. Both Pteri- FIG. 198. A cycad with columnar stem. After STRAS- BURGER. 210 A TEXT-BOOK OF BOTANY dophytes and Spermatophytes have vascular systems, but only the latter produce seeds. 122. General characters of Gymnosperms. The Gymno- sperms are one of the two groups of seed-plants, the most familiar ones in temperate regions being pines, spruces, hemlocks, cedars, etc., the group commonly called ever- greens. It is an ancient group, for its representatives were associated with the giant club-mosses and horsetails in the forest vegetation of the Coal-measures. Only about four hundred species exist to-day as a remnant of its former display, although it still forms extensive forests. Gymno- sperms are very diverse in habit. They are all woody forms, but they may be gigantic trees, trailing or straggling shrubs, or high-climbing vines. There are two prominent living groups of Gymnosperms. FIG. 200. A cycad with tuberous or short thick stem. Cycads are tropical forms with large fern-like leaves. The stem is either a columnar shaft crowned with a rosette GYMNOSPERMS 211 of large compound leaves, with the general habit of tree- ferns and palms (Figs. 198 and 199); or they are like great tubers, crowned in the same way (Fig. 200). The tuberous stems are often more or less buried, as in our only cycad from the United States (Florida), illustrated in Fig. 200. In ancient times cycads were very abundant, but now they are rep- resented by about eighty species scat- fprpH i hrnno-Vi tViP nri FlG> 20L ~ Two view8 of the 8perm of a showing its spiral form and many cilia. ental and occidental tropics. They are especially interesting in their resem- blances to ferns, and some of them might be mistaken for ferns did they not bear large seeds. In addition to their fern-like leaves, they have in the structure of the stem many fern characters; and they have coiled sperms with many cilia (Fig. 201), as do the ferns. They are very interesting to study; but it is easier to obtain the Gym- nosperm characters from the other group, whose forms are far more familiar and easily obtained. Conifers are the common Gymnosperms, often forming great forests in temperate regions. Some of the forms are widely distributed, as the pines; while some are now very much restricted, as the gigantic redwoods (Sequoia) of the Pacific slope. The habit of the body is quite characteristic, a central shaft extending to the very top (Fig. 42). In many cases, the branches spread horizontally, with dimin- ishing length to the top, forming a conical outline, as in the firs. This habit gives the conifers an appearance very distinct from that of the other trees. Another peculiar feature is the needle-leaf. These leaves have a small surface and very heavy protecting cells, being 212 A TEXT-BOOK OF BOTANY able to endure the cold of winter (Figs. 30 and 31). As there is no regular period for the fall of leaves, as in the deciduous trees, the trees are always clothed with them, and hence are called evergreens. A notable exception to the evergreen habit of conifers is that of the common larch or tamarack, which sheds its leaves every season. The great body of the plant is highly organized for work, with its roots, stem, and leaves, and an elaborate vascular system connecting them all. The wood of the conifers is peculiar in its very regular grain, splitting easily; and its generally "soft" character is quite distinct from the so- called "hard woods." Throughout the body there are also numerous resin-ducts, whose contents give a peculiar aroma to the wood. 123. Strobili. The cones borne by the conifers are well known, and suggest at once the strobili of certain Pteridophytes. There are two kinds of strobili, however, one being the conspicuous seed-bearing cones of common observation, the other much smaller and much less per- sistent cones (Fig. 202). In Selaginella ( 118), it will be remembered, there are two kinds of sporangia in a single strobilus; but in conifers these two kinds of sporangia are in separate strobili or cones. In describing the two cones the pine may be used as an illustration. The small cone (Fig. 202, d, and Fig. 203, A) is made up of sporophylls that look like small scales; and on the lower surface of each scale there are two sporangia (Fig. 203, B and C), each sporangium containing very numerous small spores (microspores). All of these structures received names long before their relations to the lower plants were known; but as these names are well known it is convenient to use them. The small spores were called pollen grains or simply pollen; the sporangia containing them were called pollen sacs ; and the sporophyll bearing the sporangia was called a stamen. The strobilus or cone, therefore, is a GYMNOSPERMS 213 group of stamens; and to distinguish it from the other cone it may be called the staminate cone. It should be remem- i a b 3 FIG. 202. Tip of pine branch, showing carpellate cones of first year (a), second year (6), and third year (c); also a cluster of staminate cones (rf). bered, however, that all these structures are found also among Pteridophytes, though they are not called by these names. The large cone of the pine is made up of sporophylls 214: A TEXT-BOOK OF BOTANY that become very thick and hard (Fig. 204, A), and that are packed closely together until they spread apart to let out the seeds (Fig. 202, c). On the upper side of each sporophyll, near its base, there are two sporangia (Fig. 204, B and C), in each one of which there is a single large spore (megaspore). So large is the spore that it looks like a FIG. 203. Staminate cone of pine: A , section of cone, showing sporophylls (stamens) bearing sporangia (pollen sacs); B, longitudinal section of stamen, through one pollen sac; C, cross-section of stamen, showing both pollen sacs; D, the winged pollen grain. After STRASBURGER. conspicuous cavity in the center of the sporangium. These structures also bear old names that may be used. The sporangia were called ovules ; and the sporophyll bearing them was called a carpel. The large spore was regarded only as a cavity in the ovule. The cone, therefore, is a group of carpels; and to distinguish it from the staminate cone it may be called the carpellate cone. GYMN'OSPERMS 215 It is evident that the pine-tree, bearing these sporangia, is the sporophyte in the life-history; that is, it is the sex- less generation. The sporophyte has now become so prom- FIG. 204. Carpellate cone of pine: A, cone partly sectioned; B, young carpel (sp.orophyll) with two ovules (sporangia) ; C, old carpel with mature seeds. After BESSEY. inent that it seems to be the whole plant, and it is interest- ing to know what has become of the gametophytes with their sex-organs. 124. Gametophytes. As the pine is a heterosporous plant, there are male and female gametophytes. The small spores (pollen grains) germinate and produce very small male gametophytes. As in Selaginella ( 118), only a few cells are formed, and these remain in the pollen grain (Fig. 15 216 A TEXT-BOOK OF BOTANY 203, D). Such a gametophyte has become so small that it can be seen only under the microscope. Among the cells formed, however, are two sperms. These sperms have no cilia, and hence it is evident that they do not reach the egg by swimming. The single large spore within the ovule (spo- rangium) is peculiar in never leaving it; that is, it is never shed, as are other spores. It pro- duces a many-celled fe- malegametophyte,justas does Selaginella ( 118); and on this gametophyte archegonia are formed (Fig. 205). Since the large spore is not shed, the female gametophyte it produces lies embed- ded in the center of the ovule, like an internal parasite (Fig. 205, g). It is evident now why the gametophytes of such plants are not ordinarily seen, for one is within the pollen grain and the other is within the ovule. 125. Fertilization. Before fertilization can take place, the pollen grain, which develops the male gametophyte with its sperms, must be brought to the ovule, which contains the female gametophyte with its archegonia. The pollen grains (microspores) are formed in very great abundance, are dry and powdery, and are scattered far and wide by FIG. 205. A, section showing the relative po- sitions of bract (b), scale (s), and ovule (o) in a pine cone, the female gametophyte (g) being very young ; B, enlarged section through the ovule a year later, showing the female gametophyte (0) bearing two arche- gonia (a) which are being reached by the penetrating pollen tubes (t). GYMXOSPERMS 217 the wind. In the pines and their allies the pollen grains are winged (Fig. 203, Z>), so they are well organized for wind distribution. This transfer of pollen from the stami- nate cone to the carpellate cone is called pollination, and the agent of transfer is the wind. So abundant is the pol- len of conifers that it sometimes falls like a yellow shower, and the occasionally reported "showers of sulphur" are really showers of pollen from some forest of conifers. Some pollen must reach the ovules, and to insure this it must fall like rain. To aid in catching the falling pollen the scale- like carpels of the cone spread apart; and the pollen grains sliding down their sloping surfaces collect in a little drift at the bottom of each carpel, where the ovules are found. In this position each of the most favorably placed pollen grains begins to put forth a tube (pollen tube). This tube, containing the two sperms in its tip, grows through the ovule, and reaches the archegonia (Fig. 205, t). Then the sperms are discharged, and when they reach the egg fusion takes place and fertilization is accomplished. 126. Embryo. The oospore that has been formed within the archegonium at once germinates and begins to form the young plantiet (embryo), which of course is still within the ovule. This embryo continues to grow, feeding upon the female gametophyte that surrounds it. It is evident that this embryo is the young sporophyte of the next generation. 127. Seed. While the embryo is developing, some im- portant changes are taking place in the ovule outside of the female gametophyte. The most notable change is the formation of a hard, bony covering, which hermetically seals the structures within, so that further development is checked. In this way the ovule (sporangium) has been transformed into what is called a seed, the distinguishing structure of seed-plants. If a pine seed is cut open, the embryo (young sporophyte) may be seen embedded in the center (Fig. 206); around 218 A TEXT-BOOK OF BOTANY it is packed nutritive tissue (often called endosperm}, which is the female gametophyte; and outside of that there is found the bony seed-coat (testa). In this condition of suspended animation the embryo may continue for a long time, certainly until the next season, P erha P s for man y seasons - When the seed comes into favorable conditions and "awakens," the embryo escapes male gametophyte), an( j grows into the pine-tree. This which is invested by . the hard testa. awakening of the seed is usually called its "germination," but it must not be confused with the germination of spores and oospores. The "germination" of the seed is merely the resumption of growth by the embryo and its escape from the seed. In seed-plants, therefore, there are two distinct periods in the growth of the sporophyte, the period within the seed (when it is called an embryo), and the period outside of the seed; and these two periods may be separated from one another by a long period of time. For an account of seed germination see Chapter V. 128. Timber from Conifers. The conifers are the most important source of timber in the United States, yielding at least three-fourths of our supply. They are usually called "soft woods" in distinction from the so-called "hard woods," such as oak; but there are soft and hard woods in both groups. The United States is notable for its variety of pines, broadly grouped into the soft white pine and the hard yellow pines. Our principal supplies come from the white pine forests about the Great Lakes and the yellow pine forests of the Southern States; but the forests of the former region have been cut over so ruthlessly for so long a time that the supply of white pine is diminishing. A few years ago the white pine furnished nearly one-third of all the timber produced by the United States. It is very GYMNOSPERMS 219 important to learn how to obtain white pine with the least possible waste, for the usual methods will soon destroy all of our supply. The pine forests of the South, yielding in increasing amount the very valuable timber of the hard wood yellow pines, are very extensive. Chief among these yellow pines is the Georgia pine, being the principal species over an area fifty to one hundred and fifty miles, wide and extend- ing along the coast region from North Carolina to eastern Texas. This great Southern pine region is producing more and more timber as the supply from the Northern white pine is diminishing. The coniferous forests mentioned above belong to the general Atlantic region, which extends from the Atlantic Coast to the Mississippi Valley; but there is a Pacific region extending from the Rocky Mountains to the Pacific Coast, all of whose immense forests are conifers. These Western forests are mainly in the mountains, and have been most wastefully treated in cutting for timber, clearing, and per- mitting the ravages of fire. Two famous coniferous trees of California are the redwood and the big tree. The former yields a very valuable lumber, and the latter is the largest American tree. The big trees are found in scattered groves along the western slopes of the Sierra Nevada, a number of which are carefully preserved. The height of the standing trees reaches 325 feet, but a fallen tree is estimated to have been over 400 feet high. The diameter of the trunk near the ground sometimes reaches 30 to 35 feet. 129. Resin and turpentine. The conifers in general contain resins, and from certain pines the common resin (or rosin) and turpentine of commerce are obtained. Usu- ally incisions are made into the wood of the trees and a resi- nous liquid exudes, which is crude turpentine. This liquid is distilled, the oil or spirit of turpentine coming off and being collected, and the resin remaining behind in the still. CHAPTER XIII ANGIOSPERMS 130. General characters. This is the greatest group of plants, both in numbers and importance. It comprises more than 100,000 species, and forms the most conspicuous part of the vegetation of the earth. It includes herbs, shrubs, and trees in profusion, and represents the plant kingdom at its highest development. There is the greatest possible variety in habit, size, and duration: from minute floating forms to gigantic trees; erect, prostrate, and climbing; aquatic, terrestrial, epiphytic; from a few days to centuries in duration. The most striking feature of the Angiosperms to the ordinary observer is that the majority of them produce what every one recognizes as flowers; and hence they are often spoken of as flowering plants. The production of flowers, however, is not the real distinction of the group, but it is a very prominent feature and suggests the group to most people better than any other character. The general structure of the roots, stems, and leaves of this great group was presented in Chapters II, III, and IV, so that there remain for consideration the flower and the structures associated with it. 131. The flower. It is impossible and unnecessary to define a flower, but it is not at all difficult to recognize ordinary flowers. They are objects of such common ex- perience that no one is at a loss to understand what is meant when the word is used. The parts of a flower may 220 ANGIOSPERMS 221 be understood best by selecting for description some simple flower that has all the floral members, as, for example, the buttercup. In such a flower there are four distinct sets of members (Fig. 207). The outermost set has the color and the form of small leaves, each member being called a sepal, and the whole set the calyx. The next inner set is usu- ally the showy one, with members of rel- atively large size, delicate texture, and bright color, each member being called a petal, and the whole set the corolla. The set just within the co- rolla comprises the stamens, which produce the pollen. The central set is made up of the carpels, which contain the ovules that are to become seeds. The endless variations of these sepals, petals, stamens, and carpels, make the differences among flowers, and it is astonishing in how many ways the variations of four parts can be combined. It will be impossible to describe even the conspicuous variations and combinations, but certain general tendencies may be pointed out. It is important for the student to examine as many of the common flowers of his neighborhood as possible, and to discover how they differ from one another; for it is these floral differences that are most used in classifying Angiosperms. 132. Sepals. While the sepals generally look like small green leaves, this is by no means always true. Sometimes they are as brightly colored as petals; and often they appear FIG. 207. Flower of peony : k, sepals; c, petals; a, stamens; g, carpels. After STRASBURGER. 222 A TEXT-BOOK OF BOTANY united, so that the calyx is a little cup or tube (Fig. 208). In any case, the calyx is useful in the bud condition of the flower in protecting the more delicate parts within. Some- times the sepals and the petals look so much alike that they are spoken of together as the perianth, as in the common lily (Fig. 274). Occasionally there is only one floral set outside the stamens; and it has become the custom to call it a calyx, assuming that the corolla is lacking. In still other cases, there are no floral members outside the sta- mens; and then the flower is said to be naked. 133. Petals. The attractiveness of flowers usually depends upon their petals, and hence their differences in A B C FIG. 208. Flower of tobacco: A., sympetalous corolla, calyx urn-like; B, tube of corolla cut open and showing attachment of stamens; C, the pistil, showing ovary, style, and stigma. After STRASBURGER. color and form are things of common experience. In many flowers the petals are entirely distinct from one another and can be pulled off separately. In many other flowers, ANGIOSPERMS 223 however, the petals appear to be united so that the corolla becomes a cup, urn, tube, funnel, or the like (Figs. 208 and 209). This condition of the corolla is so constant in the highest group of Angiosperms that the group is called the Sympetalce, because the corollas are sympetalous (petals together). In many flowers with sympetalous corollas there is an irregular development, so that the mouth of the tube, FIG. 209. Sympetalous flowers: A, bluebell; B, phlox; C, dead-nettle; D, snap- dragon; E, toadflax. After GRAY. instead of being regular, is divided into two unequal lips, as in the mints and many others (Fig. 209, C E). Such flowers are said to be bilabiate (two-lipped), and on this account the Mint Family is named Labiatce. Such corollas may have further irregularities in the form of more or less conspicuous projections at the base called spurs (Fig. 209, E). It must not be supposed that irregular growths are found only in connection with sympetalous corollas; for the sweet pea represents a great family in which the petals are all separate, and yet they are very much unlike; and in the violet, whose petals are distinct, one of them has a conspicuous spur. The corolla is useful in protecting the young stamens and carpels, but it is alsc associated with the visits of insects, a subject which will be spoken of later. A TEXT-BOOK OF BOTANY 134. Stamens. From our study of Gymnosperms ( 123), the stamen of the Angiosperm flower is recognized as a spo- rophyll bearing sporangia, which pro- duce the small spores (microspores) called pollen grains. The stamen of Angiosperms, however, has two very distinct regions. There is a stalk, which is usually slender and long, called the -filament; and at the top of this there is the knob-like sporan- gium-bearing region called the anther (Fig. 210). A cross-section of a very young FIG. 210. Front (A) and anther usually shows that it contains back () views of a sta- f our sporangia, that is, four regions in men, showing filament mi\ (/) and anther ( P ), the which spores are formed (Fig. 211). latter including two poi- Ag th ant her matures, the two re- len sacs. After SCHIM- PER. gions on each side run together, so Fio. 211. Cross-section of a very young anther of a lily, showing the four de- veloping sporangia. ANGIOSPERMS 225 that the anther comes to contain only two spore cham- bers (Fig. 212). These two spore chambers are plainly FIG. 212 Cross-section of a mature anther of a lily, much larger than that shown in Fig. 211, showing the two chambers formed by the four sporangia, and also the region of opening (). FIG. 213. Anthers opening by terminal pores: A, Solanum; B, Arbutus; C Vaccinium. A and B, after ENGLER and PRANTL; C, after KERNER A TEXT-BOOK OF BOTANY FIG. 214. Section of the flower of an Althaea, showing sepals (a), petals visible from the outside, looking like two sacs, called pol- len sacs. Ordinarily, therefore, the Angiosperm stamen is said to have two pollen sacs. In most cases the pollen sacs must open so that the pollen may escape, and the method of opening differs in different flowers. By far the most common way is for each pollen sac to split open length- wise, and this line of splitting is usually plainly seen on the surface of the unopened sac (Fig. 210, A). In some cases, however, each pollen sac opens at the top, either by a short slit or by a pore-like opening (Fig. 213, A and B); and in some cases, as among the (6), tube of stamens (c) enclosing heaths, this pore-like Open- style (rf), and ovules (e). After . , t BERG and SCHMIDT. ing may be extended into a more or less prominent tube (Fig. 213, C). There are still other special methods of opening pollen sacs, but they are comparatively rare. In sympetalous corollas it is most common for the stamens to appear fastened to the tube of the corolla (Fig. 208, B), and this condition is usually described as "stamens inserted on the tube of the corolla." Stamens may also appear united, forming a tube, as in mallows (hollyhock, etc.) (Fig. 214); or they may be in two sets, as in the sweet pea, in which nine of the stamens appear united and the tenth one is free (Figs. 241 and 283). 135. Carpels. It has been noted that carpels are the sporophylls that be'ar the peculiar sporangia called ovules ( 123). There is a striking difference, however, between the carpels of Gymnosperms and Angiosperms, a difference that gives names to the two groups. In Gymnosperms the ANGIOSPERMS 227 ovules are exposed on the surface of the carpel, while in the Angiosperms they are enclosed by the carpel as in a closed vessel. Gymnosperm means "seed naked/' and Angiosperm means "seed in a vessel "; hence the names of the groups refer to this difference in the carpels. The carpel of an Angiosperm flower has the general shape of a flask (Figs. 207 and 215, A). The bulbous bottom in which the ovules are enclosed is called the ovary; the neck of the flask, which may be short or long, is called the style; and upon the style, either on its top, which is often knob-like, or along its side, there is a specially pre- pared surface to receive the pollen, known as the stigma. This stigmatic surface, when ready to receive the pollen, is sticky; the style, unlike the neck of a flask, is usually solid; so that the ovary is the only part of the carpel that is hollow. The ovules in an ovary vary in number from a single one to a great number, and they are borne in a variety of positions on the inner wall of the ovary. In many flowers the carpels remain separate (Figs. 207 and 215, A), as in the buttercups ; but it is very common for all the carpels of a flower to unite in the formation of a single structure, whose general outline is that of a single car- pel. That is, it has a single ovary and may have a single style (Figs. 208, C, and 215, C). It is convenient to have a word to apply to this ovule-containing structure, whether it consists of one carpel or of several organized together, FIG. 215. A, simple pistils (each one a single carpel); B and C, compound pistils (each one composed of several carpels). After BERG and SCHMIDT. A TEXT-BOOK OP BOTANY and such a word is pistil. A pistil, therefore, is any organ- ization of carpels that appears as a single organ with one ovary. A pistil composed of one carpel is called a simple pistil (Figs. 207 and 215, A), and one composed of more than one carpel is a compound pistil (Figs. 208, C, and 215, C). When a flower has one pistil, it is necessary to dis- cover whether it is a simple or a compound pistil, and if it is the latter to determine the number of carpels that enter into its structure. Sometimes the styles are separate (Fig. 215, B], or the single style is cleft more or less deeply; and in either case the answers to both questions are very apparent. But often the style is single throughout and does not indicate the number of carpels. In that case the ovary must be cross-sectioned, and if the section reveals more than one ovule chamber the compound character and the number of carpels are usually apparent (Fig. 216, B). Sometimes, however, a compound ovary may have only one ovule chamber, and in this case the number of A B FIG. 216. Diagrammatic cross-section of compound ovaries: A, a one-charnbered ovule composed of three carpels; B, a three-chambered ovule. After SCHIMPER. carpels may be indicated by the number of rows of ovules on the wall (Fig. 216, A}. It is necessary to know something about the structure of the Angiosperm ovule (Fig. 217). That it is a sporangium containing one large spore (megaspore) that is never shed, was pointed out in connection with the Gymnosperms ANGIOSPERMS 229 ( 123). On the outside of this ovule one or two special coverings are developed, called integuments. These integu- ments grow up about the ovule, but do not completely cover it at the top, leaving a little opening called the micropyle (little gate). This micropyle is a very important B Fio. 217. Diagrammatic longitudinal sections of ovules, showing outer (01) and inner (it) integuments, micropyle (m), nucellus (n), and megaspore (em), the last often called embryo sac: A, erect ovule; B, curved ovule; C, inverted ovule. feature in the ovule and also later in the seed. The body of the ovule within the integuments is called the nucellus, and within the nucellus the large spore (megaspore) lies embedded (Fig. 217). The three types of ovule are shown in Fig. 217: the erect ovule (A), the curved ovule (B), and the inverted ovule ((7), the last being the most common. 136. Floral numbers. In many flowers there is no regularity in the number of members in each set. For example, in the water-lily petals and stamens occur in indefinite numbers; and in the buttercup the same is true of stamens and carpels. In most flowers, however, definite numbers appear either in some of the sets or in all of them. When these definite numbers are present, they are prevail- ingly either three or five; that is, there are either three or five sepals, petals, stamens, and carpels; although it is very common to have two sets of stamens, in which case they number six or ten. These numbers appear so constantly in great groups that the two grand divisions of Angio- 230 A TEXT-BOOK OF BOTANY sperms, called Monocotyledons and Dicotyledons, are char- acterized by them, the former having the parts of the flower in threes, the latter in fives. This does not mean that all flowers of these two divisions have one or the other number, but that these are the prevailing numbers in case there is a definite number at all. Not a few Dicotyledons have flowers with the parts in threes, and a still larger number have them in fours. 137. Staminate and pistillate flowers. In many cases stamens and pistils are not found together in the same flower. In such cases there are staminate flowers, that is, those without pistils; and pistillate flowers, that is, those without stamens. These two kinds of flowers may be borne upon the same plant, which is then said to be monoecious (one household); or upon different plants, which are then said to be dioecious (two households). These terms are applied indifferently to the plants or to the flowers, either the plants or the flowers being spoken of as monoecious or dioecious. In a dioecious plant, therefore, FIG. 218. Hypogynous flower of Potentilla (A), and epigynous flower of apple (B). After ENGLEB and PRANTL. one can speak of staminate and pistillate plants, one bear- ing fruit and seed and the other not. Many of our common trees, as willows and poplars, are dioecious; and many more, as oaks, walnuts, and hickories, are monoecious. ANGIOSPERMS 231 138. Hypogynous and epigynous flowers. In many flowers the sepals, petals, and stamens are seen to be FIG. 219. Dogtooth violet, with hypogynous flowers (Lily Family). attached under the ovary, that is, the ovary appears within the flower (Fig. 218, A). Such a flower is said to be 16 232 A TEXT-BOOK OF BOTANY hypogynous (under the pistil) , and in descriptions of flowers this condition is often called "ovary superior." In many other flowers, on the other hand, the sepals, petals, and stamens all seem to be attached to the top of the ovary; that is, the o^ary ap- pears beneath the flower (Fig. 218, B). Such a flower is called epigynous (upon the pistil), or described often as "ovary inferior." This is a very important dis- tinction, because it characterizes great groups of plants; for example, all mem- bers of the Lily Family are hypogynous (Fig. 219), and all members of the Ama- ryllis and Iris Families are epigynous (Fig. 220). It is also interesting to note that all the plants of highest rank in their respective lines have epigynous flowers. 139. Flower clusters. In many cases a single flower terminates the stem, or flowers may occur in the axils of ordi- But more frequently flow- . , _ . A , f , ers occur in definite clusters, which are characteristic and help to distinguish plants. It is unnecessary to enumerate all the forms of flower clusters and their names, but some of the more important may be noted. One of the most common kinds of clusters is that in which the flowers arise along an axis, resulting in a more or less elongated and often drooping cluster. This is called a raceme, and the flowers may be loosely or densely arranged (Fig. 221). If in such a cluster the flowers have no stalks, and rest directly on the axis, the cluster is called a spike, as in the common plantain (Fig. 222). If the cluster is flat-topped, with the flower-stalks rising and ers (Amaryllis Fami- nar y leaves. ly). After STRAS- J BURGER. ANGIOSPERMS 233 spreading like the braces of an umbrella, it is an umbel, as in cherry (Fig. 223), wild parsnip, carrot, etc. (Fig. 224). If one can imagine the flowers of an umbel without any stalks, so that they would be packed closely together at the 234: A TEXT-BOOK OF BOTANY top of the main axis, the cluster is called a head, the most notable illustrations being such plants as the sunflower or dandelion, whose so-called r^-^ " flowers " are compact clus- j ters or heads of numerous small flowers (Figs. 298 and 299). FIG. 223. Umbel of cherry. After DUCHARTRE. FIG. 224. Umbel of hemlock. After SCHIMPER. ANGIOSPpRMS 235 140. The gametophytes. The gametophytes of Angio- sperms are even more reduced than those of Gymnosperms ( 124). In order to see them, special preparations for the microscope are necessary, but with the help of illustrations some idea of them may be obtained. By the pollen grain (microspore) three cells are formed, and two of them are male cells or sperms; these three cells represent the male gametophyte (Fig. 225). Within the large spore (megaspore) , which is retained in the ovule, seven cells usually ap- pear; and one of these is an egg, no archego- FIG. 225. Pollen grain containing a three -celled male gameto- phyte; one cell represented by its nucleus, the two other cells being male cells. FIG. 226. The female gametophyte of a lily before fertilization, within the old mega- spore wall eight cells or their nuclei appear- ing, one of which is an egg (e) ; the pollen tube enters through the micropyle (m). nium to contain it being formed. These seven cells repre- sent the female gametophyte before fertilization (Fig. 226). The sperms produced by the pollen must reach the egg within the ovule. The stamens chat produce the pollen may be in the same flower as the pistil that contains the ovules with their eggs, or they may be in another flower on the same plant, or they may be borne by an entirely different plant. In any event, the first thing done is to transfer the pollen to the pistil. This transfer, that is, 236 A TEXT-BOOK OF BOTANY pollination ( 125), is effected in many Angiosperms by insects, and how this is brought about will be described later. The pollen grains that reach the stigma, the specially prepared surface for receiving them, begin to put out pollen tubes. These tubes grow through the stigma and enter the style; grow down the style and enter the cavity of the ovary; reach the ovules and enter their micropyles; and finally penetrate the ovule to the egg (Fig. 227). Through- out this progress of the tube the male cells are in its tip, and when the egg is reached they are discharged from the tube and one of them fuses with the egg. This is the act of fertiliza- tion, and through it the egg becomes an oospore. An important difference between Gymnosperms and Angiosperms should be noted here. In Gymnosperms the pollen reaches the ovules, for they are exposed; but in Angiosperms the pol- len reaches only the surface (stigma) FIG. 227.-Diagrammatic f the P lstil that encloses the OVUleS. representation of pollen 141. Embryo. The oospore, lying tubes penetrating the , . , , , , style; one of them en- in the midst of the ovule, at once be- tering the ovary cavity, ~ ms to nr erm i na t e , and forms a young passing down its wall, . and reaching the female plant or embryo. While the embryo is forming, the ovule develops a hard coat outside, and a seed is the result (Fig. 228). The general structure of the seed and how the young plant escapes from the seed have been described in Chapter V. The two great divisions of Angiosperms are named ANGIOSPERMS 237 FIG. 228. Seed of violet, one figure show- ing the hard testa, the other the em- bryo (young sporophyte) that has developed from the oospore. After BAILLON. from the peculiar character of their embryos. In one division the root is developed at one end of the embryo and the single cotyledon at the other end, the stem coming out on one side. In the other division the root is developed at one end of the embryo and the stem at the other end, two cotyle- dons coming out on oppo- site sides just behind the stem tip. Therefore, the first division is called Mono- cotyledons (one cotyledon), and the second is called Di- cotyledons (two cotyledons). There are many other differ- ences between Monocotyledons and Dicotyledons, but this difference between the embryos has been selected to form the names. The embryos of Angiosperms differ much as to the com- pleteness of their development within the seed. In some plants the embryo is merely a mass of cells, without any organization of root, stem, or leaf. In many plants, on the other hand, the embryo becomes highly developed, showing all the principal organs and the plumule con- taining several well-organized young leaves (Chapter V). 142. Seed. The seed is evidently an ovule (sporangium) containing a female gametophyte which has developed a new sporophyte (embryo). This complex structure is invested by the hard seed-coat, and is a protected resting condition of the plant. The seed-coat (testa) in Angiosperms is exceedingly variable in structure and appearance. Sometimes it is smooth and glistening, sometimes pitted, sometimes rough with warts or ridges. In many cases prominent append- 238 A TEXT-BOOK OF BOTANY ages are produced, as wings, tufts of hairs, etc., which assist in seed dispersal, a subject which will be considered later. 143. Fruit. Accompanying the changes in ovules in- volved in the formation of seeds, there are other changes in the surrounding parts resulting in the formation of a fruit. These changes may involve only the ovary wall, or they may include also other adjacent structures; but the whole resulting structure, whatever it may include, is called a fruit. The fruits of Angiosperms are so exceedingly diverse that it will be possible to give only a very general outline of the various kinds. For convenience, those fruits will be considered first that represent only the enlarged and modified ovary. Such fruits may be placed in two groups: those that ripen dry and those that ripen fleshy. (1) DRY FRUITS. In these the ovary wall not only changes, but also usually becomes hard or parchment-like. Dry fruits may open to discharge their seeds, but often when there is only one seed in an ovary the fruit does not open. Thus there are two groups of dry fruits: the dehiscent (open- ing) and the indehis- cent (unopening). a. Dehiscent fruits. Dry fruits that open are in general called pods, and usually they open by splitting, as the pods of peas and beans. The great fam- ily to which peas and FIG. 229.-Pod of sweet beans belong is named FlG - 230. Capsule of nea dehismncr. Af- iris dphisrincr. After pea dehiscing, ter GRAY. for its pod, being iris dehiscing.- GRAY. ANGIOSPERMS called the Leguminosce, a legume being a special kind of pod (Fig. 229). When a pod is derived from a compound pistil, forming a fruit of several cham- bers, it is more commonly called a cap- sule; and capsules differ from one an- other in the way the chambers are opened (Fig. 230). b. Indehiscent fruits. The most com- mon form of dry fruits that do not open is that in which the modified ovary wall invests the solitary seed so closely that the fruit looks like a seed, and is com- monly called a seed. The grain of cere- als is such a seed-like fruit, as is also the akene of sun-flowers, dandelions, etc. (Fig. 231). (2) FLESHY FRUITS. In some cases the whole ovary becomes a thin-skinned pulpy mass in which the seeds are em- bedded, as the grape, currant, gooseberry, tomato, etc., such a fruit being a berry. . Modifications of the berry are seen in such fruits as the orange and the lemon, in which the skin is leathery; and in such fruits as melons and pumpkins, which be- come covered with a hard rind. Very distinct from these are the stone-fruits (drupes), as peach, plum, cherry, etc., in which the ovary wall ripens in two layers, the inner one being very hard, forming the "stone/ 7 and the outer one being pulpy (Fig. 232). In general, fleshy fruits do not open; but the banana is a peculiar fleshy fruit that de- hisces. Fro. 231. Akene of dandelion, which ta- pers above into a long beak bearing a tuft of hairs. After GRAY. Fro. 232. Section of peach, showing pulp and stone formed from ovary wall and enclosing the seed (kernel). After GRAY. 240 A TEXT-BOOK OF BOTANY All of the fruits mentioned above include only a modi- fied ovary wall with its contents, but many of the most FIG. 233. Raspberry: A. flower-stalk, with calyx, old stamens, and prominent receptacle, from which the berry (a cluster of small stone-fruits) has been removed (J5). After BAILEY. FIG. 234. Strawberry: an enlarged pulpy receptacle in which numerous small akenes are embedded. common fruits do not answer to this description. A few of the most conspicuous of these will serve as illustrations. A number of the best-known fruits have been named "berries" that are not berries as described above. For r FIG. 235. Longitudinal and transverse sections of apple, showing the five-celled ovary (core) embedded in the fleshy cup of the flower. example, a raspberry is a mass of very small stone-fruits that slips from the enlarged top of the flower axis (recep- ANGIOSPERMS 241 tacle) like a cap (Fig. 233). A strawberry is a very much enlarged and fleshy receptacle, in the surface of which minute akenes are imbedded (Fig. 234). A blackberry is not only a cylindrical mass of small stone-fruits, but also includes the fleshy receptacle. In such fruits as apples, pears, and quinces, the fleshy part is the modified cup-like base of the flower surrounding FIG. 236. Pineapple in surface view and section. the ovary, which with its contained seeds is represented by the core (Fig. 235). An extreme case is the pineapple, in which a whole flower-cluster has become an enlarged fleshy mass, including axis and bracts (Fig. 236). CHAPTER XIV FLOWERS AND INSECTS 144. Pollination. Among Gymnosperms the pollen is transferred by the wind, and this is true also of many Angiosperms. But the prevailing method of pollination among Angiosperms is the use of insects as the agents of transfer. This mutually helpful relation between flowers and insects is a very remarkable one, and in some cases it has become so intimate that they cannot exist without each other. Flowers are modified in many ways in rela- tion to insect visits, and insects are variously adapted to flowers. The pollen may be transferred to the stigma of its own flower (self-pollination), or to the stigma of some other flower of the same kind (cross-pollination). In the latter case the two flowers concerned may be upon the same plant or upon different plants, which may be quite distant from one another. Since flowers are very commonly ar- ranged to secure cross-pollination, it must be more advan- tageous in general than self-pollination. The advantage of this relation to the insect is to secure food. This the flower provides in the form of .either nectar or pollen; and insects visiting flowers may be grouped as nectar-feeders, represented by moths and butterflies, and pollen-feeders, represented by the numerous bees and wasps. The presence of these supplies of food in the flower is made known to the insect by the display of color, by odor, or by form. It should be said that the attraction of insects to 242 FLOWERS AND INSECTS 243 flowers by color has been doubted, since it is claimed that some of the common flower-visiting insects are color-blind, but remarkably keen of scent. However this may be for some insects, it seems to be sufficiently established that many insects recognize their feeding ground by the display of color. It is evident that all insects attracted by nectar or pollen are not suitable for the work of pollination. For instance, ordinary ants are fond of such food, but as they walk from plant to plant any pollen dusted upon them is almost sure to be brushed off on the way and lost. The most favorable insect is the flying one, which can pass from flower to flower through the air. It will be seen, therefore, that the flower not only must secure the visits of suitable insects, but also must guard against the depredations of unsuitable ones. 145. Self-pollination. It is evident that in many cases self-pollination is likely to occur. In some flowers the sta- mens and carpels are so related to one another in position that when pollen is being shed some of it may fall upon the stigma. Even the visit of an insect, which usually results in cross-pollination, may result in self-pollination. It must not be understood that only cross-pollination is really provided for, and that when self-pollination occurs it is more or less of an accident. In addition to the numer- ous cases of what may be called accidental self-polli- nation in flowers usually cross-pollinated, self-pollination is definitely provided for more extensively than once was supposed. It is found that many plants, as violets, for example, in addition to the usual showy insect-pollinated flowers, produce flowers that are not at all showy, that in fact do not open, and are often not prominently placed. These inconspicuous closed flowers are called cleistogamous flowers; and in these flowers self-pollination is necessary, and very effective in producing good seed. 244 A TEXT-BOOK OF BOTANY 146. Yucca and Pronuba. This is a remarkable case of self-pollination by means of an insect. Yucca is a plant of the southwest- ern arid regions of North America, and Pronuba is a moth; and the two are very dependent upon each other. The bell - shaped flowers of Yucca hang in great ter- minal clusters. In each pendent flower FIG. 237. The pendent flower of Yucca, showing (Fig- 237) there are position of stamens and the ribbed ovary. After gjx hanging sta- mens, and an ovary ribbed lengthwise, with a fun- nel-shaped stigmatic opening in its top (Fig. 238). The numerous small ovules occur in rows beneath the furrows. RILEY and TRELEASE. FIG. 238 Longitudinal section of an ovary of Yucca, showing the funnel- shaped stigmatic opening (s), and the rows of ovules attached to the wall (o). After RILEY and TRELEASE. FIG. 239. The position of Pronuba on the stamen of Yucca when collecting pollen (.4) and when thrusting it into the stigmatic funnel (B). Af- ter RILEY and TRELEASE. FLOWERS AND INSECTS 245 During the day the small female Pronuba rests quietly within the flower, but at dusk becomes very active. She travels down the stamens, and resting on an open pollen sac scoops out the somewhat sticky pollen with her front legs (Fig. 239, A). Holding the little mass of pollen against her body, she runs to the ovary, stands astride one of the furrows, and piercing through the wall with her ovipositor deposits an egg in an ovule. After depositing several eggs in this way, she runs to the top of the ovary and begins to crowd into the funnel- shaped stigmatic cavity the mass of pollen she has collected (Fig. 239, ). These actions are re- peated several times, until many eggs have been deposited and repeated pollination has been effected. As a result of this, seeds are formed which develop abundant nourishment for the moth larvae, which become mature and bore their way out through the wall of the capsule (Fig. 240). 147. Cross-pollination. In those flowers in which cross- pollination is the rule, self-pollination is hindered in a variety of ways. In the cases about to be considered, stamens and carpels are together in the same flower; of course, in dioecious plants there can be no such thing as self-pollination. It is necessary to remember also that when the stigma is ready to receive the pollen, it excretes upon its surface a sweetish, sticky fluid, which holds and feeds the pollen, inducing the development of pollen tubes. FIG. 240. A mature capsule of Yucca, showing perforations made by larvae of Pronuba in escaping. After RILEY and TRELEASE. 246 A TEXT-BOOK OF BOTANY In this condition the stigma is said to be ready or mature. The pollen is mature when it is ready to fall out of the pollen sacs or to be removed from them. In obtaining nectar or pollen as food, the visiting insect receives pollen on some part of its body which will be likely to come in contact with the stigma of the next flower visited. Cross-pollinating flowers may be illustrated under three heads, distinguished from one another by their methods of hindering self-pollination; but it must be understood that almost every kind of flower has its own way of solving the problems of pollination. It is an exceedingly interesting and profitable exercise for the student to examine as many cross-pollinating 1 flowers as possible, with the view of de- termining in each case how self-pollination is hindered, how cross-pollination is secured, and how the visits of unsuitable insects are discouraged. (1) Position. In these cases the pollen and the stig- ma are ready at the same time; but their position in refer- ence to each oth- er, or in reference to some conforma- tion of the flower, makes it unlike- ly that the pol- len will fall upon the stigma. The three following illustrations, se- lected from hun- dreds, may be given : In the family (Leguminosce) to which the pea, bean, etc., belong, Fia. 241 . Rose aeacia : A , keel projecting from hairy calyx, the other petals having been removed; B, protrusion of tip of style when keel is depressed ; C. section showing position of parts within keel. After GRAY. FLOWERS AND INSECTS 247 the several stamens and the single carpel are in a cluster enclosed in a boat-shaped structure (keel) formed by two of the petals (Fig. 241). The stigma is at the summit of the style and projects somewhat beyond the pollen sacs, some of whose pollen lodges on a hairy zone on the style below the stigma. While the stigma is not alto- gether secure from receiving some pollen, the position does not favor it. The projecting keel is the nat- ural landing place for a bee visiting the flower; and it is so inserted that the weight of the insect depresses it, and the stig- ma comes in contact with its body. Not only does the stigma strike the body, but by the glan- cing blow the surface of the style is rubbed against the insect; and upon this style, below the stigma, the pollen has been shed and is rubbed off against , . . , the insect. At the next flower Visited the Stigma IS likely to Strike the pol- len obtained from the pre- FIG. 242. Longitudinal section of flower of iris, showing a single stamen between the drooping petal and the petal-like style; the stigmatic shelf is seen above the stamen, at the top of the style; the nectar vious flower, and the style will deposit a new supply of pollen. It is interesting to press down slightly the keel of such a flower and see the style apparently dart out. In the iris or common flag, each stamen is in a kind of pocket between the petal and the petal-like style; while the stigmatic surface is on the top of a flap or shelf which 17 248 A TEXT-BOOK OF BOTANY the style sends out as a roof to the pocket (Fig. 242). With such an arrangement it would seem impossible for the pollen to reach the stigma unaided. The nectar is in a little pit at the bottom of the pocket. As the insect crowds its way into the nar- rowing pocket, its body is dusted by the pollen; and when it visits the next flower, and pushes aside the stigmatic shelf, it is likely to deposit upon it some of the pollen previously re- ceived. In the orchids, remark- able for their strange and beautiful flowers, the story of pollination is still more complicated. There are usually two pollen sacs, and the pollen grains are not dry and powdery, but cling together in a mass (pollin- iwri), which must be pulled out bodily. An illustration of a common method of PIG. 243. Flower of rein orchis: A, com- plete flower, showing three broad se- pals, three narrower petals (one of which forms the long lip and the much longer spur), two pollen sacs, between pollination may be obtained which extends the concave stigmatic surface (at the bottom of which the opening to the tube is seen); B, more chis (Fig. 243). enlarged view of pollen sacs, stigmatic surface, and buttons ; C, a pollinium 11 tWO pollen rpn nr- Each of the maSSCS termi- removed; D, a button enlarged. Af- na tes in a Sticky disk Or ter GRAY. button; and between them extends the concave stigmatic surface, at the bottom of which is the opening into the long tube-like spur in the bottom of which the nectar is found. Such a flower is FLOWERS AND INSECTS 249 adapted to the large moths, with long proboscides which can reach the bottom of the tube. As the moth thrusts its proboscis into the tube, its head is pressed against the sticky button on each side, so that when it flies away these buttons stick to its head and the pollen masses are torn out. When the next flower is visited these pollen masses are thrust against the stigmatic surface. (2) Consecutive maturity. In these cases pollen and stig- ma of the same flower are not mature at the same time. This is a common method of preventing self-pollination, and it is evident that it is effective. When the pollen is being shed, the stigma is not ready to receive; or when the stigma is ready to receive, the pollen is not ready to be shed. When the flowers of the ordinary figwort first open, the style bearing the stigma at its tip is found protruding B C FIG. 244. Protogynous flower of figwort: .4, first stage, with stigma receptive; B, section of A, showing stamens within the corolla; C, second stage, with stigma past and anthers in position for shedding. After GRAY. from the urn-like flower, while the four stamens are curved down into the tube, and are not ready to shed their pollen (Fig. 244, A and B}. At some later time, the style bearing the stigma wilts, and the stamens straighten up and pro- trude from the tube (Fig. 244, C). In this way, first the 250 A TEXT-BOOK OF BOTANY receptive stigma, and afterward the shedding pollen sacs occupy the same position. A visiting insect will probably find flowers in both conditions; and, while striking against protruding and shedding pollen sacs in some flowers, it strikes against a protruding stigma in other flowers, and thus carries pollen from one to the other. Such flowers are called protogynous , which means "pistil first." More frequently, however, flowers are protandrous, which means "stamens first." For example, when the showy flowers of the common fireweed, or great willow herb, first open, the eight shedding stamens project prominently, the style being sharply curved downward and backward, carrying the stigmatic lobes well out of the way (Fig. 245, A). Later, the stamens bend away and the style straightens A B FIG. 245. Protandr&us flower of willow herb: A, first stage, with anthers in posi- tion for shedding and style curved downward; B, second stage, with anthers past and stigmatic lobes in position for receiving pollen. After GRAY. up and exposes the stigma (Fig. 245, B). The result of the visits of an insect is the same as in the case of the pro- togynous flowers. So many cases of protandrous flowers occur among common wild and cultivated plants that illustrations should be discovered easily. (3) Difference in pollen. In these cases there are gen- erally two forms of flowers, which differ from each other in the relative lengths of tneir stamens and styles. In the accompanying illustration it will be seen that in one FLOWERS AND INSECTS 251 flower the stamens are short and included in the tube, while the style is long and projecting, with the four stig- matic lobes exposed well above the corolla (Fig. 246, A). A FIG. 246. Flowers of Houatonia: A, form with short stamens and long style; B, form with long stamens and short style. After GRAY. In the other flower the relative lengths are exactly reversed, the style being short and included in the tube, and the stamens long and projecting (Fig. 246, B). It appears that the pollen from the short stamens is more effective upon the short style; and that the pollen from the long stamens is more effective upon the long style. The body of the visiting insect fills the corolla tube and projects above it. In visiting flowers of both kinds, one region of the body receives pollen from the short stamens, and another region from the long stamens. In this way the insect is soon carrying about two bands of pollen, which come in contact with corresponding stigmas. 252 A TEXT-BOOK OP BOTANY 148. Figs. Perhaps the most remarkable case of an intimate relationship between insects and flowers is that which exists between a small wasp (Blastophaga) and the cultivated fig. The full story is too intricate and variable for presentation here, but a very general outline may give some little idea of the situation. The flowers of the fig are borne in a very peculiar way. What is called a fig is a hollow structure (Fig. 247, A], completely closed except for a minute open- ing at the top, and bearing small flow- ers in large num- bers upon the inner wall (Fig. 247, B). Figs are dioecious, so that some trees bear only figs with staminate flowers (Fig. 247, C), and others only figs with pistillate flow- FIG. 247. The fig: A, branch bearing a fig; B, sec- erS (Fig. 247, D). The fig that has been cultivated for very many centuries in countries about the Mediterranean is the pistillate tree. In order to make it fruit properly, fig-bearing branches from staminate trees are hung in the pistillate trees. These staminate figs were called "wild figs" or ca'prifigs, and the process of placing them on the pistillate tree was called caprification. Only in recent times has the meaning of this very ancient process become known. As the plants are dioecious, caprification is evidently bringing the staminate flowers near enough to the pistillate flowers to secure a transfer of the pollen. As both kinds of flowers are enclosed in the fig, tion of fig showing flowers within; C, staminate flower ; D, pistillate flower. After WOSSIDLO. FLOWERS AND INSECTS 253 it is evident that neither the wind nor an ordinary insect can transfer the pollen. This is effected by the small fig wasp that passes its whole existence within the figs. Its real home is the staminate fig (caprifig), and there it deposits its eggs and dies. The new generation of fig wasps crawl out of the old fig, and entering another one that is young deposit their eggs and die, and so on. A staminate fig-tree usually bears three crops of caprifigs each year, the troe never being without a crop; and so three generations of fig wasps are produced in the year, and there is always a home for them. When a branch bearing staminate figs is placed in a tree bearing pistillate ones, the young wasps crawling out of the former enter the latter, which at this stage closely resemble the caprifigs. Having entered, the wasps find themselves in a trap, for the flower structures are such that they cannot deposit eggs properly. But their bodies are covered with pollen from their former home, and running about among the pistillate flowers they pollinate them very completely. As a consequence, the pistillate fig ripens, forms numerous seeds, and acquires the peculiar nutty flavor that characterizes it. Pistillate figs ripen without this process, but they do not set seed nor acquire the characteristic flavor, nor can they be dried for shipping. They can only be used as fresh figs, and are not at all the ordinary figs of commerce, known as Smyrna figs. During the last years of the past century the United States Department of Agriculture, after several failures, succeeded in introducing the fig wasp into California, so that real Smyrna figs are now being grown in our own country. 149. Hybrids. In the transfer of pollen by wind and insects, some of it may reach stigmas belonging to a differ- ent kind of plant. If this plant is nearly related to the one that has produced the pollen, fertilization may result. 254 A TEXT-BOOK OF BOTANY When the seeds formed in this way germinate, they produce plants that are called hybrids] that is, plant's whose two parents belong to different species or races. The hybrid usually shows some combination of the characters of both parents, but it may be very different from either. In this way new kinds of plants often arise in nature, and advantage is taken of this fact to produce new forms in cultivation. This cross-pollination between plants of differ- ent kinds, resulting in cross-fertilization, is usually spoken of simply as crossing, and the use of crossing in producing new forms will be spoken of more fully in the chapter on plant breeding. An illustration of what is meant by hybrids may be obtained from corn. There are several races of corn that differ in the color of the grains, which are white, yellow, red, or lead-colored. If a white race be crossed with a red race, the resulting ears will be hybrids, and will very likely show both colors in the same ear. When the grains are sown and produce new plants, these plants are hybrids and will show resemblances to both parents. CHAPTER XV SEED-DISPERSAL 150. Reasons for dispersal. If all seeds dropped about the parent plants, there soon would not be room enough for any more to grow, and those that did grow would in- terfere with one another seriously. It is of advantage both to the parent plant and to the young plants for the seeds to be scattered beyond the reach of such rivalry. Accordingly, there are many ways by which seeds are dis- persed, and sometimes they are carried to great distances. When fruits open to discharge seeds, the seeds themselves are scattered; but when fruits do not open, the fruit itself is transported. 151. Dispersal by discharge. In some plants there is a mechanical discharge of seeds provided for in the structure of the seed-vessel, such t fruits often being called FIG. 248. The fruit of violet dig- FIG. 249. The pods of a wild bean (Lotus) charging seeds. After BAIL- twisting in discharging seeds. After LON. BA.ILLON. 255 256 A TEXT-BOOK OF BOTANY sling-fruits. In the violet and the witch-hazel, when the seed-vessel splits, its walls press upon the seeds so that they are pinched out, as a moist apple-seed is projected by being pressed between the thumb and the finger (Fig. 248). When the pod of the wild bean bursts, the two valves twist violently and throw the seeds (Fig. 249). In the touch-me- not, or the balsam, a strain is devel- oped in the grow- ing wall of the seed-vessel, so that at rupture, which may be brought FIG. 250. Winged fruit of maple. After KEENER. about by slight pressure, the pieces suddenly curl up and throw the seeds. The squirting cucumber is so named because it becomes very much distended with water, which is finally forcibly ejected FIG. 251. Winged seed of Bignonin. After STRASBTTRGER. along with the mass of seed. In tropical forests there are plants whose large seed-vessels explode with a loud report. SEED-DISPERSAL 257 This method may be regarded as the poorest of all the methods of dispersal, for at the very best no seed-vessel can discharge its seeds more than a very short distance. 152. Dispersal by currents of air. Many seeds are so light as to be carried about by currents of air. Ordinarily, however, the wind-dispersed seeds or fruits develop special appendages to aid in their flight, commonest among which are wings and tufts of hair. For example, wings are de- veloped by the fruit of ma- ples (Fig. 250) and elms, and by the seeds of catalpa and its allies (Fig. 251). Plumes and tufts of hair are devel- FIG. 252. Akenes of dandelion with tufts of hair. After KEENER. FIG. 253. Akenes of Senecio with tufts of hair. After KEENER. oped by the seed-like fruits of thistle, dandelion (Fig. 252), and many of their relatives (Fig. 253); and by the seeds of milkweeds (Fig. 254), willow herbs (Fig. 255), etc. On plains, or level stretches, where winds are strong, a curious habit of seed-dispersal has been developed by certain plants known as tumbleweeds or field rollers (Fig. 256). These plants are profusely branching annuals with 258 A TEXT-BOOK OF BOTANY a small root system in light or sandy soil. When the work of the season is over, and the absorbing rootlets have shriveled, the plant is easily broken from its FIG. 254. Seed of milkweed with tuft of hair. After GRAY. FIG. 255.- -Seed of willow herb with tuft of hair. FIG. 256. A common tumbleweed. SEED-DISPERSAL 259 roots by a gust of wind, and is trundled along the surface like a light wicker ball, the ripe seed-vessels dropping their seeds by the way. In case of an obstruction, such as a fence, great masses of these tumble weeds may be seen lodged against the windward side. This method of dispersal is far more effective than the mechanical discharge; but it is fitful, and its range usually is not very great. Thistle-down may be floated into a neighboring field, and a strong wind may carry the com- paratively heavy-winged fruits of the maple and the elm some distance; but at best the scattering is only over a neighborhood. 153. Dispersal by currents of water. Many seeds are buoyant, or become so after soaking in water, and may be carried great distances by currents. For example, the banks and flood-plains of streams may receive seeds from a wide area, dependent on the extent of the drainage system. Along the lower stretches of rivers such as the Mississippi, the Missouri, or the Ohio, almost every season new plants are added to those growing along the banks, and some of them may have come from great distances. This kind of distribution, therefore, may become almost continental in extent. Still more far-reaching is the dispersal brought about by oceanic currents, both by waves carrying seeds along the coast, and also by the deeper currents that extend from continent to continent or to oceanic islands. It has been found that many seeds can endure even prolonged soaking in sea-water and then germinate. From a series of experiments, Darwin estimated that at least fourteen per cent of the seeds of British plants can retain their vitality in sea- water for twenty-eight days. At the ordinary rate of movement of ocean currents, this length of time would permit seeds to be transported over a thousand miles. It is thought that the appearance on islands of 260 A TEXT-BOOK OF BOTANY certain plants belonging to an adjacent continent may often be explained in this way. 154. Dispersal by animals. Only a few illustrations of this very large subject can be given. Water-birds are great carriers of seeds, which are con- tained in the mud clinging to their feet and legs. This mud from the borders of ponds is usually completely filled with seeds of various plants. One has no con- ception of the number until it is actually computed. The following extract from Darwin's Origin of Species illustrates this point : "I took, in February, three tablespoonfuls of mud from three different points beneath the water, on the edge of a little pond. The mud when dried weighed FIG 257. Akene only 6 1 ounces; I kept it cov- of Spanish nee- ere d up i n m y study for six dies with barbed appendages.-Af- weeks > pulling up and counting ter KEENER. each plant as it grew; the plants were of many kinds, and were altogether 537 in number; and yet the viscid mud was all contained in a breakfast cup!" Water-birds are generally high and strong fliers, and the seeds may be trans- ported thus to the margins of distant ponds and lakes, and so become very widely dispersed. In many cases seeds or fruits or heads develop grappling appendages of various kinds, forming the various burs, which barbed appendages. lay hold of animals brushing past; and so the seeds are dispersed. Common illustrations of fruits with grappling appendages are Spanish needles SEED-DISPERSAL 261 (Fig. 257), beggar-ticks (Fig. 258), stick seeds, etc.; and similar appendages are developed in connection with the involucres of cockle-bur (Fig. 259, A), burdock (Fig. 259, B), etc. Fleshy fruits are at- tractive as food to cer- tain birds and mam- mals. Many of the seeds (such as those of A grapes) may be able tO FIG. 259. Heads of cockle-bur (A) and burdock resist the attacks of the ^ i^.-\^K^^ nd&ge9 f the digestive fluids and es- cape from the alimentary tract in a condition to germi- nate. As if to attract the attention of fruit-eating ani- mals, fleshy fruits usually become brightly colored when ripe, so that they are plainly seen in contrast with the foliage, CHAPTER XVI MONOCOTYLEDONS 155. Classification. The Angiosperms are so numerous that it requires much time through several seasons to get acquainted fairly well with them in any one neighborhood. The elementary student should begin at once to cultivate this acquaintance by learning to recognize the most promi- nent groups and the most common representatives of each group. For example, there should be no difficulty usually in recognizing whether a given plant is a Monocotyledon or a Dicotyledon; since the floral number, the venation, and the stem arrangement of vascular bundles will determine that in most cases. In each of these two great divisions of Angiosperms, however, there are numerous families, and one should be- come acquainted early with the most conspicuous families of a neighborhood. For example, a very conspicuous family of the Monocotyledons in every neighborhood is that which contains the grasses; but in every neighbor- hood there will occur also ten to twenty other prominent families of Angiosperms that deserve recognition. A family is made up of smaller groups called genera (singular genus). For example, in the great family to which the asters belong, the different asters resemble one another more than they do any other members of the family; and so there is the aster genus. In the same family the different goldenrods are grouped together in a golden- rod genus. The different kinds of aster or of goldenrod MONOCOTYLEDONS 263 are called species. Therefore, a group of related species forms a genus; and a group of related genera forms a family. An acquaintance with the plants of a neighborhood should begin by learning to recognize not merely important families but also conspicuous and common genera and species. The technical name of a plant is the combination of its generic and specific names, the former always being written first. For example, Quercus alba is the name of the com- mon white oak, Quercus being the name of the genus to which all oaks belong, and alba the specific name that distinguishes this oak from other oaks. No other names are necessary, as no two genera of plants can bear the same name, and no two species of a genus can have the same name. The so-called Manuals or Keys are books that contain descriptions of plants, so arranged that one who knows the meaning of the terms used can find the name of any plant described. Ability to use such a manual is very desirable to cultivate, for it is the most accurate and effective method of forming a speaking acquaintance with plants. 156. Families of Monocotyledons. About forty mono- cotyledonous families are recognized, containing numerous genera and about twenty thousand species. Four fami- lies will be selected, which include the great majority of Monocotyledons; and these should be recognized at sight. These families are conspicuous in numbers, or in appearance or in usefulness; and for any or all of these characters they deserve acquaintance. 157. Grasses. The Grass Family (Graminece) is one of the largest groups of plants. It is world-wide in its dis- tribution, and is remarkable in its display of individual plants, often growing so densely over large areas as to form a close turf. The flowers are very simple having no calyx or corolla, 18 A TEXT-BOOK OP BOTANY and the grain is the characteristic seed-like fruit. The flowers occur in small close clusters, and associated with them are peculiar bracts characteristic of the family (Fig. 260). For example, these bracts form the so-called chaff of wheat and other cereals, where they persist and more or less envelop the grain. These little clusters of bracteate flow- ers are arranged to form either a loose and spread- ing general cluster, as in red top and oats (Fig. 262), or else a compact, spike-like cluster, as in timothy and wheat (Fig. 261). When the uses of grasses are considered, it becomes evident that this is by far the most impor- tant family of plants to man. It is possible to suggest only some of the conspicuous forms. (1) CEREALS. This group includes those grasses that are cultivated for their seed-like fruits or grains, and they represent the chief interest of agriculture. What cereals mean as a food-supply for the world is too well known to need explanation. The most extensively cultivated cereals are as follows: Wheat. This is certainly the best known and most valuable of all cereals. The original home of wheat is unknown, for it has been cultivated from the very earliest times. It is a crop peculiarly adapted to regions of cold FlQ. 260. Oats : A, part of a flower-cluster, showing the bracts, in the axils of which flowers appear ; B, a single flower, with its enveloping bract, three stamens, and pistil whose ovary bears two plumose styles. After BAILLON. MONOCOTYLEDONS 265 winters, and hence the greatest supply comes from temper- ate regions. The Northern United States and Canada have vast areas especially well-adapted to the cultivation of wheat; and in 1899 (last census) the United States alone produced more than one-fourth of the wheat of the world, being the great- est wheat-producing coun- try. In this production the chief wheat-growing States, in the order of their output, were Minnesota, North Dakota, Ohio, and South Dakota. The varieties of wheat are very numerous, and new ones are constantly being produced in the effort to get the very best variety for every combina- tion of climate and soil. There are spring and win- ter wheats, bearded and beardless wheats (Fig. 261), soft and hard wheats, and wheats of various col- ors. Winter wheat is sown in the fall, and hence must be a variety able to endure the winter; while spring wheat is sown as early in the spring as possible. Since wheat grows best during the cool part of the year, it is very conveniently related to the corn crop, which makes its chief growth during the warm months. The time of har- vesting varies with the latitude, ranging from early in May in Texas to August in some northern States. L Fiu. 201. Bearded and beardless wheat. After ENGLER and PRANTL. 266 A TEXT-BOOK OF BOTANY Oats. Oats may be distinguished from wheat, rye, and barley by the flower clusters being loose and spreading (Fig. 262), rather than in compact cylindrical clusters (spikes). It also has been culti- vated from the most ancient times, and to-day the United States and Russia pro- duce the greatest crops. Oats are usually sown as early in the spring as possible, developing best in the cooler weather; and in northern latitudes the crop ma- tures in ninety days or less. Oats do not require so rich soil as wheat, and FIG. 262. Oats. After BAILLON. hence can be grown successfully where wheat would not thrive. In 1899 the United States pro- duced more bush- els of oats than of wheat. Rye. This cere- al does not seem to have been so long in cultivation as the FIG. 263. Rye MONOCOTYLEDONS 267 others (Fig. 263). It is extensively cultivated in Northern Europe; and Russia is the greatest rye-producing country in the world, producing more bushels of rye than the United States produces bushels of wheat. The rye crop of the United States is very small comparatively, being less than one-twenty-fifth as large as the wheat crop, and less than one-thirtieth as large as the oat crop. resembling a smooth peach (nectarine) in external appear- ance, and having the smooth stone of a plum. They also DICOTYLEDONS: ARCHICHLAMYDE^J 289 originated in China or Japan, and the dangers in culti- vation are the same as those of the peach. The apricot has never developed commercial importance in the eastern United States except in a few places, notably in New York. In California, however, it is one of the most important com- mercial fruits of the State, having been introduced into it by the Mission Fathers. Plums are of so many kinds that they can hardly be spoken of all together. The numerous varieties have been derived from at least three species, one European, one Japanese, and one native. The most extensively grown and commercially important plums are from the European stock; and the two great areas of cultivation are California, and the Northeastern States north of Pennsylvania and west to the Great Lakes. In California the prune industry has been extensively developed, a prune being simply a plum that has dried sweet (without fermentation) without removing the stone (pit). Cherries are of several varieties, derived from two Euro- pean species. In general they are classified as sour cher- ries, which are largely grown in the eastern United States, especially western New York, for canning; and sweet cher- ries, which are most extensively cultivated on the Pacific Coast. There are a number of native species in the United States, and among them the black cherry furnishes a timber much valued on account of its beauty when polished. (3) POME-FRUITS. The peculiar character of this type of fruit has been explained ( 143) (Fig. 235), and the name has been used in that of fruit culture in general, which is called pomology. The following forms all belong to the genus Pirus. Apples have been cultivated from the most ancient times; and the thousands of varieties have all come from two wild species native to southwestern Asia and adjacent Europe, one giving rise to the common apples, the other 290 A TEXT-BOOK OF BOTANY to the crab-apples. This is the most important fruit ui the temperate regions, and North America is the greatest apple-growing region of the world. For commercial pur- poses there must be a combination of such features as pro- FIG. 282. The common pear: A, flower cluster; B, section of a single flower; C, section of a fruit (core indicated by dotted outline). After WOSSIDLO. ductiveness, quality, and long-keeping; and the best region of the country to produce all these extends from Nova Scotia to Lake Michigan. Other important commercial regions are Virginia, the Plains, Arkansas and the Ozarks, and the foot- hills of the Pacific Coast. Each year these regions produce about one hundred million barrels of apples. When first introduced into this country, the apple was prized chiefly for the manufacture of cider and vinegar; but it is used now more extensively than any other fruit as a fresh and evapo- DICOTYLEDONS: ARCHICHLAMYDE^E 291 ruled fruit. Apples are usually propagated by budding and grafting ( 24) the desired variety on hardy young trees. Pears are chiefly derived from a single European species and were introduced into this country by the earliest set- tlers (Fig. 282). Their most successful cultivation is in the Northeastern States (from New England to the Great Lakes) and on the Pacific Coast. In the central States extensive pear culture is attended with great risk on account of a dangerous disease known as pear-blight or fire-blight, the leaves turning brown or black as if scorched. This is one of the bacterial diseases ( 77). Unlike most fruits, pears are very much improved when picked green and ripened indoors. Quinces are well known, but have not been developed in variety or in commercial importance as have apples and pears, this probably being due chiefly to the fact that they cannot be eaten raw. The most important quince orchards in the United States are in western New York. 166. Legumes. This is by far the greatest family (Legu- ininnsii ) of the Archichlamydcac, and is chiefly distinguished by its very irregular (lowers and its pods, which are derived from a single carpel and become more or less elongated and sometimes remarkably conspicuous (Fig. 283). It is the peculiar pods (legumes) that have given name to the fam- ily. The ordinary flowers, represented by the sweet pea, were thought to resemble a butterfly, and hence were said to be, papilionaceous. The upper petal (standard) is the largest, and erect or spreading; the two lateral petals (wings) are oblique and descending; while the two lower petals are coherent by their lower edges and form a projecting boat- shaped body (keel}, which encloses the stamens and pistil. The relation of this structure to pollination by insects has been described ( 147). This family, in its irregular flowers adapted to insect-pollination, holds the same position among Archichlamydese that f he orchids do among Monocotyledons. 292 A TEXT-BOOK OF BOTANY In so vast a family it will be impossible to enumerate all the forms that are well known on account of their common oc- currence or usefulness, but some of them may be mentioned. The sweet pea, wistaria, and lupine suggest the numerous herbaceous forms with showy flowers. In this family also Fio. 283. A leguminous plant: A, flowers and pods; B, petals separated to show standard (a), wings (6), and keel petals (c). After WOSSIDLO. are found the numerous sensitive plants ( 17) character- istic of southwestern arid regions (Fig. 284). Among the trees the following may be mentioned: common locust, prized for both its showy flowers and its valuable timber; honey locust, beset with conspicuous thorns (Fig. 60) ; red- bud, with numerous pink flowers appearing upon the naked branches in early spring; and the singular coffee-tree. Among the useful forms, the so-called forage plants are important; that is, plants used for pasturage or hay, just as are the grasses. The most common of these is clover, a DICOTYLEDONS: ARCHICHLAMYDE^ 293 genus (Trifolium) containing many species. The most im- portant one to the farmer is the common red clover, afford- ing valuable pasturage and clover hay, and also improving the soil (77). The smaller white clover is also a very fa- miliar plant associ- ated with grasses in lawns, pastures, etc.; and its flow- ers are especially attractive to bees. Alfalfa (lucerne) is another important forage plant related to the clovers, and is especially valua- ble in the West where irrigation is employed. It is a native of western Asia, has long been cultivated in Eu- rope, and was in- troduced into Cali- . FIG. 284. A sensitive plant, showing the mconspicu- fomia about the ous flowers with numerous stamens, and the sensi- middle Of the last tive pinnately compound leaves. -After MEYER and ncHtiMANN. century. Since then it has become the most extensively grown forage plant in the arid regions of the Pacific and Rocky Mountain States. Besides the forage plants, the seeds of certain others are very familiar as food. The cultivated peas are natives of southern Europe and Asia, and have been cultivated for many centuries. They are distinguished as garden peas and field peas, the latter being rather a forage plant. The two 294 A TEXT-BOOK OF BOTANY types of garden peas are those with smooth seeds and those with wrinkled seeds, the former being earlier and hardier (hence most common in the market), the latter better in quality. Beans are of many kinds, but the common bean of Europe does not succeed well in the United States. Our common garden and field bean is the kidney bean, which reached the United States from South America by way of Europe. The lima bean is also of South American ori- gin, and is most extensively grown in California. Peanuts (goobers) are curiously developed and very familiar pods. After the flower has fallen, its stem bends downward and pushes the young pod into the sandy soil, where it matures, and hence is sometimes called groundnut. Several of our native legumes also have this curious habit. The peanut is thought to be a native of Brazil, and is now grown in all warm regions of the world. In the United States it has become an important commercial crop of the Southern States since 1866, being chiefly grown in Virginia, North Carolina, Georgia, and Tennessee; the annual yield being four million bushels. 167. Umbellifers. This is the highest family (UmbelUf- erce) of the Archichlamydeae, and the name has been sug- gested by the fact that the small flowers are massed in flat-topped clusters called umbels ( 139) (Fig. 224). The family is distinguished also by the fact that the ovaries are inferior ( 138). In general they are perennial herbs of north temperate regions. Parsnips and carrots are the thick tap-roots of two of the species, and celery is the blanched leaf-stalks of another. Some species are charac- terized by their aromatic foliage or fruit, as coriander, fen- nel, and caraway; and one species yields the deadly hem- lock. 168. Other useful Archichlamydeae. Many well-known ornamental plants do not belong to the representative fam- ilies described above, as violets, pinks, geraniums, nastur- DICOTYLEDONS: ARCHICHLAMYDE^E 295 tiums, fuchsias, etc.; and some very useful plants also belong to scattered families. These latter may be grouped as follows: (1) FIBERS. The fiber plants are numerous, but there are three very conspicuous ones among the Archichlamydeae. Cotton. The cotton plant is by far the most important fiber plant grown, being cultivated over a greater area and used for a larger number of purposes than any other fiber plant (Fig. 285). The cultivated va- rieties have originated from several tropical spe- cies, but in the States the Sea Island cotton and the upland cotton are grown almost exclusively. The genus (Gossypium) belongs to the Mallow Family (Mal- vacece), to which the hol- lyhock and the hibiscus also belong, the most con- spicuous peculiarity of the flower being the ap- Fl - 285. The cotton plant: A, flowering , . branch ; B, fruit (boll) bursting ; C, seed parent Coalescence Of the uith fibers (lint). After WOSSIDLO. numerous stamens into a central column (Fig. 214). The capsule (boll) of the cot- ton plant contains numerous seeds, which are covered with long hairs (lint) that are the cotton fibers (Fig. 285, C). At maturity the bolls burst, and the lint protrudes in a fluffy, cottony mass (Fig. 285, B). The cotton-gin was in- vented to separate the lint from the seeds, and the revolu- tion it brought about in the cotton industry is well known. The Sea Island cotton, with its long and silky fibers, is 20 296 A TEXT-BOOK OF BOTANY the most valuable variety, reaching its greatest perfection along the coast region of South Carolina, Georgia, and Florida. The upland cotton is cultivated over a wider area, but is by no means of so fine a grade. In 1900, the greatest cotton-growing States, in the order of the number of acres under cultivation, were Texas, Georgia, Alabama, Missis- sippi, and South Carolina. There are valuable by-products from the cotton plant, the seeds yielding the well-known cotton-seed oil. Flax. The fiber of flax forms linen thread and cloth, and the extent of its use is second only to that of cot- ton. The species used is a small annual (Linum) native about the Mediterranean, and cultivated from the very ear- liest times (Fig. 286). The fibers are found in the stems, which are subjected to a series of processes for separating the fibers from the other parts. The oil yielded by the seeds is the well-known linseed oil, used in paints, varnishes, etc. Russia is the greatest flax- growing country in the world; but for excellence of fiber Bel- gium excels, where it is ased in the manufacture of the famous Brussels lace. In the United States flax has been long cultivated in many States for its oil; but only recently has its cultivation for fiber at- tracted attention, and that chiefly in Michigan, Wisconsin. Minnesota, and Washington. FIG. 286. The flax plant. After BAILLON. DICOTYLEDONS: ARCHICHLAMYDELE 297 Hemp. This well-known fiber comes from an annual plant native to southern Asia, but long cultivated in Europe, and also naturalized in the United States (Fig. 287) 298 A TEXT-BOOK OF BOTANY It is a member of the Nettle Family (Urticacece). As in flax, the fibers used occur in the superficial region of the stem, outside the regular wood fibers. The most extensive cultivation of hemp is in European Russia; and it is somewhat cultivated in the United States, especially in Illinois, Missouri, and Kentucky. The name is applied also to any fiber that serves the same purposes as true hemp; for example, Manila hemp, which is obtained from a species of banana which is native in the Philippine Islands and extensively cultivated there. (2) BERRIES. The conspicuous berries not mentioned are the currants and the gooseberries, which are members of a small family (Saxifragacece) closely related to the Rose Family. These familiar plants belong to the same genus (Ribes) and are natives of the cool temperate regions. Therefore, their chief cultivation is in northern Europe and in the Northern United States and Canada. The ordinary varieties of white and red currants are well known and well cultivated in this country, but in no country has the gooseberry been developed to such size and quality as in England. (3) GRAPES. Grapes are true berries, but they are so important as to deserve separate mention. The genus is Vitis; and it gives name not only to the family (Vitacece), but also to the culture of grapes (viticulture). The cultiva- tion of grapes for the manufacture of wine and raisins is as old as the history of man. The varieties cultivated in the Old World all belong to a single species (Vitis vinifera), which is now extensively grown in all countries bordering on the Mediterranean, and north to central Europe. This same European vine was introduced on the Pacific slope by the early missionaries; and now, excepting a few famous regions in Europe, California leads in the production of wine and raisins, having the largest vineyards in the world. In the northeastern States, however, native varieties have DICOTYLEDONS: ARCHICHLAMYDE^E 299 been developed, more for what are called dessert purposes than for wine and raisins; and this culture has reached its highest perfection in New York, New Jersey, Maryland, Virginia, and Ohio. No cultivated plant is attacked by more diseases than the grape, nor have any plant diseases been more fully studied. (4) CITROUS FRUITS. These fruits all belong to a sin- gle genus (Citrus), whose species are shrubs or small trees, natives of tropical and subtropical Asia (China-India). The citrous fruits are numerous, but the three forms chiefly cultivated in the United States and common in markets are as follows: Oranges are extensively cultivated in the United States in central and southern Florida, the delta region of the Mississippi, and California. All the varieties are derived from a single species (Citrus Aurantium), and may be grouped as bitter oranges and sweet oranges, the latter being the chief market form. The very popular seedless navel oranges of California were introduced in 1870 from Brazil by the United States Department of Agriculture, being a chance seedling variety. A closely allied species (Citrus nobilis) produces the varieties of mandarin or kid-glove oranges. True mandarins are small and light orange in color, and are not so much prized in market as the dark orange or reddish forms known as tangerines. Grape-fruits are extensively cultivated in Florida and California, all the varieties, most of which have originated in Florida, coming from Citrus Decumana, a native of the Malayan and Polynesian Islands. The original and best name for this fruit is pomelo, although it is sometimes called shaddock as well as grape-fruit. In reality, the pomelo or grape-fruit is the common round-fruited form of the markets, while the shaddock is a very different plant with a pear-shaped fruit. 300 A TEXT-BOOK OP BOTANY Lemons also are cultivated in Florida and California; but they are not so hardy as the orange, and hence their cultivation is more restricted. The chief foreign sup- ply comes from Italy, Spain, and Portugal. The lemon is a variety of the citron (Citrus medico); and another variety is the lime, which furnishes the commercial lime- juice. (5) TEA. The tea plant is a shrub native to sub- tropical Asia, and its dried leaves are one of the most im- portant articles of com- merce (Fig. 288). It has been cultivated in China and Japan for many cen- turies, and in the last cen- tury extensive plantations were established also in India, Java, and Ceylon. There are three distinct pickings in a season; some of the young leaves are picked in April for a fine quality of tea (young hyson) which can- not stand shipping to a distance; the ordinary picking for the general market begins in May; and later there is a third picking, which makes a low-grade tea. Different qualities and colors are produced by the different treatment of the same leaves, the numerous varieties being either green tea, in which the leaves are roasted quickly, or black tea, in which they are dried slowly until they are almost black. Outside of oriental nations the chief tea drinkers are the Russians, the British, and the Dutch. FIG. 288. Flowering branch of the tea plant. After BAILLON. DICOTYLEDONS: ARCHICHLAMYDELE 301 (6) CHOCOLATE. Chocolate is obtained from the seeds of the cacao-tree, a native of Mexico, which was introduced into Europe by the Spaniards, and is now cultivated in all tropical countries. The fruit is about the size of a small cucumber and contains numerous large flat seeds embedded in its flesh. The seeds are crushed to a fine paste, which is heated and run into molds. Coco is obtained from choco- late by removing from it some of its oil. CHAPTER XVIII DICOTYLEDONS: SYMPETAL-SJ 169. General characters. The Sympetalse include the families of highest rank, about fifty in number, among which there are many well-known plants, and some of great use. The representative families are easily recognized, and five of them will be presented, with which a real ac- quaintance with the Sympetalse may well begin. 170. Heaths. In this family (Ericacece) there are often ten stamens, in two sets, so that there are five cycles of floral parts; and thus such forms are easy to distinguish from the following families, in whose flowers there are only four cycles. Heaths are usually woody plants, often shrubs, sometimes trailing, occasionally trees. One of the most peculiar and constant features of the family is that the anthers usually open at the top and generally by terminal pores ( 134) (Fig. 213, B and C). The species belong chiefly to the cooler regions, often being the prominent vegetation in cold bogs and on heaths, to which latter they give name (Fig. 289). Trailing arbutus, bearberry (kinnikinick), heather, rho- dodendron (Fig. 290), azalea, mountain laurel, winter- green, and corpse-plant (Indian pipe) are familiar forms; while huckleberries, blueberries, and cranberries are staple fruits. The cranberries grow wild in mossy (sphagnum) bogs in the cool temperate regions of both America and Europe. Two kinds usually appear in market: the small DICOTYLEDONS: SYMPETAI^E 303 cranberry, obtained from wild plants; and the large cran- berry, extensively cultivated in several Northern States, especially in Massachusetts, New Jersey, and Wisconsin. Fio. 289. Heath plants: A, Lyonia; B and C, two species of Catfiope. After DRUDE. Huckleberries, a market name that includes blueberries, have not as yet been cultivated for commercial purposes, but are picked from wild plants, large areas of which are 304 A TEXT-BOOK OF BOTANY sometimes protected. In Maine, the protected "blueberry barrens" is said to include an area of about 150,000 acres. FIG. 290. A flower-cluster of rhododendron. After HOOKER. 171. Nightshades. This great family (Solanacece) in- cludes plants with more or less conspicuous and regular tubular corollas. The flowers have four cycles, a character which distinguishes this family from the former one; and regular corollas, a character which distinguishes it from the next one. Perhaps the most familiar illustration of the general type of flower is the morning-glory, which belongs to DICOTYLEDONS: SYMPETAL.E 305 a small related family. A very general feature of the nightshades is their rank-scented foliage, the leaves and Fio. 291. Branch of thorn-apple (Nightshade Family), showing flowers and fruit. After BA.ILLON. fruits of some of them being very poisonous. Among the familiar plants are capsicum (red pepper), ground cherry, belladonna, matri- mony vine, henbane, petu- nia, and thorn-apple (jim- son-weed) (Figs. 291 and 292); while the three fol- lowing are of great com- mercial importance: Potato. -^This most com- mon of all vegetables is often called Irish potato, because of its general use in Ireland; but it is a na- tive of the mountainous region of America from southern Colorado to Chili. Like corn (maize), potatoes were found in cultivation by natives FIG. 292. Thorn-apple (Nightshade Family) : A, longitudinal section of flower; B, dehiscence of the fruit (bur). Af- ter BAILLON. 306 A TEXT-BOOK OF BOTANY upon the discovery of America, and were introduced into Europe by the Spanish conquerors, probably from Peru. For nearly two centuries, however, their importance was not appreciated; but now there are ten times as many bushels of potatoes produced in Europe as in the United States, the entire European crop being said to aggregate more bushels than the entire wheat crop of the world. New York is our great potato-producing State. There are hun- dreds of varieties, new ones replacing old ones every year; but they are all derived from a single species (Solanum tuberosum). It should be remembered that these tubers are subterranean stems ( 27) enlarged as depositories of starch, the stem structure being indicated superficially by the eyes (bracts with axillary buds). In planting, the tubers are cut in pieces, each piece containing one or two eyes and as much of the food-supply as possible. Tomato. The tomato was once called love-apple, and was thought to be poisonous. It is grown more extensively in North America than elsewhere; and in the United States there is no vegetable so extensively grown for canning, about 300,000 acres being required to produce the annual crop. The principal tomato-growing States are Maryland, New Jersey, Indiana, and California. The numerous kinds vary in form and color, all coming from a single species (Lyco- persicum esculentum) , which is native to the Andean region of South America. Tobacco. It is well-known that the Indians used tobacco long before the discovery of America, but never excessively (Fig. 208). From America its use was introduced into Europe, gradually extending to the Asiatic nations, until now the Turks and Persians are the greatest smokers in the world. In the United States tobacco culture began in Vir- ginia, at the first settlement of the colony; and it became the leading industry also of Maryland, North Carolina, South Carolina, Georgia, and Kentucky at their first settle- DICOTYLEDONS: SYMPETALJ5 307 ment. To-day Florida, Connecticut, Pennsylvania, and Wisconsin lead in the production of the finer grades; while the States producing the other grades are, in their order, Kentucky, Virginia, North Carolina, Maryland, Ohio, In- diana, and Missouri. The finest tobacco in the world is grown in Cuba, that from Florida ranking second; while the tobacco of Borneo, Ceylon, and the Philippine Islands is not much inferior. The growing plant is handsome, with showy flowers, and is often used as an ornamental plant. The single species is Nicotiana Ta- bacum, and is of South American origin. 172. Labiates. This family (La- biatcp") has received its name from its two-lipped or bilabiate corolla ( 133). This does not mean that all plants with bilabiate flowers be- long to this family; but if this char- acter is associated with square stems and opposite leaves, and also with an ovary so deeply lobed that it looks like four little nutlets in the bottom of the flower, the plant can be regarded as a member of the f am- FIG. 293.-Catnip (Mint Fam- i /TT <-/~vo\ mi e ^ Hy)'- A , flower-cluster; B, ily (Fig. 293). The foliage is usu- Bing i e flower . c? pistilt ally aromatic, and the family is com- showing the deeply four- lobed ovary. After BAJX- monly called the Mint Family. Many LON. common wild plants and garden herbs will be recognized as belonging here, familiar names being sweet basil, pennyroyal, lavender, mint, hoarhound, hys- sop, savory, marjoram, thyme, balm, sage, rosemary, cat- nip (Fig. 293), etc. 173. Madders. This very large tropical family (Rubia- cece) is represented in our flora by only a few forms, such as bluets, buttonbush, partridgeberry, etc., which may be 308 A TEXT-BOOK OF BOTANY recognized generally by the regular tubular corolla, the inferior ovary, and the floral number four. However, the tropical members of the family yield two important products that should not escape mention. C^fee. The coffee plant (Coffea arabica) is a native of Arabia and Abyssinia, and is a slender tree becoming fifteen to twenty-five feet high (Fig. 294), but rarely allowed to become more than half that height in cultivation. The fruit is a dark scarlet berry (Fig. 295) containing two horn-like seeds, which are ordinarily called coffee-beans (Fig. 296). The use FIG. 294. The coffee-tree. After BAILLON. FIG. 295. Fruiting branch of coffee. After BAILLON. of coffee can be traced back in Arabia for only about five hundred years, and its use in Europe extends over only half that time. Coffee plantations have been established in regions of high annual temperature (ranging from 60 to 90), Brazil producing more coffee than all other coun- DICOTYLEDONS: SYMPETAI^E 309 tries combined. Other prominent coffee-grow- ing countries are Mexi- co, Central America, Java, Sumatra, India, Ceylon, Arabia, Ha- waiian Islands, and the West Indies. Of the many thousand tons shipped from these countries, the United States consumes nearly one-half, averaging over nine pounds a year for each inhabitant. Mocha Flo. 297. Flowering branch of a cinchona plant. After BAILLON. FIG. 296. Coffee-plant : A , flowering branch ; B, berry ; C, section of berry ; D, seeds (coffee-beans). After WOSSIDLO. coffee comes from Ara- bia, while the sources of the other kinds are usually indicated by the names. Cinchona. This is the name of a genus containing numerous species of trees that grow in South America, chiefly along the east- ern slopes of the west- ern mountains (Fig. 297). The bark yields the well-known quinine, 310 A TEXT-BOOK OP BOTANY as well as other alkaloids, and is commonly called Peru- vian bark. It is stripped from the trees by the Indians and carefully dried. Although the trees are becoming more scarce every year, no attempt has been made to cultivate them where they are native; but in Java, British India, Ceylon, Japan, and Jamaica there are extensive plan- tations of cinchona. 174. Composites. This is the highest family (Compos- ite) of Dicotyledons, and contains the most numerous species. Composites are found everywhere, but are most numerous in temperate regions, where they are usually herbs. The name of the family suggests the most conspicuous feature; namely, the organization of the numerous small flowers into a compact head which resembles a single flower, formerly called a compound flower. So common are the Composites that the general structure of the head should be understood. Taking the head of Arnica as a type (Fig. 298, A), the outermost set of organs consists of more or less leaf-like bracts or scales (involucre), which resemble sepals (not seen in figure) ; within these there is a circle of flowers with conspicuous yellow corollas (rays), which are split above the tubular base and flattened into a strap-shaped body (Fig. 298, B), and much resembling petals; within the ray-flowers is the broad expanse called the disk, which is closely packed with very numerous small tubular flowers known as disk-flowers. If a disk-flower be removed, it will be discovered that the ovary is inferior, and that arising from it, around the tubular corolla, there is a tuft of delicate hairs (pappus) which represent the sepals (Fig. 298, C). This pappus surmounting the akene ( 143) in Composites may be lacking; it may be a tuft of hairs, as in Arnica, thistle, and dandelion; it may be a cup or a set of scales; or it may develop grappling appendages, as in Spanish needles (Fig. 257) and beggar-ticks (Fig. 258). Most of the DICOTYLEDONS: SYMPETALuE 311 heads of composites have the general structure described for Arnica; but in the dandelion and its allies the disk- B FIG. 298. Arnica: A, plant bearing an open head, showing the conspicuous rays and disk; B, ray-flower; C, disk-flower. After HOFFMAN. flowers are like the ray-flowers, with conspicuous strap- shaped corollas (Fig. 299). 21 312 A TEXT-BOOK OF BOTANY Some of the well-known forms, either wild or in culti- vation, are ironweed, ageratum, blazing star, goldenrod, daisy, aster, everlasting, rosin weed (compass plant), rag- A D FIG. 299. Dandelion: A, two flower-stalks, one head being closed and showing the double involucre, the other open and showing all the corollas strap-shaped, B, single flower; C, akene; D, receptacle, with single pappus-bearing akene. After STRASBURGER. weed, cockle-bur, zinnia, sunflower, dahlia, cosmos, mari- gold, chrysanthemum, tansy, sage-brush, burdock, thistle, and dandelion. The only plant extensively used for food is lettuce. 175. Other useful Sympetalae. Some well-known plants that are not included in the families given above, but that DICOTYLEDONS: SYMPETAL^ 313 should be recognized as Sympetalae, are honeysuckle, elder, lobelia, bluebell, primrose, morning-glory, lilac, milkweed, gentian, phlox, mullein, snapdragon, and verbena. Some additional prominently useful plants are as follows: Sweet potato belongs to the same genus (Ipomoea) as the morning-glory, having long trailing stems and clusters of the well-known large oblong or elongated roots. It is not known whether it is native to the East Indies or America, but it is extensively cultivated in all warm countries. In the United States the cultivation of the sweet potato as a commercial crop is confined almost exclusively to the South- ern States, but important areas are found also in New Jer- sey, Ohio, Indiana, and Illinois. The varieties called yams in the South are all sweet potatoes, and the name really be- longs to a very different plant. Olive. The olive-tree has been known and cul- tivated from the most ancient times, and has entered largely into the life and customs of Med- iterranean peoples (Fig. 300). It is thought to be a native of southern Europe and Asia Minor, and thrives best in dry climates such as those of 1 . . T , . FIG. 300. Flowering branch of olive. Syria and Assyria. It is After B AI LLO N. cultivated also at the Cape of Good Hope, in Australia, and in California. It is a very long-lived tree, a thousand years having been 314 A TEXT-BOOK OF BOTANY reported for some individuals. The oil obtained from the fruit is in as common use in Mediterranean countries as butter and lard in the United States. The products that reach this country are olive-oil and pickled olives; but dried olives also are much used in certain olive-grow- ing regions. GOURD FRUITS. The tropical and subtropical family (Cucurbitacece) that is popularly called the Gourd Family contains numerous forms that are used by tropical peoples not only as food, but also in the manufacture of various utensils. The fruit is characterized by its very large size and hard rind, and the flesh within is often edible. The best-known edible forms in the United States are as fol- lows: Watermelon is a native of tropical Africa, and has been cultivated from the most ancient times. There is no coun- try where watermelon culture is conducted on so extensive a scale as in the United States. The chief commercial sup- ply comes from the Southern States, the so-called Georgia watermelon being the best-known variety; but a very large melon industry has been developed also in Colorado. Muskmelons all belong to a single species (Cucumis Melo), which is native to the warmer parts of Asia, but is now cultivated all over the world. It is said that one-half of the muskmelon crop is grown in New Jersey; but in the western markets Michigan and Colorado are very im- portant centers. The two general types of muskmelons are the furrowed type, with hard rinds, known as canta- loupes; and the netted type, with softer rinds, known as nutmeg melons. Two important varieties of nutmeg mel- ons have been developed recently: the Osage melon, from southwestern Michigan; and the Rocky Ford melon, from Colorado. Cucumbers belong to the same genus as muskmelons, and are derived from a species (Cucumis sativus) native to DICOTYLEDONS: SYMPETALuE 315 southern Asia. They are grown in all parts of the United States, and their extensive use as pickles, etc., is well known. Pumpkins were cultivated by the Indians in their fields of maize, as they are now, and are probably of tropical American origin, although no wild plants are known. Some M/unshes belong to the same species (Cucurbita Pepo), but others are of Asiatic origin. CHAPTER XIX PLANT BREEDING 176. Definition. The purpose of plant-breeding is to improve cultivated plants, just as the purpose of animal- breeding is to improve domesticated animals. Great pro- gress has been made in the science of plant-breeding, so that it is possible now in many cases to breed for certain desired improvements with great confidence that they will be secured. The skilful plant-breeder not only must know how to make plants grow, but he must know also the laws connected with the reproduction of plants. 177. Variation. The fact with which the plant-breeder starts is that plants tend to vary. If all the seeds from one parent plant are sown, the plants that come from them will all resemble the parent in a general way; this handing down of similarities from one generation to the next is called heredity. But while there is this general resemblance to the parent, there are variations, one or more of the new plants perhaps resembling the parent less than the others do. It is this fact that makes plant-breeding possible; and instead of relying upon nature to present to him all the variations he needs, the plant-breeder by changing conditions increases the tendency of plants to vary, and also by crossing multi- plies variations. The important thing is to obtain as many and as wide variations as possible. 178. Vegetative propagation. If among varying plants there appears one that is desirable, it may be possible to propagate it vegetatively, that is, without using the seed. 316 PLANT-BREEDING 317 Such propagation is much more certain, for propagation by seed introduces variations. Some plants are propagated naturally in ll.is way, as those with thickened underground shoots (rootstocks, tubers, bulbs) or with runners (straw- berry, etc.). Others are propagated by artificial methods. For ex- ample, cuttings, often called slips, are pieces of the plant that are found to be able to grow when put in the soil, as of geraniums, grape-vines, etc. Even leaves may be used as cuttings, as in the begonia; and cuttings of the potato tuber are used in its propagation. Grafts are cuttings inserted in plants ( 24) (Fig. 55), and it is common for the plant in which a jraft is inserted (stock) to differ from the plant that is being grafted on it, securing among other things greater hardiness and a saving of time; for example, it is common to graft pears on quince stock. Budding is a variety of grafting in which only buds from the desired variety are grafted upon stocks. Grafting and budding are very com- mon in the cultivation of tree fruits. Layering consists in bending down a stem to the ground and covering it for a short distance with soil; when roots strike into the soil from a covered joint, the connection with the parent plant is cut, and a new plant is thus obtained ( 23). This process is common with such plants as gooseberries, blackberries, etc., and resembles in a general way the natural method of propagation by runners. 179. Crossing. The artificial production of hybrids ( 149) is used extensively to secure new varieties which may be desirable. The process consists in removing the young stamens from the flower to be operated upon; at the proper time placing upon the stigma pollen from the de- sired plant, and covering the flower or flower-cluster thus pollinated with a gauze or paper bag to prevent the ap- proach of any other pollen. The seeds thus obtained are carefully collected and planted, and the new plants observed. 318 A TEXT-BOOK OF BOTANY Among them there may be found one or more with a desired variation, or at least the beginnings of it. These plants are preserved and the others destroyed. Often many thousands of young plants are thus started, and most of them de- stroyed. 180. Selection. When a desired variation has appeared, the work of improving and establishing it must follow. This is done by means of selection, and it involves great care and patience. The selected plants are carefully guarded, no foreign pollen being allowed access to their flowers. Their seeds are planted, and among the new plants that come up those showing the desired variation are preserved and the others are destroyed. This selection goes on generation after generation until only the desired variety is produced. It is then said to be established, and can usually be de- pended upon to produce its kind. Even after a variety has thus been established, great care must be used in selecting from the best plants seeds for planting, or the variety will "run down/' It is a great mistake to suppose that seeds from inferior plants will do just as well for sowing as seeds from the best plants. Farmers have learned this in selecting their seed-corn, seed-wheat, etc. ; and their success depends upon their wise selection of the seeds to plant. It is important to know that in this selection of seed the character of the individual plant that produces it is the important thing. To select for planting the largest ears of corn from a pile of corn does not result so well as to select in the field the plants that produce on the average the best ears. The process of selection is being applied also in the development of varieties that resist certain diseases. For example, in a field that has been ravaged by some disease a few plants may be found that have resisted the attack successfully. This means that the variation in these plants is a very desirable disease-resisting power. Starting with PLANT-BREEDING 319 these plants, therefore, selection may be able to develop a race remarkably free from this particular disease. This method of combating disease may sometimes prove more effective than any attempt to save the plants that are sub- ject to it. The story of the development of the best-known varie- ties of cultivated plants is a very interesting one, telling how promising varieties have been discovered, and with what wonderful patience they have been developed into usefulness. The recent great increase in knowledge of the principles of plant-breeding has made the development of desirable varieties more definite and rapid than it has ever been before. CHAPTER XX FORESTRY 181. Definition. The term forestry is difficult to define, for it includes much more than is usually supposed. In general, it is the management of forests, so that they may serve their purpose; but the purpose of a forest includes many things. Forestry does not deal with individual trees, but with an assemblage of trees; perhaps it would be best defined as the management of woodland. There are two prom- inent aspects of forestry. Forests furnish wood crops, as wheat-fields furnish wheat crops; and from this standpoint forestry resembles agriculture. But forests also hold im- portant relations to climate, water-supply, etc.; and from this standpoint they are to be considered as features of the earth's surface. 182. History of forestry. The history of forestry in every country has been the same. At the first settling of a country by civilized people, the forests were looked upon as impediments to agriculture, and the clearing of the forest was a part of pioneer work. As forests cover most of the best land, this pioneer clearing was necessary. After agriculture became established, forests ceased to be regarded as impediments, and came to be prized as the source of timber supply. They were wastefully ravaged for this purpose, the best trees being culled out, countless young ones destroyed, and fires completing the reckless waste. European countries passed through this stage many years ago, and the United States is just emerging from it. When 320 FORESTRY 321 this wasteful use of forests has proceeded so far that the disastrous consequences are in plain sight, the forestry stage begins, and the proper management of forests is established. In European countries forestry has been long established and has become highly developed, especially in Germany and France. In the United States the Government has established a Bureau of Forestry, and certain States have adopted a definite forest policy. 183. Supply forests. This name has been suggested for those forests used primarily as a source of wood-supply. The crop of wood differs from ordinary crops in that it is natural growth and needs a long period to mature. The problem is to obtain as much wood from the forest as pos- sible year after year, without diminishing its productive- ness; in other words, to use it and preserve it at the same time. There is a best time for cutting, that is, harvesting, in the life of each kind of tree, a time determined by its size and the quality of its wood. The forest habit the grow- ing of trees close together secures the lofty symmetrical trunk, with branches carried high, the most favorable form for use. Trees that are "ripe" not only can but should be removed, that the younger ones may come to vigorous maturity. In this way a continuous succession of suitable trees becomes ready for removal, and every tree in the forest is given an opportunity to do its best. The thought- less cutting of trees usually secures one good crop from a forest; while a forest managed by a forester yields a suc- cession of good crops. When the forester takes charge of a forest that has had no management, he first removes the undesirable trees; but the lumberman would remove the most desirable. The forester knows, however, that in this way the quality of the remaining trees will be improved, and in the long run he will get a larger and better crop. The cutting is so arranged that the openings left will give opportunity for A TEXT-BOOK OF BOTANY seedlings to develop; so that in a forest properly managed there are trees in every stage of development, from seed- lings to those ready to be cut. Such management is being adopted not only in large forests that are prominent sources of wood-supply, but also on individual farms, where the wood-lot is as carefully managed as the grain-field. De- tailed plans for such management can now be obtained from the Bureau of Forestry or from State foresters, so that ignorance is no longer any excuse for mismanagement. 184. Protective forests. This name has been suggested for those forests that are used primarily as a soil cover. Such forests are used also as supply forests, but their chief purpose is to cover the soil. Forests are great regulators of water-flow, retaining the water of rains and letting it pass gradually into the streams. When they are removed, streams that formerly contained a steady supply of water are subject to alternations of flood and extremely low water. When forests are removed from water-sheds and the head- waters of rivers, this result becomes disastrous. The head- waters of prominent rivers are generally in mountainous regions; and the removal of forests there results not only in flooded rivers, but also in slopes stripped of their soil and deeply gullied. In such regions, therefore, the forest both regulates the water-flow and protects the soil. In consequence of these facts, the Government has set apart certain forest areas upon the head-waters of the prin- cipal rivers as forest reservations. These reservations are guarded from fire and from ruthless cutting, but are cut for timber under proper forestry management. Especially are such reservations imperative in the West where irrigation is necessary, which must depend upon a steady supply of water from the mountains. On January 1, 1905, there were sixty-two such reservations in various parts of the West, including over sixty-three million acres. States also have established forest reservations, most prominent among FORESTRY 323 which are New York and Pennsylvania; while Michigan, .Minnesota, and other States are following their example. 185. Reforestation. In many regions where forests have been removed completely, and on the treeless prairies and plains, trees must be started and a forest cover gradu- ally developed. In European countries, where many hill slopes had been cleared of all trees and the soil gullied and washed away, reforestation has been conducted on a large scale. Many a hilly Oriental country, now barren, was once forest-clad and fertile, as Palestine, whose streams have disappeared, and Mesopotamia, once a garden watered by the Euphrates, but now a desert. In the United States extensive reforestation is required only on the prairies and plains, where active measures are taken to stimulate tree-planting; and perhaps eventually some real forests may be developed in these treeless regions. It may be well to call attention to the fact that tree-plant- ing, such as "Arbor Day "stimulates, is not forestry; and that the real problem of forestry in the United States to- day is the proper management of existing forests. CHAPTER XXI PLANT ASSOCIATIONS 186. Definition. The earth's surface presents such di- verse conditions for plant life that plants become grouped according to the conditions favorable for their growth. These groups of plants, living together in similar condi- tions, are called plant associations, or sometimes plant so- cieties or plant communities. For example, a meadow is a plant association growing in conditions that favor certain grasses; a forest is an association growing where certain trees are favored, etc. In these associations grasses and trees are simply the conspicuous types; but numerous other plants, which the same conditions favor, are associated with them. Each plant association, therefore, indicates a special set of conditions for plant growth, and to discover these conditions is a very important kind of field work. 187. Water. Water is probably the most important con- dition that determines plant associations. The available amount of water for plants varies in different areas, from the very small supply in deserts to the abundant supply in swamps and lakes. The character of the soil has a very important effect upon water-supply; for some soils retain water and others do not, so that what is called the water- level is of varying depths ( 39). Not only are the amount of water and the depth of the water-level important, but also the substances that the water contains in solution, which may prevent certain plants from growing and permit others. 334 PLANT ASSOCIATIONS 325 In any given area the amount of available water may not remain the same. For example, the margins of ponds may slowly encroach upon the open water; ponds may be- become converted into bogs; and bogs into dry ground. In his drainage operations and removal of forests man has made changes in the water-supply over extensive areas. All of these changes involve the destruction of old plant associa- tions and the coming in of new ones. 188. Temperature. The temperature of the air and of the soil during the growing season is very important in determining the presence of different plants upon any area. For each kind of plant there is what may be called a zero temperature, below which it is not in the habit of work- ing. The succession of plants during a single growing sea- son illustrates the distribution of plants by temperature, spring plants being able to endure greater cold than can those of the summer. This distribution in time indicates the more important distribution in space that is brought about by differences in temperature. Permanent changes in the temperature of a region, af- fecting the distribution of plant associations, are evident only in tracing the history of plants back into what are called geological times. At certain times arctic conditions prevailed in regions now temperate, and this had an im- mense influence on plant life. Plant associations are not determined by one condition, but by a combination of conditions. The simplest illustra- tion of this fact may be obtained by combining the water and the temperature conditions. For example, if there is a combination of scanty water with high temperature, a de- sert is the result; but if the combination is abundant water and high temperature, luxuriant vegetation is the result. Since the possible combinations of water-supply, tempera- ture, and other conditions are endless, it is evident that there are very numerous plant associations. 326 A TEXT-BOOK OF BOTANY 189. Light. All green plants cannot have an equal amount of light, and some have learned to live with a less amount than others. In a general way this difference is recognized in the terms light-plants and shade-plants, and it permits plants to grow in strata. For example, in a forest association the tall trees form the highest stratum; below this there may be a stratum of shrubs, then tall herbs, then low herbs, then mosses and lichens growing close to the ground. If a forest is cleared, the remaining plants of the association are very much affected; and if a forest encroaches upon another association it is sooner or later destroyed. The development of the vernal habit in connection with deciduous forests, which was described in 27, is a means by which certain plants avoid the forest shade and secure the forest soil. 190. Wind. In regions of strong and more or less continuous wind, as near the seacoast, around the Great Lakes, and on the prairies and plains, this condition has much effect upon the character of the plants. Wind is a great drying agent, and increases the loss of water from plants by transpiration ( 15), so that plants exposed to it must be able to check transpiration. 191. The great groups of associations. For convenience, the very numerous plant associations are grouped on the basis of their water-supply. Such a classification is not a natural one, for no single condition determines an asso- ciation; but for general purposes it serves well to introduce the associations to observation. On this basis there are three great groups of associations, as follows: (1) Hydrophytes. The name means "water-plants," and applies to those associations with an abundant water- supply, growing in water or in very wet soil. (2) Xerophytes. The name means "drought plants," and applies to those associations with a scanty water-sup- ply. True xerophytes are exposed to dry soil and air. PLANT ASSOCIATIONS 327 (3) Mesophytes.}fr\\\'wi\ the two extremes of the wa- ter-supply there is a -n-at middle region of medium water- supply, and plants of these medium conditions are meso- phyn-s ("medium plants"). It is evident that mesophytes pass irray various oaks, chestnuts, and hick- ories. The flood-plain forests of New Kngland are not so rich as those of the Alleghany region and the central West, the dominant forms being elm. linden, ash, maple, syca- more, tulip-tree, etc. iM."). Tropical forests. - The forests of the rainy tropics may be regarded as the climax of the world's vegetation (Fig. 319), for the conditions favor con- stant plant activity at the highest possible pressure. Such great forest growths are found within the region of the trade-winds, where there is heavy rainfall, great heat, and very rich soil, as in the East Indies, and along the Amazon and its tributaries. So abundant is the precipitation that the air is often saturated and the plants drip with the moisture. The striking characteris- tics of the great mixed trop- ical forest are as follows: (1) There is no regular period for the development or fall of leaves, and hence there is no time FIG. 320. A gutter-pointed leaf of a rainy foi-f.-t. After SCHIMPER. 356 A TEXT-BOOK OF BOTANY of bare forest or of forests just putting out leaves. Leaves are continually being shed and formed, but the trees always appear in full foliage. (2) The density of growth is remark- able, resulting in a gigantic jungle, with plants at every level, interlaced by great vines and covered by perching plants. (3) Such forests display not only an immense num- ber of individual plants, but also an extraordinary num- ber of species. (4) The various devices for shedding the abundant rain from the leaves give to them a very charac- teristic appearance. Prominent among them are the gut- ter-pointed leaves, the tip being prolonged as a sort of spout and the veins depressed, the whole surface of the leaf resembling a drainage system (Fig. 320). INDEX Absorption, 78, 86. Adaptation, 328, 337. Air pores, 168. Air roots, 82. Air spaces, 18. Akene, 239. Aleurone grains, 89. Alfalfa, 293. Algae, 98, 165; blue-green, 98; brown, 116; green, 102; red, 124. Alga-like Fungi, 144. Alternation of generations, is:?; fern, 196; liverwort, 171; moss, 180. Amaryllidaceae, 278. Ament, 283. Angiosperms, 220. Annual rings, 54. Anther, 224. Antheridium, Bryophyte, 184; fern, 193; Fucus, 124; liverwort, 169; mildew, 145; moss, 177; (Edogonium, 110; Peronospora, 143; red Algae, 127; Selaginella, 204; Vaucheria, 112. Anthoceros, 173, 183. Antitoxin, 135. Apples, 289. Apricots, 288. Arbor Day, 323. Archegonium, Bryophyte, 184; conifer, 216; fern, 193; livenvort, 169; moss, 177; Selaginella, 205. Archichlamydeae, 282. Ascomycetes, 146. Ascus, 146. Assimilation, 88. Associations, 324; see Plant asso- ciations. Axil, 42. Bacteria, 130; disease, 134, 135; fermentation, 134; nitrogen fix- ation, 134, 135; reproduction, 132; resistance, 133; root-tuber- cles, 136; spores, 133; structure, 131. Bamboo, 271. Banana, 280. Bark, 55. Barley, 267. Basidia, 155. Basidiomycetes, 158. Bast, 51; root, 74. Bean, 294. Berry, 239, 286, 298. Big tree, 219. Blackberry, 287. Black knot, 147. Blade, 6. Blueberry, 303. Blue-green Algae, 98. Bog moss, 181. Bracket Fungi, 156. Branches, root, 76. Brown Algae, 116. 357 358 INDEX Bryophytes, 183, 208. Bud, 67; accessory, 69; adventi- tious, 70; axillary, 68; flower, 68; leaf, 68; naked, 69; scaly, 35, 69; terminal, 68. Budding, 317; of cells, 138. Bulb, 66; self-burial, 67. Bulblet, 66. Buttercup, 284. Cactus desert, 341. Calyx, 221. Cambium, 53; cork, 54; roots, 75. Cantaloupe, 314. Caprification, 252. Caprifig, 252. Capsule, 239. Carbohydrate, 18. Carpel, 226; Angiosperms, 221; Conifers, 214. Catkin, 283. Cedar-apple, 152. Cell, 15, 103. Cellulose, 103. Cell-wall, 103. Cereal, 264. Chaparral, 344. Cherry, 289. Chlorophycese, 102. Chlorophyll, 22. Chloroplast, 17, 104; Spirogyra, 113. Chocolate, 301. Cinchona, 309. Citron, 300. Citrous fruits, 299. Cladophora, 108. Clay, 77. Clinging roots, 81. Cloves, 292. Club-moss, 200. Cluster-cup, 151. Coal, 205. Coconut-palm, 274. Coenocyte, 111. Coffee, 308. Compass plant, 29. Composite, 310. Composites, 310. Cone, carpellate, 214; staminate, 213. Conferva forms, 116. Conifers, 211. Conjugate forms, 116. Conjugation, 107. Coral Fungi, 157. Cork cambium, 54. Corn, 268. Corolla, 221. Cortex, 50. Cotton, 295. Cotyledon, 85; escape of, 91. Cranberry, 302. Crossing, 254, 317. Cross-pollination, 245. Crucifera, 286. Cucumber, 314. Cucurbitacese, 314. Currant, 298. Cuticle, 26. Cutting, 317. Cyanophyceae, 98. Cycads, 216. Cytoplasm, 104. Darlingtonia, 37. Date-palm, 275. Deciduous forest, 350. Deciduous habit, 32. Desert, Cactus, 341; salt and al- kaline, 344; subtropical, 341. Diastase, 88. Dicotyledons, 50, 230, 282; em- bryo, 237; Sympetalae, 302. INDEX 359 Differentiation, 102. Digestion, 87. Dion;i i a, 40. B, bacteria, 134, 135. Disk, 310. Dotted duct, 53. Downy mildew, 142. Drosera, 38. Drought, 337. Drought plants. 32U. Drupe, 239, 288. Dune, 338. Krt ocarpus, 120. Egg, Angiosperms, 235; CEdogo- nium, 110. Embryo, 85; Angiosperms, 230; Conifers, 217. Kndosperm, SO; Conifers, 218. Enzyme, 88. Epidermis, leaf, 15, 24; Marehan- tia, 167; stem, 50. Epiphyte, 82. Equisetum, 197. EriracesR, 302. Evergreens, 33. Family, 262. Fat, 89. Fermentation, bacteria, 134; yeasts, 138. Ferns, 183; antheridia, 193; ar- chegonia, 193; fertilization, 195; gametophyte, 193; general char- acters, 184; leaves, 187; life- history, 187, 196; sperms, 194; sporangia, 191; sporophyte, 187, 195; vascular system, 188. Fertilization, 107; Angiosperm, 236; conifer, 216; fern, 195; Fucus, 124; liverwort, 169; Mucor, 142; CEdogonium, 110; 24 Peronospora, 143; red Algae, 126; rusts, 152; Spirogyra, 114; Ulothrix, 107. Fiber, 295. Fig, pollination, 252. Figwort, pollination, 249. Filament, 22 J. Fl:i\, 296. Flower, 220; apocarpous, 284; bilabiate, 223; cleistogamous, 243; clusters, 232; dioacious, 230; Epigynous, 231; hypogy- nous, 231; insects, 242; monoe- cious, 230; n:ik<>d,222; numbers, 229; papilionaceous, 291 ; pistil- late, 230; protandrous, 250; pro- togynous, 250; staminate, 230; sympetalous, 223. Foliage leaves, 34. Forest, deciduous, 350; protective, 322 ;v rescrv:it ions. 322; supply. 321; tropical, 355; xerophytic, 344. Forestry, 320. Frond, 64, 187. Fruit, 238. Fucus, 118, 122. Fungi, 129, 165. Gametangium, 122. (Jamete, 107. Gametophyte, 171; Angiosperm, 235; Conifer, 215; Equisetum, 200; fern, 193; Lycopodium, 202; Selaginella, 204. Genus, 262. Geotropism, 90. Germination, conditions, 86; seed, 84, 218. Gills, 155. Girdling, 55. Glosocapsa, 98. 360 INDEX Gooseberry, 298. Gourd fruit, 314. Grafting, 56, 317. Grafts, 317. Grain, 239. Gramineae, 263. Grape, 298. Grape-fruit, 299. Grasses, 263. Green Algae, 102. Green felt, 111. Green slime, 101. Growth, leaf, 23; root, 76; stem, 59. Guard-cells, 16. Gulf weed, 118. Gymnosperms, 50, 207; general character, 210. Hair, 26. Hay grass, 271. Head, 234. Heaths, 302. Heliotropism, 93. Hemp, 297. Heredity, 316. Heterocyst, 100. Heterospory, 207; Selaginella, 204. Horsetails, 197. Host, 129. Houstonia, pollination, 250. Huckleberry, 303. Humus, 77. Hybrid, 253, 317. Hydrophytes, 326, 328. Hydrotropism, 90. Hypocotyl, 85; escape of, 89. Indusium, 191. Insects and flowers, 242. Integument, 229. Internode, 41. Involucre, 310. Iodine, source, 120. Iridaceae, 278. Irish moss, source, 126. Iris, pollination, 247. Irritability, 90. Jungermannia, 172. Keel, 247, 291. Kelp, 117. Labiatae, 223, 307. Labiates, 307. Laminaria, 117. Lawn grass, 271. Layering, 47, 317. Leaf, arrangement, 5; autumnal colors, 33; Bryophyte, 184; de- ciduous, 32; evergreen, 33; fall, 32; fern, 187; foliage, 34; form, 7; growth, 23; gutter-pointed, 356; horizontal, 9; mosaic, 13; motile, 30; night position, 32; parts, 6; profile, 29; protection, 24; rain, 32; relation to light, 8; rosette habit, 11; shading, 10; special forms, 34; structure, 15; vena- tion, 6; water reservoir, 29. Leafy axis, erect, 181. Leafy liverworts, 172. Legume, 239. Legumes, 291. Leguminosae, 239, 291; pollination, 246. Lemon, 300. Liana, 48. Lichen, 160. Life-history, moss, 176; mushroom. 153; red Algae, 127; rusts, 149; Selaginella, 205; Ulothrix, 107. Life-relations, 3. INDEX 361 Light, plant associations, 326. Liliaceic, 277. Lilies, 277. Lime, 300. Liverworts, 165. Lucerne, 293. Lycopodium, 202. Lycopods, 201. Madders, 307. Maize, 268. Male cell, 235. Mandarin, '_ )( .M>. Mangrove swamp, 336. Maple sap, 58. Man-bant ia, 167. Meadows, 345. Megaspore, Angiosperm, 235; coni- fer, 214; Selaginella, 205. Mesophyll, 17. Mesophytes, 327, 345. Microbe, 130. Micropyle, 229. Microspore, conifers, 212; Sela- ginella, 205. Mildew, 144; downy, 142. Midrib, 7. Mold, black, 139. Monocotyledons, 50, 56, 230; classification, 262 ; embryo, 237. Morel, 148. Mosaic, 13. Moss, 175 ; flower, 177 ; groups, 181. Motile leaves, 30. Mucor, 139. Mushroom, 153. Muskmelon, 314. Mustard Family, 286. Mycelium, 140. Mycorhiza, 159. Nectar, 36, 242. Needle-leaves, 211. Nepenthes, 38. Nightshades, 304. Nitrogen fixation, 134, 135. Node, 5, 41. Nostoc, 99. Nucellus, 229. Nucleus, 103. Nutmeg melon, 314. Nutrition, 3. Oats, 266. (Edogonium, 108. Olive, 313. Oogonium, Fucus, 124; mildew, 145; (Edogonium, 110; Perono- spora, 143; red Algae, 126; Vaucheria, 112. Oospore, 107. Orange, 299. Orchidaceae, 278. Orchids, 278; pollination, 248. Organ, 3. Oscillatoria, 100. Osmosis, 79. Ovary, 227. Ovule, Angiosperm, 228; conifer 214. Palisade layer, 25. Palisade tissue, 17. Palms, 271. Pappus, 310. Parasite, 129. Pasture grass, 271. Pea, 293. Peach, 288. Peanut, 294. Pear, 291. Peat, 175; bogs, 336. Perianth, 222. 362 INDEX Peronospora, 142. Petal, 221, 222. Petiole, 6. Phseophyceae, 116. Phloem, 52; root, 74. Photosynthesis, 18, 87. Phototropism, 92. Phycomycetes, 144. Pileus, 155. Pine, timber, 218. Pineapple, 281. Pirus, 289. Pistil, 228. Pitcher-plant, 35. Pith, 50; ray, 51. Plains, 341. Plant associations, 324; cactus desert, 341; deciduous forest, 350; mangrove swamp, 336; meadow, 345; mesophytic thick- et, 348; peat-bog, 336; plain, 341; pond weed, 328; reed- swamp, 331; rock, 338; salt and alkaline desert, 344; salt marsh and meadow, 336; salt steppe, 344; sand, 338; subtropical desert, 341; swamp, 331; swamp forest, 336; swamp thicket, 332; tropical forest, 355; xerophytic forest, 344; xerophytic thicket, 344. Plant-breeding, 316. Plasmolysis, 115. Plastid, 104. Pleurococcus, 102. Plum, 289. Plumule, 86; escape of, 91. Pod, 238. Pollarding, 70. Pollen, 242; Angiosperm, 224; conifer, 212. Pollen-sac, 226; conifer, 212. Pollen-tube, Angiosperm, 236; conifer, 217. Pollination, Angiosperm, 242; conifer, 217. Pollinium, 248. Pome, 289. Pomelo, 299. Pomology, 289. Pond-scum, 113. Pondweed association, 328. Pore Fungi, 156. Potato, 305. Prairie, 345. Profile leaves, 29. Pronuba and Yucca, 244. Prop-root, 80. Protection, leaves, 24. Proteid, 88. Prothallium, 193. Prothallus, 193. Protoplasm, 87, 103. Prune, 289. Prunus, 288. Pteridophytes, 183, 207, 208 PurTball, 158. Pumpkin, 315. Pyrenoid, 114. Quince, 291. Quinine, 309. Raceme, 232. Rain, leaves, 32. Ranunculacese, 284. Raspberry, 287 . Ray, 310. Reaction, 93. Receptacle, 240. Red Alga3, 124. Redwood, 219. Reed swamp, 331. Reforestation, 323. INDEX 363 Reproduction, 3; asexual, 107; blue-green Algae, 101; red Algae, 126; sexual, 107; vegetative multiplication, 101. Reservations, forest, 322. Resin, 219. Kopiration. s7. Rhi/oid, HIT. Rhi/ome, 03; self-burial, G7. Rhodophyceae, 1'Jl. Hil, 7. Riccia, 172. Ricciocarpus, 172. Rice, 269. Rockweed, 118. Root, 71; absorption, 78; air, 82; bast, 74; branch, 7<>; cambium, 75; cliniring. M; cuttings. 70; growth, 7<>; diameter increase, 75; hair, 71; internal structure. 74; phloem, 74; primary, 72; prop, 80; secondary, 72; special forms, 80; tap, 7~; vascular cylinder, 74; water, 80; wood, 71; xylem, 74. Root-cap, 73. Root-cuttings, 70. Root-fungus, 159. Root-hair, 74, 7v Root-pressure, ~v Rootstock, 63; self-burial, 67. Root-tubercles, 13. Sargassum, 119. Sarracenia, 35. Scale. I'li. 31. Srinn. 60. Scouring rush, 198. Sea lettuce, 110. Seed, absorption of water, 80; Aniriosperiu, '-37; conifer, 217; disper.-al. -J.Vi; germination, 84, 218; structure. B4. Seed-dispersal, L'55; air. -J. r .7: animals. L'C.O; discharge, 255; \\ ater, 259. Selaginella, 203. Select!..!.. 818. Self-burial, 07. Self-pollination, 243. Sensitive plant, 30. Sepal, 221. Sequoia. 211, 219. Shaddock, 299. Shade-plant. 320. Shoot, 41. Sieve plate, 53. Sieve vessel, 53. Siphon forms, 110. Societies, 324. Soil, 77. Solanaoesp, 304. Sorus, 191. Species, 203. Sperm, Angiosperm, 235; conifer, Jill; cycad, 211; fern, 194; liverwort, 109; moss, 177; CEdo- gonium, 110; red Algae, 120. 364 INDEX Spermatophytes, 208. Spike, 232. Spirogyra, 113. Spongy tissue, 18. Sporangium, Angiosperm, 224; brown Algse, 121; conifer, 212; Equisetum, 199; fern, 191; Mucor, 141; red Algse, 126; Selaginella, 203. Spore, 106; Angiosperm, 224, 235; brown Algae, 121; Equisetum, 199; green Algae, 106; mildew, 145; (Edogonium, 108; red Algae, 126; rusts, 149, 151; swimming, 106; Vaucheria, 112. Spore-case, moss, 180. Spore-fruit, mildew, 146; red Algee, 126. Sporophyll, 207; Equisetum, 199. Sporophyte, 171; Anthoceros, 173; conifer, 215; club-moss, 202; fern, 187, 195; Jungermannia, 173; leafy, 207; Lycopodium, 202; Marchantia, 170; moss, 179. Spring flowers, 67. Spur, 223. Squash, 315, Stamen, 224; Angiosperm, 221; conifer, 212. Standard, 291. Starch, 21. Stem, 41; annual, 53; climbing, 47; direction, 42; erect, 42; ex- ternal structure, 41; growth, 59; internal structure, 50; perennial, 53; prostrate, 45; special forms, 59. Steppes, 344. Stigma, 227. Stimulus, 90. Stipe, 155. Stipule, 6. Stock, 56, 317. Stoma, 16. Stone-fruit, 239, 288. Strawberry, 286. Strobilus, club-moss, 202; conifer, 212; Equisetum, 198; Lycopo- dium, 202; Selaginella, 203. Style, 227. Subsoil, 78. Subtropical desert, 341. Sucker, 70. Sugar-cane, 270. Summer spore, 149. Sundew, 38. Swamp, 331; forest, 336; thicket, 332. Sweet potato, 313. Swimming spore, 106. Sympetalae, 223, 282, 302. Tangerine, 299. Tap-root, 72. Tea, 300. Temperature, plant associations, 325. Tendril, 35, 48, 60. Testa, 85, 218, 237. Tetraspore, 126. Thallophytes, 165, 183, 208. Thicket, mesophytic, 348; xero- phytic, 344. Thorn, 35, 62. Timber, conifer, 218; hardwood, 284. Toadstool, 153. Tobacco, 306. Tomato, 306. Tracheary vessels, 52; annular, 52; dotted, 53; pitted, 53; spiral, 52. Transpiration, 22. INDEX 365 Tree group, 282. Tropical forest, 355. Truffle, 147. Tuber, 65; self-burial, 67. Tumbleweed, 257. Turgor, 104. Turpentine, 219. Twiner, 47. Ulothrix, 105. Umbel, 233. UmbellifenB, 294. Vacuole, 115. Variation, 316. Vascular bundle, 51. Va-ruUir cylinder, 50, 74. Vascular system, 76; fern, 188. Vaurheria, 111. Vegetative multiplication, 101. Vegetative propagation, 316. Vein, IS, 53. Venation, 6. Venus fly-trap, 40. Vernal habit, 67. Viticulture, 298. Water, absorption by root, 78; absorption by seed, 86; plant associations, 324. Watermelon, 314. Water plants, 326. Water reservoirs, in plants, 29; pollution of, 102. Water-root, 80. Water-sprout, 70. Wheat, 264. Wheat rust, 149. White pine, timber, 218. Wind, plant associations, 326. Wings, 291. Winter spore, 150. Wood, 51; root, 74. Wounds, healing, 55. Wrack, 118. Xerophytes, 326, 337. Xylem, 51; root, 74. Yeast, 138. Yellow pine, timber, 218. Yucca, pollination, 244. Zygospore, 107. (9, NATURE STUDY AND AGRICULTURE Practical Nature Study and Elementary Agriculture A Manual for the Use of Teachers and Normal Students. By JOHN M. COULTER, Director of the Department of Botany, University of Chicago : TQHN G. COULTER, Professor of Biology, ALICE JEAN PATTERs^w^iftepartment ofjo, in charge of Nature Studp, Illinois State Normal Univemity. 1 2 mo, cloth, $1.35 ne \^ / This hook is an attempt, oft^ry4&fJ^ (QeXj^^lp the teacher of nature study to 1 in IMT)MT inih |l( lllliinT^Triii work, and to make his work more definite. The volume has grown out of the experience of the authors. The material has largely been used in regular class work, and found efficient under conditions similar to those of the average school. Part I is devoted to presenting the principles of nature study, its mission and spirit, as well as the dangers which the study entails and how to avoid them. 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