A aiedi nh se aun Pie eee etic aro) aaron Sieleleretaratere ee ehe ne ete RTM tae ee IE Ar Pr ar gr aR AT TE IE arelelalera, siglel stat etetetyt st rir totes CR MRC t bheh shee + eleletstelaletatery ptalgetl tle Ph IE CMO TOCA Me eae aay bearatenr ac aeae hehehe Ir 263% ve pf en Vee ee Apa st ean heheh eo OT Peehit ahah * Patent C7 AL SUE Wb ae ae SECs MES tntee eee Fae ieaes dees Peer ere aah ak Be CIC IE IE CPt Pte at) tte wale a gle! ney alate tel Beer ESRI at tes tte BBs etch aca ese BOO MIC a ILC hehe pi et ei ReSaa Sie ACEI ICN eth ? C Deu) wleteteteTete ty Cates ietet OCOTRE IC Se Rei pe cee i ir) blerea elate Cornell University Library Bthaca, New York GEORGE FRANCIS ATKINSON BOTANICAL LIBRARY 1920 iiiiilionNann i) | olin,anx OUTLINES OF PLANT LIFE WITH SPECIAL REFERENCE TO FORM 7 AND FUNCTION BY CHARLES REID BARNES Professor of Plant Physiology in the University of Chicago NEW YORK HENRY HOLT AND COMPANY 1900 A753 1435 Copyright, 1900, BY HENRY HOLT & CO. ROBERT DRUMMOND, PRINTER, NEW YORK. PREFACE. OUTLINES OF PLant Lire has been prepared at the request of the publishers to meet the wants of those schools which can give only a part of a year to botany and prefer a sim- pler text than the author’s earlier work. To simplify the already elementary Plant Life has not been easy. The present book differs from the former one chiefly in (1) the omission of all account of the minute anatomy of plants, upon the assumption that no laboratory work with the compound microscope is possible; (2) in the elimination of the greater part of the chapter on sexual re- production because of the difficulty of comprehending its processes and their significance without laboratory study, which is almost impossible in many schools under existing conditions of time and equipment; (3) in the omission of some of the less important paragraphs here and there, and the reduction of others to small type, indicating at a glance parts which may be omitted without interrupting the conti- nuity of the discussion. The parts on Physiology and Ecology are less changed than others, because these are the subjects toward which, happily, elementary study is being more and more directed, since they give meaning to the study of form and structure. The study of the parts of a loom may be interesting in itself, but it becomes of the greatest significance when it enables the student to understand the working of the machine and the output of the factory. How can any teacher or pupil iii iv PREFACE. longer be content with studying the various name-plates on the machines ? For those who wish to follow the author’s laboratory direc- tions the placing of them after the paragraph or chapter to which they are related may be a convenience. At least it will emphasize the idea that this book is not intended to be memorized and recited, but to serve as an explanation and extension of knowledge acquired at first hand by the study of plants. Teachers will find some suggestions which may be of ser- vice in the use of this book in the preface to Plant Life. The explanations and acknowledgments there made need not be repeated here. C. R. B. THE UNIVERSITY OF CHICAGO, January I5, 1900. CONTENTS. ; PAGE PREFACE . ‘ . . Pe * ‘ 4 m ‘ . hii PART I: THE PLANT ae CHAPTER I. INTRODUCTION . : . . a) Pa II. SINGLE-CELLED PLANTS AND COLONIES . 7 . III. FILAMENTOUS ALGA. . A : 5 . - 16 IV. THE THALLUS OF THE HIGHER ALGZ . : + 23 V. THE FUNGUS BODY . : : : . , - 30 VI. LIivERWORTS AND MOSSES 5 7 : : - 41 VII. FERNWORTS AND SEED PLANTS : . . - 53 VIII. THE RooT . . . : : : : - 59 IX. THE SHOOT. a : . . : 7 - 72 X. THE sTEM ‘i . : < 7 ‘ . . 8 XI. THE LEAVES . 3 ss é ‘ : 3 - 96 PART II: PHYSIOLOGY. CHAPTER XII. INTRODUCTION. . : ; : . - IIS XIII. THE MAINTENANCE OF BODILY FORM . . » 119 XIV. NUTRITION . . : é ‘ . z - 124 XV. GROWTH. : . . . - 154 XVI. THE MOVEMENTS OF PLANTS a ‘ - - 164 PART III: REPRODUCTION. CHAPTER XVII. VEGETATIVE REPRODUCTION . ‘ ‘ . 185 XVIII. SEXUAL REPRODUCTION. ; ‘ i . 218 PART IV: ECOLOGY. CHAPTER XIX. FoRMS OF VEGETATION . ; ; . + 237 XX. MESOPHYTES : . . % : » 231 XXI. XEROPHYTES AND HALOPHYTES . : . + 237 vi CONTENTS. PAGE XXII. HypDRoPpHYTES . ‘ 5 . i : . 246 XXIII. ADAPTATIONS TO OTHER PLANTS AS SUPPORTS . 249 XXIV. Symsiosis . a : . . . 7 + 252 XXV. ANIMALS AS FOOD, FOES, OR FRIENDS . 7 . 261 XXVI. PROTECTION AND DISTRIBUTION OF SPORES AND SEEDS 3 3 : 3 : r + 270 APPENDIX I. DIRECTIONS FOR COLLECTING AND PRESERVING MA- TERIAL. : : ‘ ‘ A : . 287 Il. APPARATUS AND REAGENTS . 3 , . + 293 III. OUTLINE OF CLASSIFICATION . . 5 s « 297 IV. REFERENCE BOOKS . : : . 3 . + 301 INDEX . ‘ i 7 ‘ a a ‘ : < . + 303 OUTLINES OF PLANT LIFE. PART I: THE PLANT BODY. CHAPTER I. INTRODUCTION. 1. Living matter.—By the combination of powers called life, each living thing controls, for a longer or shorter time, a certain amount of material, which constitutes its body. This material is arranged into definite form ; some remains only for ashort time as part of the body and is then discarded; other material remains part of the body as long as life exists. That which is changing most rapidly is the living substance, called protoplasm. If there are parts of the bedy not living, they have been formed by the protoplasm and are generally controlled by it. 2. Members.—When the body is large, it is easy to see that it is made up of more or less distinct parts. These are its members. Asa rule, the smaller it is, the fewer and less dis- tinct are the members. There are many thousands of plants in which the body does not have any members, but can be distinguished only into the units of which it is built, called cells. Still others consist of a single cell. : In the largest plants the more important members may be divisible into smaller subordinate ones. When these are in- 2 OUTLINES OF PLANT LIFE. spected they too are seen to be made up of a great many minute parts, each consisting of a bit of living protoplasm and some other things which it has made. These parts are called cells. (See (J 4.) Thus, a corn plant has two principal members, a root, below ground, and a shoot above ground. The root consists of many subordinate mem- bers, the roots and the rootlets; the shoot consists of stem and leaves ; the leaves of sheath and blade, etc, But a duckweed shoot has no dis- tinction of stem and leaf, and only a single root. The pond scums have no members, but consist of a row of cells; while in many diatoms the body is a single cell. : , 3. Reproduction.—Every plant must provide for its own existence. To do this, it must possess means for securing, or for making, and using food. During this feeding period its most striking characteristic is growth. It must also provide before it dies for the production. of new plants of the same kind. When the plant is very simple, both duties must be done by the same cell, but in more complex plants special cells, and in many cases special members, are provided for reproduction. ‘The two processes are sometimes carried on at the same time, but more commonly reproduction occurs at some particular or limited period. It is convenient to consider first the form of the plant body and those members which are not concerned in reproduction. Parts I and II therefore, treat of the work and parts of the plant which promote its own life and growth, i.e. the vegeta- tive body. Part III discusses the form and action of the re- productive parts, so far as these can be studied without a microscope. 4. The cell.—A plant-cell is a minute portion of living matter, called profoplasm, generally surrounded by a mem- brane, called the cel/-wadl (fig. 1). The protoplasm is the essential part of the cell. It con- structs the cell-wall, Rarely, if ever, is it uniform through- INTRODUCTION. 3 out, but shows distinct parts, each having special work to do. In the most complete and active cells the greater part of the protoplasm consists of a finely granu- lar or nearly transparent, colorless portion, in which the other ‘parts seem embedded. Protoplasm is not a single sub- stance, but a mixture of several dif- ferent substances, so intimately mixed and so easily destroyed that it isnot possible to analyze it. More- over, the nature and amount of the components are probably variable. In all but the youngest cells there are one or more bubbles of water in the protoplasm. 5. Nucleus.—The nucleus is one Fic. 1.—A_ cell (the megaspore) from a lily ovule, filled with anular protoplasm, in which is embedded a large spherical nucleus, containing a nucle- olus, and accompanied by two centrospheres, a. he line around the protoplasm repre- sents the cell-wall, with those of the adjacent cells connected. Magnified s00 diam. — After : . Guignard. of the most important. parts of the cell. It is generally spherical or ovoid, but in long cells it may become elongated (fig. 2, 2). The nucleus may divide into two, and this is commonly followed by the formation of a partition-wall separating the cell into two parts, each con- taining one of the daughter-nuclei. 6. Plastids.—In most cells there are also other parts, called plastids. In young cells these are small, rounded, colorless bodies. As the cell grows older they increase in size and number.. When mature and in cells which lie near the surface of green plants, they are commonly roundish. or biscuit-shaped, of spongy texture, and colored yelllowish- green by a substance known as chlorophyll. These are con- sequently known as chloroplasts or chlorophyll-bodies (fig. 2). In.other cells, particularly those for the storage of food, they may develop into smaller, denser, flattened or roundish, uncolored bodies, whose work is usually to gather starch into 4 OUTLINES OF PLANT LIFE. grains (fig. 3). In other cells, particularly in highly colored parts, the plastids may become of most diverse form and size, and take on a red or yellow color (fig. 4). 7. Wall. — The cell-wall is Fic. 2. Fic. 3. Fic. 2.—A cell from the interior of the leaf of the oat, showing its wall, and some inclusions of the protoplasm. z, the nucleus; c, chloroplasts; 0, an oil-drop. Mag- nified about 1000 diam.—After Zimmermann. Fic. 3.—Part of the cell contents of an inner cell of white potato. z, nucleus ; s, starch grains, each having been formed by a leucoplast, 7, which is still attached to one side of the grain; 4, crystalloid. Magnified about 1000 diam.—After Zimmermann. formed by the protoplasm. In green plants when first formed it consists chiefly of ced/ulose, with which, as it grows older, various other substances may be mixed. Some of these \/ A ar A B CG Fic. 4.—A, chromoplasts from flower leaves of an orchid; B, from the root of carrot; C, from the fruit of mountain-ash. Embedded in the protoplasmic body of the chromoplast are sometimes proteid crystalloids, 4, pigment-crystals, 7, or starch- grains, s. Magnified about 1000 diam —After Schimper. “ey \ 2 are present even in the young wall, and may increase with age; others are characteristic of special changes which the wall may undergo. INTRODUCTION. 5 8. Growth of the cell-wall.—aAs the cells become older the wall may increase in thickness. It must also increase in area as the cells grow in size. The growth in area is usually accomplished by putting new particles between the older ones. Growth in thickness is rarely uniform. Pits or pores are formed in the wall when it thickens except at these spots. When the thin parts are large and only certain spots or lines grow thicker, the wall shows projecting spikes, bands, or threads. if ‘CHAPTER II. SINGLE-CELLED PLANTS AND COLONIES. In the lakes and pools, in ditches and slow streams, on the surface of damp rocks and wood, may be found many sorts of microscopic plants, whose entire body is merely a single cell. 9. Fission-alge.—The simplest forms of the single-celled green water plants are the fission-alge. In the central part of the cell is the nucleus, and the whole of the protoplasm is colored by the yellowish-green dye, chlorophyll. Along with it, there is a blue coloring matter, so that in mass these algee look bluish-green or even black- ish. For this reason they are called blue-green algze to distinguish them from those in which only the yellow- green color is present. 10. Gelatinous colonies.—The cell- wall may be thin, but commonly it is composed of several layers, of which the outer are changed into mucilage. This swells into a transparent jelly when Fic. 5.—A_ blue-green alga (Gleocapsa). Single _indi- viduals, A, and colonies Magaled eae wet, either becoming alike throughout S. Bae or showing distinct layers. When a number of such forms grow in company (fig. 5), this jelly-like material blends into a single mass in which the associated plants seem to be embedded. 6 SINGLE-CELLED PLANTS AND COLONIES. 7 11. Gelatinous filament-colonies.—In other cases, instead of being held together only by the weak jelly-like portion of the cell-wall, the plants, still practically independent the one of the other, remain connected by the firmer portions of the wall into rows, forming irregularly coiled or serpentine fila- ments, which are embedded in a profuse jelly (fig. 6). The Fic. 6.—WNostoc. A,a‘ gelatinous colony, irregularly lobed. Natural size. B, a por- tion of a serpentine filament with five heterocysts (one at each end by which it was separated from the rest of the cells composing the filament, and three intermediate ones) and the jelly belonging to it. Magnified about 400 diam.—After Thuret and Janczewski. real independence of the cells, even though they remain con- nected, is shown by the fact that such a chain may be broken up into any number of pieces and each piece will retain all its powers. Here and there in the chain there occur cells unlike the rest, whose purpose seems to be to break the chain into pieces, which work their way out of the jelly and grow into independent colonies. The association of considerable numbers of these plants in colonies gives rise to masses of jelly which vary from the size of a pin-head to 2-5 centimeters in diameter. They may be found adhering to water-weeds as clear- or dirty-green masses, or sometimes floating free (A, fig. 6). i EXERCISE I. Nostoe or Rivularia.—1. Observe the size and form of the colonies and the consistence of the jelly enclosing them. ([ 11.) 8 OUTLINES OF PLANT LIFE. 2. Crush a bit of a Mostoc colony ora whole one of Rivularia between two glass slips, remove the upper slip, cover with water and observe the coiled (Nostoc) or radiating straight filaments (Rivularia) embedded in the jelly. (Fig. 6.) 12. Filaments of loose organization.— Of very near kin to these plants are the oscillarias, which have received this name from the pendulum-like swinging of their tips (fig. 7). In them the cell- walls remain connected more extensively and more firmly, so that each cell is disk-shaped, and the filament is much less easily separated into its parts. Moreover less of the wall has become jelly-like, so that often this part is not apparent and is difficult to see even when the plants are looked at with the micro- Pig. 1 Oitteria ath scope. Even though invisible, it may tipi fe # porion of ae be detected by the slippery feel of the ees Se diam. — After plants when rubbed gently between the fingers. EXERCISE II. Oscillaria. x. Observe the color of a bit of Osci//aria. ({ 9.) 2. With needles tease out the specimen in a drop of water on a glass slip; observe the delicate thread-like form. (Fig. 7.) 3. Transfer a bit of living Osci//aria to a small glass dish or white in- dividual butter plate with a little water; protect it from drying up with a cover; 24 hours later observe the position of the filaments. (J 12.) 4. Demonstration. Dip a considerable mass of Osci//aria in hot water for a moment and put in a white butter plate with as small a quantity of water as will cover it, As the water evaporates observe the color depos- ited on the dish at the edge of the water. ({ 9.) 13. Feeding habits.—The feeding habits of the oscillarias are worth notice. These plants are found in permanent pud- dies and ditches where organic matéer is decaying. The sig- SINGLE-CELLED PLANTS AND COLONIES. 9 nificance of this is that some of the ancestors of the green oscillarias probably had offspring which, instead of living upon food prepared by means of the green coloring matter (4 185 ff.), learned to use the organic matter in the water, at first perhaps no more than the present oscillarias do; but gradually they came to live exclusively upon it. As a conse- quence, they lost their green color and became incapable of existing where organic food cannot be had. Bacteria. 14, Fission-fungi.—Along with the loss of color and change of habit went a diminution in size. They have now become so different that they are known as fission-fungi, and popu- larly as bacteria, bacilli, microbes, germs, etc. These plants, probably the descendants of common ancestors with the fis- sion-algze, are the smallest known living things (figs. 8, 9). The diameter of many sorts does not exceed .0005 of a milli- meter. That would allow 175 to lie side by side upon the edge of the paper on which this book is printed. Thoughso minute these plants have the same sort of protoplasm and cell-wall as larger ones. They increase in number rapidly by each cell dividing into two, which separate readily into independent plants. 15. Gelatin.—In the fission-fungi, as in the fission-alge, considerable masses of jelly-like material are produced, in which the plants may lie embedded. The films, sometimes smooth, sometimes wrinkled, which appear on an infusion of organic matter, such as tea or broth, are formed by masses of bacteria which rise to the surface and become embedded in the gelatinous material they produce (4, fig. 8). Demonstration.—Steep a cupful of chopped hay in hot water for fifteen minutes, and set the infusion, loosely covered, in a warm place. After a day or two, show the film of bacteria which covers the surface of the liquid. 10 OUTLINES OF PLANT LIFE. 16. Cilia.—Most species are furnished with organs of movement consisting of fine threads of protoplasm protruded Fic. 8.—Various bacteria. a, Micrococcus, the “ blood-portent’’; 5, zoogloea form - of the same; c, Bacterium acetz, the ferment of vinegar ; @, Sarcina, a harmless parasite of the human intestine. a@, 4, magnified 300 diam.; c, 2000 diam.; d, 800 diam.—After Kerner. gil dead ‘WE yer A ar oo Fic. 9.— Bacteria stained to show cilia. A, cilia tufted at one end; 3B, cilia irregularly distributed over body; C, cilium single at oneorbothends. J, the bacillus of typhoid fever; C, the bacillus of Asiatic cholera. Magnified 775 diam.—After Migula. through the wall. These, by their sudden contraction on one side, lash about like whips, and propel the cell by jerky, darting motions through the fluid in which it swims. These SINGLE-CELLED PLANTS AND COLONIES. II lashes, called cea, may be single at the ends of the cell (C, fig. 9), or many at ends or sides (A, fig. 9), or the whole cell may be covered with them like hairs (B, fig. 9). They may be withdrawn or drop off when the plant comes to rest, as when they form the scums previously mentioned. These plants are most interesting on account of their rela- tion to health and disease, decay, fermentation, etc., which cannot be discussed here.* 17. Yellow-green alge.—Among the single-celled green plants, one of the most common groups is that represented by fig. 10, which shows one of a large series, in which the body consists of a single cell with its wall, protoplasm, nucleus, and a few relatively large chloroplasts. In this greater specialization of the protoplasm, these plants show the only advance upon the blue-green alge. The wall in such as this Pleurococcus is almost uniform and quite thin. The cells of some kinds are frequently associated in colonies, embedded in jelly or not. EXERCISE III. Pleurococeus.—1. Examine with a lens pieces of bark bearing Pleuro- coccus and similar alge. Note the irregular distribution of the green granular heaps of plants. Is there any similarity to the distribution of higher plants over uncultivated areas ? 2. After soaking a piece of bark for a few minutes, scrape off with the nail or a dull knife blade some of the green material, spread it as well as possible in a drop of water on a slip of glass, cover it with a piece of thin glass, avoiding air-bubbles, and examine with a lens. Observe the minuteness of some of the specks, which are mostly single plants The larger ones are clusters of plants. 3. Demonstration. Show a slide under microscope and have pupils * For further information on these plants, see Frankland: Our Secret Friends and Foes ; Prudden.: Story of the Bacteria, Dust and its Dan- gers, Drinking-water and Ice Supplies ; Russe//- Dairy Bacteriology ; Frankel (tr. by Linsiey): Bacteriology (medical). 12 OUTLINES OF PLANT LIFE. observe the form and color of single plants, many consisting of two or more cells still juined together, resulting from cell division. (17, fig. 10.) Fic. 10.—Pleurococcus viridis, A,a a individual; 2B, a colony shortly after division ; C, the same after separation. agnified 540 diam.—After Strasburger. Ng i inn NAAT A EX Fic. 11.—Various diatoms, a, Syxedra,; b, Pleurosigma; c, ad, Grammatophora, side and top views; ¢, colony of GowAhonema, with branched stalks attached to an alga; /, g, single cells of same, more magnified, top and side views; 4, colony of Diatoma, the cells connected into a zigzag band; 7, #, colony and individuals (top and side views) of Fragillaria; 1, m,n, Cocconema. In m the pair is surrounded by jelly preliminary to the escape of the protoplasm and the formation of two new cells (auxospores) which has been completed in ~.— After Kerner. 18. Shelled plants.—Other one-celled plants constitute a group known as diatoms, found in both fresh and salt waters, either attached or free-swimming (figs. 11, 12). The dia- SINGLE-CELLED PLANTS AND COLONIES. 13 toms are very various in form, and present two different aspects. When seen from the side they are generally elon- gated-rectangular. When looked at from above they are short-cylindric, disk-shaped, boat-shaped, or variously curved or angular. ‘They are peculiar in having the cell-wall so filled with silica that scarcely any other material is left. In- deed the plants may be heated to a red heat and boiled in acid without destroying the form and markings of the cell- wall, so completely has it become silicified. To permit growth this rigid cell-wall is constructed in two pieces which fit together like the two parts of a pill-box (fig. 12). -Each Fic. 12.—A single diatom (Navicula amphirhynchus). A, top view; B, side view, showing overlapping of the valves. The parts shaded by lines are the chloroplasts ; the dotted part the protoplasm, with nucleus about the center of cell. Magnified 750 diam.—After Pfitzer. of these pieces, or valves, is sculptured into regular patterns in lines and dots, which are often so excessively minute or close together as to be barely visible with the highest powers of the microscope (4, fig. 11). Seen in mass, as they may often be on the sides of a glass aquarium, living diatoms ap- pear yellowish-brown. The chloroplasts, which are some- times single and always few, have a brownish color in addi- tion to the green chlorophyll. It is not uncommon for the diatoms to form colonies by the adhesion of several or many individuals by means of gelatinous cell-walls. These colonies are ribbon-like, or zig- 14 OUTLINES OF PLANT LIFE. zag chains, or even branched filaments (4, 7, fig. 11). Other sorts may be attached singly or in clusters by a gelati- nous stalk (e, fig. 11). In all cases the jelly, like the rest of the cell-wall, is a product of the protoplasm. The slow gliding movements of some free diatoms are due to the pro- trusion of strands of protoplasm through slits in the valves. Fic. 13.—Various desmids. a, Micrastertas; 6b, Cosmarium ; c, Xanthidium ; Os OCs eres e, Staurastrum ; f, Aptogonum. Magnified about 200 diam. 19. The desmids.—These form another group of one- celled green alge. They have neither the brownish color nor siliceous wall characteristic of diatoms, but are bright green cells of remarkably diverse and often beautiful forms. As a rile the cell is flattened and is divided almost into two by a deep constriction near the middle (a, 4, ¢, e, fig. 13). Often the body of the cell is covered with warts or spine-like SINGLE-CELLED PLANTS AND COLONIES. 15 projections (4, ¢, fig. 13), or is prolonged into horn-like or hair-like lobes. These plants also frequently cohere into colonies (/, fig. 13). In that case tooth-like projections of the cell-wall may interlock. 20. Summary.—The simplest plants consist of a single cell, which is often protected by a copious mucilage. By this means also the plants are often associated in colonies of various forms. Among the green plants some possess in addition a blue coloring matter; others a brown. Many can move about from place to place. The bacteria are de- generate relatives of the blue-green algze which have lost their green color, and thus their power to make their own food. CHAPTER III. FILAMENTOUS ALG. OpviousLy some of the plants mentioned in the last chap- ter, such as the oscillarias, are colonies of cells well on the Fic. 14.—A, one of the final stages in cell-division. The daughter- nuclei are still connected by fila- ments, and across the equatorial plane particles of new cell-wall material are formed. J, the com- pletion of cell-division; the daughter-nuclei have rounded off and the new wall is Jike the lateral walls. Magnified 880 diam. —After Strasburger. way to complete union into co- herent filaments whose elements are attached to each other by con- siderable areas of the cell-wall. In order clearly to understand this condition, we must consider the mode of origin of the individual cells composing the row. 21. Fission.—Under conditions mostly unknown to us, in the course of its growth a cell may divide by a process known as fission. The material of the nucleus passes through «a complex series of changes and separates into two parts. In a plane between these daughter-nuclei particles are deposited to form a cell-wall (4, fig. 14). A Fic. 15.—Diagrams of cell-division. spherical cells, z, 4, by the wall 1. 2, 3, parallel to 1. divided by wall 3 into @’’, a’’. a has divided b In this way a single one-celled plant of Pleuro- 958 2 ele[ 2 3.21 2 B 4, division of a spherical cell into two hemi- &, the same after further division in planes 2, y wall 2 into 2’ and another cell which has again 6 has divided into 4’, 6’, the inner of which has elongated preparatory to a division into 4’’, 4’’, as by wall 3. division, by wall 2, at right angles to 1. C, fig. A, after a second 16 FILAMENTOUS ALG. coccus (A, fig. 10) may divide into two, so that it consists of two hemispherical cells, each capable of independent growth (fig. 23, A). In the filamentous alge the cells formed by such divisions remain connected throughout their whole extent, and as the successive divisions are parallel a cell row results (B, fig. 15). When the divisions are in two . planes the cells forma flat sheet (¢, fig. 15); and when in three planes, a mass. 22. Filamentous alge. —There is a large number of plants in which the vege- tative body throughout life has the form of a filament. The green plants of this sort live almost entirely in water or in wet places, and may be conveniently desig- nated as filamentous alge. 23. Pond scums. — Among these none are more beautiful or interest- ing than the pond scums, represented in our waters by several genera (Spiro. gyra, Zygnema, Mougeotia and some others*). They * To the same group also belong the single-celled desmids already described. 17 Fig. 17. Fic. 16. Fie. 18. Fic. 16.—A cell from filament of Spzrogyra. ch, chloroplast (there are three in this cell); P, pyrenoids; %, nucleus. Magnified 200 diam, —After Strasburger. Fic. 17.—Two cells from filament of Zygnema, showing the gelatinous sheath greatly swollen, and stellate chloroplasts, in which is a pyrenoid, with the nucleus in a strand of protoplasm bene them. Magnified 245 diam.—After ebs. Fic. 18.—A cell from filament of Mougeotia. The darker body nearly filling cell is the chloro- plast (face view) in which are pyrenoids, #, and tannin vesicles, 2g. If seen from a direction at right angles it would appear as a narrow stripe in the center of the cell. z,thenucleus. Mag- nified about 200 diam.—After Zimmermann, 18 OUTLINES OF PLANT LIFE. may be readily recognized, during their vegetative period, by their unbranched filaments, bright green color, and slippery “« feel’’ between the fingers.* Under the microscope, they are at once distinguished from other filamen- tous algze by the shape of their chloroplasts. In Spirogyra these form.one or more flattish, spirally wound ribbons, notched on the edges, and em- bedded in the protoplasm near the cell-wall (c#, fig. 16). In Zygnema there are generally two irregularly star-shaped chloroplasts (fig. 17) ; while in Mougeotia a single flat, plate-like chloroplast, nearly as wide as the cell, traverses its center (fig. 18). See also fig. 19. Embedded in the chloroplasts of these and other algz are usually seen one or more angular, colorless bodies, often surrounded by a jacket of starch. These are stores of reserve food, known as pyrenotds (f, figs. 16, 18). In these plants there is little or no difference between the parts of the filaments. If broken into two, each part may continue growing with no damage to any part except the cells which were ruptured in severing the plant. EXERCISE IV. Spirogyra.—lIf fresh material is available examine a few filaments in a white dish for color. If preserved material is used, stain red by immers- ing for a few minutes in eosin (cheap red ink will answer). Examine with a lens. Observe : 1. Length; whether broken or whole; whether with or without branches. 2. The delicate partitions, like white lines, crossing the green (or red) filaments, dividing the protoplasm of one cellfrom another. Can the form of the chloroplasts be seen? (Cf. fig. 16.) This can be readily seen only in the larger species. (J 23.) ; 3. Demonstration. Mount a few fresh filaments in water. Show under moderate power the form of the chloroplasts; the reserve food nodules ; the nucleus, (Fig. 16.) * This slipperiness is due to the gelatinous outer part of the cell-wall (fig. 26), which is only visible after special treatment or on examining the filaments in a thin mechanical solution of Chinese ink. FILAMENTOUS ALGA. 19 24. Base and apex.—But other filamentous algze show a distinction between base and apex. In UWlothrix (fig. 19) the basal cell is elongated and pointed, and is colorless, because it is not furnished with chloroplasts like the others. By this pointed cell the plant is loosely attached, at least when young, to the substratum, while the green por- tion waves freely in the water. Thus arises a distinction into two parts, viz., the r/zzo:d and the thallus. In Cladophora, Vaucheria, and their allies, the plants are generally attached by a well- developed rhizoid region, which is often branched (w, fig. 20), as is also the thallus. In contrast with the preceding, therefore, localization of growth, producing branching, may be observed. 25. Branching.—A branch begins by the growth in area of a limited portion of the cell- wall. Since growing cells are usually stretched by the water they absorb, the pressure upon the enlarged region causes the wall to bulge out- = ward there. The convexity gradually increases Fic. 19.— UZo- as the region grows, until the swelling becomes ie vache ae : _ ment with rhi- an outgrowth whose further lengthening consti- —zoid cell, 7, at tutes a branch similar to the main filament. deta ae Growth in length may be limited to the tip of soeacnee a filament, or to a narrow zone including one or more cells, or it may occur indifferently in any cell, or in all cells. EXERCISE V. Cladophora.—If fresh material is at hands observe in a white dish ; if preserved specimens are used stain for a few minutes in eosin. ’ a, How is the plant attached ? 20 OUTLINES OF PLANT LIFE. 2. Observe form and particularly the abundant branching. Can a single main axis be traced? How many branches arise at one point? - Fic. 20.—A young plant of Vaucheria, developing from'the spore. A, mature spore; B, the same after germination has. begun; C, plant further developed from spore, sf, with growing apex, s, and rhizoid, w, by which it attaches itself to the mud. The chloroplasts are numerous and close together next the wallon all sides. Magnified 28 diam.—After Sachs. 26. Partition walls unnecessary.—Many alge, while ex- ternally like others, which are divided into true cells, have not the units of structure separated by cell-walls. In Vaucheria, for example, the whole of the vegetative body forms a single chamber, in which lies the undivided protoplasm, corre- sponding to many cells, as shown by the numerous nuclei which are distributed through it. The external walls of the cells are formed, but the partition walls are not formed. 27. External segmentation.—A plant body of this con- struction may attain considerable size and complexity, as in Caulerpa (fig. 21),* even to mimicking, upon a small scale, the form of leafy plants. In such cases the external walls become considerably thickened, and across the chamber, from one side to the other, run irregular bars of similar material which act as braces to prevent the collapse of the outer walls (fig. 22). In Caulerpa, particularly, a high degree of development as to external form is reached (fig. 21). There is a stem-like * Note carefully the scale of the figures. FILAMENTOUS ALGA. 21 axis, Y-s, creeping in the mud, which bears green leaf-like branches, 4, on one side and clusters of colorless root-like - - WARY as 7 ote ANN Cea ZAM c AS DONA ptr 54) s OTS Sot ORY =k\ 5 qu" . A \ Fic. 21.—Part of a plant of Caulerpa. See text, 727. Two-thirds natural size.— After Sachs. branches, w, on the other. Not only are a base (posterior end) and an apex (anterior end) distinguishable, but the plant shows a difference between an upper (dorsal) and under (ventral) side, the leaf-like thallus lobes arising from /X% the dorsal side, while rhizoids spring from the ventral side. 28. The thallus.—To the loose ag- gregation of single cells into colonies of ; : Fic. 22.— Transverse section definite form, as well as to the body of axis of Cause, show- . et s é ing cross-bars to stiffen wall. formed by their more intimate union in Magnified about 25 diam.— “ : After Murray. the cell rows and masses just described, the name /hallus is applied. The term is most frequently applied to those more complicated forms which constitute the vegetative bodies of the higher alge, which are now to be described. 29. Summary.—Instead of being loosely associated in col- 22 OUTLINES OF PLANT EIFE. onies, plant cells may remain firmly united in rows or sheets. Such an aggregation of cells is then called @ plant. The form of the plant depends upon the mode of division of the cells. The body may be thread-like, and alike at both ends. Or it may be distinguishable into a base and apex, or even into a root-like part, the rhizoid, and a shoot-like part, the thallus. Either may branch. Branching is due to more rapid local growth of certain regions. In some plants the protoplasm is not, or only incompletely, divided by cell- walls. CHAPTER IV. THE THALLUS OF THE HIGHER ALG. 30. The larger alge.— From the thread-form alge, whose body is a single row of cells, it is but a step to those forms whose body consists of a single sheet of cells. One common form has a leaf-like body, which grows attached to stones or other alge. The broader forms are sometimes 20-25 cm. wide. The body of the sea-lettuce is somewhat similar in structure, but consists of two layers of cells, and, as fig. 23 shows, is very clearly distinguishable into an. organ of attachment, the rfzzozd, and the leaf- like part for which the name ¢hallus may be kept. So, from the thread-like bodies we pass through sheet-like to massive bodies of a broadly extended form. Likewise there may be found all in- termediate forms between the thread- like algae and those whose bodies {62742 the seajtetiee, shaw. are slender, but are more than one 3yzching 't tp rocks. Natural row of cells thick. In other marine algz a still higher specialization of members is reached. One of the red seaweeds may be used to show the gradual advance in complexity. 23 24 OUTLINES OF PLANT LIFE. Polysiphonia. 31. External form.—The body of Polysiphonia, a slender alga (fig. 24) which grows in abundance upon rocky sea- coasts, is much branched. The main axis -is made up in its larger parts of five or more rows of cells, the central row being surrounded bya jacket of at least four others (fig. 25); but at the tips even of the main axis there is only a single row of cells, as in the simplest alge (fig. 26). The body of Polystphonia, there- Fic. 24. Fic. 25. Fic. 24.—An entire plant of Polysifhonia, showing mode of branching. Natural size. —After Kiitzing. h 7 Fic. 25.—Transverse section of one of the branches of Folysiphonia, showing a minute central cell with four large and four small cells surrounding it. Magnified about 50 diam.—F rom a drawing by Mr. Grant Smith. Fic. 26.— Apex of a branch of Folyszphonia which has nearly ceased growing. Mag- nified about 100 diam.—F rom a drawing by Miss Rowan. fore, is one of the simplest forms composed of cells massed together. 32. Growth.—Growth in length can take place only at the ends of the main axis and its branches, because there each apical cell (fig. 26) produces, by division near its base, the new cells whose later division and enlargement make the mature axes. 33. Color.—In this plant, as in very many of the marine alge, there is present, in addition to the green of the chloro- plasts, a special red coloring matter. To the naked eye, this THE THALLUS OF THE HIGHER ALG. 25 color overpowers the green and gives the plant a pink tinge. In other red algze it is often present in greater quantity and variety of hue, so that brilliant reds and purples, with shadings of brown and green, mark the more striking species. EXERCISE VI. Polysiphonia.—Place a plant in a glass dish over a black or white back- ground. Observe 1. The form of the body and the mode of branching. (Fig. 24.) 2. The mode of attachment at the base, if specimens are entire. 3. Demonstration. Mount the tip of one of the branches and show the high, dome-shaped, afzca/ cel/, with segments cut off successively from its base, to be later themselves divided longitudinally. ([ 32, fig. 26.) 4. Cut a transverse section of a medium-sized axis and observe the four large peripheral cells, surrounding a central cell; the latter tobe seen only under compound microscope. (ff 31, fig. 25.) Between the very simple body of Polysiphonia and the much larger and more complex body of the common bladder-wrack, or Fucus vesiculosus, there are all gradations, which cannot be described here. Fucus. 34, External form.—The body of Fucus (fig.27) is large as compared with the plants previously described. It is often 75-100 cm. long by 1-2 cm. broad, of greenish-brown color and somewhat leathery texture. Near the base the thallus is contracted into a stalk whose extremity is broadened into a sucker-like disk (often irregularly branched) which attaches the plant firmly to the wave-washed rocks, on which it grows. Above, the thallus is flattened, with a thicker rib in the mid- dle (fig. 28), and branches abundantly by forking. These branches, though often twisted, really lie in the same plane as the flattening (fig. 27). Here and there the, thallus has 26 OUTLINES OF PLANT LIFE. pairs of oval bladdery swellings, which, by the gases they con- tain, give greater buoyancy to the plants in the water. Fic. 27.—Upper part of a plant of Fucus vesicu.osus. +, midrib of thallus; 2, bladders ; s, swollen tips covered by numerous elevations, in each of which is a pit which contains many sex-organs. ‘T'wo thirds natural size.—After Luerssen. 35. Growing point.—The very tip of each growing branch is notched and at the bottom of the notch is a group of cells which by division produce all the parts of the thallus. This THE THALLUS OF THE HIGHER ALG. 27 youngest region, found also at the tips of the growing axes of the higher plants, is the growzng poiné. It has no limit below, but as the parts further and further from the apex are exam- ined, they are seen to become more and more unlike with age until the mature form is reached. 36. Mature thallus.—If the mature part of the thallus be cut at right angles and a thin slice be cut off one end, placed on a glass slip and examined with a lens, it shows two distinct regions ; a central one, quite translucent, the f7f4, bounded by an outer brownish opaque region, the corfex. The central part is very full of mucilage, produced by a change in the substance of the cell-walls of the pith region. In the bladders this mucilaginous pith does not increase to fill the central space, but this is occupied by a great chamber filled with air and other gases. In the midrib the structure is plainly denser than elsewhere, except in the stalk below, which is like an enlarged midrib without the side wings. 37. Division of labor.—Complete examination of other parts, the attachment disk, the hair pits (fig. 28) with which Pp Fic. 28.—A transverse section of the thallus of Fucus, showing midrib, 7; cortex, c; pith, ; anda hair pit, 2. Magnified 10 diam.— From a drawing by Mr. C. E. Allen. many species are covered, etc., would reveal still other ways in which unlikeness arises with age from the uniformity of the growing point. With the change of form there is always di- vision of labor, which we can interpret only in a very imper- fect fashion from our own standpoint. The compact cortex is nutritive and probably in part protective ; the bladders serve to increase the buoyancy of the plants when the tide is in; while the abundant mucilage, found in the interior, probably serves to retain the moisture when the plants are exposed by 28 OUTLINES OF PLANT LIFE. the ebbing tide ; the hair pits are useless, so far as known ; and the strong, elastic disk and stalk above hold the plants in place as they sway constantly back and forth in every wave of the rising or falling tide. 88. Color.—The coloring matter in Fucus and other brown seaweeds is of two kinds, a green (chlorophyll), and a brown. These colors are found chiefly in the cortex, which is, there- fore, the food-making tissue (see {] 190), while the internal tissues may be used for storage of reserve food. EXERCISE VII. Bladder Wrack. (fucus vesiculosus).—Place a plant in a glass dish or a pan of water. Observe 1. The general form of the body or thallus; its mode of branching. (¥ 34) 2. The thicker central region forming a midrib, with thinner wings. (Figs. 27, 28.) 3. Downwards, the thickening of rib and death of wings to form sta/k near base. 4. The lobed attachment disk at base of stalk. 5. The swollen regions of the wings here and there. Cut into one of these and observe that it is a bladder. 6. The notched tips of some branches ; the enlarged and more or less distorted tips of most, forming the receptacles. 7. Scattered on the thallus minute elevations, from which protrude through an opening at the top a tuft of fine hairs. These are the mouths of the hair pits. (Fig. 28.) 8. Crowded on the receptacles, larger warts with a hole at top and sim- ilar protruding hairs. These are the mouths of larger pits, comceptacles, which contain the sex-organs. Cut two thin transverse sections of the thallus, one through the bladder and the other through the general thallus. The latter should include a hair pit. Examine them with a lens and observe 9. In the latter, the denser outer tissues ; the cortical region ; the looser inner ones, of elongated threads and much mucilage, the medullary region; the thicker denser midrib; the form of the hair pit. Io. Note the difference between the structure of the bladder and the unswollen wing. Which region is altered to form the bladder ? THE THALLUS OF THE HIGHER ALG. 29 39, Summary.—Comparing the thread-forim with the thin broad alge, we find the body of the latter often nearly as simple ; but, when the body is thicker, it is often seen to con- sist of unlike regions. The outer parts are arranged so as to enable the plant to make food for itself by getting the proper material from the water and absorbing the light that falls upon the surface. The inner parts, being too much shaded by the outer to serve for food making, are used for other pur- poses. Special organs for floating the plant are formed in some of the brown seaweeds. Other algz, of slender form, are more complex by having the older cells of an at first single row divided by partitions parallel to the length into five or more cells. With greater complexity of the body, growth in length usually becomes localized at the tips where all the cells are rapidly dividing. CHAPTER V. THE FUNGUS BODY. Funci are plants without the green coloring matter chloro- phyll (see 4 6), whose body is generally made up of long filaments, either loosely or densely interwoven and united. 40. Origin.—As the bacteria (see 4] 14), the smallest and simplest plants, were probably derived from the lowest alge by slowly adapting themselves to get ready-made food, so, at various times in the past and therefore at various points in the ascending scale of algal life, certain alge have adapted themselves to the use of food which they could secure from other beings. Then, having no use for the chlorophyll and chloroplasts, they have gradually lost them. The adoption of the habit has proved highly successful, both among the simple bacteria and the more highly organized true fungi. The ancestors of the present species were—how long ago no one can say—probably at first chiefly, if not exclusively, aquatic. Some, at the present time, have the same habit, growing in infusions of organic matter. Others attach them- selves to dead or even living animals or plants in the water. The bodies of dead or living organisms furnish places of growth for a great number of species which have adapted themselves to other than aquatic life. Many live in the soil because it contains in its upper layers more or less organic matter from the offal of plants and animals, or from their dead bodies. 41. Hyphe.—The filaments of which the fungus body is composed are called hyphz. Each is the result of growth 30 THE FUNGUS BODY. 31 from a single cell, and is comparable to the thread-like body of the filamentous algz. There is, naturally, a great variety in the hyphe of differ- ent species of fungi. Some are relatively large; others very small; some of even diameter and caliber, others irregular and with unequally thickened walls; some very thin-walled, others very thick-walled. Between these extremes is to be found a complete gradation. They grow in length at the apex only. In many kinds partitions are formed at more or less regular intervals, as the growth in length proceeds, while in others no partition-walls are formed. Even when transverse partitions form, they do not separate the filaments into cells, but each chamber, or sometimes the whole filament, represents several or many cells. (Compare (J 26.) 42. Branching.—As the hyphe elongate, branching may occur. Ifa branch is to be formed, a limited area of the cell-wall begins to grow more rapidly than the rest. This allows a slight bulging of the growing region; the swelling increases and soon takes the form of a branch, like the main axis. It may remain short or continue to grow indefinitely in length. Commonly a cross-wall is formed at the base of the branch. Ifsuch a branch arises first as a minute pimple, so that it remains connected with the parent axis by a small neck, and has only limited growth in length, it is called a bud ''5.29-—Beer-yeast(Sacchoro- myces cerevisi@). a,a full- and the process is known as budding Roa Pe Seats e c.colonies formed by budding, (fig. 29). Such branches are usually ¢cjoueeaore sil tached : H Magnified 750 diam.—After easily broken off, thus readily produc- pagntiee 75 ing independent plants. (See further under Reproduction, 4] 261.) In some species of fungi, 32 OUTLINES OF PLANT LIFE. profuse branching is the rule; in others, the branches are few. 43. Mycelium.—When branching is profuse, or when a considerable number of individuals grow near together, the filaments often become interwoven and entangled in so com- plex a web that it is impossible to follow a single hypha for SDR ZANE ACANAN SOS RRA EERO NEDA ZETIA RR ANSI SCARS () Ci er AN RST 2A G77 ERIN CARERS A) PALA hes EAA 7D PRES 4 OSA PER L/S) 3 Wye ANN c Fic. 30.—A single plant of Mucor Mucedo, showing the mycelium as it developed from a single spore. It bears a single erect reproductive branch rising above the fluid. Magnified 25 diam.—After Brefeld. any distance. Such a mat of hyphee is called a mycelium, a term which is also used to designate the vegetative hyphe collectively, whether forming a felted mass or not (figs. 30, 31). The mycelium may be formed wholly upon the surface of the object upon which the fungus lives ; or part of it may THE FUNGUS BODY. 33 lie on the surface, and part may penetrate that object ; or all of it may be hidden within the substratum.* In some of the common molds (Mucorini), the cobwebby threads lying upon the surface of the substratum constitute the exposed part of the mycelium, while other hyphe: penetrate deeper; in others (Penicillium, etc.), the superficial hyphz become so Fic. 31.—A section of part of the aerial body of Polyporus. sf, hyphe running at an angle to the section, cut across; , crystals of oxalate of lime. agnified about 500 diam.— After Vogl. interwoven that they may be lifted off the substratum (as from jellies, jams, syrups, etc.) as a coherent layer. But in most cases, especially when the fungus grows on a solid medium, the hyphz become adherent to it and permeate it so that they cannot be separated from it, even by the most careful dissection. * This non-committal term may be used to designate the material upon which the vegetative part of the fungus grows, whether it be a living body, a dead organism, or organic matter in solid or liquid form. 34 OUTLINES OF PLANT LIFE. EXERCISE VIII. Black mold (AAzzopus nigricans).—Before any white or black dots ap- pear on the mold examine the vegetative hyphae. (J 41.) These are of two kinds, (2) those running over the surface of the bread ; (4) those penetrating it. 1. Examine a. Lift up a few threads with a needle and mount them in water. Study with a lens. Are they white or colorless? Why then is the body composed of them (the mycelium, J 43) white? 2. Examine 4. With needles tease out hyphe from a bit of bread in water ; free them as far as possible from the débris and mount. Com. pare with a. After mold has begun to show black dots (spore cases, | 271) examine 3. Determine how the branches are placed which bear the spore cases. (Fig. 30.) 4. Compare the white (young) and black (mature) spore cases. Can you find the very smallest ones? 5. Snip off a few ripe spore cases with scissors, handling them cau- tiously to avoid breaking or tangling them ; mount in alcohol * and ex- amine. Crush (if not already broken) and observe numerous dust-like particles, the spores, which escape. (Fig. 146.) 44, Parasites.—Especially is this true of those fungi which grow in the interior of living organisms. The higher plants are liable to be fastened upon by parasitic fungi, and compelled to act as Aosés to their unbidden and unwelcome guests. Such a host plant may be entered when a mere seedling, in which case the fungus grows with its growth, or it may not be attacked until older or even mature. The host may be permeated in all its parts by the fungus filaments ; or certain members only, such as the leaves, flower parts or twigs, may be affected. The effect of the fungus upon the host is often scarcely visible to the unaided eye ; sometimes a local disturbance is manifested by swelling, unnatural color or growth ; sometimes the affected members become distorted * Because water will not wet them. Replace alcohol as it evaporates ; it does so rapidly. THE FUNGUS BODY. 35 and useless or are even killed ; sometimes the disease is gen- eral and is followed, slowly or quickly, by general death of the host. (See further 41] 184, 369.) 45. Infection.—These internal parasites obtain entrance to their hosts in various ways. Sometimes the young hypha, growing from a special reproductive body (spore),* so min- ute that it may easily float in the air and fall upon a leaf, creeps along the surface till it finds one of the microscopic openings in the skin of the leaf, into which it grows (sf, fig. 32). These external openings are connected with irregular Fic. 32.—Young hyphz of Zxobasidium developing from spores, sf, entering the air-pores of the leaf of the cranberry. Others, from sf’, sf’’, penetrate the skin directly. Magnified about 600 diam.—After Woronin. spaces between most of the cells of the softer parts (fig. 106), which are also the parts in which the food-supply is most abundant. In these, therefore, the fungus develops, break- ing out to the surface again to form or set free its reproduc- tive bodies. Or, the young hyphz may excrete at their tips a substance * See J 263 and the following. 36 OUTLINES OF PLANT LIFE. which so softens or dissolves the cell-walls of the host that they penetrate these cells readily, not only at the surface (sp’, sp’’, fig. 32), but in the interior.* They then branch é Fic. 33.-— Hyphe of 7ra- metes Pini perforating at c the walls ot a wood-cell of Scotch pine and destroying the primary wall of the cell. @, e., holes made by hyphe. Magnified about 800 diam. —After R. Hartig. freely, often growing in the spaces between the cells, often passing through the cells themselves (fig. 33). Plants are often attacked when mere seedlings. From either a bit of my- celium or a spore that has survived the winter or the dry season, a hypha grows, which, almost as soon as the seedling emerges from the seed, pene- trates it. The fungus, in these cases, may develop quickly and kill the young plant (as in the ‘‘ damping off’’ disease in greenhouses), or it may develop slowly and not reach its maturity until the host is also mature. 46. Haustoria.—Those fungi which grow upon the surface of living plants (and those which grow in the internal air-spaces) often have special branches for fastening themselves to the host or absorbing food from it. In the surface fungi these are usually very short, disk- like or lobed branches which do not penetrate the cells of the host. In other cases they are branches of minute diameter, which enter the cells, and either enlarge into a knob (fig. 34) or branch profusely (fig. 35). * The penetration of cell-walls is probably assisted by such pressure as the growing hypha can exert. THE FUNGUS BODY. 37 Fic. 34.—Epidermis and a few cortical cells of cowberry with mycelium of Calyptospora occupying the intercellular spaces and pressing knob-like ends against the cells from which a slender branch penetrates the wall and enlarges in the interior into sac-like haustoria, 6, 6, a,c, reproductive branches. Magnified 420 diam.—After R. Hartig EXERCISE IX. Mildew (Aicrosphera), a surface parasite.—Examine dried leaf bear- ing mildew. Observe “1. The whitish interlacing hyphze on surface of leaf, forming the mycelium. (¥ 43-) / 2. The distribution of the fungus: does it cover the whole leaf or only occur in patches? Compare the earlier and later gathered leaves as to this. 3. Demonstration. Scrape a bit of the mycelium from the surface of the leaf after moistening it for a few minutes with a 5% solution of potassic hydrate. Mount and show (a) the colorless branching hyphe ; (4) the erect branches bearing the spores ; (c) the spores. 4. Examine, as before, one of the older leaves. Observe the yellow- ish dots scattered over the mycelium, the immature /frzfs. Associated with these the black mature fruits, which contain sporangia with spores. (4 271.) White rust (Cystopus portulace), an internal parasite. 1. Demonstration. Boil a leaf of purslane for a minute or two in 5% potassic hydrate. Tease apart the tissues of leaf with needles on a slide, 38 OUTLINES OF PLANT LIFE. mount and show the mycelium of the fungus consisting of tangled hyphe ramifying among the cells of leaf. (J 44, 45-) Examine a dried leaf. Observe 2. The white blisters (spore beds) here and there on the surface; the thin membrane (the epidermis of the leaf) by which they are covered ; in older blisters the cracking and final disappearance of this skin. (| 260, fig. 141.) 3. The white powdery sfores which jar out or can be dislodged with needle. 47. Fusion.—When the hyphz ofa fungus grow very close together, they frequently cohere and become so changed in appearance as to lose all trace of resemblance to filaments. Not only fusion but thickening and division occur, and a section of the resulting structure has much the appearance of Fic. 35. Fic. 36. Fic. 35.— Branching haustoria of Peronosfora. mt, m1, the hypha traversing an inter- cellular space of the host; z, z, two haustoria penetrating two cells of the host and branching therein. The other contents of host-cells not shown. Magnified about 400 diam.— After De Bary. - Fic. 36.—A section through the mycelium of a lichen showing hyphz near upper sur- face, a, and lower surface, 4, fused into a false tissue; only in central region are the Harber meLounnable: The dark spheres are imprisoned alge. Magnified 650 diam. —After Bornet. a section of the tissues of a higher plant (fig. 36). These changes are particularly apt to occur at and near the surface THE FUNGUS BODY, 39 of the more massive parts, where they are necessary to impart firmness, rigidity, or durability. The interweaving and fusion of the hyphe sometimes pro- duce cord-like or strap-like structures of considerable size. The mycelia of the higher fungi frequently form them, and they may be found in the leaf-mold of forests or in rotten stumps or between boards in wet places. 48. Lichens.—The body of lichens is a mycelium woven about the simpler alge, rarely about other small green plants, which are thus imprisoned. The fungus hyphe usually pre- dominate and in great measure determine the form of the body and its texture. Sometimes the alge are present in such numbers that the hyphz seem merely distributed among them. In form the body may be broad and thin (fig. 215), or slender and shrub-like ; in some cases it is so thin and adherent, or so interwoven with the substratum, that it seems to form a mere crust over it. In texture it may be tough and leathery, with the hyphee near the surface fused into a false tissue (a, 4, fig. 36). When gelatinous alge, such as Nostoc (see 4] 11) are imprisoned, the body may be gelatinous while wet. In all cases the algze supply the fungus with food, and are in turn supplied with water absorbed by the spongy mycelium. (See further {J 164, 185, 367.) EXERCISE X. Lichen (Physcia stellaris).—-Soften a plant by soaking it in water for a few minutes. Observe 1. The mycelium, forming a connected leaf-like lobed thallus. Com- pare as many other forms as are available. ({ 48, fig. 215.) 2. Compare the color when dry and wet. In the latter condition, the mycelium is more translucent and the imprisoned green alge show through more plainly. (Figs. 36, 216.) 3. The tufts of hyphee extending from lower surface to bark, the hold- fasts or rhizines. 4. Occupying the central region on the upper surface, the round colored disks, the clusters of spore cases. 40 OUTLINES OF PLANT LIFE. Cut a vertical section through a part of the thallus. Observe 5. The layers of the thallus; above and below, dense layers, the upper and lower cortical layers ; between them, the medullary layer, with green alge distributed unequally through it. (Fig. 36.) 49. Summary.—The fungi, though descended from the alge, have adapted their body to new conditions of life so completely that it shows little resemblance to that of the alge. All have colorless (non-green) bodies, composed of slender hyphee, frequently much branched and interwoven, and either applied to the surface or penetrating the substratum. Some kinds live on dead organic matter (saprophytes); some are external and some internal parasites. The latter enter the host: through pores, or by perforating the skin, often causing deformity or disease or death. When strength or protection or durability is necessary, the hyphe may become insepara- bly fused into a false tissue. Lichens are special kinds of fungi, associated for life with simple alge from which they derive their food. CHAPTER VI. LIVERWORTS AND MOSSES. 50. Alternation of generations.—In the liverworts and mosses, as in all the plants higher in the scale, there occur two well-marked phases in the course of their lives. One of these phases is marked by the formation of sexual repro- ductive cells, or gametes, the egg and sperm (see 4] 304), whence it is called the sexual phase, or the gamefophyle. The other is characterized by the formation of non-sexual repro- ductive cells, the spores (see {] 263), whence it is called the non-sexual phase, or sforophyfe. These two phases alternate with each other; i.e., the eggs produced by the gametophyte do not form a new gametophyte but a sporophyte ; and the spores of the sporophyte do not form a new sporophyte but a gametophyte. Representing the gametophyte by G and the sporophyte by S the sequence is Geo Sm>Gr>Se>GrS, and so on, generation after generation. Often the gameto- phyte forms other gametophytes repeatedly, but usually the succession is interrupted, sooner or later, by the formation of fertile eggs and from these a sporophyte. In such cases the sequence may be represented thus: GGGG»>S»-GGGreS »>GG, etc. The sporophyte of these plants zever propagates its own form. To this regular sequence of the two phases the phrase alternation of generations has been applied.* * Rather obscure suggestions of the alternation of generations are to be found among the algze and fungi, but they are not definite enough to warrant discussion in this book. Let the student notice, however, that this feature does not appear suddenly in plant life, though introduced abruptly into the account of it. 41 42 OUTLINES OF PLANT LIFE, In each phase, a body of form and structure suited to its special work is produced. In the higher liverworts and mosses both phases have nutritive work to do, but in many this is confined to the gametophyte, and in all the gameto- phyte carries on the greater part of it. To this phase, there- fore, attention is first given. Liverworts. 51. The thallus.—The form and structure of the vegeta- tive body of the simplest liverworts is scarcely different from that of some of the green alge. The body is a thallus with rhizoids (fig. 37). The rhizoids are usually filaments arising Fic. 37.—A, plants of Riccta sorocarpa, on the ground. Gametophyte phase. Nat- ural size. 8, a vertical section of one of the thick lobes of the thallus, showing nearly uniform structure. The thallus has nearly covered over two young sporophytes which appear as though in the interior. Rhizoids arise from the ventral side and flanks. Magnified about 25 diam.—After Bischoff. from the under side and flanks of the thallus. They serve to fasten the thallus to the substratum, and perhaps assist it in absorbing water. The thallus is usually thin and flat, though sometimes much crisped. Most liverworts lie broadside to the substratum. Very rarely is the thallus erect and attached by a narrow stalk. 52. The dorsiventral thallus.—In the simplest forms the thallus is uniform in structure from upper to under side. In others there is a decided difference between the two sides. The upper part is green, while the under is not. In one family there are large air-chambers in the upper part of the LIVERWORTS AND MOSSES. 43 thallus, from the floor of which arise green filaments (fig. 38). On the under side, also, are frequently found scale-like out- growths as in fig. 38, 7. A part which shows constant differences between an upper (dorsal) and an under (ventral) side is said to be dorsiventral. Fic. 38 Fic. 39. Fic. 38.— Portion of a vertical section of the thallus of Luxuzlaria cruciata. a, dor- sal, 6, ventral epidermis ; c, an air-pore ; ¢, air-chamber, from whose floor rise green filaments, ¢; 7, partition between adjoining air chambers; g, colorless cells contain- ing starch, some showing net-like thickenings of the walls, others with oil-bodies, % ; z,a ventral scale; /, a rhizoid. Magnified 110 diam.--After Nestler. Fic. 39.—Lunularia cruciata, on horizontal thallus and rhizoids with two erect 0: branches (one young, one mature), for carrying sex-organs. Natural size.— After Bischoff. These differences are usually called forth by the action of light (see J 325). 58. Branching.—-The branching of the thallus is always by forking, in a single plane or direction, as in Fucus, but the branches do not always develop equally. Sometimes special branches, instead of remaining horizontal, grow up- right and develop into peculiar forms adapted to producing the sexual reproductive organs (fig. 39). 44 OUTLINES OF PLANT LIFE. EXERCISE XI. A thallose liverwort (A/archantia polymorpha).—Examine an entire plant in water. Observe 1. The flattened horizontal body (¢#ad/us) with central line, the mid- rib, and thinner wings on each side. 2. The notched apex (the wings outgrow the midrib somewhat). 3. The mode of branching (forking). Examine the tips and find one just branched. Do not confuse with notch of apex ; when a tip branches there will soon appear two notches. Does the branch appear on the side of the older thallus, or are the branches equal at first? Are they equal when older? ({ 53.) 4. The green lens-shaped bodies (6v00d-buds) growing at certain spots along the midrib, surrounded by an outgrowth which forms a cup-like rim about the cluster. Remove a brood-bud and observe its form, especially in full grown ones the two opposite notches, the growing points. (297, fig. 177.) 5. The air-chambers (avco/z) of the upper part of the thallus, showing through the skin, best seen in older parts and with a lens. What is their form? Are they all alike? (¥ 52.) 6. The openings into the air-chambers, in the skin over each one, like a little pinhole. 7. Compare the under surface with the upper. Observe the numerous hairs. Discover the difference in place of origin and direction of growth of these. (J 51.) 8. Carefully pull off with forceps as many of these hairs as possible and notice the dark-colored overlapping outgrowths along the midrib, curving outward as they are followed forward, attached along their edges. These are the so-called ‘ leaves.” Cut a transverse section of the thallus through a brood-bud cup. Observe g. The origin of the brood-buds (only the younger still remaining) over the midrib. 10. The difference between tissue of upper and under parts of thallus. (If fresh plants are available observe especially the difference in color.) 11. Demonstration. Cut a very thin transverse section of the thallus. Select a part passing through stoma and show (1) The air-chamber ; its roof, the skin, with chimney-like stoma in center ; its sides a vertical plate of cells; its floor, with branched fila- ments of chlorophyll-bearing cells. (Fig. 38.) LIVERWORTS AND MOSSES. 45 (2) The large-celled colorless tissue forming the lower half of section ; the sections of ‘ leaves” arising near midrib and concave towards center. 54. The shoot.—In the greater number of liverworts the mature vegetative body is a shoot, which is differentiated into stem and leaves (figs. 40, 41). Even in such a body the dorsiventral character is well marked. The stem is slender and bears three (rarely more or fewer) rows of leaves, of which the two dorsal rows are the larger, Fic. 40. Fic. 4r. Fic. 40.—Gametophyte of Bazzania Nove-Hollandia. Besides the ordinary branches there are slender ones (flagella) with sparse minute leaves. Natural size.—After Lindenberg and Gottsche. Fic. 41.—4, dorsal view; 8, ventral view of a piece of fig. 40, magnified about 12 diam., showing the stem, bearing two dorsal rows of large leaves and one ventral row of small ones.—After Lindenberg and Gottsche. while the under leaves are much smaller, even to being incon- spicuous or wanting. These leaves consist of a single sheet of uniform cells richly supplied with chloroplasts, as are also the outer cells of the stem. ‘Their form is very varied and often of great beauty. They are usually crowded so closely as to overlap each other more or less, and hide the stem completely (fig. 41). 46 OUTLINES OF PLANT LIFE. EXERCISE XII. A leafy liverwort (Pored/a platyphylla). 1. In what position do the plants grow with reference to the sub- stratum ? Disentangle carefully a single plant.* Observe 2. The growing apex; the dying base; the distinctly dorsiventral habit. Enumerate the differences between the upper and under sides. (4 54.) 3. The mode of branching: a central axis, with lateral branches, themselves with lateral branches ; i.e., monopodial and bipinnate. ({ 58.) 4. The yellowish or brownish stem, covered with leaves unequally distributed. 5. The two rows of large leaves on the upper flanks of the stem. How do they overlap? Turn the shoot over and note a third row of small underleaves in the center below ; also right and left the lobes of the upper leaves. Determine the form of the under and upper leaves. Make an enlarged paper pattern of the latter showing how their ventral lobes are arranged. (Figs. 40, 41.) 6. Demonstration. Mount a leaf and point out the uniformity of cells and their abundant chloroplasts. Mosses. In the mosses the complexity of the mature vegetative body is somewhat greater. It is always developed as a shoot dif- ferentiated into stem and leaves. 55. Rhizoids——The shoot is anchored, as in the liver- worts, by numerous usually much branched rhizoids (A, fig. 42; w, fig. 43). Similar filaments may be produced, often in great numbers, along the stem and especially inthe axils of the leaves, or they may even arise from the leaves them- selves, when the plants grow in dense patches or in a very moist place. 56. The stem is usually cylindrical and covered by the crowded leaves. In structure it generally shows an advance upon that of the liverworts, which is nearly uniform, in hav- * If dry, first soften by placing plants in hot water for a few minutes. LIVERWORTS AND MOSSES. 47 ing the whole of the outer region occupied by a distinct mass of mechanical tissue for stiffening the stem, and, near the center, a strand known as “‘ conducting tissue,’’ which may act as a line of transfer for water or food. Fic. 42.—A, gametophyte of Polytrichum commune, with rhizoids below. 2, gameto- phys of Hylocomium splendens, bearing three sporophytes near top. Natural size. —After Kerner. 57. The leaves are also more highly developed than in liverworts. They are always sessile and are arranged in two (rarely), three, or more vertical ranks along the stem, and consist usually of a single sheet of green cells, the d/ade (figs. 43, 44), and a central rib running from base to apex (fre- quently wanting), which is composed of elongated conduct- ing and strengthening cells (figs. 43, 44). In some the 48 OUTLINES OF PLANT LIFE. amount of green tissue is increased by the formation of verti- cal plates similar to the blade (fig. 44). 58. Branching.—The stem branches, often very profusely. Sometimes the growth of the lateral branches, as of the original main axis, is checked by the formation of sex organs. In that case a new branch is likely to arise some distance Fic. 43. Fic. 43.—A, leaf of a moss (Funaria Americana), showing central rib. Magnified about 40 diam.; 8, upper portion of the same leaf, highly magnified, showing single ae of cells forming the blade and the narrower cells of the thick rib —After ullivant. Fic. 44.—Tip of leaf of a moss (Oligotrichum aligerum), showing the thickened rib, and the plate-like ridges on blade and rib greatly increasing the surface of nutritive tissue. Magnified about 75 diam.—After Sullivant. below the apex, so that the stem is merely a succession of lateral branches (fig. 45). This mode of branching is called sympodial. In other cases the main axis continues its growth unchecked, and more or fewer branches also develop. These lie plainly upon the sides of a central axis. This mode of branching is called monopodial. Often the growth of the lateral axes is definitely limited and their development regu- lar, forming a pinnate branch-system. If the secondary axes LIVERWORTS AND MOSSES. 49 themselves branch, there is formed a bipinnate or even tri- pinnate system, as in figure 42, B. 59. Protonema.—In its early stages the vegetative body of the /eafy liverworts and the mosses is either a flat thallus, similar to the mature form of the thallose liverworts, or a branching filamentous body, called the pro- Zonema, almost identical with the form of the branched filamentous alge. Upon this protonema the leafy shoot arises as a lateral bud, which soon outstrips it in growth and develops leaves. The pro- tonema may live for some months, but generally perishes after having produced a few leafy plants. 60. Sporophyte. — The sexual phase in the liverworts and mosses has almost no vegetative functions. It consists at maturity non- of a yellowish or brown spherical or cylindrical case (fig. 46), which is sessile or raised upon a short or long stalk and contains (a few or) hundreds or thousands of repro- Fic. 45.—Axis of a moss (Ortho- trichum) showing sympodial branching. S}, S?, 53,84, suc- cessive clusters of sex-organs, produced at apex, which check the growth of axis. Beneath each a lateral growing point develops, producing successively the branches 41, 4%, 48, Magni- fied 10 diam.— After Bruch & ductive cells called spores. The : Schimper. pointed or swollen base of this stalk is called the ‘‘ foot,’’ and is embedded in the gameto- phyte (/, fig. 47) to absorb food from it. 61. Nutrition.—The surface of the young sporophyte, when large and well developed, as it is in the higher liver- worts and mosses, is green. To a limited extent, therefore, it is able to make food; but not sufficient for its needs, for these are great on account of its rapid growth and the amount 50 OUTLINES OF PLANT LIFE. Fic. 46 —A, two capsules of Bryum ; from the right-hand one the lid has fallen, show- ing the teeth. Magnified 5 diam. JZ, four gametophyte shoots ot \plachnum am- pullaceum, bearing four sporophytes. Natural size. C, a capsule of one of the same sporophytes, showing enlarged apophysis, a, below the spore case, s. Mag- nified 10 diam. JD, capsule of Splachnum duteum, with umbrella-like apophysis, a, below spore case, s. Magnified 2 diam. required to supply each spore. The foot, being in close contact with the tissue of the gameto- phyte, acts as an absorbing organ, receiving food solutions from it. The sporophyte thus lives, in part at least, as a parasite upon the gametophyte. In some mosses there is a tendency to increase the nutritive work of the sporophyte by developing at the top of the stalk, below the spore case, a mass of green tissue. Jn Bryum (4, fig. 46) this gives the capsule a pear- shape, while in Splachnum (8, C, D, fig. 46) it is so far developed as to ex- ceed the spore case. In some species it is expanded into a miniature um- brella which, one can imagine, might readily become divided into leaves. The intimate attachment of Fic. 47.—Young sporophyte of Phas- cum cuspidatun, c, columella: / sporophyte to gametophyte con- t, i stem; |; : iene re “Spore tinues throughout the life of the case; sf, spore-mother-cells. Mag- : ape oie P Ors ‘After Kienitz.Gerlo#, former. Sometimes the gameto- LIVERWORTS AND MOSSES. SI phyte perishes at the close of the growing season, but more commonly it is perennial, growing and branching at the anterior end as the older posterior parts die away. 62. Summary.—Liverworts and mosses show a distinct alternation of generations. The vegetative body of the sim- pler liverworts is a flat thallus, like that of the larger alge, but the higher forms have the central part developed as a roundish stem, and the wings so branched as to form separate leaves. The latter form is general in all the mosses, which further have the stem and often the leaves stiffened by the differentiation of mechanical tissues. The non-sexual genera- tion in all is relatively small and depends for its food upon the sexual generation. EXERCISE XIII. A moss (Mnium cuspidatum).—Examine plants with capsules attached. Observe the two connected plants : i. The leafy stemmed plant or gametophyte. (§ 50.) 2. The slender plant attached to its tip, the sporophy¢e, consisting of a wire-like stalk, the sefa, enlarged above to form the hanging capsule. (| 60, fig. 46.) 3. Boil for a few minutes in 5 per cent. potassic hydrate, rinse in water and gently pull sporophyte until it separates from the gametophyte. Observe the smooth pointed end which was sunk in gametophyte. If properly separated no sign of tearing can be seen. (Fig. 47.) Examine gametophyte in water. Observe 4. The differentiation of the body into stem and leaves. 5. The brown hairs (rhzzozds) about the stem, which attach plant to ground. Do they branch? ({ 55.) 6. The strength of the stem ; test it by breaking it with a lengthwise pull. Cut a thin transverse section and observe dark colored mechanical tissues in outer region. (J 56.) 7. The form and structure of the foliage leaves: note mdrid of me- chanical cells (test strength) ; Zamna of one layer of cells large enough to be visible under lens ; dorder of mechanical cells, some projecting - pretty regularly as ¢eeth. (4 57, fig. 43.) 8. Smaller, scale-like leaves on part of the stem. 52 OUTLINES OF PLANT LIFE. Examine sporophyte with mature capsule. Observe g. The slender seta. 1o. The thin yellow inverted cafsu/e, from whose end a piece has fallen leaving it open. (J 274, fig. 46.) 11. About the edge of the capsule a fringe of pointed projections, teeth, curved inward, constituting the Zeristome. Break off these outer teeth and notice the pale fringed membrane within, forming the inner peristome or exdostome. (Figs. 46, 148.) 12. Among these, or to be pressed out of capsule, many fine spores. Examine young sporophytes of this or other mosses. Observe 13. The cylindrical form of the eméryo sporophyte. 14. The Aood covering its apex and carried up by it until the develop- ing capsule forces it off. 15. The 4d which falls off to open capsule. CHAPTER VII. FERNWORTS AND SEED-PLANTS. Fernworts. Amonc the still more complex plants, the ferns and their allies, the same ‘‘ alternation of generations’’ can be seen. The two ‘ generations,’’ or phases, have, however, changed much in relative size. Whereas in the liverworts and mosses the gametophyte is much the larger and more conspicuous, as well as the longer-lived, among fernworts the sexual phase is so much smaller that it is seldom seen; and in some species it is almost microscopic. On the other hand, the sporophyte is the phase which is usually seen and the only part popularly known. 63. The gametophyte.— The vege- tative body of this phase of the fern- worts in its best developed forms is a small, flattened, green body of oblong, orbicular, or cordate outline, commonly less than half a centimeter in diameter, rarely as muchas 2 cm. (fig. 48). It Fic. 48.—Ventral side of the gametophyte of a is strikingly like a thallose liverwort in general form, being distinctly dorsiventral and having rhizoids on its under side, which fasten it in place. Only the central part of the gametophyte consists of more than one layer of cells. Onthe under side of this central ‘* cushion,’’ sex organs. fern, Asplenium. The notched end is the an- terior. Rhizoids near posterior end. The small circles show position of male organs; the chim- ney-like projections near anterior end the female organs. Magnified 10 diam.—After Kerner. as it is called, are borne the 53 54 OUTLINES OF PLANT LIFE. 64. Reduction of gametophyte.—In a few of the fern- worts the gametophyte is filamentous, or tuberous, and more or less completely subterranean and colorless ; such derive their food from decaying plant-offal. In higher plants of this group the gametophyte becomes still further reduced in size and structurally simplified, until in some species it is hardly more than a few cells surrounding Fic. 49.—Sporophyte of a fern, Polrpodium vulgare, showing horizontal underground stem, bearing secondary roots and leaves. Natural size.—From Bessey. the sex organs. These reduced forms grow by the use of food stored in the spore from which they originate. The gameto- FERNWORTS AND SEED-PLANTS. 55 phyte of such species has lost. wholly its vegetative character, and is restricted in function to the production of the sex organs. ; 65. The sporophyte.—In contrast with the smallness and simplicity of the gametophyte is the relatively large size and complexity of the sporophyte (fig. 49). It is always differ- entiated into stem and leaves, and, with rare exceptions, roots also. It is also noteworthy that, as compared with mossworts, the chief work of nutrition has been shifted from the gametophyte to the sporophyte ; and this even when the gametophyte has its largest size and greatest duration, while nutritive work is wholly abandoned in the smaller forms. The sporophyte has also become the long-lived stage, the gametophyte being usually transitory (only exceptionally living more than one season), while the sporophyte lives through one season in the few annuals, and commonly for several or even many years. 66. Members.—The mature sporophyte is differentiated into root, stem, and leaves. The important adaptations of the structure and forms of these members are so similar to those of the seed plants that they will be discussed in connection with them. EXERCISE XIV, Maidenhair fern (4diantum pedatum). I. THE GAMETOPHYTE, 1. Observe its shape and size ; the notch at the growing point (anterior end); the dying (posterior) end; the thicker central region, with thin wings. (J 63, fig. 48.) z. On the under side, a cluster of rizoids near the posterior end. 3. Compare this plant with the thallus of AZerchantia. If gametophytes with young sporophytes attached are available, ob- serve 5. That the young sporophyte is fastened to the under side of the gam- etophyte. 56 OUTLINES OF PLANT LIFE. II. THe SPoROPHYTE. Taking the underground parts in a dish of water, observe 1. The slender wire-like roots. How are they branched? ({ 83 ff.) Where are they attached to the stem? Trace an unbroken oné to the tip. The following points can only be seen on roots carefully gathered and cleaned. What difference of color near tip? Can you find many fine tangled root hairs ? Where present? Where absent? ({ 73.) Cut a transverse section of an old root, mount and observe 3. The outer brown mechanical tissues (also used for storage). (J 78.) 4. The central whitish tissue, chiefly the s¢e/e, in which the visible openings are the larger vessels. ({ 75.) 5. In what position does the stem naturally stand? Observe its occa- sional éranching (J 89); the surface covered with chaffy scales, the grow- ing apex and dying dase. 6. Its modes and internodes; the nodes are indicated by the attachment of a single leaf at each; the internodes are the intervals between the nodes. How are the leaves placed? (J 104.) Cut a transverse section of the stem and observe 7. The outer brown mechanical tissues (also used for storage). “(J 108.) 8. The circular, oval, or C-shaped white tissues, most of which belong to the ste/e. Trace the course of the stele through at least two internodes by cutting a series of rather thick (I mm.) sections, observing the mode in which the stele branches to pass out into a leaf. Cut also a longitudinal section through the base of a leaf stalk and trace course of stele. ({ 109.) Taking a perfect leaf, dried under pressure, observe g. The stalk or Jetiole, with its branches. Note the mode of branch- ing; the petiole divides into two equal divergent branches; each of these forks, one branch carrying leaflets while the other again forks, and so on. (TJ 126, 128.) 10. The ardness of the mechanical tissues at surface of polished petiole. 11. The /aflets. Note (a) shape as to outline and margin, comparing basal, median, and terminal leaflets of any branch; (4) the veins, con- taining branches of the stele; (c) the green tissues between the veins (J 127.) 12. Demonstration. Strip off a bit of epidermis, mount and show (a) the irregular form of epidermal cells; (6) the intercellular openings with guard cells (stomata). (J 137-) 13. At the edges of the leaflets on the under side crescentic brown spots, clusters of spore cases. (J 275, figs. 149, 150.) FERNWORTS AND SEED-PLANTS. 57 14. Boil a leaflet for a minute in water. With a needle turn back a flap which covers the spore cases; observe that it is a specialized portion of the edge of leaflet. 15. On the under side of the flap a mass of yellowish spheroidal bodies, the spore cases. Scrape away most of them and notice the relation of their points of attachment to the veins. Mount some of the spore cases and observe 16. Their shape ; the s¢aZk by which they were attached. (Fig. 236.) 17. The darker ridge, azzu/us, which serves to burst them when ma- ture. (Fig. 236.) 18. Study the manner of dursting. Tear a bit of indusium from a dried specimen previously soaked in water, removing most of the sporangia. Allow it to dry while watching it with a lens, illuminating from above. 19. Demonstration. Mount sporangia and spores and show their structure, especially the annulus. Seed-plants. 67. Development. Among the highest plants, those which produce seeds, the differentiation of the body is essen- tially the same as in fernworts. The alternation of sexual and non-sexual phases is still traceable, though greatly obscured by the extreme reduction of the gametophyte. This tendency to the reduction of the sexual phase, which was re- marked in passing from the mossworts to the fernworts, continues, until in the highest seed-plants the gametophyte is wholly microscopic. Even by the aid of the microscope, it is possible to identify only the sex- ual organs which it produces, and one or more cells which are, perhaps, the rudiments of its vegetative body. The sporophyte, consequently, is the only phase of the seed-plant visible to the unaided eye. The body of the sporophyte exhibits the same members, viz., stem, root, and leaf, having the same general form, and subject to the same modifications, as in the fernworts. An account of the vegetative members of the fernworts and seed- plants occupies the following three chapters. t 58 OUTLINES OF PLANT LIFE. EXERCISE XV, Marsh Marigold (Cadtha palustris). 1. Examine the roots. Observe (a) their surface, wrinkled from short- ening; (4) their structure. 2. Cut a transverse section as in fern; observe that mechanical tissues are wanting. 3. Bisect longitudinally the base of a plant. Observe, as shown by the origin of leaves, the variable length of internodes; at base the inter- nodes are very short so that leaves are crowded; in the middle the inter- nodes are long and leaves distant; above, the internodes become shorter until, in the flower, they are not developed and the leaves are very much crowded. (J 104.) Study one of the well developed foliage leaves ({] 123). Observe 4. The broad rounded blade with slight branches (teeth) at the margin. 5. The long slender stalk, petiole, gradually passing into 6. The sheathing base, in upper leaves branched to form two stipules. (7 125.) 7.. Examine and compare the various forms of leaves: (a) the lowest, having sheathing bases without petiole or blade, passing gradually into (4) the best developed foliage leaves; (c) these near the flowers losing pet- iole and diminishing blade, becoming bracts; (d) the yellow perianth leaves; (e) next within these the yellowish stamens, (/) the flattened pod- like green carfels each forming a simple pistil. (YT 133, 134.) (Further study of flewer, p. 210.) 68. Summary.—In fernworts and seed-plants the sexual generation is small, often microscopic, while the non-sexual generation is conspicuous and often long-lived. The nutri- tive work of the gametophyte is either temporary, ceasing when the sporophyte develops green leaves, or is entirely wanting. The sporophyte forms stems, leaves, and roots and does most of the nutritive work. These members are very various in form and are described in the following chapters. CHAPTER VIII. THE ROOT. 69. True roots.—It has been pointed out that, among the lower plants, there are very many which possess structures similar in form and function to the root, and by some called by this name. Although these parts serve to hold the plant in place, and perhaps to absorb material from the substratum, they are not to be looked upon as equivalent to the roots of the higher plants either in origin or structure. In the alge, fungi, liverworts, and mosses, the gametophyte is the promi- nent phase. In no case does the gametophyte produce true roots. It is not until the sporophyte becomes an independent plant that true roots are found in the vegetable kingdom. It is, therefore, only among fernworts and seed-plants that these organs are to be found. When the sporophyte is developed as an independent plant, it becomes necessary for it to pro- duce some organ capable of holding it in place, or of absorb- ing materials from the outside, or of doing both. The organ developed to meet this need is the root. 70. Primary and secondary roots.—In accordance with their origin, roots are either primary or secondary. Primary roots are the first formed roots, i.e., those which are de- veloped directly by the young embryo. In both fernworts and seed-plants the primary root is rarely wanting, but often short-lived, dying after the plant has established itself and has formed secondary roots to take its place. In many cases, 59 60 OUTLINES OF PLANT LIFE. however, the primary root persists throughout the life of the plant. Secondary roots are later formed. They are roots which arise upon stem or leaf, or even upon the primary root itself. In the last case they are distinguished from branches of the primary root, which arise in regular succession toward the apex, by originating out of this regular order. Secondary roots are also called adventitious roots. They may take their origin at any point upon any of the members. Their point of origin will depend largely upon external conditions. A wound may cause them to appear. They are especially likely to be formed upon those parts which are in contact with the substratum, or from those parts which are kept moist. Upon stems they are most apt to appear near the nodes. (See {| 104.) Ifthe plant as a whole is surrounded by very moist air, roots may appear at any point of the surface. Secondary roots arising thus upon a part of the plant exposed to the air, and growing for all or part of their existence in the air, are also called aerta/ roots, Familiar examples are to be seen about the lower part of the stem of Indian corn, the English ivy, the poison-oak, the trunks of palms and tree- ferns. Secondary roots often arise in regular succession toward the growing apex of the stem, particularly in plants which have creeping or subterranean stems. 71. Growing point.—Primary and secondary roots do not differ materially in their structure. Near the tip they consist of a mass of actively dividing cells, the growing point of the root (compare 4] 87). The real tip of the root is covered by a mass of cells called the root-cap (ef, fig. 50), which is at- tached only to the growing point. Since the cells of the free surface of the root-cap are older and firmer than the inner ones and the growing point, and lie in front of them, they serve to protect these more delicate parts as the growth constantly pushes the apex forward through the soil. THE ROOT. 61 The youngest parts of the root are very much alike, but as they become older they grow unlike. The just mature por- tion of roots shows three characteristic regions, namely, (1) an outer layer or layers, the epidermis ; (2) an inner region, the stele ; (3) between these, the corlex. 72, 1. The epidermis usually becomes many-layered. At the apex it constitutes the roof-cap (ep, fig. 50). On the other parts of the root it sometimes sloughs off entirely, exposing the cells of the cortex itself, as in the monocotyledons (lilies, grasses, sedges, etc.) ; or, more commonly, only the outer layer sloughs off, leaving the inner- most as the covering of the cortex. It is too delicate to be distinguished by the unaided eye, except at the tip and further back where it produces root-hairs. 73. (2) Root-hairs. — Those cells which form the surface of the root, whether they be the original epidermis or cortical ones which have been exposed f He) HT fe en Fic. 50.—Median longitudinal section through the extremity of a rvot of Marsilia. The larger triangular cell near center of figure is the apical cell. The segments from the inner faces may be readily traced backward; thus the dotted line ec points to the fourth, c to the sixth segment from the posterior right-hand face of apical cell. ef, root-cap (epidermis); ec, cortex; c, stele; ex, endodermis (part of cortex); Ae, pericycle (part of stele) Magnified about 100 diam. —After Van Tieghem. by its loss, usually develop a large number of hairs, known as root-hairs (figs. 51, 52). These root-hairs are branches of the superficial cells (fig. 52), and may be looked upon as simple extensions of them, as the finger of a glove is the extension of its palm. Only one root-hair arises from a superficial cell. They are usually unbranched and without transverse partitions. 62 OUTLINES OF PLANT LIFE, Only in rare cases are they wanting. They live for a shorter or longer time, but are always,.as compared with the duration of the root, quite, transient. The older part of the root, therefore, is without root-hairs because of their death. Fic. 51.—Transverse section of a young root grown in soil, showing root-hairs with adhe soii-particles, the cortex, and the stele. Magnified about 20 diam.—After rank. The youngest part of the root is likewise free from them, because they have not yet been produced. As the root grows in length, new root-hairs are continually being pro- THE ROOT. 63 duced and the older ones are dying at an equal rate, so that a zone of hairs is found only upon the younger parts of the roots. 74, (6) The root-cap.—If the finger be supposed to rep- resent the root, a short finger-stall, if it were attached to the tip of the finger, might be fairly taken to represent the fosttzon of the root-cap. Only in rare cases is the root-cap entirely wanting. Serving to protect the tenderer portion of the root behind, the root-cap is itself constantly exposed to injury. The outer and older parts of the root-cap are, therefore, either worn away through me- chanical contact ; or, dying, they degener- ate and break down into a slightly muci- laginous material which facilitates the passage of the root through the substratum. This degeneration or the mechanical wear is constantly repaired within at the grow- ing point. The thickness of the root- cap, therefore, is maintained throughout its existence without considerable change. 75. 2. The stele.—Occupying the cen- ter of the root, and surrounded on all sides by the cortex, is an aggregate of tissues called the central cylinder, or stele (figs. 51, 53). The most noticeable part of this are the groups of elongated cells or cell- fusions,* called vascular bundles, or vas- cular strands. These strands are of two kinds, wood strands, specially for the con- Fic. 52.—A nearly ma- ture root-hair, showing structure and rélation to superficial cell of root; grown in water and therefore not dis- torted as in fig. 51. m, nucleus embedded in protoplasm; vacuole single and very large. Highly magnified. —After Frank. * These are continuous chambers formed by the breaking down of the partition-walls between the abutting ends of cells. They are usually de- void of living contents. 64 OUTLINES OF PLANT LIFE. ducting of water, and bast strands for carrying foods. (See “| 172-174, 197.) They are so placed that they alternate with each other about the outer part of the stele (figs. 51, 53). The strands may be in contact with one another in Fic. 53.—Transverse section of the stele and a portion of the surrounding cortex of the root of calamus__ s, s, innermost layer of cortex, adjoining outermost layer of stele; p, wood strands; A, bast strands. In the center of the stele and between the bundles is conjunctive tissue. Highly magnified.—After Sachs the center, or the center of the stele may be occupied by a pith (fig. 53). The number of vascular strands constituting the stele is various, being as few as four or as many as forty. The ordinary number, however, is from eight to twenty. (See fig. 53.) 76. 3. The cortex generally consists of large thin-walled cells which have become partially separated from one another, leaving larger or smaller intercellular spaces (fig. 53). THE ROOT. 65 77. Duration.—Even when the primary root persists throughout the entire life of the plant secondary roots often appear. When the primary root perishes, its functions must be performed wholly by secondary roots, which are developed in succession upon those parts where they are useful. The secondary roots themselves may be either permanent or transient. In creeping plants particularly, whether growing on land or in water, the functions of the root are likely to be handed on to successively younger roots, the old ones perish- ing and dropping off. If the roots endure for a. considerable time, they may retain their primitive structure and form, or they may undergo secondary changes which unfit them for absorbing organs, and adapt them to subserve various special functions. 78. Secondary changes.—Shortly after any portion of the root has ceased to increase in length, and, therefore, within the first season, it ordinarily undergoes minor second- ary changes which may or may not be followed by more profound alterations. These changes affect its primary structure in various ways and to various degrees according to the parts concerned. In some cases the older roots differ from the younger in scarcely more than the loss of the external layer of cells, from which the root-hairs arose. The sloughing off of this layer carries with it the hairs themselves and exposes the next inner layer of cells, which had before become slightly altered so as to be rather impervious to water. Upon their exposure, this alteration proceeds further, so that they become almost or quite incapable of absorbing the soil-water to which they may be exposed. It follows from this that it is only the younger part of the root, that is, the portion which has not undergone secondary changes, which is capable of absorbing water. In many roots this is the only change which occurs. In a greater number the root is also strengthened. 66 OUTLINES OF PLANT LIFE. In a large number of roots, the secondary changes result in increasing the diameter, sometimes very greatly, by the formation of concentric layers of new tissue in two or more regions, called the cambium regions. The outer growing layer, or cork cambium, usually formed in the cortex, produces tissues which are of such a nature as to protect the parts within. They constitute the periderm, and are ordinarily cork-like, i.e., thin-walled and impervious to water. Those cells which lie outside Fic. 54 —A, diagram of primary structure. B, C, diagrams showing the results of secondary thickening from the stelar cambium in the two extreme forms. ¢, cortex; en, its innermost layer; 4, outermost layer of stele; A’, primary bast; p%/’, sec- ondary bast; x’, primary wood ; 2’’x’’, secondary wood ; cé, stelar cambium ; 7, sec- ondary pith-rays ; #, pith.—After Van Tieghem a layer of cork are therefore cut off from a supply of food and soon perish. The inner growing layer, or stedar cambium, is developed within the stele and follows a tortuous course, lying outside the wood strands and inside the bast strands (fig. 54). As a result of tangential divisions in this region, tissues similar to those already existing in the stele are pro- duced. The relative amount of the new tissues goes far to deter- mine the character of the mature root. 79. (2) Woody roots.—If mechanical tissues predomi- nate, the root will become strong and rigid, as in the case of trees and shrubs. When the root is long-lived, the forma- tion of new tissues is usually resumed with each season, and the central part, especially, shows in cross-section concentric rings indicating the yearly additions. As the root thickens THE ROOT. 67 the outside parts become fissured lengthwise. Thus, in an old and large root of the woody type, all the parts outside the central wood constitute a éark, which becomes furrowed lengthwise, like the bark of the stems of many trees. Such secondary thickening finally produces in the roots a structure which is almost identical with that of stems which have under- gone secondary thickening. (Compare 4 111.) 80. (4) Fleshy roots.— But if thin-walled cells are the chief products, the root often becomes very thick and fleshy, as in the carrot, turnip, radish, sweet potato, beet, dahlia, artichoke, etc. Such roots serve the plant as storehouses of reserve food, and are consequently useful to animals as food. This thickening for storage purposes may affect either the primary or secondary roots, or both. 81. (c) Float roots——Plants which grow in water or in very wet swamps sometimes modify their roots to serve as floats. In these cases, the voluminous cortex consists of large cells, with huge intercellular spaces which are filled with air. The root thus serves to buoy up the parts of the plant to which it is attached, and assist in its respiration. (See { 202.) 82. (d) Tendrils, thorns, etc.—In a very few plants, aerial roots are modified into /endrils, being slender, sensitive to contact, clasping the objects which they touch, if of suit- able size, and thus assisting the plant to climb; in some in- stances they are altered into ‘horns, being short, rigid, and sharp-pointed ; in others, being exposed to the light, they develop chloroplasts, which enables them to act as organs for the manufacture of food. 83. Branching.—Both primary and secondary roots may branch. The mode of branching is commonly monopodial, i.e., the central axis grows most vigorously, and bears lateral branches upon its sides. The normal branches arise from lateral growing points, which originate in regular succession 68 OUTLINES OF PLANT LIFE. behind the apical growing point. But sometimes branches appear out of this regular order. Such are called ad- ventitious roots. (See 4] 70.) Branches generally originate oppo- site the wood strands, or with definite relation to them, (See figs. 55, 56.) The number of vertical ranks of bran- ches can, therefore, be predicted with some certainty from the structure of the root, but the longitudinal intervals at which the branches will be formed cannot, because they are unequal (fig. 55): When secondary roots arise from the shoot, they have a fixed relation to the leaves, or they are formed upon the buds produced in the axils of the leaves, or they may arise at indefinite points along the internodes. In the first case, roots may be produced either opposite a leaf, or in pairs, right and left of the base of the leaf. 84. Origin.—The origin of root- branches and of secondary roots is rarely external; that is, the root is not commonly produced by growth at the surface of a member. In the great majority of cases the origin of the roots is internal; that is, the forma- tion of the root is begun by the growth Fic 55.—Seedling pea,showing in the interior of the member pro- three vertical ranks of branch- es along the main root. These are numbered 1, 2,3. Natural size.—After Frank. ducing it. In most cases growth begins very near to the surface of the THE ROOT. 69 stele. Soon a growing point is formed (fig. 56). The rootlet is thus in its early stage completely hidden, being buried beneath the cortex, through which it gradually makes its way, partly by disorganizing the tissues by pressure, and, probably, NY () UE ? Fic. 124.— Diagrams representing the transverse heliotropism of leaves of the garden nasturtium (Trope@olum). Potted plants were subjected successively to light strik- ing them in the direction shown by arrows. The petioles curved so as to place the blades at right angles to the incident light.—After Véchting. bring about a different reaction, so that the leaves set them- selves edgewise to the light. A fixed light position is usually reached by leaves by the time they become mature, and this is generally at right angles to the source of greatest light. Branches of trees show the leaves so arranged as to size and position that they shade each other as little as possible, form- ing the so-called /eaf mosaics (figs, 125, 126). The leaves of window plants also exhibit these movements very strikingly, THE MOVEMENTS OF PLANTS. I7I because usually illuminated from one side. Plants kept in darkness have their leaves irregularly placed. iS Fic. 125.—Leaf mosaic formed by a horizontal shoot of Norway maple. The lengthen- ing of the petioles of individual leaves to avoid shading of the blade is marked. About one-third natural size.— After Kerner. Fic. 126.—A rosette of leaves of a bellflower (Campanula pusilla), shoving length- ening of petioles of lower leaves so’ as to carry blades from under upper leaves.— After Kerner. EXERCISE XL. To show the effect of direction of light as a stimulus on leaves. Set a potted plant (geranium, sunflower, nasturtium, or mallow) in the dark for 24 hours; then place it before a window, shading it so that 172 OUTLINES OF PLANT LIFE. light reaches it chiefly from one direction. Mark certain leaves and record the position of the plane of the blade; 24 hours later observe the position and compare with first. To show effect of direction of light as a stimulus upon stems and roots. Grow seedlings of white mustard thus: Tie loosely over the mouth of a jelly-glass a double piece of fine bobbinet ; fill vessel with tap water to the:net, on which place seeds; set in dark, replacing water as it evapo- rates, until seedlings are 3 cm. high, with roots as long or longer. Then place in a box, blackened inside, into which light is admitted through a hole 4-5 cm. in diameter, at right angles to stems and roots. Observe curvatures 24 hours later. 244, (6) Combined movements due to variations in the intensity of light or heat or both are especially exhibited by flowers, whose opening and closing are frequently determined thereby. With some plants the predominant stimulus is heat ; with others, light. Closed flowers of the tulip or crocus may be made to open in 2 to 4 minutes by raising the temperature 15° to 20°. The flowers of the white water-lily and of the dandelion open in sunlight and close in shade. By marking upon their leaves a series of equidistant parallel lines with Chinese ink, and measuring later the distances to which they have been spread, all such movements can be clearly shown to be due to accelerated growth of the outer or inner surfaces, respectively, The protection of the flower parts or their proper working is secured by these movements, which must not be confounded with those due to the direction of light or heat rays. 245. (c) Geotropism.—Geotropism is the state of a plant or an organ when it is irritable to the force of gravity. Since gravity is exerted always in the same direction, it is plain that reactions to this force cannot be studied, as in the case of light, by altering the absolute direction in which gravity acts, but only by so changing the position of the plant that the force acts in a relatively different direction. The reaction to this stimulus and the fixed gravity position must not be confused with the simple effect produced by the THE MOVEMENTS OF PLANTS. 173 weight of the parts concerned. Such effects are to be seen in the downward bending of some plants with slender branches, or the curvature of the flower or fruit stalks by the weight of the parts. True geotropic curvatures are brought about by acceleration of the growth of the irritable cells, and the curvatures produced may even be contrary to the direc- tion of the force. If seedlings be grown in boxes upon the rim of a wheel rotating slowly in a vertical plane, so that they are successively subjected to the action of gravity in relatively different directions, it will be seen that while their Fic. 127.—Seedling mustard plants grown on a cube of peat, 7, attached to the slowly rotating axle, 4, A, of a clinostat. The direction of growth of roots and stems is controlled only by the nearness of moist surfaces, the action of gravity and light bein eliminated. Note the variable direction of roots and stems, At m and wo aeria hyphz of a mold have taken direction as far from the repellant moist surfaces as pos- sible, One half natural size.— After Sachs, : members grow in nearly straight lines, the direction assumed by the stems and roots is quite as frequently abnormal as normal, because the effect of gravity which normally deter- mines the direction of growth of these axes is neutralized, since it now acts upon them from a new direction at each successive moment (fig. 127). If the wheel upon which such seedlings are grown be rotated at a high speed, the cen- 174 OUTLINES OF PLANT LIFE. trifugal force will become a constant one, and, acting in place of the neutralized force of gravitation, will determine the direction which the stems and roots willassume. Since the primary stems of most plants are negatively geotropic, when grown under such conditions they will turn toward the center of the wheel, while the positively geotropic roots grow toward the rim. Similarly, if the wheel be rotated rapidly in a horizontal plane the parts will be controlled by a com- bination of the force of gravity and the centrifugal force (the latter predominating if the speed is great); the stem will grow inward and upward, while the roots will grow down- ward and outward (fig. 128). Fic. 128.—Part of centrifuge. a, the axle, rotated at a high speed by water or electric motor, to which is attached the circular metal piate, 7, 7, carrying a disk of cork, a. To the latter are attached two seedling beans, 4, 8, by means of pins; s¢, the primary stem; 4, the primary root. Over the seedlings the cover, 2, is placed to keep them moist. After a few hours the lateral roots have turned into the direction of the cen- trifugal force, which was sufficiently powerful to overcome that of gravity except near axis of rotation, +. One halt natural size..-—After Sachs. EXERCISE XLI. To show the effect of gravity as a stimulus on roots. Arrange the marked root of a seedling bean as in {J 205, except that the root is horizontal, and a pin just above the extremity marks its posi- tion. After 24 hours observe curvature and which spaces have become curved. Compare with those which have grown most. — To show the effect of gravity asa stimulus on growing regions of upright leaves. THE MOVEMENTS OF PLANTS. 175 Support an onion, roots down, in a vessel of water so that it is half im- mersed, until the leaves are about 10 cm. long. Then turn it so that leaves are horizontal and observe where curvature occurs. 246. Transverse geotropism.—Not all stems, however, ‘are negatively geotropic, nor all roots positively geotropic. The central axis of both root and stem in the majority of plants is so, but lateral branches of both place themselves at an angle to the action of gravity, sometimes at a right angle, at other times at a highly obtuse or acute angle. That is, they are more or less transversely geotropic. Whatever the normal position of any organ, it will be regained by the growing parts as rapidly as possible when the plant is forcibly displaced. This can only be brought about by the curva- tures produced by unequal growth of the younger parts. If a potted plant be laid upon its side for a short time and then erected before any response to the stimulus occurs its growing parts still curve to one side, although not so far as if they had been allowed to remain in the horizontal position. 247. Grasses.—In only a few cases do the maturer parts of plants regain their power of growth under the stimulus of Fic. 129.—Part of a wheat-stalk, showing strong geotropic curvature. The shoot was placed horizontal, and the growth of the basal part of the interncde with the leaf-sheath connected with it was stimulated on the under side, the upper remaining short. No curvature occurs in the older part of the internode. About two thirds natural size. —After Pfeffer. gravity. The basal portion of the internodes of grasses, however, remain for a long time capable of growth; hence, when grasses are blown down or trampled their stems erect themselves by the geotropism of this basal growing zone and of the leaf-sheath (fig. 129). 176 OUTLINES OF PLANT LIFE, EXERCISE XLII. To show the effect of gravity on the growing regions of the stems of grasses, Cover the bottom of a deep dish about 25 cm. long with a layer of wet sand, and bank this against one end to the top. Into this bank stick horizontally several grass stems having at least one node; cover with a glass plate. After 24-48 hours observe curvature. Cut a longitudinal section of the node and observe what part the leaf-sheath takes in this curvature. 248. _ oot-cage.—Experiments upon the response of root- lets to the stimulus of gravity when their position is altered may be carried on by means of a root-cage. It consists essentially of two parallel panes of glass fastened to- gether, between which, in finely sifted soil, the rootlets are grown. By inclining this root-cage at various angles it may be shown that not only the primary root, but its branches, strive to regain I Fic. 130.—Part of the root system of a broad bean, grown in a root-cage, first in the normal, then in the inverted, and again in the normal position. The arrows show the direction in which vity acted in the different positions. othe black por- tion of the roots were the parts growin, during inversion. ‘Two thirds natura size.—After Sachs. their normal angle with the direction of gravity. This is illustrated in figure 130, in which the dark portion of the rootlets represents the grow- ing parts while the cage was inverted. They then took about the same angle with the horizon as when in normal position. 249. Twining plants.—The movements of twining plants are due to a peculiar reaction to gravity. Asthe upper inter- nodes of a seedling elongate they soon become too weak to support themselves and bend over, becoming nearly horizon- tal. When this occurs the growth of the right or left flank of THE MOVEMENTS OF PLANTS. 177 the stem near the bend is accelerated (whence the stem is said to be /aferaily geotropic). The horizontal part is thus swung around, twisting the stem and bringing a new flank under the influence of the stimulus. If in its continued rotation the stem comes in contact with a nearly erect support the free part con- tinues to rotate, growing longer at the same time, and encircles the support. The part below the point of contact now becomes nega- tively geotropic, and its growth on all sides is equally accelerated. The coils are thereby straightened until the stem clasps the support very closely, from which it is often pre- vented from slipping by angles or outgrowths of various kinds, which roughen the surface (fig. 131). While gravity thus plays a large part in determining the position of both aerial and subterranean Frye, 131.4, a bit of the stem of * the hop, showing the six angles, organs, it must be remembered each carryingarow of emergences, that it works conjointly with many ah ee eee other stimuli. The position of the fe¢3 dim, tree smergences members is, therefore, a resultant “e™*" ° of the reactions to the various external forces which stimu- late them. 250. (¢d) Hydrotropism.—Hydrotropism is the state of a plant or an organ when it is irritable to moisture. Hydro- tropic organs may bend toward or away from a moist surface. Roots are particularly sensitive to the presence of moisture. If a cylinder of wire gauze be filled with damp sawdust and a number of seeds planted near its surface they germinate and the roots start to grow in the normal direction—i.e., directly downward. If now the cylinder be suspended at an angle, as shown in figure 132, the roots which pass into the air, 178 OUTLINES OF PLANT LIFE. stimulated by the moisture, curve toward the damp sawdust. Upon entering it the stimulus ceases, and they start again to grow downward, being positively geotropic. Again the stimulus of the moist surface overcomes that of gravity, and they turn back to it, often threading themselves in and out of the wire gauze. Since only one-sided action of a stimulus Fic. 132.—Apparatus for demonstrating hydrotropism. a, @, a zinc disk, with hooks to which is attached a cylinder or trough of wire netting filled with damp sawdust. In this are planted peas, g, whose roots, 4,7, &, 7, first descend into the air but soon turn toward the damp sawdust again. 7 has threaded itself in and out of the netting.— After Sachs. determines direction of movement, if the air be saturated they continue to react to the stimulus of gravity alone. 251. (ec) Movements due to contact.— Contact, either gentle or forcible, and friction act as stimuli to modify the growth of many plant parts. Only rarely is the main axis of a plant sensitive to mechanical stimuli, except, perhaps, to long continued contact (or pressure) in the case of some twining plants. But in many plants tendrils and leaf-stalks are irritable to contact, even to a degree far surpassing that of our nerves of touch. If the tip of a tendril ({ 225), while still capable of growth, THE MOVEMENTS OF PLANTS. 179 come in contact with a solid body, it will quickly become concave on the side touched, and thus will wrap. about the object, if it be of suitable size. This curvature is due first to the shortening of the cells upon the concave side and later to unequal growth on the convex and concave sides. Finally this effect extends to all parts of the tendril, which begins to curve. As both ends are fast, it is a mechanical necessity that the curves become spiral coils, both right- and left- handed, accompanied by a twisting of the tendril on its axis (fig. 69). After the coils are formed the tissues of the tendril become thick-walled and rigid, so that the plant is attached to the support by a spiral spring. Other tendrils do not nutate, but are negatively helio- tropic, and by contact their tips are stimulated to develop disks which apply themselves closely to the support and send into its irregularities short outgrowths from the surface cells. Such plants are adapted to support themselves by walls, tree- trunks, etc. The Japanese ivy and one form of the Virginia creeper are notable examples. The coiling of the leaf-stalks is not unlike the first curva- tures described for tendrils (fig. 100). EXERCISE XLII. To show effect of contact as a stimulus to tendrils. Stroke with a pencil the concave side of the tip of a tendril of passion vine, squash, wild cucumber, or balsam-apple, on a warm day or ina hothouse, and observe curvature which follows in a few minutes. 252. (B) Movements of turgor.—The movements already described are confined to members which are growing, either throughout, or in some part. As turgor can affect only tissues whose cell-walls are elastic (| 156), the movements pro- duced directly by variation in turgor can occur only in such mature members as are provided with special motor organs. In almost all cases these are leaves. Stimuli which regulate 180 OUTLINES OF PLANT LIFE. growth (] 242) may also affect motor organs, producing like curvatures. But elongation of any part of a motor organ by increased turgor is reversible, not permanent (cf. & 213) ; it is therefore not growth. 253. Motor organs. — The motor organ in leaves is usually the leaf base ({ 124) or a modi- fied portion of the stalk, some- times greater but generally less in diameter than the rest. Its Fic. 133- Fic, 134. Fic. 133.—Transverse sections through petiole of scarlet runner. .4, through the rigid portion ; 2, through the motor organ. G, g, vascular strands; c, cortex; 72, pith; v, deep channel along ventral side of petiole. Magnified about 10 diam.—After Sachs. Fic. 134. —Portion of a scarlet runner, which, originally growing erect, has been inverted for several hours, resulting in geotropic curvatures of the primary motor organs P, P', +, The lowest pair of leaves show secondary motor organs at the juncture of petiole and blade. Similar ones are present in the upper compound leaves, but are not clearly shown in the figure. The arrows show the position of the petioles when the plant was first inverted. About two thirds natural size.—After Sachs. ~cortex consists of large cells, and the stele occupies a rela- tively small part of the transverse section. In other parts of the petiole the stele is much larger, or there may be several THE MOVEMENTS OF PLANTS. 181 steles distributed about the center. (See 4 136.) In figure 133, A and B# show the contrast. If the leaf be a compound one, there are usually secondary motor organs at the base of the leaflets, as in the leaf of the bean (fig. 134). Variation in the turgor of the cells of the cortex upon one side or the other produces a sharp curvature of the motor organ, which alters the position of the leaf or leaflet (fig. 134). The con- cave surface of the motor organ becomes deeply wrinkled transversely, while the convex surface is smooth. 254. Spontaneous movements.—Only a few plants exhibit spontaneous movements by means of motor organs. The lateral leaflets of the telegraph plant (s, fig. 135), under normal conditions of rather high temperature (about 32° C.), show jerky movements of such direction that their tips describe an irregular el- lipse, which is completed in 1 to 3 minutes. The leaflets of the clovers and oxal is show much slower movements described in the next paragraph. More commonly the turgor movements F or ae Relig in are induced. The most common stimuli {rds natural size,—After are light and contact, although many others suffice to induce them. 255. Light movements.—Movements produced by the variations of light have long been known as ‘‘sleep move- ments.’? They are best observed upon the leaves of the bean family, though many other plants exhibit them. Figure 136 shows the positions assumed by various leaves toward nightfall. It will be seen that in compound leaves the leaf- lets sometimes rise, so as to apply their outer faces to each other ; others sink, so that the under surfaces are in contact; others become folded in various ways. This position is main- tained throughout the night. Upon the increase of light in 182 OUTLINES OF PLANT LIFE. the morning, the day position is assumed. The cutting off of light artificially from any of these plants causes them SS . = : = _¥ vy A ee | Fic. 136.—Photeolic movements. a, leaf of a mimosa in day position; a’, the same in night position. 4, leaf of Covoni/a varza in day position; 4’, the same in night po- sition. c, leaf of Amorpha fruticosa in day position; c’, the same in night position. d, leaf of Tetragonolobus in day position ; @’, same in night position.—After Kerner. within a short time to assume the nocturnal position. Their purpose is not certainly known. EXERCISE XLIV. To show effect of intensity of light as a stimulus on certain leaves. Observe the position of the leaflets of white, red, or sweet clover, bean, locust, or oxalis at 3 P.M., 6 P.M., at dusk (or after nightfall by using a lantern) and at 8 a.m. In the morning darken with a box a plant show- ing these movements. After an hour or two, observe the position of leaf- lets. 256. Contact movements.—Some organs are sensitive to contact, as the leaves of Venus’ fly-trap, and other related THE MOVEMENTS OF PLANTS. 183 plants. The motor organ in the Venus’ fly-trap (figs. 224, 137) is the cushion of tissue running along the back of the leaf between the two lobes. By the sudden variation in turgor of some of these cells the two halves of the leaf are thrown quickly together when one of the six bristles upon its Fie. 138. Fic. 139. Fic. 137.—Part of a transverse section of a leaf of Venus’ fly-trap. 7, the cushion of tissue constituting the motor organ; 4, one of the sensitive bristles which, upon being touched, cause the leaf to close: ¢, one of the interlocking teeth. The minute pro- jections over inner (ventral) surface are glands which secrete the digestive fluid and later absorb the food. Magnified about 5 diam.—After Kurz. Fic. 138.—A leaf of the sensitive plant fully expanded. Natural size.— After Duchartre. Fic. 139.—A leaf of the sensitive plant after stimulation The motor organ at the base of each leaflet has thrown it forward and upward; the motor organs at the base of the four divisions have moved them together. The motor organ at the base of the main petiole has moved the whole leaf sharply downward. Natural size.-- After Duchartre. upper surface is touched. The sensitive plant drops one of its leaflets or the whole leaf quickly when stimulated by con- tact, heat, or electricity. The position of the leaves when normally expanded is shown in figure 138, and their position after stimulation by figure 139. The stamens (4 287) of some flowers and the stigmas ({[ 283) of others are sensitive 184 OUTLINES OF PLANT LIFE. to a touch, shortening, elongating, or bending in such a way as to promote pollination ( {J 295). The motor organs of the leaves of a number of the bean and oxalis families also react to more violent mechanical stimuli. Their movements are similar to those described in € 255. 257. Summary.—By irritability, that is, the sensitiveness of protoplasm to external agents, plants are able to regulate all their activity and adjust themselves to the world about them. Under unfavorable conditions this sensitiveness is temporarily lost. If permanently lost, it is death. It is more marked in some parts than others and its effects in these parts are capable of being transmitted to distant parts. The reactions of plants to stimuli are most easily observed when they result in movements. Movements of the proto- plasm itself seem to be automatic, but can be directed by ex- ternal stimuli. Movements of multicellular plants are due either to unequal growth or to unequal turgor. Light, heat, gravity, moisture, or contact may so influence the rate of growth, or the amount of turgor as to cause curvature of growing parts or of a special motor organ. The parts affected may thus be turned toward or away from the source of the stimulus, or may be placed transverse to it. Movements in response to gravity, light, and heat are most important. These work conjointly to determine the position of organs. PART Ill: REPRODUCTION. CHAPTER XVII. VEGETATIVE REPRODUCTION. 258. Introduction.—Having considered in Parts I and II the structures and functions by which the nutrition of the individual is secured, Part III is devoted to the consideration of the structure and functions of some of the simpler repro- ductive organs and the functions by which a succession of similar individuals is insured. (For fuller discussion see Plant Life.) One of the fundamental powers of protoplasm is its ability to produce new organisms as offspring from the older ones. In the simpler plants the two great functions, nutrition and reproduction, are often carried on by the same cell. This must always be so in the unicellular plants. In the higher plants, however, these two functions become completely separated, organs being specialized for each, so that the functions may be more certainly and efficiently performed. Any part capable of growing into a new individual may be called a reproductive body, and the part on which or in which it is produced is a reproductive organ. If the reproductive bodies consist of one or two cells only, they are usually called spores. If they are cell-masses, they are generally called brood duds or gemme to distinguish them from ordi- 185 186 OUTLINES OF PLANT LIFE. nary buds. In both cases it is necessary that the cells to be separated from the parent should be capable of growth—that is, in the condition known as the embryonic phase ({ 215). The reproductive organs produced by some plants are ex- ceedingly complex and varied, while others form reproduc- tive bodies in very direct ways. The reproductive bodies themselves are generally very simple. In addition to com- plex reproductive organs, there are sometimes accessory parts by which the plant adapts its reproductive functions to the conditions under which it lives. Among these accessory structures are many, as among the flowers of seed plants, by which the aid of other plants or animals is secured. 259. Vegetative and sexual reproduction.—In all the diversity of organs and processes two chief methods may be distinguished, called vege/ative reproduction and sexual repro- duction. Vegetative reproduction consists in the formation of repro- ductive bodies ‘by processes of growth only. The modes in which they arise are varied in detail, but consist essentially in the production by the parent of a body, unicellular or multicellular, which at maturity develops, under suitable conditions, into a new plant. It is scarcely to be doubted that the earliest methods of reproduction were vegetative, and that sexuality has been acquired by a gradual adaptation of cells previously devoted wholly to ordinary processes of growth. Sexual reproduction consists in the formation of reproduc- tive bodies by the union of two specialized cells, neither of which alone is capable-of developing into a new plant. I. Fission and budding. 260. Fission.—In single-celled plants cell division and reproduction are practically identical, since shortly after division occurs the two cells so produced separate and lead VEGETATIVE REPRODUCTION. 187 an independent existence (C, fig. 10). Such a method of reproduction evidently interferes little with the processes of nutrition, which probably are scarcely even suspended during the process of reproduction. 261. Budding.—A slight variation of the method of fission just described is to be found in those single-celled plants, such as the yeasts, whose growth is so localized as to form upon one side a small enlargement which ultimately attains the size of the parent, with which it is connected by a very narrow neck (fig. 29). Across this neck the partition wall is formed in the usual way. This becomes mucilaginous, rendering the adhesion of the daughter cell at this point so weak that it is easily separated from the parent. This method of reproduction is known as budding. 262, Fragmentation.—In those plants which consist of a row of cells more or less closely united, the breaking up of the filaments into separate pieces, either through external force or the death of one of the cells, may produce a number of smaller colonies or of new individuals, each of which may grow to full size. In some of the more loosely organized filament-colonies, such as Nostoc (see § 11, and fig. 6), there are specialized cells whose function seems to be to loosen pieces of definite length, which creep out of the jelly, grow, and thus produce new colonies. ; The greater size reached by most multicellular plants soon renders impossible the continuance of this method of repro- duction, éxcept among those whose cells are all alike. Should such separation into nearly equal parts occur among more highly specialized plants, it is evident that one portion might easily be left without nutritive organs adapted to its needs. The higher plants, therefore, specialize certain regions or members, where, by division or budding or similar processes, reproductive bodies may be formed. 188 OUTLINES OF PLANT LIFE, II. Spores. 263, Sexual and non-sexual spores.—A spore is a single- Fic. 140.—Develupment and escape of zoospores of an aquatic fungus (Saprovegnia lactea). The ends of two hyphz are shown, the ter- minal cells being spore cases. In a, the protoplasm is gathering to form spores. From 6 many of the. zoospores have escaped through the perforation in the wall near the upper end of the cell, From c¢ at have escaped but one, which is just slipping through the opening (here in pro- file). Magnified 300 diam.—After Kerner. or it may divide into several or many. celled body capable of producing a new plant. Spores may be formed either by a process of growth or by the union of two cells. The former are called non- sexual spores; the latter, sexual spores. Only non-sexual spores are discussed in this chapter. 264. Motile spores. — Spores may be either naked and motile or furnished with a cell-membrane and non-motile. The former are commonly produced by plants which pass all or part of their lives in water, such as the alge and aquatic fungi. They are usually pear-shaped and furnished with one or more cilia, by means of which they swim about (figs. 109, 140). When locomotion was supposed to be a distinctive power of ani- mal bodies they were called 200- Spores, aname still retained. They are also called swarm-spores. Zoospores are formed either in a general body-cell, not visibly different from the other body- cells, or in a cell specialized in form and structure, the spore case. The entire contents of the spore case may form a single zoospore, The zoospores are VEGETATIVE REPRODUCTION. 189 set free by the rupture or by the solution of a portion of the enclosing wall (fig. 140). They may begin to move before the rupture of the wall, in accomplishing which their activity may materially assist. “They then work their way out and swim freely in the water. After a time of movement they usually lose their cilia, either withdrawing them into the protoplasm or dropping them off, come to rest, and begin to grow into a new plant. 265. Non-motile spores are formed by all classes of land plants without exception. They are often produced in great profusion, especially by the fungi, the mosses, the ferns, and the seed plants. 266, Form and food.—Their form is exceedingly various. Many are spherical or ovoid, while some are cylindrical or Fic. 141,—Part of a vertical section of a leaf of a willow, attacked by a fungus (A/e/amp- sora salicina), eo, epidermis of upper side lifted by the youre teleuto-spores, z, de- veloping from the spore-bed above the ends of the palisade cells of the host (Jaz); ex, epidermis of the under side, broken through by the spore-bed from which spring uredo-spores, s¢, and paraphyses, ~. ¢o will also finally be ruptured to set free 7. Magnified 260 diam.—After Prantl. even needle-shaped (figs. 141, 143, 166), Irregular forms, also, are not uncommon. The same plant may produce at 190 OUTLINES OF PLANT LIFE. different stages or in different parts spores which are unlike in form and nature (compare / and s¢, fig. 141). In almost all cases there is a supply of reserve food within the spore, which varies in amount with the conditions under which they are formed. It is ordinarily greater in resting spores than in those intended for immediate growth. 267. Growth.—-Spores germinate by absorbing water, thus bursting the more rigid outer layer or layers of the cell- wall. The inner layer then grows in area to accommodate the increasing protoplasm, which so controls the mode of growth as to produce a plant of definite form. In many cases the plant produced is essentially like that which gave rise to the spore. In others it is different, but sooner or later in the life cycle the same form recurs. 268. Origin.—Non-motile spores are either free, being produced at the ends of branches specialized for that pur- pose, or enclosed in a spore case. Often the same plant forms spores by both methods at different stages in its development. 269. Free spores.—The formation of free spores is con- fined to the lower plants, and is especially characteristic of the non-aquatic fungi. The branches producing spores may occur singly, or, more commonly, they are grouped at certain points, forming a spore-bed (fig. 141). If the fungus develops its mycelium in the interior of a host, the formation of a spore-bed is often necessary to rupture the host, so that the spores may be brought to the surface and set free. Thus the spore-beds of parasitic fungi commonly blister the surface of the host by lifting up its outer tissues (eo, fig. 141). Spores may be produced either singly at the ends of the branches, or in chains (fig. 142). A modification of the production of spores singly occurs when the branch destined to produce them gives rise to two to eight very slender branches, each of which enlarges at the VEGETATIVE REPRODUCTION. Ig! tip into a single spore, so that the main branch appears to carry two to eight spores upon slender stalks (fig. 143). Fic. 142. Fic. 143. Fic. 142.— An outline showing the formation of a spore-chain of the blue-green mold (Penicillium glaucum). 6, branch of spore-bearing hypha, budding beneath two older spores. Across the narrow neck a partition wall is formed, the'spores round off, and from this wall a device, ¢, for loosening the spores is developed. The terminal spore is oldest. Highly magnified.— After Frank. : 2 Fic. 143. Longitudinal. section through the edge of a gill of a mushroom (Coprv7xus) after spore-formation is*completed. 7, interwoven hyphz of the gill, branching to form the spore bed, composed of sterile branches, 4, swollen branches, c, and spore- bearing branches, 4. The latter give rise to four slender branches, whose tips enlarge to form each a single spore. # and do not produce spores. Magnified 300 diam.— After Brefeld. , 270. Fructifications—In the higher fungi whose my- celium is developed within a dead substratum many hyphe are aggregated to constitute a reproductive structure or fruc- tification, which is the only conspicuous part of the fungus. (For an account of the vegetative parts, see {J 43, 47). The body of the fructification is made up of hyphe, more or less interlaced and adherent, and is of a form adapted not only to break through the substratum, but also to furnish an extensive surface for the spore-beds (fig. 143). The fructification may be irregularly lobed, sessile and gelatinous, or much branched and cylindrical or flattened ; the shapes being- adapted in various ways to form an exten- sive surface on which spores may be formed (figs. 144, 145). 192 OUTLINES OF PLANT LIFE. 271. Simple spore cases.—Spores are also formed loose in the interior of cells. Each spore-containing cell is Fic. 144.—A fructification of Clavarta aurea. The spore beds cover the upper part of the branches. Natural size.— Fic. 1 After Kerner. ans Fic. 145.—A fructification of a mushroom, Amanita phalloides. , the cap or pileus; z, the veil, originally connected with edge of cap, covering the gills which radiate from the stipe, st, to the edge of cap; vo, the volva. The surface of the gills is covered with the spore beds. Most mushrooms showing a distinct volva are poison- ous. Natural size.—After Kerner. called a stmple spore case (fig. 146). In the lower plants, the spore case may be merely one of the general body-cells, or it may be specialized in form as well as in function. It may be spherical, sac-like, or linear. The number of spores formed within a simple spore case may be two or more, up to several hundred. Simple spore cases may be formed singly or they may be grouped. 272. Compound spore cases—In the higher plants, in- VEGETATIVE REPRODUCTION. 193 cluding the mossworts, fernworts; and seed plants, the spore case is always formed of two or more spore-producing cells, surrounded by a covering of cells (one or more layers) which do not produce spores. These spore cases may be developed Fic. 146. Fic. 147- Fic. 146.—Longitudinal section of the simple spore case of a mold (AZucor). The aerial hypha, %, has partitioned off a cell, s, within which spores are produced. The walls of this spore case are studded with needle crystals of calcium oxalate. The partition protrudes far into the spore case. Magnified 260 diam.— After Kerner. Fic. 147.—Longitudinal section of the stem, s, of a moss gametophyte, bearing leaves, Embedded in the stem is the sporophyte, consisting of a stalk, s¢, and a compound spore case, of which w is the wall, formed of a sheet of cells, enclosing the spores, sf (contents not shown). Magnified 100 diam.—After Hofmeister. either from superficial or from internal cells. Asa conse- quence, the mature sporangia will be either free or more or less enclosed within the tissues of the organ by which they are borne. 273. The sporophyte.——Among the mossworts, fernworts, and seed plants reproduction by spores has become so fixed and important that one stage in the plant is devoted espe- cially to producing them. This phase is different from that producing sex cells, the difference becoming greater the more complex the plant. The stage set apart for spore production is called the sporophyte. In the mossworts the sporophyte has very little green tissue, and therefore carries on little nutritive work, but depends for its supply of food chiefly 194 OUTLINES OF PLANT LIFE. upon the sexual stage, with which it is connected throughout spr Fic. 148.—Longitudinal section of the young capsule of atrue moss(Bryumz). 5, spore case. Atthis stage the mother cells of the spores, sf7z, have become free (only a few are shown, still en- closing the spores, which are later re- leased!; sw, the wall ot.the spore case, lined by the remains of another layer of cells now disorganized ; c, the columella, of partly collapsed cells; zs, intercellular space; cz, wall of the capsule;