sre nee New York State College of Agriculture At Cornell University Sthaca, N.Y. Library I.P. Roberts Collection Gift of Roger M. Roberts. Cornell University Libra Elementary botany. Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924000606107 (:a2a2¢s27"047) ‘(biz aBed 9as) VLATOARY SVDAD ELEMENTARY BOTANY BY GEORGE FRANCIS ATKINSON, Pu.B. Professor of Botany in Cornell University SECOND EDITION, REVISED NEW YORK HENRY HOLT AND COMPANY 1899 ec Ke? A 8 8944 £7) 3¢ Copyright, 1898, BY HENRY HOLT & CO. ROBERT DRUMMOND, PRINTER, NEW YORK. PREPIACE, UNTIL recent years the prevalent method of teaching botany in the secondary schools, and in the first courses in many col- leges, has been based on the ‘analysis’? of flowers. The method had its impetus in the study of systematic botany pur- sued with such vigor by the pioneers of the science in America. The great progress in our knowledge of the morphology and physiology of plants during the last quarter of this century has changed the whole problem of elementary instruction in botany, and led to almost universal dissatisfaction with the old method of secondary instruction in this subject. It is now generally recognized that a study of the lower plants, like the alge, fungi, liverworts, mosses, and ferns should form a part of a course of secondary education in botany. To meet this end a number of books have sprung into exist- ence during the past few years. If the need for some guid- ance in the selection of topics, and an outline of the character of the study, could be met by umber alone of books, this want would be fully met in the new treatises recently published, and there would be no place for the present book. But a judicious selection of a few forms to illustrate function, process, and relationship throughout the wide range of plant life, and the training in logical methods of induction, and accuracy of draw- ing conclusions, is vastly more important in its influence on the character of the pupil, even though he forget all about the plants studied, than the handling of a great variety of objects, and the drawing of haphazard conclusions, which are left to the pupil in a large number of cases by the methods pursued in many of the recent elementary works. iii iv PREFACE. For several years the author has been deeply interested in the teaching of elementary botany, and has had an opportunity to study methods in a practical way, in having charge of the in- struction of a large class of beginners, the majority of whom had never studied the subject before. One of the great diffi- culties encountered in attempting to introduce the study of the lower plants is the fact that these plants are in most cases en- tirely unknown to the pupil. The difficulty does not lie in the attempt to introduce the study of unknown objects. But it lies rather in the attempt to study the lower plants, at the outset, in a more or less thorough manner, to learn their characters, rela- tionships, etc., in order to group them into their natural orders. This is attempting too much for the young beginner, to whom these plants are totally unfamiliar objects. The method followed in this book has been thoroughly tested in practical work. It is to first study some of the life processes of plants, especially those which illustrate the fundamental prin- ciples of nutrition, assimilation, growth, and irritability. In studying each one of these topics, plants are chosen, so far as possible, from several of the great groups. Members of the lower plants as well as of the higher plants are employed, in order to show that the process is fundamentally the same in all plants. Then another process is studied in a similar way, using so far as possible, especially where the lower plants are concerned, the same plant. In this way the mind is centered on this process, and the discovery to the pupil that it is fundamentally the same in such widely different plants arouses a keen interest not only in the plants themselves, but in the method which attends the discovery of this general principle. In the study of the life processes, the topics can be arranged so that they show progres- sion of function. At the same time it is well for the teacher to select for this study of the life processes those plants which represent well the great groups, and show gradual progression of form and struc- ture, and also those which are easily obtained. A second period of the session can then be devoted to study- PREFACE, Vv ing a few representatives of the different groups of the alge, fungi, liverworts, mosses, ferns, and the higher plants. This should be done with special reference to form, reproduction, general classification, progression, and retrogression of parts or organs, in passing from the lower to the higher plants. In taking up this study of representative forms now, if a wise selec- tion has been made in dealing with the life processes, the same plant can be used here in most cases. These plants now are faniuliar to the pupil, and the mind can be centered on form, organs, reproduction, relationship, etc. In this study of gen- eral morphology it is very important that a careful study be made of some of the lower plants, and of the ferns. Here the sexual organs are well formed, and the processes of reproduc- tion can be more easily observed. In the higher plants the sexual organs are very much reduced, and the processes more difficult to observe. It is only through a study of the lower plants that we are able to properly interpret the floral structures, and the sexual organs of the spermatophytes, and to rid our- selves of the erroneous conceptions which the prevalent method of elementary instruction has fixed so firmly on the lay mind. A third period of the elementary course may be employed in studying special morphology of the higher plants. Even here it seems to the author wise that the ‘‘analysis’’ of plants should be deferred until after a general notion of the characters and habit of several of the important families has been obtained. The pupil may be told the names of the several plants used as examples, and emphasis can be laid on ordinal and generic characters, which can then be recognized in many plants with- out resort to a key. The matter of determining the names of plants by the old method can, if desired, be pursued to greater advantage after this critical study of relationships has been made, even though the pupil may pursue it independently at a later time. In the study of plants one should not lose sight of the value of observing plants in their natural surroundings. If judiciously pursued it forms at once a means of healthful recreation, of com- munion with the very soul of nature, and of becoming ac- vi PREFACE. quainted with the haunts, the lives, the successes and failures of plants; the influences of soil, moisture, and other environ- mental conditions upon plants, and, what is also important, the influence which plants exert upon their environment. Classes may be taken into the field, at different seasons of the year, to observe flower and bud formation, pollenation, seed production, seed distribution, germination of seeds and nutrition of the embryo, protection of plants against foes and extremes of weather; the relationships of plants in colonies, and their dis- tribution in plant formations, etc. In all this study a knowl- edge of some of the lower plants is important. It is not intended that the matter in the book should be mem- orized for the purpose of recitations. It should be used as a guide to the practical work, and asareference book. The para- graphs arranged in coarse print are intended in general to indi- cate the studies which will serve as the basis for the practical work by the student. In most cases the material for these studies can be quite easily obtained and the laboratory work is not difficult. The paragraphs in fine print are intended to fur- ther illustrate the subject by discussion and illustration of the more difficult phases of each topic. Some of these can be made the basis for demonstrations by the teacher before the class, and all will serve as a convenient means of getting at the important reference matter by the student in a single book. Suggestions on the study and the taking of notes, etc., by the student are given in the appendix. Acknowledgments.—The author desires here to express his gratefulness to his associates in the botanical department of Cor- nell University who have read the manuscript and have made useful suggestions (Messrs. E. J. Durand, B. M. Duggar, kK. M. Wiegand, and Professor W. W. Rowlee). Valuable suggestions were also given by Dr. J. C. Arthur, of Purdue University, who kindly read the chapters on physiology, and by Professor W. F. Ganong, of Smith College, who read some of the chapters on ecology and the tables on the homologies of the gymnosperms and angiosperms. PREFACE. vii Ilustrations.—The large majority of the illustrations are new, and were made with especial reference to the method of treatment followed in the text. Most of the photographs were made by the author. Others were contributed by Professor P. H. Mell, of the Alabama Polytechnic Institute, Auburn, Ala.; Professor Rowlee, Cornell University ; Mr. H. J. Webber, Washington, D.C.; by the New Jersey Geological Survey through the courtesy of Mr. Gifford Pinchot, of New York; by Mr. B. M. Duggar, Cornell University, and Mr. Herman von Schrenk, of the Mis- sour] Botanical Garden. Many of the drawings, especially those of microscopic objects, were made by the author; others by Mr. H. Hasselbring, Cor- nell University, and Dr. Bertha Stoneman, now professor of botany in the Huguenot College, Wellington, Cape Colony, South Africa. The drawings to illustrate the gross characters of plants were made by Mr. W. G. Holdsworth, Michigan Agri- cultural College; Mr. Joseph Bridgham, Providence, R. L.; Messrs. W. C. Furlong and W. C. Baker, Cornell University ; and a few by Miss Edna Porter, Buffalo, N. Y., and by Mrs. E. L. Nichols and Mrs. J. G. Needham, Cornell University. Pro- fessor Chas. A. Davis kindly furnished the sketches from which the drawings of the transformed trillium flower were made. Other illustrations have been obtained from the following sources: from the author’s Study of the Biology of Ferns, through the courtesy of the Macmillan Co.; and from the Annals of Botany, Jahrbiicher fiir wissenschaftliche Botanik, Flora, Botanical Gazette, Vines’ Student’s Text Book of Botany, and Warming’s Botany. Above all the author is under great obligations to Professors Ikeno and Hirase, of the Imperial University of Japan, Tokio, for their unparalleled courtesy in sending drawings of the sperma- tozoids, and of fertilization, in cycas and gingko, in advance of their publication. CorNELL UNIVERSITY, June, 1898. CONTENTS. (References are to paragraphs.) PART I.—PHYSIOLOGY. CHAPTER I. PROTOPLASM. The plant spirogyra, 4. Chlorophyll bands in spirogyra, 5. The spirogyra thread consists of cylindrical threads end to end, 6. Protoplasm, 7. Cell-sap in spirogyra, 8. Reaction of protoplasm to certain reagents, 9. Earlier use of the term protoplasm, 11. Protoplasm in mucor, 12. Mycelium of mucor, 13. Appearance of the protoplasm, 14. Move- ment of the protoplasm in mucor, 15. Test for protoplasm, 16. Protoplasm in nitella, 17. Form of nitella, 18. Inter- node of nitella, 19. Cyclosis in nitella, 20. Test for proto- plasm, 21. Preteplusm in one of the higher plants, 22. Movement of protoplasm in the higher plants, 23. Move- ment of protoplasm in cells of staminal hair of spiderwort, 24. Cold retards the movement, 25. Protoplasm occurs in the living parts of all plants, 26.......-.-....... 00.24, page CHAPTER II. ABSORPTION, DIFFUSION, OSMOSE, Osmose in spirogyra, 30. Turgescence, 31. Experiment with beet in salt and sugar solutions, 32. Osmose in the cells of the beet, 34. The coloring matter in the cell-sap does not readily escape from the living protoplasm of the beet, 35. The coloring matter escapes from dead protoplasm, 36. Osmose experiments with leaves, 37. Absorption by root- hairs, 39. Cell-sap a solution of certain substances, 4o. Diffusion through an animal membrane, 41. Importance of these physical processes in plants, 44..-....-...--...-- page x CONTENTS. CHAPTER III. ABSORPTION OF LIQUID NUTRIMENT. Formula for solution of nutrient materials, 46. Plants take liquid food from the soil, 50. How food solutions are car- ried into the plant, 51. How the root-hairs get the watery solutions from the soil, 52. Plants cannot remove all the moisture from the soil, 53. Acidity of root-hairs, 56...page CHAPTER IV. TURGESCENCE. Turgidity of plant parts, 58. Restoration of turgidity in shoots, 59. Tissue tensions, 61. Longitudinal tissue tension, 62. TYATSVETSS LISS LENEION, 06600005 ¢c005e axceee awwnss pa CHAPTER V. ROOT PRESSURE. Root pressure may be measured, 67. Experiment to demon- Strate root pressure, 68... 26. cesses meee Gee ee eee page CHAPTER VI. TRANSPIRATION. Loss of water from excised leaves, 71. Loss of water from growing plants, 72. Water escapes trom the surfaces of living leaves in the form of water vapor, 73. Experiment to compare loss of water in a dry and a humid atmosphere, 74. The loss of water is greater ina dry than in a humid atmosphere, 75. How transpiration takes place, 76. Struc- ture of a leaf, 79. Epidermis of the leaf, 80. Soft tissue of the leaf, 81. Stomata, 82. The living protoplasm re- tards the evaporation of water from the leaf, 83. Action of the stomata, 84. Transpiration may be in excess of root pressure, 85. Negative pressure, 86. Lifting power of transpiration, 87. Root pressure may exceed transpiration, 88. Injuries caused by excessive root pressure, 89. Dem- onstration of stomates and intercellular spaces, 92..... page CONTENTS. CHAPTER VII. PATH OF MOVEMENT OF LIQUIDS IN PLANTS. Place the cut ends of leafy shoots in u solution of some red dye, 94. These solutions color the tracts in the stem and leaves through which they flow, 95. Structure of the fibro-vascu- lar bundles, 98. Woody portion of the bundle, 99. Bast portion of the bundle, 100. Cambium region of the bundle, tor. Longitudinal section of “the bundle, 102. Vessels or ducts, 103. Sieve tubes, 105. Fibro-vascular bundle in In- dian corn, 107. Rise of water in the vessels, 108. Synopsis Of TISSUES; TIO: cscs wucananaeenas aaasies CERES page CHAPTER VIII. DIFFUSION OF GASES. Gas given off by green plants in the sunlight, 111. What this gas is, 117. Oxygen given off by green land plants also, 118. Absorption of carbon dioxide, 119. The gases are exchanged in the plants, 122. A chemical change of the gas takes place within the plant cell, 123. Gases as well as water can diffuse through the protoplasmic membrane, I24 page CHAPTER IX. RESPIRATION. Oxygen from the air consumed during germination of seed, 127. Carbon dioxide given off during germination, 128. Respi- ration is necessary for growth,130. Energy set free during respiration, 132. Respiration in a leafy plant, 133. Respi- ration in fungi, 134. Respiration in plants in general, 135. Respiration a breaking-down process, 136. Detailed result of the above experiment, 137. Another way of performing the experiment, 138. Intramolecular respiration, 139..page CHAPTER X. THE CARBON FOOD OF PLANTS. Starch formed as a result of carbon conversion, 141. Iodine used as atest for starch, 142. Schimper’s method of testing xii CONTENTS. for the presence of starch, 143. Green parts of plants form starch when exposed to the light, 147. Starch is formed only in the green parts of plants, 148. Translocation of starch, 149. Starch in other parts of plants than the leaves, 151, Form of starch grains, 153.0. .6..62:ssseseaseees page CHAPTER XI. CHLOROPHYLL AND FORMATION OF STARCH. @ Fungi cannot form starch, 155. Etiolated plants cannot convert carbon, 156. Chlorophyll and chloroplasts, 157. Form of the chlorophyll bodies, 158. Chlorophyll is a pigment which resides in the chloroplast, 159. Chlorophyll absorbs energy from sunlight for carbon conversion, 160. Rays of light concerned in carbon conversion, 161. Starch grains formed in the chloroplasts, 162. Carbon conversion in other than green plants, 164. Influence of light on the movement of chlorophiyll bodies; 165.2 caus cards kacuemea ooo dey usc page CHAPTER XII. NUTRITION; MEMBERS OF THE PLANT BODY. Nutrition of liverworts, 167. Riccia, 167. Marchantia, 168. Frullania, 169. Nutrition in the mosses, 170. The plant body, 171. Members of the plant body, 172. Stem series, 173. Leaf-series, 174: The root, 175s s cis Feuer de Sos Mae eH SERA Sp Ohta eo page 322 CHAPTER XLVIII. DIMORPHISM OF FERNS. Dimorphism in the leaves of ferns, 624. The sensitive fern, 625. Transformation of the fertile leaves of onoclea to sterile ones,626. The sporangia decrease as the fertile leaf expands, 628. The ostrich fern, 629. Dimorphism in tropi- Cal ‘ferns, (630cc0 _——— aN cover glass avER a tuft of the branches ee ? near the growing end. Examined with —_ the microscope the green chlorophyll bodies, which form oval or oblong discs, are seen to be very numer- ous. They lie quite closely side by side and form in perfect rows along the inner surface of the wall. One peculiar feature of the arrangement of the chlorophyll bodies is that there are two lines, extending from one end of the internode to the other on opposite sides, where the chlorophyll bodies are wanting. ‘These are known as neutral lines. They run parallel with the axis of the internode, or in a more or less spiral manner as shown in fig. 9. 20. Cyclosis in nitella.—The chlorophyll bodies are stationary on the inner surface of the wall, but if the microscope be properly focussed just beneath this layer we notice a rotary motion of particles in the protoplasm. There are small granules and quite large masses of granular matter which glide slowly along in one direction on a given side of the neutral line. If now we examine the protoplasm on the other side of the neutral line, we see that the movement is in the opposite direction. If we examine this move- ment at the end of an internode the particles are seen to glide around the end from one side of the neutral line to the other. So that when conditions are favorable, such as temperature, healthy state of the plant, etc., this gliding of the particles or apparent streaming of the proto- plasm down one side of the ‘* cell,’? and back upon the other, continues in an uninterrupted rotation, or cyc/os’s. There are many nuclei in an internode of nitella, and they move also. 21. Test for protoplasm.—If we treat the plant with a solution of iodine we get the same reaction as in the case of spirogyra and mucor. The proto- we becomes yellowish brown. Fig. 8. Portion of plant nitella. 22. Protoplasm in one of the higher plants.—WWe now wish to examine, and test for, protoplasm in one of the higher plants. 10 PHYSIOLOGY. Young or growing parts of any one of various plants—the petioles of young leaves, or young stems of growing plants—are suitable for study. Tissue from the pith of corn (Zea mays) in young shoots just back of the growing point or quite near the joints of older but growing corn stalks fur- BBG: nishes excellent material. Cyclosis in nitella. If we should place part of the stem of this plant under the microscope we should find it too opaque for observation of the interior of the cells. ‘This is one striking difference which we note as we pass from the low and simple plants to the higher and more complex ones ; not only in general is there an increase of size, but also in general an increase in thickness of the parts. The cells, instead of lying end to end or side by side, are massed together so that the parts are quite opaque. In order to study the interior of the plant we have selected it must be cut into such thin layers that the light will pass readily through them. For this purpose we section the tissue selected by making with a razor,.or other very sharp knife, very thin slices of it. These are mounted in water in the usual way for microscopic study. In his_section_we i e polygonal in form, This is brought about by mutual pressure of all the cells. The granular protoplasm is seen to form a layer just inside the wall, which is connected with the nuclear layer by radiating strands of the same substance. The nucleus does not alv, e at middle of the cell, but often is near one ve da with alcohol and treat with iodine the characteristic yellowish- brown color appears. So we conclude here also that this sub- stance is identical with the living matter in the other very differ- ent plants which we have studied. 23. Movement of protoplasm in the higher plants.—Cer- tain parts of the higher plants are suitable objects for the study of the so-called streaming movement of protoplasm, especially the delicate hairs, or thread-like outgrowths, such as the silk of PROTOPLASM. II corn, or the delicate staminal hairs of some plants, like those of the common spiderwort, tradescantia, or of the tradescantias grown for ornament in greenhouses and plant conservatories. Sometimes even in the living cells of the corn plant which we have just studied, slow streaming or gliding movements of the granules are seen along the strands of protoplasm where they radiate from the nucleus. 24. Movement of protoplasm in cells of the staminal hair of “« spiderwort.’’—A cell of one of these hairs from a stamen of a tradescantia grown in glass houses is shown in fig. 10. The Fig. 10. Cell from stamen hair of tradescantia showing movement of the protoplasm, nucleus is quite prominent, and its location in the cell varies con- siderably in different cells and at different times. There is a layer of protoplasm all around the nucleus, and from this the strands of protoplasm extend outward to the wall layer. The large spaces between the strands are, as we have found in other cases, filled with the cell-sap. An entire stamen, or a portion of the stamen, having several hairs attached, should be carefully mounted in water. Care should be taken that the room be not cold, and if the weather is cold the water in which the preparation is mounted should be warm. With these precautions there should be little diffi- culty in observing the streaming movement. The movement is detected by observing the gliding of the granules. These move down one of the strands from the nucleus along the wall layer, and in towards the nucleus in another strand. After a little the direction of the movement in any one portion may be reversed. 25. Cold retards the movement.—While the protoplasm is moving, if we rest the glass slip on a block of ice, the move- ment will become slower, or will cease altogether. Then if we 12 PHYSIOLOGY. warm the slip gently, the movement becomes normal again. We may now apply here the usual tests for protoplasm. ‘The result is the same as in the former cases, 26. Protoplasm occurs in the living parts of all plants.— In these plants representing such widely different groups, we find a substance which is essentially alike in all. Though its arrange- ment in the cell or plant body may differ in the different plants or in different parts of the same plant, its general appearance is the same. Though in the different plants it presents, while alive, varying phenomena, as regards mobility, yet when killed and subjected to well known reagents the reaction is in general identical. Knowing by the experience of various investigators that protoplasm exhibits these reactions under given conditions, we have demonstrated to our satisfaction that we have seen proto- plasm in the simple alga, spirogyra, in the common mould, mucor, in the more complex stonewort, nitella, and in the cells of tissues of the highest plants. 27. By this simple process of induction of these facts concerning this substance in these different plants, we have learned an im- portant method in science study. Though these facts and deduc- tions are well known, the repetition of the methods by which they are obtained on the part of each student helps to form habits of scientific carefulness and patience, and trains the mind to logical processes in the search for knowledge. 28. While we have by no means exhausted the study of protoplasm, we can, from this study, draw certain conclusions as to its occurrence and appearance in plants. Protoplasm is found in the living and growing parts of all plants, It is a semi-fluid, or slimy, granular, substance ; in some plants, or parts of plants, the protoplasm exhibits a streaming or gliding movement of the gran- ules. Itis irritable. In the living condition it resists more or less for some time the absorption of certain coloring substances. The water may be with- drawn by glycerine. The protoplasm may be killed by alcohol. When treated with iodine it becomes a yellowish-brown color, CHAPTER Il. ABSORPTION, DIFFUSION, OSMOSE. 29. We may next endeavor to learn how plants absorb water or nutrient substances in solution. There are several very instructive experiments, which can be easily performed, and here again some of the lower plants will be found useful. 30. Osmose in spirogyra.—Let us mount a few threads of this plant in water for microscopic examination, and then draw under the cover glass a five per cent solution of ordinary table salt (NaCl) with the aid of filter paper. We shall soon see that the result is similar to that which was obtained when glycer- ine was used to extract the water from the cell-sap, and to con- tract the protoplasmic membrane from the cell wall. But the process goes on evenly and the plant is not injured. The proto- plasmic layer contracts slowly from the cell wall, and the move- ment of the membrane can be watched by looking through the microscope. ‘The membrane contracts in such a way that all the contents of the cell are finally collected into a rounded or oval mass which occupies the center of the cell. If we now add fresh water and draw off the salt solution, we can see the protoplasmic membrane expand again, or move out in all directions, and occupy its former position against the inner surface of the cell wall. This would indicate that there is some pressure from within while this process of absorption is going on, which causes the membrane to move out against the cell wall. The salt solution draws water from the cell-sap. There is thus a tendency to form a vacuum in the cell, and the pressure on the outside of the protoplasmic membrane causes it 2 13 14 PHYSIOLOGY. to move toward the center of the cell. When the salt solution is removed and the thread of spirogyra is again bathed with water, the movement of the water is award in the cell. This would suggest that there is some substance dissolved in the cell-sap which does not readily filter out through the membrane, but draws on the water outside. It is this which produces the pressure from within and crowds the mem- brane out against the cell wall again. Fig. 13. Spirogyra from salt solution into water. Fig. c1. Spirogyra before placing in salt solu- tion. Spirogyra in 5% salt solution. Fig. 12. 81. Turgescence.—Were it not for the resistance which the cell wall offers to the pressure from within, the delicate proto- ABSORPTION, DIFFUSION, OSMOSE. 15 plasmic membrane would stretch to such an extent that it would be ruptured, and the protoplasm therefore would be killed. If % we examine the cells at the ends of the threads of spirogyra we shall see in most cases that the cell wall at the free end is arched _ outward. This is brought about by the press- Before treatment with salt ~=->—~ solution. = eo Go ee ure from within ~* Fig. 15. upon the proto- After treatment with plasmic mem- salt solution. brane which itself presses against ~*&y the cell wall, and causes it to Fig. 16. arch outward This is beauti- From salt solution placed in water. Figs. 14-16.—Osmosis in threads of mucor. fully shown in the case of threads which are recently broken. The cell wall is therefore e/astc; it yields to a certain extent to the pressure from within, but a point is soon reached beyond which it will not stretch, and an equilibrium then exists between the pressure from within on the protoplasmic membrane, and the pressure from without by the elastic cell wall. This state of equilibrium in a cell is /urges- cence, or such a cell is said to be /urgescent, or turgid. 32. Experiment with beet in salt and sugar solutions.— We may now test the effect of a five per cent salt solution on a portion of the tissues of a beet or carrot. Let us cut several slices of equal size and about 5mm in thickness. Immerse a few slices in water, a few in a five per cent salt solution and a few in a strong sugar solution. It should be first noted that all the slices are quite rigid when an attempt is made to bend them between the fingers. In the course of one or two hours or less, 16 PHYSIOLOGY. if we examine the slices we shall find that those in water remain, as at first, quite rigid, while those in the salt and sugar solutions are more or less flaccid or limp, and readily bend by pres- Fig. 17. Fig. 18. Fig. 19. Before treatment with salt After treatment with salt From saltsolution into water solution. solution. again. Figs. 17-19.—Osmosis in cells of Indian corn. sure between the fingers, the specimens in the salt solution, perhaps, being more flaccid than those in the sugar solution. The salt solution, we judge after our experiment with spirogyra, Fig. 20. Fig, 21. Fig. 22. Rigid condition of fresh beet Limp condition after lying i igi i ‘ : section. i salt solution. ving in Rigid again after lying again in water. Figs. 20-22.—Turgor and osmosis in slices of beet. withdraws some of the water from the cell-sap, the cells thus losing their turgidity and the tissues becoming limp or flaccid from the loss of water. ABSORPTION, DIFFUSION, OSMOSE. 17 33. Let us now remove some of the slices of the beet from the sugar and salt solutions, wash them with water and then immerse them in fresh water. In the course of thirty minutes to one hour, if we examine them again, we find that they have regained, partly or completely, their rigidity. Here again we infer from the former experiment with spirogyra that the sub- stances in the cell-sap now draw water inward; that is, the diffusion current is inward through the cell walls and the proto- plasmic membrane, and the tissue becomes turgid again. 34. Osmose in the cells of the beet.—We should now make a section of the fresh tissue of a red colored beet for examination with the microscope, and treat this section with the salt solution. Here we can see that the effect of the salt solution is to draw water out of the cell, so that the protoplasmic mem- Fig. 23. Fig. 24. Fig. 25. Before treatment with salt After treatment with salt Later stage of the same. solution. solution. Figs. 23-25.—Cells from beet treated with salt solution to show osmosis and movement of the protoplasmic membrane. brane can be seen to move inward from the cell wall just as was observed in the case of spirogyra.* Now treating the section with water and removing the salt solution, the diffusion current is in the opposite direction, that is in- * We should note that the coloring matter of the beet resides in the cell- sap. It is in these colored cells that we can best see the movement take place, since the red color serves to differentiate well the moving mass from the cell wall. The protoplasmic membrane at several points usually clings tena- ciously so that at several places the membrane is arched strongly away from the cell wall as shown in fig. 24. While water is removed from the cell-sap, we note that the coloring matter does not escape through the protoplasmic membrane, 18 PHYSIOLOGY. ward through the protoplasmic membrane, so that the latter is pressed outward until it comes in contact with the cell wall again, which by its elasticity soon resists the pressure and the cells again become turgid. 85. The coloring matter in the cell-sap does not readily escape from the living protoplasm of the beet.—The red coloring matter, as seen in the sec- tion under the microscope, does not escape from the cell-sap through the pro- toplasmic membrane. When the slices are placed in water, the water is not colored thereby. The same is true when the slices are placed in the salt or sugar solutions. Although water is withdrawn from the cell-sap, this coloring substance as ey echt ar if it does it escapes slowly ene. after a consider- able time. Pee gaol 2 fot BAS 36. The er matter escapes tA fo worn, mar however, we heat the water containing a slice of beet up to a point which is sufficient to kill the protoplasm, the red coloring matter in the cell-sap filters out through the protoplasmic membrane and colors the water. If we heat a preparation made for study under the microscope up to the thermal death point we can see here that the red coloring matter escapes through the membrane into the water outside. This teaches that certain substances cannot readily filter through the living membrane of protoplasm, but that they can filter through when the protoplasm is dead. A very important condition, then, for the suc- cessful operation of some of the physical processes connected with absorption in plants is that the protoplasm should be in a living condition. 37. Osmose experiments with leaves.—We may next take the leaves of certain plants like the geranium, coleus or other plant, and place them in shallow vessels containing water, salt, and sugar solutions respectively. The leaves should be immersed, but the petioles should project out of the water or solutions. Seedlings of corn or beans, especially the latter, may also be placed in these solutions, so that the leafy ends are immersed. After one or two hours an examination shows that the specimens in the water are still turgid. But if we lift a leaf or a bean plant from the salt or sugar solution, we find that it is flaccid and limp. The blade, or lamina, of the leaf droops as if wilted, though it is still wet. The bean seedling also is flaccid, the succulent stem bending nearly double as the lower part of the stem is held upright. This loss of turgidity is brought about by the loss of water from the tissues, and judging from the experiments on spirogyra and the beet, we con- clude that the loss of turgidity is caused by the withdrawal of some of the water from the cell-sap by the strong salt solution. 38. Now if we wash carefully these leaves and seedlings, which have been in the salt and sugar solutions, with water, and then immerse them in fresh water for a few hours, they will regain their turgidity. Here again we are led to infer that the diffusion current is now inward through the protoplasmic membranes of all the living cells of the leaf, and that the resulting turgidity of the individual cells causes the turgidity of the leaf or stem. ABSORPTION, DIFFUSION, OSMOSE. 19 39. Absorption by root hairs.—If we examine seedlings, which have been grown in a germinator or in the folds of paper or cloths so that the roots will be free from particles of soil, we see near the growing point of the roots that the surface is covered with numerous slender, delicate, thread- like bodies, the root hairs. Let us place a por- tion of a small root containing some of these root hairs in water on a glass slip, and prepare it for examination with the microscope. We see that each thread, or root hair, is a continuous tube, or in other words it is a single cell which has become very much elongated. The proto- plasmic membrane lines the wall, and strands of b protoplasm extend across at irregular intervals, the Me interspaces being occupied by the cell-sap. : We should now draw under the cover glass some of the five per cent salt solution. The protoplasmic membrane moves away from the cell wall at certain points, showing that plasmolysis is taking place, that is, the diffusion current is out- ward so that the cell-sap loses some of its water, and the pressure from the outside moves the membrane inward. We should not allow the salt solution to work on the root hairslong. It should be very soon removed by drawing in fresh water before the protoplasmic membrane has been broken at intervals, as is i dh Mt fe ar ia eae Fig. 27. eo eS ee ee eA Pee ere apt to be the case by the strong diffusion current and the consequent Root hair of corn strong pressure from ; : Fig. oe: ; before: cand after : Seedling of radish, showing root treatment with 5% without. The membrane hairs. salt solution. of protoplasm now moves 3 outward as the diffusion current is inward, and soon regains its former position next the inner side of the cell wall. The root hairs then, like other parts of the plant which we have 20 PHYSIOLOGY. investigated, have the power of taking up water under press- ure. 40. Cell-sap a solution of certain substances. —From these experiments we are led to believe that certain substances reside in the cell-sap of plants, which behave very much like the salt solution when separated from water by the protoplasmic membrane. Let us attempt to interpret these phenomena by recourse to diffusion experiments, where an animal membrane separates two liquids of difterent concentration. 41. Diffusion through an animal membrane.—For this experiment we may use a thistle tube, across the larger end of which should be stretched and tied tightly a piece of a bladder membrane, A strong sugar solution (three parts sugar to one part water) is now placed in the tube so that the bulb is filled and the liquid extends part way in the neck of the tube. This is im- mersed in water within a wide-mouth bottle, the neck of the tube being sup- ported in a perforated cork in such a way that the sugar solution in the tube is on a level with the water in the bottle or jar. In a short while the liquid begins to rise in the thistle tube, in the course of several hours having risen several centimeters. The diffusion current is thus stronger through the mem- brane in the direction of the sugar solution, so that this gains more water than it loses. 42. We have here two liquids separated by an animal membrane, water on the one hand which diffuses readily through the membrane, while on the other is a solution of sugar which diffuses through the animal membrane with diff- culty. The water, therefore, not containing any solvent, according to a general law which has been found to obtain in such cases, diffuses more readily through the membrane into the sugar solution, which thus increases in volume, and also becomes more dilute. The bladder membrane is what is sometimes called a diffusion membrane, since the diffusion currents travel through it. 43. In this experiment then the bulk of the sugar solution is increased, and the liquid rises in the tube by this pressure above the level of the water in the jar outside of the thistle tube. The diffusion of liquids through a membrane is osmosis. 44, Importance of these physical processes in plants.—Now if we recur to our experiment with spirogyra we find that exactly the same processes take place. The protoplasmic membrane is the diffusion membrane, through which the diffusion takes place. The salt solution which is first used to bathe the threads of the plant is a stronger solution than that of the cell-sap within the cell. Water therefore is drawn out of the cell-sap, but the substances in solution in the cell-sap do not readily move out. As the bulk of the cell-sap diminishes the pressure from the outside pushes the protoplasmic membrane away from the wall. Now when we remove the salt solution and bathe ABSORPTION, DIFFUSION, OSMOSE. 21 the thread with water again, the cell-sap, being a solution of certain sub- stances, diffuses with more difficulty than the water, and the diffusion current is inward, while the protoplasmic membrane moves out against the cell wall, and turgidity again results. Also in the experiments with salt and sugar solu- tions on the leaves of geranium, on the leaves and stems of the seedlings, on the tissues and cells of the beet and carrot, and on the root hairs of the seed- lings, the same processes take place. These experiments not only teach us that in the protoplasmic membrane, the cell wall, and the cell-sap of plants do we have structures which are capable of performing these physical processes, but they also show that these processes are of the utmost importance to the plant ; not only in giving the plant the power to take up solutions of nutriment from the soil, but they serve also other pur- poses, as we shall see later. CHAPTER III. ABSORPTION OF LIQUID NUTRIMENT. 45. We are now ready tq inquire how plants obtain food from the soil or water. Chemical analysis shows that certain mineral substances are common constituents of plants. By growing plants in different solutions of these various substances it has been possible to determine what ones are necessary constitu- ents of plant food. While the proportion of the mineral ele- ments which enter into the composition of plant food may vary considerably within certain limits, the concentration of the solu- tions should not exceed certain limits. A very useful] solution is one recommended by Sachs, and is as follows : 46. Formula for solution of nutrient materials: Water ca iniawctaunaceiagad qayao am bawlte axerinie 1000 cc, PotassiMMi DIALS od. 2.408 vio oemacarmnnmarnid en 0.5 gr. SOGIUM CHIGMAC 50.4 5:3. saat cooatm crnauday sony ee ee O.5 *f Calciunsulphatéss <2. 04 svinsdnteeegseees sae O35 Magiiésium Sulphate: ..scs 2.2200 2sneeeeoes 0.5 Calciuit PHOSPNALC sei jae ee Rdjermeavecitic vayesscuen O.5. ** The calcium phosphate is only partly soluble. The solution which is not in use should be kept in a dark cool place to prevent the growth of minute alge. 47. Several different plants are useful for experiments in water cultures, as peas, corn, beans, buckwheat, etc. The seeds of these plants may be germi- nated, after soaking them for several hours in warm water, by placing them between the folds of wet paper on shallow trays, or in the folds of wet cloth. The seeds should not be kept immersed in water after they have imbibed enough to thoroughly soak and swell them. At the same time that the seeds are placed in damp paper or cloth for germination, one lot of the soaked seeds 22 ABSORPTION NUTRIMENT., 23 should be planted in good soil and kept under the same temperature condi- tions, for control. When ghe plants have germinated one series should be grown in distilled water, which possesses no plant food; another in the nutrient solution, and still another in the nutrient solution to which has been added a few drops of a solution of iron chloride or ferrous sulphate. There would then be four series of cultures which should be carried out with the same kind of seed in each series so that the comparisons can be made on the same species under the different conditions, The series should be numbered and recorded as follows : No. 1, soil. No. 2, distilled water. No. 3, nutrient solution. No, 4, nutrient solution with a few drops of iron solution added. 48. Small jars or wide-mouth bottles, or crockery jars, can be used for the water cultures, and the cultures are set up as follows: A cork which will just fit in the mouth of the bottle, or which can be supported by pins, is perforated so that there is room to insert the seedling, with the root projecting below into the liquid. The seed can be fastened in position by insert- ing a pin through one side, if it is a large one, or in the case of small seeds a cloth of a coarse mesh can be tied over the mouth of the bottle instead of using the cork. After properly set- ting up the experiments the cultures should be arranged in a suitable place, and observed from time to time during several weeks, In order to obtain more satisfactory results several dupli- cate series should be set up to guard against the error which might arise from variation in indi- vidual plants and from accident. Where there are several students in a class, a single series set up by several will act as checks upon one another. If glass jars are used for the liquid Fig. 28. cultures they should be wrapped with black Culture cylinder to show position of ‘ corn seedling (Hansen). paper or cloth to exclude the light from the liquid, otherwise numerous minute algze are apt to grow and interfere with the experiment. Or the jars may be sunk in pots of earth to serve the same purpose. Ifcrockery jars are used they will not need covering. 49. For some time all the plants grow equally well, until the nutriment stored in the seed is exhausted. The numbers 1, 3 and 4, in soil and nutri- ent solutions, should outstrip number 2, the plants in the distilled water, No. 4 in the nutrient solution with iron, having a perfect food, compares favor- ably with the plants in the soil. 24 PHYSIOLOGY. 50. Plants take liquid food from the soil.—From these ex- periments then we judge that such plants take up the food they receive from the soil in the form of a liquid, the elements being in solution in water. (See note at close of chapter. ) If we recur now to the experiments which were performed with the salt solution in producing plasmolysis in the cells of spirogyra, in the cells of the beet or corn, and in the root hairs of the corn and bean seedlings, and the way in which these cells become tur- gid again when the salt solution is removed and they are again bathed with water, we shall have an explanation of the way in which plants take up nutrient solutions of food material through their roots. 51. How food solutions are carried into the plant.—We can Fig. 29. Section of corn root, showing rhizoids formed from elongated epidermal cells. see how the root hairs are able to take up solutions of plant food, and we must next turn our attention to the way in which these ABSORPTION NUTRIMENT. 25 solutions are carried farther into the plant. We should make a section across the root of a seedling in the region of the root hairs and examine it with the aid of a microscope. We here see that the root hairs are formed by the elongation of certain of the surface cells of the root. These cells elongate perpendicularly to the root, and become 3mm to 6mm long. ‘They are flexuous or irregular in outline and cylindrical, as shown in fig. 29. The end of the hair next the root fits in between the adjacent superfi- cial cells of the root and joins closely to the next deeper layer of cells. In studying the section of the young root we see that the root is made up of cells which lie closely side by side, each with its wall, its protoplasm and cell-sap, the protoplasmic membrane lying on the inside of each cell wall. 52. In the absorption of the watery solutions of plant food by the roct hairs, the cell-sap, being a more concentrated solution, gains some of the former, since the liquid of less concentration flows through the protoplasmic membrane into the more concentrated cell-sap, increasing the bulk of the lat- ter. This makes the root hairs turgid, and at the same time dilutes the cell- sap so that the concentration is not so great. The cells of the root lying in- side and close to the base of the root hairs have a cell-sap which is now more concentrated than the diluted cell-sap of the hairs, and consequently gain some of the food solutions from the latter, which tends to lessen the content of the root hairs and also to increase the concentration of the cell-sap of the same. This makes it possible for the root hairs to draw on the soil for more of the food solutions, and thus, by a variation in the concentration of the sub- stances in solution in the cell-sap of the different cells, the food solutions are carried along until they reach the vascular bundles, through which the solu- tions are carried to distant parts of the plant. Some believe that there is a rhythmic action of the elastic cell walls in these cells between the root hairs and the vascular bundles. This occurs in such a way that, after the cell becomes turgid, it contracts, thus reducing the size of the cell and forcing some of the food solutions into the adjacent cells, when by absorption of more food solu- tions, or water, the cell increases in turgidity again. This rhythmic action of the cells, if it does take place, would act as a pump to force the solutions along, and would form one of the causes of root pressure. 53.° How the root hairs get the watery solutions from the soil.—If we examine the root hairs of a number of seedlings which are growing in the soil under normal conditions, we shall see that a large quantity of soil readily clings to the roots. We should note also that unless the soil has been recently watered there is no free water in it ; the soil is only moist, We are curious 26 PHYSIOLOGY. to know how plants can obtain water from soil which is not wet. If we at- tempt to wash off the soil from the roots, being careful not to break away the B 2 Fig. 30. Root hairs of corn seedling with soil particles adhering closely. root hairs, we find that small particles cling so tenaciously to the root hairs that they are not removed. Placing a few such root hairs under the microscope it appears as if here and there the root hairs were glued to the minute soil particles. 54, If now we take some of the soil which is only moist, weigh it, and then permit it to become quite dry on exposure to dry air, and weigh again, we find that it loses weight in drying. Moisture has been given oft. This moisture, it has been found, forms an exceedingly thin film on the sur- face of the minute soil particles. Where these soil particles lie closely to- gether, as they usually do when massed together in the pot or elsewhere, this thin film of moisture is continuous from the surface of one particle to that of an- other. Thus the soil particles which are so closely attached to the root hairs connect the surface of the root hairs with this film of moisture. As the cell- sap of the root hairs draws on the moisture film with which they are in con- tact, the tension of this film is sufficient to draw moisture from distant parti- cles. Jn this way the roots are supplied with water in soil which is only moist. 55. Plants cannot remove all the moisture from the soil,—If we now take a potted plant, or a pot containing a number of seedlings, place it in a moder- ately dry room, and do not add water to the soil we find in a few days that the plant is willing. The soil if examined will appear quite dry to the sense of touch. Let us weigh some of this soil, then dry it by artificial ABSORPTION NUTRIMNENT. 27 heat, and weigh again. It has lost in weight. This has been brought about by driving off the moisture which still remained in the soil after the plant began to wilt. This teaches that while plants can obtain water from soil which is only moist or which is even rather dry, they are not able to withdraw all the moisture from the soil. 56. Acidity of root hairs.—If we take a seedling which has been grown in a germinator, or in the folds of cloths or paper, so that the roots are free from the soil, and touch the moist root hairs to blue litmus paper, the paper becomes red in color where the root hairs have come in contact. This is the reaction for the presence of an acid salt, and indicates that the root hairs ex- crete certain acid substances. This acid property of the root hairs serves a very important function in the preparation of certain of the elements of plant food in the soil. Certain of the chemical compounds of potash, phosphoric acid, etc., become deposited on the soil particles, and are not soluble in water. The acid of the root hairs dissolves some of these compounds where the particles of soil are in close contact with them, and the solutions can then be taken up by the roots. 57. This corrosive action of the roots can be shown by the well-known experiment of growing a plant on a marble plate which is covered by soil. After a few weeks, if the soil be washed from the marble where the roots have been in close contact, there will be an outline of this part of the root system. Several different acid substances are excreted from the roots of plants which have been found to redden blue litmus paper by contact. Experiments by Czapek show, however, that the carbonic acid excreted by the roots has the power of directly bringing about these corrosion phenomena, ‘The acid salts are the substances which. are most actively concerned in reddening the blue litmus paper. They do not directly aid in the corrosion phenomena, In the soil, however, where these compounds of potash, phosphoric acid, etc., are which are not soluble in water, the acid salt (primary acid potassium phos- phate) which is most actively concerned in reddening the blue litmus paper may act indirectly on these mineral substances, making them available for plant food. This salt soon unites with certain chlorides in the soil, making among other things small quantities of hydrochloric acid. NoTe.—It should be understood that food substances in solution, during absorption, diffuse through the protoplasmic membrane independently of each ‘other and also independently of the rate of movement of the water from the soil into the root hairs and cells of the root, CHAPTER IV. TURGESCENCE. 58. Turgidity of plant parts.—As we have seen by the experiments on the leaves, turgescence of the cells is one of the conditions which enables the leaves to stand out from the stem, and the lamina of the leaves to remain in an expanded position, so that they are better exposed to the light, and to the currents of air. Were it not for this turgidity the leaves would hang down close against the stem. 59. Restoration of turgidity in shoots.—If we cut off a living stem of geranium, coleus, tomato, or ‘ balsam,’’ and allow the leaves to partly wilt so that the shoot loses its turgidity, it is possible for this shoot to regain turgidity. The end may be freshly cut again, placed ina vessel of water, covered with a bell p jar and kept ina room where the temperature WY is suitable for the growth of the plant. The <7 shoot will usually become turgid again from the water which is absorbed through the cut end of the stem and is carried into the leaves where the individual cells become turgid, and the leaves areagain expanded. Such shoots, and the excised leaves also, may often be made turgid again by simply immersing them in water, as one of the experiments with the salt solution would teach. Fig. 31. Restoration ~ turgidity 60. Turgidily may be restored more certainly and Sachs). ‘ is F ai quickly in a partially wilted shoot in another way, The cut end of the shoot may be inserted in a U tube as shown in fig. 31, the end of the tube around the stem of the plant being made air-tight. The arm 28 TURGESCENCE. 29 of the tube in which the stem is inserted is filled with water and the water is allowed to partly fill the other arm. Into this other arm is then poured mercury. The greater weight of the mercury causes such pressure upon the water that it is pushed into the stem, where it passes up through the vessels in the stems and leaves, and is brought more quickly and surely to the cells which contain the protoplasm and cell-sap, so that turgidity is more quickly and certainly attained. 61. Tissue tensions.—Besides the turgescence of the cells of the leaves and shoots there are certain tissue tensions without which certain tender and succulent shoots, etc., would be limp, and would droop. There are a number of plants usually accessi- ble, some at one season and some at others, which may be used to illustrate tissue tension. 62. Longitudinal tissue tension. —For this in early summer one may use the young and succulent shoots of the elder (sambucus); or the petioles of rhubarb during the summer and early autumn; or the petioles of richardia. Petioles of cala- dium are excellent for this purpose, and these may be had at almost any season of the year from the greenhouses, and are thus especially advantageous for work during late autumn or winter. The tension is so strong that a portion of such a petiole 1o-15¢m long is ample to demonstrate it. As we grasp the lower end of the petiole of a caladium, or rhubarb leaf, we observe how rigid it is, and how well it supports the heavy expanded lamina of the leaf. 63. The ends of a portion of such a petiole or other object which may be used are cut off squarely. With a knife a strip from 2-3mm in thickness is removed from one side the full length of the object. This strip we now find is shorter than the larger part from which it was removed. The outer tissue then exerts a tension upon the petiole which tends to shorten it. Let us remove another strip lying next this one, and another, and so on until the outer tissues remain only upon one side. The object will now bend toward that side. Now remove this strip and compare the length of the strips re- moved with the central portion. We find that they are much 30 PHYSIOLOGY. shorter now. In other words there is also a tension in the tissue of the central portion of the petiole, the direction of which is opposite to that of the superficial tissue. The parts of the petiole now are not rigid, and they easily bend. These two longitudi- nal tissue tensions acting in opposition to each other therefore give rigidity to the succulent shoot. It is only when the indi- vidual cells of such shoots or petioles are turgid that these tissue tensions in succulent shoots manifest themselves or are promi- nent. 64. To demonstrate the efficiency of this tension in giving support, let us take a long petiole of caladium or of rhubarb. Hold it by one end in a hori- zontal position. It is firm and rigid, and does not droop, or but little. Re- move all of the outer portion of the tissues, as described above, leaving only the central portion. Now attempt to hold it in a horizontal position by one end. It is flabby and droops downward because the longitudinal tension is removed, 65. Transverse tissue tension.—To illustrate this one may take a willow shoot 3-s5cm in diameter and saw off sections about zcm long. Cut through the bark on one side and peel it off in a single strip. Now attempt to replace it. The bark will not quite cover the wood again, since the ends will not meet. It must then have been held in transverse tension by the woody part of the shoot. CHAPTER V. ROOT PRESSURE. 66. It is a very common thing to note, when certain shrubs or vines are pruned in the spring, the exudation of a watery fluid from the cut surfaces. In the case of the grape vine this has been known to continue for a number of days, and in some cases the amount of liquid, called ‘‘sap,’’ which escapes is con- siderable. In many cases it is directly traceable to the activity of the roots, or root hairs, in the absorption of water from the soil. For this reason the term roof pressure is used to denote the force exerted in supplying the water. from the soil. 67. Root pressure may be measured.—It is possible to measure not only the amount of water which the roots will raise in a given time, but also to measure the force exerted by the roots during root pressure. It has been found that root pressure in the case of the nettle is sufficient to hold a column of water about 4.5 meters(15 ft.) high(Vines), while the root pressure of the vine (Hales, 1721) will hold a column of water about 10 meters (36.5 ft.) high, and the birch (Betula lutea) (Clark, 1873) hasa root pressure sufficient to hold a column of water about 25 meters (84.7 ft.) high. 68. Experiment to demonstrate root pressure.—By a very simple method this power of root pressure may be demonstrated. During the summer season plants in the open may be used if it is preferred, but plants grown in pots are also very serviceable, and one may use a potted begonia or balsam, the latter being especially useful. The plants are usually convenient to obtain from the greenhouses, to illustrate this phenomenon. The stem is cut off rather close to the soil and a4 long glass tube is attached to the cut end of the stem, still con- nected with the roots, by tne use of rubber tubing as shown in figure 32, anda 31 32 PHYSIOLOGY. very small quantity of water may be poured in to moisten the cut end of the stem. In a few minutes the water begins to rise in the glass tube. In some f cases it rises quite rapidly, so that the column of water can readily be seen to extend higher and higher up in the tube when observed at quite short intervals, The height of this column of water is a measure of the force exerted by the roots. The pressure force of the roots may be measured also by deter- mining the height to which it will raise a column of mercury, 69. In either case where the experiment is con- tinued for several days it is noticed that the column of water or of mercury rises and falls at different times during the same day, that is, the column stands at varying heights; or in other words the root pressure varies during the day. With some plants it has been found that the pressure is greatest at © certain times of the day, or at certain seasons of the Fig. 32... Year. Such variation of root pressure exhibits what ae es termed a periodicity, and in the case of some ure (Deter). plants there is a daily periodicity; while in others there is in addition an annual periodicity. With the grape vine the root pressure is greatest in the forenoon, and decreases from 12-6 p.M., while with the sunflower it is greatest before io A.M., when it begins to decrease. Temperature of the soil is one of the most important external conditions affecting the activity of root pressure. CHAPTER VI. TRANSPIRATION. 70. We should now inquire if all the water which is taken up in excess of that which actually suffices for turgidity is used in the elaboration of new materials of construction. We notice whena leaf or shoot is cut away from a plant, unless it is kept in quite amoist condition, or in a damp, cool place, that it becomes flac- cid, and droops. It wilts, as we say. The leaves and shoot lose their turgidity. This fact suggests that there has been a loss of water from the shoot or leaf. It can be readily seen that this loss is not in the form of drops of water which issue from the cut end of the shoot or petiole. What then becomes of the water in the cut leaf or shoot ? 71. Loss of water from excised leaves.—Let us take a hand- ful of fresh, green, rather succulent leaves, which are free from water on the surface, and place them under a glass bell jar, which is tightly closed below but which contains no water. Now place this in a brightly lighted window, or in sunlight. In the course of fifteen to thirty minutes we notice that a thin film of moisture is accumulating on the inner surface of the glass jar. After an hour or more the moisture has accumulated so that it appears in the form of small drops of condensed water. We should set up at the same time a bell jar in exactly the same way but which contains no leaves. In. this jar there is no con- densed moisture on the inner surface. We thus are justified in concluding that the moisture in the former jar comes from the leaves. Since there is no visible water on the surfaces of the leaves, or at the cut ends, before it may have condensed there, 33 34 PHYSIOLOGY. we infer that the water escapes from the leaves in the form of walter vapor, and that this water vapor, when it comes in contact with the surface of the cold glass, condenses and forms the mois- ture film, and later the drops of water. The leaves of these cut shoots therefore lose water in the form of water vapor, and thus a loss of turgidity results. a 72. Loss of water from growing plants.—Suppose we now take a small and actively growing plant in a pot, and cover the pot and the soil with a sheet of rubber cloth which fits tightly around the stem of the plant (or the pot and soil may be enclosed in a hermetically sealed vessel) so that the moisture from the soil cannot escape. Then place a bell jar over the plant, and set in a brightly lighted place, at a temperature suitable for growth. In the course of a few minutes on a dry day a moisture film forms on the inner surface of the glass, just as it did in the case of the glass jar containing the cut shoots and leaves. Later the mois- ture has condensed so that it is in the form of drops. If we have the same leaf surface here as we had with the cut shoots, we shall probably find that a larger amount of water accumulates on the surface of the jar from the plant that is still attached to its roots. 73. Water escapes from the surfaces of living leaves in the form of water vapor.—This living plant then has lost water, which also escapes in the form of water vapor. Since here there are no cut places on the shoots or leaves, we infer that Ke loss of water vapor takes place from the surfaces of the leaves and from the shoots. It is also to be noted that, while this plant is losing water from the surfaces of the leaves, it does not wilt or lose its turgidity. The roots by their activity and pressure sup- ply water to take the place of that which is given off in the form of water vapor. ‘This loss of water in the form of water vapor by plants is ¢ranspiration. 74, Experiment to compare loss of water in a dry and a humid atmosphere.—We should now compare the escape of water from the leaves of a plant covered by a bell jar, as in the last experiment, with that which takes place when the plant is TRANSPIRATION. 35 exposed in a normal way in the air of the room or in the open. To do this we should select two plants of the same kind growing in pots, and of approximately the same leafsurface. The potted plants are placed one each on the arms ofa scale. One of the plants is covered in this position with a bell jar. With weights placed on the pan of the other arm the two sides are balanced. In the course of an hour, if the air of the room is dry, moisture has probably accumulated on the inner surface of the glass jar which is used to cover one of the plants. This indicates that there has here been a loss of water. But there is no escape of water vapor into the surrounding air so that the weight on this arm is practically the same as at the beginning of the experiment. We see, however, that the other arm of the balance has risen. We infer that this is the result of the loss of water vapor from the plant on thatarm. Now let us remove the bell jar from the other plant, and with a cloth wipe off all the moisture from the inner surface, and replace the jar over the plant. We note that the end of the scale which holds this plant is still lower than the other end. 75. The loss of water is greater in a dry than in a humid atmosphere.—This teaches us that while water vapor escaped from the plant under the bell jar, the air in this receiver soon became saturated with the moisture, and thus the farther escape of moisture from the leaves was checked. It also teaches us an- other very important fact, viz., that plants lose water more rapidly through their leaves in a dry air than in a humid or moist atmos- phere, We can now understand why it is that during the very hot and dry part of certain days plants often wilt, while at night- fall, when the atmosphere is more humid, they revive. They lose more water through their leaves during the dry part of the day, other things being equal, than at other times. 76. How transpiration takes place.—Since the water of transpiration passes off in the form of water vapor we are led to inquire if this process is simply evaporation of water through the surface of the leaves, or whether it is controlled to any appreci- able extent by any condition of the living plant. An experiment 36 PHYSIOLOGY. which is instructive in this respect we shall find in a comparison between the transpiration of water from the leaves of a cut shoot, allowed to lie unprotected in a dry room, and a similar cut shoot the leaves of which have been killed. 77. Almost any plant will answer for the experiment. For this purpose I have used the following method. Small branches of the locust (Robinia pseudacacia), of sweet clover (Melilotus alba), and of a heliopsis were selected. One set of the shoots was immersed for a moment in hot water near the boiling point to kill them. The other set was immersed for the same length of time in cold water, so that the surfaces of the leaves might be well wetted, and thus the two sets} of leaves at the beginning of the experiment would be similar, so far as the amount of water on their surfaces is con- cerned. All the shoots were then spread out on a table in a dry room, the leaves of the killed shoots being separated where they are inclined to cling together. Ina short while all the water has evaporated from the surface of the living leaves, while the leaves of the dead shoots are still wet on the sur- face. In six hours the leaves of the dead shoots from which the surface water had now evaporated were beginning to dry up, while the leaves of the living plants were only becoming flaccid. In twenty-four hours the leaves of the dead shoots were crisp and brittle, while those of the living shoots were only wilted. In twenty-four hours more the leaves of the sweet clover and of the heliopsis were still soft and flexible, showing that they still contained more water than the killed shoots which had been crisp for more than a day. 78. It must be then that during what is termed transpiration the living plant is capable of holding back the water to some extent, which in a dead plant would escape more rapidly by evaporation. It is also known that a body of water with a surface equal to that of a given leaf surface of a plant loses more water by evaporation during the same length of time than the plant loses by transpiration. 79. Structure of a leaf.—We are now led to inquire why it is that a living leaf loses water less rapidly than dead ones, and why less water escapes from a given leaf surface than from an equal surface of water. To understand this it will be necessary to examine the minute structure of a leaf. For this purpose we may select the leaf of an ivy, though many other leaves will answer equally well. From a portion of the leaf we should make very thin cross sections with a razor or other sharp instrument. These sections should be perpendicular to the surface of the leaf TRANSPIRATION. 37 and should be then mounted in water for microscopic examina. tion,* 80. Epidermis of the leaf.—In this section we see that the green part of the leaf is bordered on what are its upper and lower surfaces by a row of cells which possess no green color. The walls of the cells of each row have nearly par- allel sides, and the cross walls are per- pendicular. These cells form a single layer over both surfaces of the leaf and are termed the epidermis. Their walls are quite stout and the outer walls are cuttcularized. 81. Soft tissue of the leaf.—The cells which contain the green chloro- : phyll bodies are arranged in two dif- <0. es ore ferent ways. Those on the upper side sempuniaton btueen stomateand of the leaf are usually long and pris- leafs stoma closed. matic in form and lie closely parallel to each other. Because of this arrangement of these cells they are termed the palisade cells, and form what is called the falisade dayer, The other green cells, lying below, vary greatly in size in different plants and to some extent also in the saine plant. Here we notice that they are Fig. 35. Stoma open. Stoma closed. elongated, or oval, or Figs. 34, 35-—Section through stomata of ivy leaf. somewhat irregular in form. The most striking peculiarity, however, in their arrange- ment is that they are not usually packed closely together, but each cell touches the other adjacent cells only at certain points. This arrangement of these cells forms quite large spaces between them, the intercellular spaces. If we should examine such a section of a leaf before it is mounted in water we would see that the inter- * Demonstrations may be made with prepared sections of leaves, “we nl ! ye 38 PHYSIOLOGY. if Ay cellular spaces are not filled with water or cell-sap, but are, filled with air or some gas. Within the cells, on the other hand, we find the cell-sap and the protoplasm. © My 82, Stomata.—If we examine carefully the row of epidermal cells on the under surface of the leaf, we find here and there a peculiar arrangement of cells shown at figs. 33-35. This opening of VQ OS XK through the epidermal layer is a stoma. The cells which : immediately aT 8 @ 8 surround the openings are the guard Fig. 36. Portion of epidermis of ivy, showing irregular epidermal cells, stoma cells. The and guard cells. form of the guard cells can be better seen if we tear a leaf in such a way as to strip off a short piece of the lower epidermis, and mount this in water. The guard cells are nearly crescent shaped, and the stoma is elliptical in outline. The epidermal cells are very irregular in outline in thisview. We should also note that while the epidermal cells contain no chlorophyll, the guard cells do. 83. The living protoplasm retards the evaporation of water from the leaf.—If we now take into consideration a few facts which we have learned in a previous chapter, with reference to the physical propertics of the living cell, we shall be able to give a partial explanation of the comp.rative slowness with which the water escapes from the leaves. The inner surfaces of the cell walls are lined with the membrane of protoplasm, and within this is the cell- sap. These cells have become turgid by the absorption of the water which has passed up to them from the roots. While the protoplasmic membrane of the cells does not readily permit the water to filter through, yct it is saturated with water, and the clastic ccll wall with which it is in contact is also saturated. From the cell wall the water evaporates into the intercellular spaces. But the water is given up slowly through the protoplasmic mem- brane so that the water vapor cannot be viven off as rapidly from the cell walls as it could if the protoplasm were dead. The living protoplasmic TRANSPIRATION. 39 membrane then which is only slowly permeable to the water of the cell-sap is here a very important factor in checking the too rapid loss of water from the leaves. By an examination of our leaf section we sec that the intercellular spaces are all connected, and that the stomata, where they occur, open also into intercellular spaces. There is here an opportunity for the water vapor in the intercellular spaces to escape when the stomata arc open. 84. Action of the stomata.—Bcsides permitting the escape of the water vapor whcn the stomata are open they serve a very important office in regu- lating the amount of transpiration. During normal transpiration the stomata remain open, that is, when the amount of transpiration from the leaf is not in excess of the supply of water to the leaves. But when the transpiration from the leaves is in excess, as often happens, and the air becomes very dry, the stomata close and thus the rapid transpiration is checked. 85. Transpiration may be in excess of root pressure.—If the supply of water from the roots was always equal to that transpired from the leaves during hot, dry days the leaves would not become flaccid and droop. But during the hot and dry part of the day it often happens that the trans- piration is in excess of the amount of water supplied the plant by rout pressure. 86. Negative pressure.—This is not only indicated by the drooping of the leaves, but may be determined in another way. If the shoot of such a plant be cut underneath mercury, or underneath a strong solution of eosin, it will be found that some of the mercury or eosin, as the case may be, will be forcibly drawn up into the stem toward the roots. This is seen on quickly splitting the cut end of the stem. When plants in the open cannot be obtained in this condition, one may take a plant like a balsam plant from the greenhouse, or some other potted plant, knock it out of the pot, free the roots from the soil and allow to partly wilt. The stem may then be held under the eosin solution and cut. 87. Lifting power of transpiration.—Not only does transpiration go on quite independently of root pressure, as we have discovered from other experiments, but transpiration is capable of exerting a lifting power on the water in the plant. This may be demonstrated in the following way: Place the cut end of a leafy shoot in one end of a U tube and fit it water-tight. Partly Fig. 37. ; E Experiment to show fill this arm of the U tube with water, and add mercury lifting power of trans- to the other arm until it stands ata level in the two PiTaton- arms as in fig. 37. In a short time we note that the mercury is rising in the tube, 40 PHYSIOLOG Y. 88. Root pressure may exceed transpiration.—If we cover small actively growing plants, such as the pea, corn, wheat, bean, etc., with a bell jar, and place in the sunlight where the temperature is suitable for growth, in a few hours, if conditions are favorable, we shall see that there are drops of water standing out on the margins of the leaves. These drops of water have exuded through the ordinary stomata, or in other cases what are called water stomata, through the influence of root pressure. The plant being covered by the glass jar, the air soon becomes saturated with mois- b 8 Fig. 38. Estimation . Ge amount of ture and transpiration is checked. ern ke oe ain. Root pressure still goes on, how- water transpires from the leaf ever, and the result is shown in surface its movement in the tube . from a to 6 can be measured. the exuding drops. Root pressure (After Mangin.) is here in excess of transpiration. This phenomenon is often to be observed during the summer season in the case of low-growing plants. During the bright warm day transpiration equals, or may be in excess of, root pressure, and the leaves are consequently flaccid. As nightfall comes on the air becomes more moist, and the conditions of light are such also that transpiration is lessened. Root pressure, however, is still active because the soil isstillwarm. In these cases drops of water may be seen exuding from the margins ot | the leaves due to the excess ! of root pressure over trans- piration. Were it not for this provision for the escape of the excess of water raised by rect pressure, serious in- jury by lesions, as a result of the great pressure, might result. The plant is thus to some extent a self-regulatory : piece of apparatus so far as Fig. 39. root pressure and transpira- Guttation of tomato paae after connecting the stems by tion are concerned. means of rubber tubes with the hydrant. 89. Injuries caused by excessive root pressure.—Some varicties of to- matoes when grown in poorly lighted and poorly ventilated greenhouses suffer TRANSPIRATION. 4! serious injury through lesions of the tissues. This is brought about by the cells at certain parts becoming charged so full with water through the activity of root pressure and lessened transpiration, assisted also probably by an ac- cumulation of certain acids in the cell-sap which cannot be got rid of by transpiration. Under these conditions some of the cells here swell out forming extensive cushions, and the cell walls become so weakened that they burst. It is possible to imitate the excess of root pressure in the case of some plants by connecting the stems with a system of water pressure, when very quickly the drops of water will begin to exude from the margins of the leaves. 90. It should be stated that in reality there is no difference between trans- piration and evaporation, if we bear in mind that evaporation takes place more slowly from living plants than from dead ones, or from an equal surface of water. 91. The escape of water vapor is not the only function of the stomata. The exchange of gases takes place through them as we shall later see. A large number of experiments show that normally the stomata are open when the leaves are turgid. But when plants lose excessive quantities of water on dry and hot days, so that the leaves become flaccid, the guard cells automat- ically close the stomata to check the escape of water vapor. Some water escapes through the epidermis of many plants, though the cuticularized mem- brane of the epidermis largely prevents evaporation. In arid regions plants are usually provided with an epidermis of several layers of cells to more securely prevent evaporation there. In such cases the guard cells are often protected by being sunk deeply in the epidermal layer. 92. Demonstration of stomates and intercellular air spaces.—A good demonstration of the presence of stomates in leaves, as well as the presence and intercommunication of the intercellular spaces, can be made by blowing into the cut end of the petiole of the leaf of a calla lily, the lamina being immersed in water. The air is forced out through the stomata and rises as bubbles to the surface of the water. At the close of the experiment some of the air bubbles will still be in contact with the leaf surface at the opening of the stomata. The pressure of the water gradually forces this back into the leaf. Other plants will answer for the experiment, but some are more suitable than others. CHAPTER VII. PATH OF MOVEMENT OF LIQUIDS IN PLANTS. 93. In our study of root pressure and transpiration we have seen that large quantities of water or solutions move upward through the stems of plants. We are now led to inquire through what part of the stems the liquid passes in this upward movement, or in other words, what is the path of the ‘‘sap’’ as it rises in the stem. This we can readily see by the following trial. 94. Place the cut ends of leafy shoots in a solution of some of the red dyes.—We may cut off leafy shoots of various plants and insert the cut ends in a vessel of water to which have been added a few crystals of the dye known as fuchsin to make a deep red color (other red dyes may be used, but this one is especially good). If the study is made during the summer, the ‘‘ touch- me-not’’ (impatiens) will be found a very useful plant, or the garden-balsam, which may also be had in the winter from con- servatories. Almost any plant will do, however, but we should also select one like the corn plant (zea mays) if in the summer, or the petioles of a plant like caladium, which can be obtained from the conservatory. If seedlings of the castor-oil bean are at hand we may cut off some shoots which are 8-10 inches high, and place them in the solution also. 95. These solutions color the tracts in the stem and leaves through which they flow.—Aafter a few hours in the case of the impatiens, or the more tender plants, we can see through the stem that certain tracts are colored red by the solution, and after 12 to 24 hours there may be seen a red coloration of the 4? PATH OF MOVEMENT. 43 leaves of some of the plants used. After the shoots have been standing in the solution for a few hours, if we cut them at various places we will note that there are several points in the section where the tissues are colored red. In the impatiens perhaps from four to five, in the sunflower a larger number. In these plants the colored areas on a cross section of the stem are situated in a concentric ring which separates more or less com- pletely an outer ring of the stem from the cuntral portion. If we now split portions of the stem lengthwise we see that these colored areas continue throughout the length of the stem, in some cases even up to the leaves and into them. 96. If we cut across the stem of a corn plant which has been in the solution, we see that instead of the colored areas being in a concentric ring they are irregularly scattered, and on splitting Fig. 40. Broken corn stalk, showing fibro-vascular bundles. the stem we see here also that these colored areas extend for long distances through the stem. If we take a corn stem which is mature, or an old and dead one, cut around through the outer hard tissues, and then break the stem at this point, from the softer tissue long strings of tissue will pull out as shown in fig. 40. These strings of denser tissue correspond to the areas which are colored by the dye. They are in the form of minute bundles, and are called vascular bundles. 44 PHYSIOLOGY. 97. We thus see that instead of the liquids passing through the entire stem they are confined to definite courses. Now that we have discovered the path of the upward movement of water in the stem, we are curious to see what the structure of these definite portions of the stem is, 98. Structure of the fibro-vascular bundles.—We should now make quite thin cross sections, either free hand and mount in water for microscopic examination, or they may be made with a microtome and mounted in Canada balsam, and in this condition will answer for future study. To illustrate the structure of the bundle in one type we may take the stem of the castor-oil bean. On examining these cross sections we see that there are groups of cells which are denser than the ground tissue. These groups correspond to the colored arcas in the former expcriments, and are the vascular bundles a cui nea p panied Pig. 41. Xylem portion of bundle. Cambium portion of bundle. Bast portion of bundle. Section of vascular bundle of sunflower stem. cut across. These groups are somewhat oval in outline, with the pointed end directed toward the center of the stem. If we look at the section as a whole we see that there is a narrow continuous ring* of small cells * This ring and the bundles separate the stem into two regions, an outer one composed of large cells with thin walls, known as the cortical cells, or collectively the corfer. The inner portion, corresponding to what is called the pith, is made up of the same kind of cells and is called the medulla, or pith. When the cells of the cortex, as well as of the pith, remain thin walled the tissue is called parenchyma. Parenchyma belongs to the group of tissues called fundamental. PATH OF MOVEMENT. 45 situated at the same distance from the center of the stem as the middle part of the bundles, and that it divides the bundles into two groups of cells. 99. Woody portion of the bundle.—In that portion of the bundle on the inside of the ring, i.e., toward the ‘‘ pith,” we note large, circular, or angu- lar cavities. The walls of these cells are quite thick and woody. They are therefore called wood cells, and because they are continuous with cells above and below them in the stem in such a way that long tubes are formed, they are called woody vessels. Mixed in with these are smaller cells, some of which also have thick walls and are wood cells. Some of these cells may have thin walls. This is the case with all when they are young, and they are then classed with the fundamental tissue or soft tissue (parenchyma). This part of the bundle, since it contains woody vessels and fibres, is the wood portion of the bundle, or technically the xylem. 100. Bast portion of the bundle.—If our section is through a part of the stem which is not too young, the tissues of the outer part of the bundle will show either one or several groups of cells which have white and shiny walls, that are thickened as much or more than those of the wood vessels. These cells are éast cells, and for this reason this part of the bundle is the éas¢ por- tion, or the pr/vem. Intermingled with these, cells may often be found which have thin walls, unless the bundle is very old. Nearer the center of the bundle and still within the bast portion are cells with thin walls, angular and irregularly arranged. This is the softer portion of the bast, and some of these cells are what are called szeve tubes, which can be better seen and studied in a longitudinal section of the stem. 101. Cambium region of the bundle.—Extending across the center of the bundle are several rows of small cells, the smallest of the bundle, and we can see that they are more regularly arranged, usually in quite regular rows, like bricks piled upon one another. These cells have thinner walls than any others of the bundle, and they usually take a deeper stain when treated with a solution of some of the dyes. This is because they are younger, and are therefore richer in protoplasmic contents. This zone of young cells across the bundle is the camdbium. Its cells grow and divide, and thus increase the size of the bundle. By this increase in the number of the cells of the cambium layer, the outermost cells on either side are continually passing over into the phloem, on the one hand, and into the wood portion of the bundle, on the other hand. 102. Longitudinal section of the bundle.—If we make thin longisections of the vascular bundle of the castor-oil seedling (or other dicptyloden) gathat we have thin ones running through a bundle radially, as shown in fig. 42, we can see the structure of these parts of the bundle in side view. We see here that the form of the cells is very difierent from what is presented in a cross section of the same. The walls of the various ducts have peculiar markings on them. These markings are caused by the walls being thicker in some WS 46 PHYSIOLOGY. places than in others, and this thickening takes place so regularly in some instances as to form regular spiral thickenings. Others have the thickenings ANZ SZ Fig. 42. Longitudinal section of vascular bundle of sunflower stem; spiral, scalariform and pitted vessels at left; next are wood fibers with oblique cross walls; in middle are cambium cells with straight cross walis, next two sieve tubes, then phloem or bast cells. in the form of the rounds of a ladder, while still others have pitted walls or the thickenings are in the form of rings. 103. Vessels or ducts.—One way in which the cells in side view differ greatly from an end view, in a cross section in the bundle, is that they are much longer in the direction of the axis of the stem. The cells have become elongated greatly. If we search for the place where two of these large cells with spiral, or ladder-like, markings meet end to end, we see that the wall which formerly separated the cells has nearly or quite disappeared. In other words the two cells have now an open communication at the ends. This is so for long distances in the stem, so that long columns of these large cells form tubes or vessels through which the water rises in the stems of plants. 104. In the bast portion of the bundle we detect the cells of the bast fibers by their thick walls. They are very much elongated and the ends taper out to thin points so that they overlap. In this way they serve to strengthen tue stem. 105. Sieve tubes.—Lying near the bast cells, usually toward the cambium, are elongated cells standing end to end, with delicate markings on their cross walls which appear like finely punctured plates or sieves. The protoplasm in such cells is usually quite distinct, and sometimes contracted away from the side walls, but attached to the cross walls, and this aids in the detection of the sieve tubes (fig. 42.) The granular appearance which these plates pre- sent is caused by minute perforations through the wall so that there is a com- munication between the cells. The tubes thus formed are therefore called sieve tubes and they extend for long distances through the tube so that there PATH OF MOVEMENT. 47 is communication throughout the entire length of the stem. (The function of the sieve tubes is supposed to be that for the downward transportation of sub- stances elaborated in the leaves.) 106. If we section in like manner the stem of the sunflower we shall see simi- lar bundles, but the number is greater than eight. In the garden balsam the number is from four to six in an ordinary stem 3-4 diameter. Here we can see quite well the origin of the vascular bundle. Between the larger bundles we can see especially in free-hand sections of stems through which a colored solution has been lifted by transpiration, as in our former experi- ments, small groups of the minute cells in the cambial ring which are colored. These groups of cells which form strands running through the stem are pro- cambium strands. The cells divide and increase just like the cambium cells, and the older ones thrown off on either side change, those toward the center of the stem to wood vessels and fibers, and those on the outer side to bast cells and sieve tubes. 107. Fibrovascular bundles in the Indian corn.—We should now make a thin transection of a portion of the center of the stem of Indian corn, in order to compare the structure of the bundle with that of the plants which we have just examined. In fig. 43 is repre- sented a fibrovascular bundle of the stem of the Indian corn, The large cells are those of the spiral and reticulated and annular vessels. This is the woody por- tion of the bundle or xylem, Opposite this is the bast portion or phloem, marked by the lighter colored tissue at 7. The larger of these cells are the sieve tubes, and intermingled with them are smaller cells with thin walls. Surrounding the entire bundle are small cells with thick walls. These are elongated and the taper- Fics: ing ends overlap. They are thus slender Transection of fibrovascular bundle of and long and form fibers. In such a ae plates i ed eae bundle all of the cambium has passed esate “ hone = sem a oh oe over into permanent tissue and is said to soft bast, a form of sieve tissue ; /, thin- walled parenchyma. (Sachs.) be closed. 108. Rise of water in the vessels.—During the movement of the water or nutrient solutions upward in the stem the vessels of the wood portion of the bundle in certain plants are nearly or quite filled, if root pressure is active and transpiration is not very rapid. If, however, on dry days transpiration is in excess of root pressure, as often happens, the vessels are not filled with the water, but are partly filled with certain gases because the air or other 48 PHYSIOLOGY. gases in the plant become rarefied as a result of the excessive loss of water. There are then successive rows of air or gas bubbles in the vessels separated by films of water which also line the walls of the vessels. The condition of the vessel is much like that of a glass tube through which one might pass the “froth ’’ which is formed on the surface of soapy water. This forms a chain of bubbles in the vessels. This chain has been called Jamin’s chain because of the discoverer. 109. Why water or food solutions can be raised by the plant to the height attained by some trees has never been satisfactorily explained. There are several theories propounded which cannot be discussed here. It is probably a very complex process. Root pressure and transpiration both play a part, or at least can be shown, as we have seen, to be capable of lifting water toa considerable height. In addition to this, the walls of the vessels absorb water by diffusion, and in the other elements of the bundle capillarity comes also into play, as well as osmosis. 110. Synopsis of tissues. Epidermis. Simple hairs. Many-celled hairs. Trichomes Branched hairs, often stellate. (hairs). Clustered, tufted hairs. Glandular hairs. Root hairs. \ Guard cells of stomates. Spiral vessels. Pitted vessels. Scalariform vessels. Annular vessels. Wood fibers. Wood parenchyma. Cambium (fascicular). Sieve tubes. Phloem. { Bast fibers. Bast parenchyma. Epidermal system. Xylem. Fibrovascular system. Cork. Parenchyma. Ground tissue. Interfascicular cambium. Medullary rays. system: Bundle sheath. Sclerenchyma (thick-walled cells, in nuts, etc.). Collen- chyma (thick-angled cells, under epidermis of succulent stems). Fundamental CHAPTER VIII. DIFFUSION OF GASES. 111. Gas given off by green plants in the sunlight.—Let us take some green alga, like spirogyra, which is in a fresh con- dition, and place one lot in a beaker or tall glass vessel of water and set this in the direct sunlight or in a well lighted place. At the same time cover a similar vessel of spirogyra with black cloth so that it will be in the dark, or at least in very weak light. 112. In a short time we note that in the first vessel small bubbles of gas are accumulating on the surface of the threads of the spirogyra, and now and then some free themselves and rise to the surface of the water. Where there is quite a tangle of the threads the gas is apt to become caught and held back in larger bubbles, which on agitation of the vessel are freed. If we now examine the second vessel Oxygen gas given off by spirogyra. we see that there are no bubbles, or only a very few of them. We are led to believe then that sunlight has had something to do with the setting free of this gas from the plant. 118. We may now take another alga like vaucheria and per- form the experiment in the same way, or to save time the two may be set up at once. In fact if we take any of the green 49 50 PHYSIOLOGY. algee and treat them as described above gas will be given off ina similar manner. 114. We may now take one of the higher green plants, an aquatic plant like elodea, callitriche, etc. Place the plant in the water with the cut end of the stem uppermost, but still immersed, the plant being weighted down by a glass rod or other suitable object. If we place the vessel of water containing these leafy stems in the bright sunlight, in a short time bub- bles of gas will pass off quite rapidly from the cut end of the stem. If in the same vessel we place another stem, from which the leaves have been cut, the number of bubbles of gas Fig. 45- given off will be very few. This indicates that Bubbles of oxygen gas given off from elodea in q ° i i eee oF aelGe large part of the gas is furnished by the (Oels.) leaves. 115. Another vessel fitted up in the same way should be placed in the dark or shaded by covering with a box or black cloth. It will be seen here, as in the case of spirogyra, that very few or no bubbles of yas will be set free. Sunlight here also is necessary for the rapid escape of the gas. 116. We may easily compare the rapidity with which light of varying intensity effects the setting free of this gas. After cutting the end of the stem let us plunge the cut surface several times in melted paraffine, or spread over the cut surface a coat of varnish. Then prick with a needle a small hole through the paraffine or varnish. Immerse the plant in water and place in sunlight as before. The gas now comes from the puncture through the coating of the cut end, and the number of bubbles given off during a given period can be ascertained by counting. If we duplicate this experi- ment by placing one plant in weak light or diffused sunlight, and another in the shade, we can easily compare the rapidity of the escape of the gas under the different conditions, which represent varying intensities of light. We see then that not only is sunlight necessary for the setting free of this gas, but that in diffused light or in the shade the activity of the plant in this respect is less than in direct sunlight. 117. What this gas is.—If we take quite a quantity of the plants of elodea and place them under an inverted funnel which is immersed in water, the gas will be given off in quite large quantities and will rise into the narrow exitot the funnel. DIFFUSION OF GASES. 51 The funnel should be one with a short tube, or the vessel one which is quite deep so that a small test tube which is filled with water may in this condition be inverted over the opening of the funnel tube. With this arrange- ment of the experiment the gas will rise in the inverted test tube, slowly displace a portion of the water, and become collected in a sufficient quantity to afford us a test. When a consider- able quantity has accumulated in the test tube, we may close the end of the tube in the water with the thumb, lift it from the water and invert. Fig. 46. z r = Apparatus for col- The gas will rise against the thumb. A dry lecting quantity of oxygen from elodea. soft pine splinter should be then lighted, and (Detmer.) after it has burned a short time, extinguish the flame by blowing upon it, when the still burning end of the splinter should be brought to the mouth of the tube as the thumb is quickly moved to one side. The glowing of the splinter shows that the gas is oxygen. 118. Oxygen given off by green land plants also.—If we should extend our experiments to land plants we should find that oxygen is given off by them under these conditions of light. Land plants, however, will not do this when they are immersed in water, but il is necessary to set up rather complicated apparatus and to make analyses of the gases at the beginning and at the close of the experiments. This has been done, however, in a suffi- ciently large number of cases so that we know that all green plants in the sunlight, if temperature and other conditions are favorable, give off oxygen. 119. Absorption of carbon dioxide.—\We have next to inquire where the oxygen comes from which is given off by green plants when exposed to the sunlight, and also to learn something more of the conditions necessary for the process. We know that water which has been for some time exposed to the air and soil, and has been agitated, like running water of streams, or the water of springs, has mixed with it a considerable quantity of oxygen and carbon dioxide. 120. If we boil spring water or hydrant water which comes froma stream containing oxygen and carbon dioxide, for about 20 52 PHYSIOLOGY. minutes, these gases are driven off. We should set this aside where it will not be agitated, until it has cooled sufficiently to receive plants without injury. Let us now place some spirogyra or vaucheria, and elodea, or other green water plant, in this boiled water and set the vessel in the bright sunlight under the same conditions which were employed in the experiments for the evolution of oxygen. No oxygen is given off. 121. Can it be that this is because the oxygen was driven from the water in boiling? We shall see. Let us take the vessel containing the water, or some other boiled water, and agitate it so that the air will be thoroughly mixed with it. In this way oxygen is again mixed with the water. Now place the plant again in the water, set in the sunlight, and in several minutes observe the result. No oxygen is given off. There must be then some other requisite for the evolution of the oxygen. 122. The gases are interchanged in the plants.—We will now introduce carbon dioxide again in the water. This can be done by blowing into the water through a glass tube in such a manner as to violently agitate the water for some time, when the carbon dioxide from the ‘‘ breath’’ will become mixed with the water. Now if we place the plant in the water and set the vessel in the sunlight, in a few minutes the oxygen is given off rapidly. 123. A chemical change of the gas takes place within the plant cell.—This leads us to believe then that CO, is in some way necessary for the plant in this process. Since oxygen is given off while carbon dioxide, a different gas, is necessary, it would seem that a chemical change takes place in the gases within the plant. Since the process takes place in such simple plants as spirogyra as well as in the more bulky and higher plants, it appears that the changes go on within the cell, in fact within the protoplasm. 124. Gases as wellas water can diffuse through the proto- plasmic membrane.—Carbon dioxide then is absorbed by the plant while oxygen is given off. We see therefore that gases as well as water can diffuse through the protoplasmic membrane of plants under certain conditions. CHAPTER IX. RESPIRATION: 125. One of the life processes in plants which is extremely interesting, and which is exactly the same as one of the life pro- cesses of animals, is easily demonstrated in several ways. 126. To set up the apparatus for demonstrating respiration.—Soak a double handful of peas for 12 to 24 hours in an abundance of cool water. Prepare a small quantity of baryta water, a saturated solution, and filter some into a short wide vial. Take a glass cylinder about 35 cm high by 5 cm in diameter. Select a perforated rubber cork to fit very tightly when crowded part way in the open end of the cylinder. Prepare a long S manometer by bending a glass tube, which is about one and one half meters long by 6 mm inside diameter, into the form shown in figure 46a. Put mercury into one end of the manometer as shown in the figure, andif it is desired to show the experi- ment at a distance in the classroom, place a small quantity of a solution of eosin above each column of mercury. Insert the other end of the manometer through the perforation in the rubber cork. It must fit very tightly. If there is another perforation, plug it with a glass rod, Take a wide-mouth glass jar (a small glycerine-jelly jar is good) which will go inside the cylinder. Break a few sticks of caustic potash and drop into it. Nearly fill with water, and tie a string around the upper end so that it can be lowered in the upper part of the cylinder without spilling any of the potash solution, Prepare a support for this by inserting a glass rod about 13 cm long into a small cork, Have all the parts of the apparatus aud the material ready, and the baryta water in the open vial, so that the apparatus may be set up quickly. Have the cylinder warm, and set the apparatus up in a room where the temperature is about 20° C. (about 68° Fahr.). Place a small quantity of damp paper (not wet) in the bottom of the cylinder. Place in the soaked peas to fill about 8 cm to to cm. Upon these place the small vial of baryta water. Drop in the support and press the glass rod down far enough so that the jar of potash solution will enter and pass below the rubber cork. Insert the rubber cork containing the S manometer of mercury, placing be- tween it and the side of the cylinder a stout needle to allow the escape of air 53 54 MORPHOLOGY. 4 while the cork is pressed in tightly. This adows the mercury to remain at the same level in both arms of the tube. Now remove the,needJe and set the 5 apparatus aside where*the temperature will remain at about 20° C., and let stand for about 24 hours, The apparatus should be set up quickly, so that forming carbon di- oxide will not displace the air, 127. Carbon dioxide given off during germination while oxygen from the air is consumed.—In a short while there can be seen a whitish film on the baryta water in the vial. In less than an hour this film may become so thick that with a little agitation it breaks and settles as a white precipitate. This white precipitate is ba- rium carbonate, formed when the baryta water absorbs some of the carbon dioxide which is being given off quite rapidly by the germinating peas. The carbon dioxide is also absorbed by the caustic potash solution in the bottom of the cylinder. (wing to the slowness with which the carbon cioxide diffuses from between the peas into the potash solution an excess may be formed. This excess of carbon dioxide in the cylinder produces a pressure which is shown by the rise of the mercury in the outer arm of the tube.* In about 24 hours observe the experi- ment, If the mercury is still higher in the outer arm it shows that there is still an excess of CO, in the cylinder. At any rate lift the cylinder with the hands in such a way as to hold firmly at the same time the glass tube. Lift it up and down in such a Fig 46a. way as to spill a portion of the baryta water over against the wall of the cylinder, and to dash the potash solution into a spray. Be careful not to toss the mercury * When this inside pressure is produced it shows that more CQ, is being set free than oxygen is being consumed. This feature of the experiment dem- onstrates what is known as intramolecular respiration, a kind of respiration which can go on independently of the entrance of the oxygen. RESPIRA TION. 55 out of either arm of the tube. If the open arm of the glass tube is closed with the finger, the cylinder may be inclined so as to let a portion of the potash solution run up among the peas to come directly in contact with the CO, remain- ing there. Now rest the cylinder on the table and observe the result. The mercury now stands, if it did not before, higher in the inner arm of the S tube, showing that some constituent of the air within the cylinder was consumed during the formation of the CO,. This constituent of the air must be oxygen, since the carbon can only come from the plant. Where the baryta water was spilled over an abundance of the white precipitate of the barium carbonate is formed. 128. Simple experiment to demonstrate the evolution of CO, during germination.—Where there are a number of stu- dents and a number of large cylinders are not at hand, take bottles of a pint capacity and place in the bottom some peas soaked for 12 to 24 hours. Cover with a glass plate which has been smeared with vaseline to make a tight joint with the mouth of the bottle. Set aside in a warm place for 24 hours. Then slide the glass plate a little to one side and quickly pour in a little baryta water so that it will run down on the inside of the bottle. Cover the bottle again. Note the precipitate of barium carbonate which demonstrates the presence of Fig. 47. Z . Test for presence of CO, in the bottle. Lower a lighted taper. carbon dioxide in vessel It is extinguished because of the great quan- ep ere a tity of CO,. 129. If we now take some of the baryta water and blow our ‘‘preath’’ upon it the same film will be formed. ‘The carbon dioxide which we exhale is absorbed by the baryta water, and forms barium carbonate, just as in the case of the peas. In the case of animals the process by which oxygen is taken into the body and carbon dioxide is given off is respiration. The process in plants which we are now studying is the same, and also is respiration, The oxygen in the vessel was partly used up in the process, and carbon dioxide was given off. (It will be seen that this process is exactly the opposite of that which takes place in carbon conversion. ) 56 PHYSIOLOGY. 130. Respiration is necessary for growth.—After we have performed this experiment, if the vessel has not been open too long so that oxygen has en- tered, we may use the vessel for another experiment, or set up a new one to be used in the course of 12 to 24 hours, after some oxygen has been con- sumed. Place some folded damp filter paper on the germinating peas in the jar. Upon this place one-half dozen peas which have just been germinated, and in which the roots are about 20-25 mm long. The vessel should be cov- ered tightly again and set aside in a warm room. A second jar with water in the bottom instead of the germinating peas should be set up as a check. Damp folded filter paper should be sup- ported above the water, and on this should be placed one-half dozen peas with roots of the same length as those in the jar containing carbon dioxide. 131. In 24 hours examine and note how much Fig. 48. growth has taken place. It will be seen that the Pea seedlings; the one \ at the left had no oxygen roots have elongated but very little or none in the and little growth took first jar, while in the second one we see that the ca ond a roots have elongated considerably, if the experi- evident. ment has been carried on carefully. Therefore in an atmosphere devoid of oxygen very little growth will take place, which shows that normal respiration with access of oxygen is necessary for growth. 132. Energy set free during respiration.—From what we have learned of the exchange of gases during respiration we infer that the plant loses carbon during this process. If the process of respiration is of any benefit to the plant, there must be some gain in some direction to compensate the plant for the loss of carbon which takes place. It can be shown by an experiment that during respiration there is a slight elevation of the temperature in the plant tissues. The plant then gains some heat during respiration, Energy is also manifested by growth. 133. Beaeise sion in a leafy plant.—We may take a potted plant which has a well-developed leaf surface and place it under a tightly fitting bell jar. Under the bell jar there also should be placed a small vessel contain- ing baryta water. A similar apparatus should be set up, but with no plant, to serve asa check. The experiment must be set up in a room which is not frequented by persons, or the carbon dioxide in the room from respiration will vitiate the experi- ment. The bell jar containing the plant should be covered with a black cloth to prevent carbon assi- Fig. 49. Test for liberation of carbon dioxide from leafy plant during respiration, Baryta water in yjlation. In the course of ten or twelve hours, if smaller vessel. (Sachs ) RESPIRATION. 57 everything has worked properly, the baryta water under the jar with the plant will show the film of barium carbonate, while the other one will show none. Respiration, therefore, takes place in a leafy plant as well as in germinating seeds. 134, Respiration in fungi.—If several large actively growing mushrooms are accessible, place them in a tall glass jar as described for letermining respiration in germinating peas. In the course of twelve hours test with the lighted taper and the baryta water. Respiration takes place in fungi as well as in green plants. 185. Respiration in plants in general.—Respiration is general in all plants, though not universal. There are some exceptions in the lower plants, notably in certain of the bacteria, which can only grow and thrive in the ab- sence of oxygen. 186. Respiration a breaking-down process.—We have seen that in res- piration the plant absorbs oxygen and gives off carbon dioxide. We should endeavor to note some of the effects of respiration on the plant. Let us take, say, two dozen dry peas, weigh them, soak for 12-24 hours in water, and, in the folds of a cloth kept moist by covering with wet paper or sphag- num, germinate them. When well germinated and before the green color appears dry well in the sun, or with artificial heat, being careful not to burn or scorch them. The aim should be to get them about as dry as the seed were before germination. Now weigh. The germinated seeds weigh less than the dry peas. There has then been a loss of plant substance during respiration. 137. Detailed result of the above experiment to show that respiration is necessary for growth.—The experiment was started at 9.30 A.M. on July 8, and the roots measured 20-25mm. At 3 P.M. on the following day, 29 hours after the experiment was started, the roots were examined. Those in the CO, gas had not grown perceptibly, while those in the jar containing air had increased in length 10-zowm. In fig. 48 are represented two of the peas, drawn at the close of the experiment. a@ represents the one from the CO, jar which had the longest root, 4 represents one of the longer ones from the jar with air. Here we have also a good comparison with the peas grown in the mercury tubes, since those in the tube which contained some air were checked in growth to a considerable extent, by the accumulation of carbon dioxide in the small space in the tube, and did not represent a fair comparison of root growth in air and in CO,. In one of the experiments the two jars were allowed to stand at the room temperature for several weeks. At the end of that time the peas in the jar containing air had grown until the vines reached to the top of the jar, and the vines had branched and produced a number of green leaves. In the other jar no growth took place. In fact the peas died. At this time the gas in both of the jars was tested by lowering a lighted taper. In the jar with the growing 58 PHYSIOLOGY. peas the taper burned brightly, while in the other jar the flame was quickly extinguished. In this jar, while there was very little or no oxygen, there were present other gases than carbon cioxide because putrefactive processes were now going on in the large mass of peas in the jar. 138. Another way of performing the experiment.—If we wish we may use the following experiment instead of the simple one indicated above, Soak a handful of peas in water for 12-24 hours, and germinate so that twelve with the radicles 20-25 long may be selected. Fill a test tube with mercury and carefully invert it in a ves- sel of mercury so that there will be no air in the upper end, Now nearly fill another tube and invert in the same way. In the latter there will be some air. Re- move the outer coats from the peus so that no air will be introduced in the tube filled with the mercury, and insert them one at a time under ie the edge of the tube beneath the Lanett ee mercury, six in each tube, having Fig. 50. first measured the length of the Experiment to show that growth takes place padiélés: ‘Place ded waear eoonh. more rapidly in presence of oxygen than in ab- sence of oxygen. At the beginning of the experi- Jy, 24 hours measure the roots. ment the two tubes in the vessel represent the 3 4 . condition at the beginning of the experiment. Those in the air will have grown At the close the roots in the tube at the left were a ; hil is longer than those in the tube filled at the start considerably, while those in the with mercury. The tube outside of the vessel other tube will have grown but represents the condition of things where the peas” grew in absence of oxygen; the carbon dioxide little or none. iven off has displaced a portion of the mercury. M This also shows zatvramolecudar respiration. 139. Intramolecular respira- tion.—The last experiment is also an excellent one to show what is called 2/ramolecular respiration. In the tube filled with mercury so that when inverted there will be no air, it will be seen after 24 hours that a gas has accumulated in the tube which has crowded out some of the mercury. With a wash bottle which has an exit tube properly curved, some water may be introduced in the tube. Then insert underneath a small stick of caustic potash. This will form a solution of potash, and the gas will be partly or completely absorbed. This shows that the gas was car- bon dioxide. This evolution of carbon dioxide by living plants when there is no access of oxygen is called intramolecular respiration. It occurs markedly in oily seeds and especially in the yeast plant. QGUAPTER X. THE CARBON FOOD OF PLANTS. 140. We came to the conclusion in a former chapter that some chemical change took place within the protoplasm of the green cells of plants during the absorption of carbon dioxide and the giving off of oxygen. We should examine some of the green parts of those plants used in the experiments, or if they are not at hand we should set up others in order to make this ex- amination. 141. Starch formed as a result of carbon conversion.—We may take spirogyra which has been standing in water in the bright sunlight for several hours. A few of the threads should be placed in alcohol for a short time to kill the protoplasm. From the alcohol we transfer the threads to a solution of iodine in potassium iodide. We find that at certain points in the chlorophyll band a bluish tinge, or color, is imparted to the ring or sphere which surrounds the pyrenoid. In our first study of the spirogyra cell we noted this sphere as being composed of numerous small grains of starch which surround the pyrenoid. 142. Iodine used as a test for starch.—This color reaction which we have obtained in treating the threads with iodine is the well-known reaction, or test, for starch. We have demon- strated then that starch is present in spirogyra threads which have stood in the sunlight with free access to carbon dioxide. If we examine in the same way some threads which have stood in the dark for a day we obtain no reaction for starch, or at best only a slight reaction. This gives us some evidence that a chemical change does take place during this process (absorption 59 60 PHYSIOLOGY. of CO, and giving off of oxygen), and that starch is a product of that chemical change. 143. Schimper’s method of testing for the presence of starch. —Another convenient and quick method of testing for the pres- ence of starch is what is known as Schimper’s method. A strong solution of chloral hydrate is made by taking 8 grams of chloral hydrate for every 5cc of water. To this solution is added a little of analcoholictincture of iodine. The threads of spirogyra may be placed directly in this solution, and in a few moments mounted in water on the glass slip and examined with the microscope. ‘The reaction is strong and easily seen. 144. We may test vaucheria which has been grown under like conditions in the same way. We find here also that the starch is present in the threads which have been exposed to the sun- light, while it is absent from those which have been for a suffi- ciently Jong time in the dark. 145. We should also examine the leaves of elodea, or one of the higher green plants which has been for some time in the sunlight. We may use here Schimper’s method by placing the leaves directly in the solution of chloral hydrate and iodine. The leaves are made transparent by the chloral hydrate so that the starch reaction from the iodine is easily detected. 146. If the solution of iodine in potassium iodide is used first boil the leaves in water for a short time, then heat for some time in alcohol, or change the alcohol several times. The green color is extracted slowly by this pro- cess, and more rapidly if the preparation is placed in the sunlight. (If care is used the leaves may be boiled in alcohol.) After the leaves are decolorized they should be immersed in the solution of iodine. 147. Green parts of plants form starch when exposed to light.—Thus we find that in the case of all the green plants we have examined, starch is present in the green cells of those which have been standing for some time in the sunlight where the proc- ess of the absorption of CO, and the giving off of oxygen can go on, and that in the case of plants grown in the dark, or in leaves of plants which have stood for some time in the dark, starch is absent. We reason from this that starch is the product CARBON FOOD OF PLANTS. 61 of the chemical change which takes place in the green cells under these conditions. Because CO, is absorbed during this process, and because of the chemical changes which take place in the formation of starch, by means of which the carbon is changed from its attraction in the molecule of carbon dioxide to its attraction in the molecule of starch, the process may be termed carbon conversion. This process has been termed carbon assimilation, but since it is not truly an assimilatory process, and because sunlight is necessary in the first step of the conversion, it has also been recently termed photosyntax, or photo- synthesis. These terms, however. seem inappropriate, since the synthetic part of the process is not known to be due to the action of light. In the presence of chlorophyll light reduces the carbon dioxide, while the synthetic part of the process may not be influenced by light. Since the process is similar to that which chemists call cozers?/on, and since the carbon is the important food element derived from the air, for popular treatment the term carbon conversion seems more appropriate. 148. Starch is formed only in the green parts of variegated leaves.—If we test for starch in variegated leaves like the leaf of a coleus plant, we shall have an interesting demonstration of the fact that the green parts of plants only form starch. We may take a leaf which is partly green and partly white, from a plant which has been standing for some time in bright light. Fig. 51 is from a photograph of such a leaf. We should first boil it in alcohol to remove the green color. Now immerse’it in the potassium iodide of iodine solution for a short time. The parts which were formerly green are now dark blue or nearly black, showing the presence of starch in those portions of the leaf, while the white part of the leaf is still uncolored. This is well shown in fig. 52, which is from a photograph of another coleus leaf treated with the iodine solution. 149. Translocation of starch.—It has been found that leaves of green plants grown in the sunlight contain starch when examined after being in the sunlight for several hours. But when the plants are left in the dark for a day or two the leaves contain no starch, or a much smaller amount. This sug- gests that starch after it has been formed may be transferred from the leaves, or from those areas of the leaves where it has been formed. 62 PHYSIOLOGY. 150. To test this let us perform an experiment which is often made. We may take a plant such asa garden tropzolum or a clover plant, or other land Fig. 51. Fig. 52. Leaf of coleus showing green and white Similar leaf treated with iodine, the starch re- areas, before treatment with iodine. action only showing where the leaf was green. plant in which it is easy to test for the presence of starch. Tin a piece of circular cork, which is smuller than the area of the leaf, on either side of the leaf, as in fig. 53. Place the plant where it will be in the sunlight. On the afternoon of the following day, if the sun has been shining, we may remove the corks and test for starch, using the entire leaf, by Schimper’s method. Or < ns the method described in 146 Leaf ea Leaf of pane en treated AY be employed. ihe part with portion covered with iodine after removal of covered by the cork will not with corks to prevent cork, to show that starch is re- r theformationof starch. moved from the leaf during the give the reaction for starch, (After Detmer.) night. as shown by the absence of the bluish color, while the other parts of the leaf will show it. The starch which was in that part of the leaf the day before was dissolved and removed CARBON FOOD OF PLANTS. 63 during the night, and then during the following day, the parts being cov- ered from the light, no starch was formed in them. 151. Starch in other parts of plants than the leaves.—We may use the iodine test to search for starch in other parts of plants than the leaves. If we cut a potato tuber, scrape some of the cut surface into a pulp, and apply the iodine test, we obtain a beautiful and distinct reaction showing the presence of starch. Now we have learned that starch is only formed in the parts containing chlorophyll. We have also learned that the starch which has been formed in the leaves disappears from the leaf or is transferred from the leaf. We judge therefore that the starch which we have found in the tuber of the potato was formed first in the green leaves of the plant, as a result of carbon conver- sion. From the leaves it is transferred in solution to the under- ground stems, and stored in the tubers. The starch is stored here by the plant to provide food for the growth of new plants from the tubers, which are thus much more vigorous than the plants would be if grown from the seed. 152. The potato is only one example of a great many cases where starch is stored up as a reserve material by plants, but not always in the form of tubers. In the sweet potato and some other plants it is stored in the roots, certain ones of the roots becoming very much thickened; in the onion it is stored in certain leaves which form the onion bulb. 153. Form of starch grains.—Where starch is stored as a reserve material it occurs in grains which usually have certain characters peculiar to the species of plant in which they are found. They vary in size in many different plants, and to some extent in form also. Ifwe scrape some of the cut surface of the potato tuber into a pulp and mount a small quantity in water, or make «a thin section for microscopic examination, we find large starch grains of a beautiful structure. The grains are oval in form and more or less irregular in outline. But the striking peculiarity is the presence of what seem to be alternating dark and light lines in the starch grain. We note that the lines form irregular rings, which are smaller and smaller until we come to the small central spot termed the ‘hilum ” of the starch grain. It is supposed that these apparent lines in the starch grain are caused by the starch substance being deposited in alternating dense and dilute lavers, the dilute layers containing more water than the dense ones; others think that the successive layers from the hilum outward are 64 PHYSIOLOGY. regularly of diminishing density, and that this gives the appearance of alter- nating lines. The starch formed by plants is one of the organic substances which are manufactured by plants, and it is the basis for the formation of other organic substances in the plant. Without carbon food green plants cannot make any appreciable increase of plant substance, though a consider- able increase in size of the plant may take place. NotTr.—The organic compounds resulting from carbon conversion, since they are formed by the union of carbon, hydrogen, and oxygen in such a way that the hydrogen and oxygen are usually present in the same proportion as in water, are called carbohydrates. The most common carbohydrates are sugars (cane sugar, Cy2H».0,,, for example, in beet roots, sugar cane, etc.), starch, and cellulose. They are also classed among the non-nitrogenous substances, Other non-nitrogenous plant substances are the organic acids, like oxalic acid (H.C,0,), malic acid (H,C,H,O,), etc.; the fats and fixed oils, which occur in the seeds and fruits of many plants. Of the nitrogenous substances the proteids have a very complex chemical formula and contain carbon, hydrogen, oxygen, nitrogen, sulphur, etc. (example, a/ewen, or proteid grains, found in seeds). The proteids are the source of nitrogenous food for the seedling during germination. Of the amides, asparagin (CII yNyOs) is an example of a nitrogenous substance; and of the alkaloids, nicotin (C\>H,,Ne) from tobacco. All living plants contain a large per cent of water. According to Vines “ripe seeds dried in the air contain 12 to 15 per cent of water, herbaceous plants 60 to 80 per cent, and many water-plants and fungi as much as 95 per cent of their weight.’" When heated to roo° C. the water is driven off. The dry matter remaining is made up partly of organic compounds, examples of which are given above, and inorganic compounds. By burning this dry residue the organic substances are mostry changed into volatile products, principally carbonic acid, water, and nitrogen. The inorganic substances as a result of combustion remain as a white or gray powder, the ash, The amount of the ash increases with the age of the plant, though the per- centage of ash may vary at different times in the different members of the plant. The following table taken from Vines will give an idea of the amount and composition of the ash in the dry solid of a few plants. CONTENT OF 1000 PARTS OF DRY SOLID MATTER. al 2 | ge | sel a ¥ 15 Z| Ss | Rs »|2\/ai|¢(|e8|6| 32 )4*) ¢ | 4 af a) oe ele |§ O.0) | 88 22 |, ° a | Ss oO SE FI = = < i 7) Hn a Fu AY n n (s) Clover, in blossom... 68.3 | 21.96] 1.39 | 24.06) 7.44 | 0.72 | 6.74 | 2.06 1.62] 2.66 Wheat, grain........] 19-7 6.14] 0.44 0.66] 2.36 | 0.26 | 9.26 | 0.07 0.42) 0 04 Wheat, straw. G37 7+33| 0.74 3-09} 1 33 | 0.33 | 2.58 | 1 32 | 36 25] 0.90 Potato tubers. . 37-7 | 22.76] 0.99 0.97} 1.77 | 0.45 | 6.53 | 2 45 0.80) 1.17 Apples .... .. 14.4 5-14] 3.76 © 59] 1-26 | 0.20 | 1.96 | 0.88 562i] 0 ceass Peas (the seed) 27 3. | 11.411 0 26 1.36! 2.17 | 0.16 | 9.95 | 0 95 0.24] 0.42 CHAPTER XI. CHLOROPHYLL AND THE FORMATION OF STARCH. 154. In our experiments thus fur in treating of the absorption of carbon dioxide and the evolution of oxygen, with the accom- panying formation of starch, we have used green plants. 155. Fungi cannot form starch.—If we should extend our experiments to the fungi, which lack the green color so charac- teristic of the majority of plants, we should find that carbon con- version does not take place even though the plants are exposed to direct sunlight. These plants cannot then form starch, but obtain carbohydrates for food from other sources. 156. Etiolated plants cannot convert carbon.—Moreover carbon conversion is usually confined to the green plants, and if by any means one of the ordinary green plants loses its green color carbon conversion cannot take place in that plant, even when brought into the sunlight, until the green color~ has appeared under the influence of light. This may be very easily demonstrated by growing seedlings of the bean, squash, corn, pea, etc. (pine seedlings are green even when grown in the dark), in a dark room, or in a dark receiver of some kind which will shut out the rays of light. The room or receiver must be quite dark. As the seedlings are ‘‘ coming up;’’ and as long as they remain in the dark chamber, they will present some other color than green; usually they are somewhat yellowed. Such plants are said to be e/olafed. If they are brought into the sunlight now for a few hours and then tested for the presence of starch the result will be negative. But if the plant is left in the light, in a few days the leaves begin to take 65 66 PHYSIOLOGY. on a green color, and then we find that carbon conversion begins. 157. Chlorophyll and chloroplasts.—The green substance in plants is then one of the important factors in this complicated process of forming starch. This green substance is ch/orophyll, and it usually occurs in definite bodies, the chlorophyll bodies, or chloroplasts. The material for new growth of plants grown in the dark is derived from the seed. Plants grown in the dark consist largely of water and protoplasm, the walls being very thin. 158. Form of the chlorophyll bodies.—Chlorophyll bodies vary in form in some different plants, especially in some of the lower plants. This we have already seen in the case of spirogyra, where the chlorophyll body is in the form of a very irregular band, which courses around the inner side of the cell wall in a spiral manner. In zygnema, which is related to spirogyra, the chlorophyll bodies are star-shaped. In the desmids the form varies greatly. In cedogonium, another of the thread-like algee, illustrated in fig. 95, the chlorophyll bodies Fig. 55. Section of ivy leaf, Palisade cells above, loose parenchyma, with large intercellular spaces in center. Epidermal cells on either edge, with no chlorophyll bodies. are more or less flattened oval disks. In vaucheria, too, a branched thread-like alga shown in fig. 106, the chlorophyll bodies are oval in outline. These two plants, cedogonium and CHLOROPHYLL; STARCH. 67 vaucheria, should be examined here if possible, in order to be- come familiar with their form, since they will be studied later under morphology (see chapters on cedogonium and vaucheria, for the occurrence and form of these plants). The form of the chlorophyll body found in cedogonium and vaucheria is that which iscommon to many of the green algze, and also occurs in the mosses, liverworts, ferns, and the higher plants. It is a more or less rounded, oval, flattened body. 159. Chlorophyll is a pigment which resides in the chloroplast.—That the chlorophyll is a coloring substance which resides in the chloroplastid, and does not form the body itself, can be demonstrated by dissolving out the chlorophyll when the framework of the chloroplastid is apparent. The green parts of plants which have been placed for some time in alcohol lose their green color. The alcohol at the same time becomes tinged with green. In sectioning such plant tissue we find that the chlorophyll bodies, or chloro- plastids as they are more properly called, are still intact, though the green color is absent. From this we know that chlorophyll is a substance distinct from that of the chloroplastid. 160. Chlorophyll absorbs energy from sunlight for carbon conversion.—It has been found by analysis with the spectroscope that chlorophyll absorbs cer- tain of the rays of the sunlight. The energy which is thus obtained from the-sun, called metic energy, is supposed to act on the molecules of CO, and H,O, separating them into other molecules of C, H, and O, and that after a series of complicated chemical changes starch is formed by the union of mole- cules of carbon, oxygen, and hydrogen, the hydrogen and some of the oxygen at least coming from the water in the cells of the plant. In this process of the reduction of the CO, and the formation of starch there is a surplus of oxygen, which accounts for the giving off of oxygen during the process. 161. Rays of light concerned in carbon conversion.—If a solution of chlorophyll be made, and light be passed through it, and this light be examined with the spectroscope, there appear what are called absorption bands. These are dark bands which lie across certain portions of the spectrum. These bands lie in the red, orange, yellow, green, blue, and violet, but the bands are stronger in the red, which shows that chlorophyll absorbs more of the red rays of light than of the other rays. These are the rays of low refrangibility. The kinetic energy derived by the absorption of these rays of light is transferred into potential energy. That is, the molecule of CO, is broken up, and then by a different combination of certain elements starch is formed.* * In the formation of starch during carbon conversion the separated mole- cules from the carbon dioxide and water unite in such a way that carbon, 68 PHYSIOLOGY. 162. Starch grains formed in the chloroplasts.—During carbon conver- sion the starch formed is deposited generally in small grains within the green chloroplast in the leaf. We can see this easily by examining the leaves of some moss like funaria which has been in the light, or in the chloroplasts of the prothallia of ferns, etc. Starch grains may also be formed in the chloroplasts from starch which was formed in some other part of the plant, but which has passed in solution. Thus the functions of the chloroplast are twofold, that of the conversion of-carbon and the formation of stanch grains. 163. In the translocation of starch when it becomes stored up in various parts of the plant, it passes from the state of solution into starch grains in connection with plastids similar to the chloroplasts, but which are not’ green. The green ones are sometimes called chloroplasts, while the colorless ones are termed derkcaasts, and those possessing “other” colors, as red and yellow, in floral leaves, the root of the carrot, etc., are called chr omoplasts. 164. Carbon conversion in other than green plants.—While carbo- hydrates are usually only formed by green plants, there are some exceptions. Apparent exceptions are found in the blue-green algz, like oscillatoria, nostoc, or inthe brown and red sea weeds like fucus, rhabdonia, etc. These plants, however, possess chlorophyll, but it is disguised by another pigment or color, There are plants, however, which do not have chlorophyll and yet form carbohydrates with evolution of oxygen in the presence of light, as for example a purple bacterium, in which the purple coloring substance absorbs light, though the rays absorbed most energetically are not the red. 165. Influence of light on the movement of chlorophyll bodies. —/x fern prothallia.—lf we place fern prothallia in weak light for a few hours, and then examine them under the microscope, we find that the most of the chloro- phyll bodies in the cells are arranged along the inner surface of the horizontal wall. If now the same prothallia are placed in a brightly lighted place for a short time most of the chlorophyll bodies move so that they are arranged along the surfaces of the perpendicular walls, and instead of having the flattened surfaces exposed to the light as in the former case, the edges of the chlorophyll bodies are now turned toward the light. (See figs. 56, 57-) The same phenomenon has been observed in many plants. Light then has an influence on chlorophyll bodies, to some extent determining their position. In weak light they are arranged so that the flattened surfaces are exposed to the incidence of the rays of light, so that the chlorophyll will hydrogen, and oxygen are united into a molecule of starch. This result is usually represented by the following equation: CO, + H,O = CH,O + O,. Then by polymerization 6(CH,O) = C,H,,0, = grape sugar. Then C,H\.0, — H,O = C,H,,0, = starch. It is believed, however, that the process is much more complicated than this, and that several different com- pounds are formed before starch finally appears. CHLOROPHYLL; STARCH. 69 absorb as great an amount as possible of kinetic energy ; but intense light is stronger than necessary, and the chlorophyll bodies move so that their edges are exposed to the incidence of the rays. This movement of the chlorophyll bodies is different from that which takes place in some water plants like Fig. 56. Fig 57. Cell exposed to weak diffused light show- Same cell exposed to strong light, showing ing chlorophyll bodies along the horizontal chlorophyll bodies have moved to perpen- walls. dicular walls. Figs. 56, 57.—Cell of prothallium of fern. elodea. The chlorophyll bodies in elodea are free in the protoplasm. The protoplasm in the cells of elodea streams around the inside of the cell wall much as it does in nitella and the chlorophyll bodies are carried along in the currents, while in nitella they are stationary. CHAPTER XII. NUTRITION AND MEMBERS OF THE PLANT BODY. 166. In connection with the study of the means for obtaining nutriment from the soil or water by the green plants it will be found convenient to observe carefully the various forms of the plant. Without going into detail here the suggestion is made that simple thread forms like spirogyra, cedogo- nium, and vaucheria; expanded masses of cells as are found in the thallvid liverworts, the duckweed, etc., be compared with those liverworts, and with the mosses, where leaf-like expansions of a central axis have been differentiated. We should then note how this differentiation, from the physiological stand- point, has been carried further in the higher land plants. 167. Nutrition of liverworts.—In many of the plants termed liverworts the vegetative part of the plant is a thin, flattened, more or less elongated green body known as a thallus. Riccia.—One of these, belonging to the genus riccia, is shown in fig. 58. Its shape is somewhat like that of a minute ribbon which is forked at intervals ina dichotomous man- ner, the characteristic kind of branching found in these thalloid liverworts. This riccia (known as R. lutescens) occurs on damp soil; long, slender, hair-like ® processes grow out from the under surface of the thallus, which resemble root hairs and serve the same purpose in the processes of nutrition. Another species of riccia (R. crystallina) is shown in fig. 171. This plant : is quite circular in outline and Fig. 58. occurs on muddy flats. Some Thallus of riccia lutescens. species float on the water. 168. Marchantia.—One of the larger and coarser liverworts is figured at 59. This is a very common liverwort, growing in 20 NUTRITION; MEMBERS PLANT BODY. 71 very damp and muddy places and also along the margins of streams, on the mud or upon the surfaces of rocks which are bathed with the water. This is known as Alarchantia polymorpha. If we examine the under surface of the marchantia we see numerous hair-like processes which attach the plant to the soil. Under the microscope we see that some of these are exactly like the root hairs of the seedlings which we have been studying, and they here serve the same purpose. Since, however, there are no roots on the marchantia plant, these hair-like outgrowths are Fig. 59- Marchantia plant with cupules and gemme ; rhizoids below. usually termed here r/zzords. In marchantia they are of two kinds, one kind the simple ones with smooth walls, and the other kind in which the inner surfaces of the walls are roughened by processes which extend inward in the form of irregular tooth- like points. Besides the hairs on the under side of the thallus we note especially near the growing end that there are two rows of leaf-like scales, those at the end of the thallus curving up over the growing end, thus serving to protect the delicate tissues at the growing point. 72 PH YSIOLOG Y. 169. Frullania.—In fig. 60 is shown another liverwort, nih differs greatly in form from the ones we have just been studying in that there isa well-defined axis with lateral leaf-like outgrowths. Such liverworts are called foliose liverworts. Besides these two quite prominent rows of leaves there is a third row of poorly developed leaves on the under surface. Also from the under surface of the axis we see here and there slender out- may) growths, the rhizoids, through which much Fig. 62 of the liquid Fig. 60. Fig. 61. Under side Portion of plant of Portion of same showing forked nutriment is Frullania, a foliose more highly magni- under -row liverwort. fied, showing over- leaves ana lehes absorbed. lapping leaves. of lateral leaves. 170. Nutrition of the mosses—Among the mosses which are usually common in moist and shaded situations, examples are abundant which are suitable for the study of the organs of absorption. If we take for example a plant of mnium (M. affine) which is illustrated in fig. 64, we note that it consists of a slender axis with thin flat, green, leaf-like expansions. Examin- ing with the microscope the lower end of the axis, which is attached to the substratum, there are seen numerous brown colored threads more or less branched. (For nutrition of moulds, mushrooms, parasitic fungi, dodder, carnivorous plants, lichens, aquatic plants, etc., see Part III. Ecology.) 171i. The plant body.—In the simpler forms of plant life, as in spirogyra and many of the alge and fungi, the plant body is not differentiated into parts. In many other cases the only differentiation is between the growing part and the fruiting part. In the algze and fungi there is no differentiation into stem and leaf, though there is an approach to it in some of the higher forms. Where this simple plant body is flattened, as in the sea-wrack, or ulva, it is a frond. The Latin word for frond is ¢had/us, and this name is NUTRITION; MEMBERS PLANT BODY. 73 applied to the plant body of all the lower plants, the alge and fungi. The alge and fungi together are sometimes called the ¢hadlophytes, or thallus plants. The word thallus is also sometimes applied to the flattened body of the liver- worts. In the foliose liverworts and mosses there is an axis with leaf-like expansions. These are believed by some to represent true stems and leaves, by others to represent a flattened thallus in which the margins are deeply and regularly divided, or in which the expansion has only taken place at regular intervals. Fig. 63. Foliose liverwort (bazzania) showing dichotomous branching and overlapping leaves. 172. Members of the plant body.—In the higher plants there is usually great differentiation of the plant body, though in many forms, as in the duck- weeds, it is a frond. While there is great variation in the form and func- tion of the members of the plant body, they are reducible to a few fundamental members. Some reduce these forms to three, the root, stem, and leaf, while others to two, the voot and shoot, which is perhaps the better arrangement. Here the shoot is farther divided into stem and leaf, the leaf being a lateral outgrowth of the stem. The different forms of the members are usually des- ignated by special names, but it is convenient to group them in the single series. Examples are as follows: 173. Stem series. Tubers, underground thickened stems, bearing buds and scale leaves; ex., Trish potato. Root-stocks, underground, usually elongated, bearing scales or bracts, and a leafy shoot; ex., trillium, mandrake, etc. Root-stocks of the ferns bear expanded, green leaves. Runners, slender, trailing, bearing bracts, and leafy stems as branches; ex., strawberry vines. Corms, underground, short, thick, leaf bearing and scale bearing; ex., In- dian turnip. 74 PHVSIOLOGY. Bulbs, usually underground, short, conic, leaf and scale bearing; ex., Female plant (gametophyte) of a moss (mnium), showing rhizoids below, and the tuft of leaves above, which protect the archegonia. lily. Thorns, stout, thick, poorly developed bran- ches with rudiments of leaves (scales); ex., hawthorn. Tendrils, slender reduced stems. Flower axes (see morphology of the angio. sperms). 174. Leaf series.—Besides the foliage leaves, the following are some of their modifications: Flower parts (see morphology of the angio- sperms). Bracts and scales, small, the former usually green (flower bracts), the latter usually: chloro- phylless. Bud scales are sometimes green. Tendrils, modifications of the entire leaf (tendrils of the squash where the branched tendril shows the principal veins of the leaf), modification of the terminal pinnz of the leaf (vetch), etc. Spines (examples are found in the cacti, where the stem is enlarged and green, function- ing as a leaf). Other modifications occur as in the pitcher plant, insectivorous plants, etc. 175. The root shows less modification. Be- sides normal roots, which are fibrous in most small plants and stout in the larger ones, some of the modifications are found in fleshy roots, where nourishment is stored (ex., dahlia, sweet potato, etc.), aerial roots (ex., poison ivy, the twining form), aerial orchids, etc. For modifications of roots due to symbiotic fungi, see chapter on Nutrition in Part III. CHAPTER XIII. GROWTH. 176. By growth is usually meant an increase in the bulk of the plant accompanied generally by an increase in plant sub- stance. Among the lower plants growth is easily studied in some of the fungi. 177. Growth in mucor.—Some of the gonidia (often called spores) may be sown in nutrient gelatine or agar, or even in prune juice. Ifthe culture has been placed in a warm room, in the course of 24 hours, or even less, the preparation will be ready for study. 178. Form of the gonidia.—It will be instructive if we first examine some of the gonidia which have not been sown in the cul- ture medium. We should note their rounded or globose form, as well as their markings if they belong to one of the species with spiny walls. Particularly should we note the size, and if possible measure them with the micrometer, though this would not be absolutely necessary for a comparison, if the comparison can be made immediately. Now examine some of the gonidia which were sown in the nutrient medium. If they have not already germinated we note at once that they are much larger than those which nave not been immersed in a moist medium. 179. The gonidia absorb water and increase in size before germinating.—From our study of the absorption of water or watery solutions of nutriment by living cells, we can easily un- derstand the cause of this enlargement of the gonidium of the mucor when surrounded by the moist nutrient medium. The cell-sap in the spore takes up more water than it loses by diffu- 75 76 PHYSIOLOG ¥Y. sion, thus drawing water forcibly through the protoplasmic mem- brane. Since it does not filter out readily, the increase in Fig. 65. Spores of mucor, and different stages of germination. quantity of the water in the cell produces a:pressure from within which stretches the membrane, and the elastic cell wall yields. Thus the gonidium becomes larger. 180. How the gonidia germinate.—We should find at this time many of the gonidia extended on one side into a tube-like process the length of which varies according to time and tempera- ture. The short process thus begun continues to elongate. ‘This elongation of the plant is grozsh, or, more properly speaking, one of the phenomena of growth. 181. The germ tube branches and forms the mycelium.— In the course of a day or so branches from the tube will appear. This branched form of the threads of the fungus is, as we remember, the mycelium. We can still see the point where growth started from the gonidium. Perhaps by this time several tubes have grown froma single one. The threads of the myce- lium near the gonidium, that is, the older portions of them, have increased in diameter as they have elongated, though this increase in diameter is by no means so great as the increase in length. After increasing to a certain extent in diameter, growth in this direction ceases, while apical growth is practically unlimited, being limited only by the supply of nutriment. 182. Growth in length takes place only at the end of the thread.—If there were any branches on the mycelium when the GROWTH. 77 culture was first examined, we can now see that they remain practically the same distance from the gonidium as when they were first formed. That is, the older portions of the mycelium do not elongate. Growth in length of the mycelium is confined to the ends of the threads. 183. Protoplasm increases by assimilation of nutrient substances.—As the plant increases in bulk we note that there is an increase in the protoplasm, for the protoplasm is very easily detected in these cultures of mucor. This increase in the quantity of the protoplasm has come about by the assimilation of the nutrient substance, which the plant has absorbed. The increase in the protoplasm, or the formation of additional plant substance, is another phenomenon of growth quite different from that of elongation, or increase in bulk. 184. Growth of roots.—For the study of the growth of roots we may take any one of many different plants. The seedlings of such plants as peas, beans, corn, squash, pumpkin, etc., serve excellently for this purpose. 185. Roots of the pumpkin.—The seeds, a handful or so, are soaked in water for about 12 hours, and then placed between layers of paper or between the folds of cloth, which must be kept quite moist but not very wet, and should be kept in a warm place. A shallow crockery plate, with the seeds lying on wet filter paper, and covered with additional filter paper, or with a bell jar, an- swers the purpose well. The primary or first root (radicle) of the embryo pushes its way out between the seed coats at the small end. When the seeds are well germinated, select several which have the root 4-5cm long. With a crow-quill pen we may now mark the terminal portion of the root off into very short sections as in fig. 66. The first mark should be not more than 1mm from the tip, and the others not more than 1mm apart. Now place the seedlings down on damp filter paper, and cover with a bell jar so that they will re- main moist, and if the season is cold place them in a warm room. At intervals of 8 or ro hours, if convenient, observe them and note the farther growth of the root. 78 PH YSIOLOG ¥. 186. The region of elongation.—While the root has elon- gated, the region of elongation 7s no/ at the tip of the root. It hes a little distance back from the tip, beginning at about 2mm from the tip and extending over an area represented by from 4-5 of the milli- PACER meter marks. The ae a. root shown in fig. 66 Bae, was marked at Io a.m. on July 5. At 6 P.M. of the same day, 8 Fig. 66. Root of germinating pumpkin, showing region of elongation just back of the tip. hours later, growth had taken place as shown in the middle figure. At 9 A.M. on the following day, 15 hours later, the growth is represented in the lower one. Similar experiments upon a number of seedlings gives the same result: the region of elongation in the growth of the root is situated a little distance back from the tip. Farther back very little or no elongation takes place, but growth in diameter continues for some time, as we should discover if we examined the roots of growing pump- kins, or other plants, at different periods. 187. Movement of region of greatest elongation.—In the region of elongation the areas marked off do not all elongate equally at the same time. The middle spaces elongate most rapidly and the spaces marked off by the 6, 7, and 8 mm marks elongate slowly, those farthest from the tip more slowly than the others, since elongation has nearly ceased here. The spaces marked off between the 2-4mm marks also elongate slowly, but soon begin to elongate more rapidly, since that region is becom- ing the region of greatest elongation. Thus the region of greatest elongation moves forward as the root grows, and remains ap- proximately at the same distance behind the tip. 188. Formative region.—If we make a longitudinal section of the tip of a growing root of the pumpkin or other scedling, and examine it with the mi- GROWTH. 79 croscope, we see that there is a great difference in the character of the cells of the tip and those in the region of elongation of the root. First there is in the section a V-shaped cap of loose cells which are constantly being sloughed off. Just back of this tip the cells are quite regularly isodiametric, that is, of equal diameter in all directions. They are also very rich in pro- toplasm, and have thin walls. This is the region of the root where new cells are formed by division. It is the formative region. The cells on the outside of this area are the older, and pass over into the older parts of the root and root cap. If we examine successively the cells back from this formative region we find that they become more and more elongated in the direction of the axis of the root. The elongation of the cells in this older portion of the root explains then why it is that this region of the root elongates more rapidly than the tip. 189. Growth of the stem.—We may use a bean seedling growing in the soil. At the junction of the leaves with the stem there are enlargements. These are the zodes, and the spaces on the stem between successive nodes are the z/ernodes. Weshould mark off several of these internodes, especially the younger ones, into sections about 5m long. Now observe these at several times for two or three days, or more. The region of elongation is greater than in the case of the roots, and extends back farther from the end of the stem. In some young garden bean plants the region of elongation extended over an area of 4omm in one internode. 190. Force exerted by growth.—One of the marvelous things connected with the growth of plants is the force which is exerted by various members of the plant under certain conditions. Observations on seedlings as they are pushing their way through the soil tothe air often show us that considerable force is required to lift the hard soil and turn it to one side. A very striking illustration may be had in the case of mushrooms which sometimes make their way through the hard and packed soil of walks or roads. That succu- lent and tender plants should be capable of lifting such comparatively heavy weights seems incredible until we have witnessed it. Very striking illustra- tions of the force of roots are seen in the case of trees which grow in rocky situations, where rocks of considerable weight are lifted, or small rifts in large rocks are widened by the lateral pressure exerted by the growth of a root, which entered when it was small and wedged its way in. 191. Zone of maximum growth.—Great variation exists in the rapidity of growth even when not influenced by outside conditions. In our study of the elongation of the root we found that the cells just back of the formative region 80 PHYSIOLOGY. elongated slowly at first. The rapidity of the elongation of these cells in- creases until it reaches the maximum. Then the rapidity of elongation les- sens as the cells come to lie farther from the tip. The period of maximum elongation here is the zone of maximum growth of these cells. 192. Just as the cells exhibit a zone of maximum growth, so the members of the plant exhipit a similar zone of maximum growth, In the case of leaves, when they are young the rapidity of growth is comparatively slow, then it increases, and finally diminishes in rapidity again. So it is with the stem. When the plant is young the growth is not so rapid; as it approaches middle age the rapidity of growth increases; then it declines in rapidity at the close of the season. 193. Energy of growth.—Closely related to the zone of maximum growth is what is termed the energy of growth. This is manifested in the compara- tive size of the members of a given plant. To take the sunflower for example, the lower and first leaves are comparatively small. As the plant grows larger the leaves are larger, and this increase in size of the leaves increases up to a maxi- mum period, when the size decreases until we reach the small leaves at the top ofthe stem. The zone of maximum growth of the leaves corresponds with the maxi- mum size of the leaves on the stem. The rapidity and energy of growth of the stem is also correlated with that of the leaves, and the zone of maximum growth is coincident with that of the leaves. It would be instructive to note it Fig. 67. in the case of other plants Pp Lever auxanometer (Oels) for measuring elongation of and also in the case of the stem during growth. fruits. 194. Nutation.—During the growth of the stem all of the cells of a given section of the stem do not elongate simultaneously. For example the cells at a given moment on the south side are elongating more rapidly than the cells on the other side. This will cause the stem to bend slightly to the north. In a few moments later the cells on the west side are elongating more rapidly, and the stem is turned to the east; and so on, groups of cells in suc- cession around the stem elongate more rapidly than the others. This causes the stem to describe a circle or ellipse about a central point. Since the re- gion of greatest elongation of the cells of the stem is gradually moving toward the apex of the growing stem, this line of clongation of the cells which is GROWTH. 81 traveling around the stem does so ma spiral manner. In the same way, while the end of the stem is moving upward by the elongation of the cells, and at the same time is slowly moved around, the line which the end of the stem describes must be a spiral one. This movement of the stem, which is common to all stems, leaves, and roots, is sation. 195. The importance of nutation to twining stems in their search for a place of support, as well as for the tendrils on leaves or stems, will be seen. In the case of the root it is of the utmost importance, as the root makes its way through the soil, since the particles of soil are more easily thrust aside. The same is also true in the case of many stems before they emerge from the soil, CHAPTER XIV. IRRITABILITY 196. We should now examine the movements of plant parts in response to the influence of certain stimuli. By this time we have probably observed that the direction which the root and stem take upon germination of the seed is not due to the position in which the seed happens to lie. Under normal conditions we have seen that the root grows downward and the stem upward. 197. Influence of the earth on the direction of growth.— When the stem and root have been growing in these directions for a short time let us place the seedling in a horizontal position, so that the end of the root extends over an object of support in such a way that it will be free to go in anydirection. It should be pinned to a cork and placed ina moist chamber. In the course of twelve to twenty-four hours the root which was formerly horizontal has turned the tip downward again. If we should mark off millimeter spaces beginning at the tip of the root, we should find that the motor zone, or region of curvature, lies in the same region as that of the elongation of the root. Knight found that the stimulus which influences the root to turn downward is the force of gravity. The reaction of the root in response to this stimulus is geotropism, a turning influenced by the earth. This term is applied to the growth movements of plants influenced by the earth with regard to direction. While the motor zone lies back of the root tip, the latter receives the stimulus and is the perceptive zone. If the root tip is cut off, the root is no longer geotropic, and will not turn downward when placed in a horizontal position. Growth toward the earth 82 IRRITABILITY. 83 is progeotropism. ‘The lateral growth of secondary roots is da- geotropism. The stem, on the other hand, which was placed in a horizontal position has become again erect. This turning of the stem in Fig. 68. Fig. 69. Germinating pea placed in a hori- In 24 hours gravity has caused the root to zontal position. turn downward. Figs. 68, 69.—Progeotropism of the pea root. the upward direction takes place in the dark as well as in the light, as we can see if we start the experiment at nightfall, or place the plant in the dark. This up- ward growth of the stem is also influ- enced by the earth, and therefore is a case of geotropism. The special desig- nation in the case of upright stems is negative geotropism, or apogeotropism, or the stems are said to be apogeotropic. Fig. 70. Pumpkin seedling showing apogeotropism. Seedling at the left placed hori- zontally, in 24 hours the stem has become erect. If we place a rapidly growing potted plant in a horizontal position by laying the pot on its side, the ends of the shoots will soon turn upward again when placed in a horizontal position. Young bean plants growing in a pot began within two hours to turn the ends of the shoots upward. 84 PHYSIOLOG Y. Horizontal leaves and shoots can be shown to be subject to the same influence, and are therefore dageo/ropic. 198. Influence of light.—Not only is light a very important factor for plants during carbon conversion, it exerts great influ- ence on plant growth and movement. 199. Retarding influence of light on growth.—We have only to return to the experiments performed in growing plants in the dark to see one of the influ- ences which light exerts on plants. The plants grown in the dark were longer and more slender than those grownin the light. Light then has a retarding —_influ- ence on the elong- ation of the stem. 200. Influence Fig. 71. ; \\ of light on direc- “dark: long, siesder nor green tion of growth.—While we are growing seedlings, the pots or boxes of some of them should be placed so that the plants will Fig. 72. have a one-sided illumination. This can _ Radish seedlings grown in a the light, shorter, stouter, and be done by placing them near an open green in color. Growth re- s e Z * tarded by light. window, in a room with a one-sided illu- mination, or they may be placed in a box closed on all sides but one which is facing the window or light. In 12-24 hours, or even in a much shorter time in some cases, the stems of the seedlings will be directed toward the source of light. This influence exerted by the rays of light is heliofropism, a turning influenced by the sun or sunlight. 201. Diaheliotropism.—Horizontal leaves and shoots are diaheliotropice as well as diageolropic. The general direction IRRITABILITY. 85 which leaves assume under this influence is that of placing them with the upper surface perpendicular to the rays of light which fall upon them. Leaves, then, exposed to the brightly lighted sky are, in general, horizontal. This position is taken in direct response to the stimulus of light. The leaves of plants with a one-sided illu- mination, as can be seen by trial, are turned with Fig. 73- thei 3 ; nelr u r Seedling of castor-oil bean, before and after PPE a one-sided illumination. surfaces to- ward the source of light, or perpendicular to the in- cidence of the light rays. In this way light overcomes for the time being the direction which growth gives to the leaves. The so-called ‘‘sleep’’ of plants is of course not sleep, though the leaves ‘‘ nod,’’ or hang downward, in many cases. There — are many plants in which we can note this drooping of the leaves at nightfall, and in order to prove that it is not determined by the time of day we can resort to a well-known ex- periment to induce this condition dur- ing the day. The p[-==~ = plant which has been used to illus- trate this is the sun- flower. Some of these plants, which Fig. 74. Doark chamber with opening at one side to show heliotropism. (After Schleichert.) 86 PHYSIOLOGY. were grown in a box, when they were about 35cm high were covered for nearly two days, so that the light was excluded. At midday on the second day the box was removed, and the leaves on the covered plants are well represented by fig. 75, which was made from one of them. The leaves of the other plants in the box which were not covered were horizontal, as shown by fig. 76. Now on leaving these plants, which had exhibited Mig. 75. Sunflower plant. Epinastic con- dition of leaves induced durmg the day in darkness. Hf Fig. 76. Sunflower plant removed from darkness, leaves extending under influence of light (diaheliotro- pism.) induced ‘‘sleep’’ move- ments, exposed to the light they gradually assumed the horizontal position again. 202. Epinasty and hyponasty.—During the carly stages of growth of many leaves, as in the sunflower plant, the direction of growth is different from what it is at a later period. The under surface of the young Jeaves grows more rapidly in a longitudinal direction than the upper side, so that the leaves are held upward close against the bud at the end of the stem. This is termed Ayponasty, or the leaves are said to be Ayponastic. Later the growth is more rapid on the upper side and the leaves turn downward or away from the bud. This is termed e/7zasty, or the leaves are said to be epivastic. This is shown by the night position of the leaves, or in the induced ‘‘sleep”’ of the sun- IRRITABILITY, 87 flower plant in the experiment detailed above. The day position of the leaves on the other hand, which is more or less horizontal, is induced because of their irritability under the influence of light, the inherent downward or epinastic growth is overcome for the time. Then at nightfall or in darkness, the stimulus of light being removed, the leaves assume the position induced by the direction of growth. In the case of the cotyledons of some plants it would seem that the growth was hyponastic even after they have opened. The day position of the coty- Fig. 77- Fig. 78. Squash seedling. Position of cotyledons in Squash seedling. Position of cotyledons in light. the dark. ledons of the pumpkin is more or less horizontal, as shown in fig. 77. At night, or if we darken the plant by covering with a tight box, the leaves assume the position shown in fig. 78. While the horizontal position is the general one which is assumed by plants under the influence of light, their position is dependent to a certain extent on the intensity of the light as well as on the incidence of the light rays. Some plants are so strongly heliotropic that they change their posi- tions all during the day. 203. Leaves with a fixed diurnal position.—Leaves of some plants when they are developed have a fixed diurnal position and are not subject to 88 PHYSIOLOGY. variation. Such leaves tend to arrange themselves in a vertical or para- heliotropic position, in which the surfaces are not exposed to the incidence of light of the greatest intensity, but to the incidence of the rays of diffused light. Interesting cases of the fixed position of leaves are found in the so- called compass plants (like Silphium laciniatum, Lactuca scariola, etc.). In these the horizontal leaves arrange themselves with the surfaces vertical, and also pointing north and south, so that the surfaces face east and west. 204. Importance of these movements.—Not only are the leaves placed in a position favorable for the absorption of the rays of light which are con- cerned in making carbon available for food, but they derive other forms of energy from the light, as heat, which is absorbed during the day. Then with the nocturnal position, the leaves being drooped down toward the stem, or with the margin toward the sky, or with the cotyledons as in the pump- kin, castor-oil bean, etc., clasped upward together, the loss of heat by radiation is less than it would be if the upper surfaces of the leaves were exposed to the sky. 205. Influence of light on the structure of the leaf.—In our study of the structure of a leaf we found that in the ivy leaf the palisade cells were on the upper surface. This is the case with a @, great many leaves, and is the normal arrange- ment of ‘dorsiventral’’ leaves which are dia- heliotropic. Leaves which are paraheliotropic tend to have palisade cells on both surfaces. The palisade layer of cells as we have seen is made up of cells lying very close together, and they thus prevent rapid evaporation. They also check to some extent the entrance of the rays of light, at least more so than the loose spongy parenchyma cells do. Leaves developed in the shade have looser palisade and paren- chyma cells. In the case of some plants, if we turn over a very young leaf, so that the under side will be uppermost, this side will develop the palisade layer. This shows that light has a great influence on the structure of the leaf. 206. Movement influenced by contact.—In the case of tendrils, twining leaves, or stems, the irritability to contact is shown in a move- Fig. 79. ment of the tendril, ete., toward the object in Coiling tendril of bryony. touch. This causes the tendril or stem to coil around the object for support. The stimulus is also extended down the part of the tendril below the point of contact (sec fig. 79), and that part coils IRRITABILITY. 89 up like a wire coil spring, thus drawing the leaf or branch from which the tendril grows closer to the object of support. This coil between the object of support and the plant is also very important in casing up the plant when subject to violent gusts of wind which might tcar the plant from its support were it not for the yielding and springing motion of this coil. 207. Sensitive plants.—These plants are remarkable for the rapid response to stimuli. Mimosa pudica is an excellent plant to study for this purpose. 208. Movement in response to stimuli.—If we pinch with the forceps one of the terminal leaflets, or tap it with a pencil, the two end leaflets fold above the ‘‘ vein’’ of the pinna. This : is immediately followed by the movement of the next pair, and so on as shown in fig. 81, until all the leaflets on this pinna are closed, then the stimu- lus travels down the other pinne in a simi- Jar manner, and Sensitive-plant leaf in normal position. Fig. 81. Pinne fold- ing up after stimulus. soon the pinne approximate each other and . , a Fig. $2. the leaf then drops downward as shown Gia all, dhe alia fig. 82. “The normal position of the leaf 1s teed and lest droped. shown in fig. 80. If we jar the plant by striking it or by jarring the pot in which it is grown all the leaves quickly collapse into the position shown in fig. 82. If we examine the leaf now we see minute cushions at the base of each leaflet, at the junction of the pinne with the petiole, and a larger one at the junction of the petiole with the stem. We shall also note that the move- ment resides in these cushions. go PHYSIOLOGY. 209. Transmission of the stimulus.—The transmission of the stimulus in this mimosa from one part of the plant has been found to be along the cells of the bast. 210. Cause of the movement.—The movement is caused by a sudden loss of turgidity on the part of the cells in one portion of the pulvinus, as the cushion is called. In the case of the large pulvinus at the base of the petiole this loss of turgidity is in the cells of the lower surface. There is a sudden change in the condition of the protoplasm of the cells here so that they lose a large part of their water. This can be seenif with asharp knife we cut off the petiole just above the pulvinus before move- ment takes place. A drop of liquid exudes from the cells of the lower side. 211. Paraheliotropism of the leaves of the sensitive plant.—If the mimosa plant is placed in very intense light the leaflets will turn their edges toward the incidence of the rays of light. This is also true of other plants in intense light, and is paraheliotropism. Transpiration is thus lessened, and chlorophyll is protected from too intense light. We thus see that variations in the intensity of light have an important influence in modifying movements. Variations in temperature also exert a considerable influence, rapid ry ; yt elevation of temperature causing | 7 certain flowers to open, and ~ falling temperature causing N them to close. 212. Sensitiveness of insec- tivorous plants. — The Venus fly-trap(Dionzea muscipula)and the sundew (drosera) are in- teresting examples of sensitive plants, since the leaves close in response to the stimulus from Vig. 83. Wig. 84 insects. Leaf_of Venus fly- Leaf of Drosera ro- trap (Dionaa musci- tundifolia, some of the pula), showing winged landular hairs foldi j etiole and toothed weed as a result as 213. Hydrotropism ee obes. stimulus. Roots are sensitive to mois- ture. They will turn toward moisture. ‘This is of the greatest importance for the well-being of the plant, since the roots will seek those places in the soil where suitable moisture is present. On IRRITABILITY. gl the other hand, if the soil is too wet there is a tendency for the roots to grow away from the soil which is saturated with water. In such cases roots are often seen growing upon the surface of the soil so that they may obtain oxygen, which is important for the root in the processes of absorption and growth. Plants then may be injured by an excess of water as well as by a lack of water in the soil. 214. Temperature.—In the experiments on germination thus far made it has probably been noted that the temperature has much to do with the length of time taken for seeds to germinate. It also influences the rate of growth. The effect of different temperatures on the germination of seed can be very well noted by attempting to germinate some in rooms at various temperatures. It will be found, other conditions being equal, that in a moderately warm room, or even in one quite warm, 25-30 degrees cen- tigrade, germination and growth goes on more rapidly than in a cool room, and here more rapidly than in one which is decidedly cold. In the case of most plants in temperate climates, growth may go on at a temperature but little above freezing, but few will thrive at this temperature. 215. If we place dry peas or beans ina temperature of about 70° C. for 15 minutes they will not be killed, but if they have been thoroughly soaked in water and then placed at this temperature they will be killed, or even at a somewhat lower temperature. The same seeds in the dry condition will withstand a temperature of 10° C. below, but if they are fest soaked in water this low temperature will kill them. . 216. In order to see the effect of freezing we may thoroughly freeze a sec- tion of a beet root, and after thawing it out place it in water. The water is colored by the cell-sap which escapes from the cells, just as we have seen it does as a result of a high temperature, while a section of an unfrozen beet placed in water will not color it if it was previously washed. If the slice of the beet is placed at about — 6° C, ina shallow glass vessel, and covered, ice will be formed over the surface. If we examine it with the microscope ice crystals will be seen formed on the outside, and these will not be colored. The water for the formation of the crystals came from the cell-sap, but the concentrated solutions in the sap were not withdrawn by the freezing over the surface. ; 217. If too much water is not withdrawn from the cells of many plants in freezing, and they are thawed out slowly, the water which was withdrawn from the cells will be absorbed again and the plant will not be killed. But if the plant is thawed out quickly the water will not be absorbed, but will remain on the surface and evaporate. Some will also remain in the inter- cellular spaces, and the plant will die. Some plants, however, no matter how 92 PHYSIOLOGY. slowly they are thawed out, are killed after freezing, as the leaves of the pumpkin, dahlia, or the tubers of the potato. 218. It has been found that as a general rule when plants, or plant parts,. contain little moisture they will withstand quite high degrees of tempera- ture, as well as quite low degrees, but when the parts are filled with sap or water they are much more easily killed. For this reason dry seeds and the winter buds of trees, and other plants, because they contain but little water, are better able to resist the cold of winters. But when growth begins in the spring, and the tissues of these same parts become turgid and filled with water, they are quite easily killed by frosts. It should be borne in mind, however, that there is great individual variation in plants in this respect, some being more susceptible to cold than others. There is also great varia- tion in plants as to their resistance to the cold of winters, and of arctic climates, the plants of the latter regions being able to resist very low tem- peratures. We have examples also in the arctic plants, and those which grow in arctic climates on high mountains, of plants which are able to carry on all the life functions at temperatures but little above freezing. : MORPHOLOGY AND LIFE HISTORY OF REPRE- SENTATIVE PLANTS. CHAPTER XV. SPIROGYRA, 219. In our study of protoplasm and some of the processes of plant life we became acquainted with the general appearance of the plant spirogyra. It is now a familiar object to us. And in taking up the study of representative plants of the different ~ groups, we shall find that in knowing some of these lower plants the difficulties of understanding methods of reproduction and relationship are not so great as they would be if we were entire- ly ignorant of any members of the lower groups. 220. Form of spirogyra.—We have found that the plant spirogyra consists of simple threads, with cylindrical cells attached end to end. We have also noted that each cell of the thread is exactly alike, with the exception of certain ‘‘ hold- fasts ’’ on some of the species. If we should examine threads in different stages of growth we should find that each cell is capable of growth and division, just as it is capable of performing all the functions of nutrition and assimilation. The cells of spirogyra then multiply by division. Not simply the cells at the ends of the threads but any and all of the cells divide as they grow, and in this way the threads increase in length. _ 221. Multiplication of the threads.—In studying living material of this . plant we have probably noted that the threads often become broken by two of the adjacent cells of a thread becoming separated. This may be and is accom- . 93 94. MORPHOLOGY. plished in many cases without any injury to the cells. In this manner the Fig. 85. Thread of spiro- gyra, showing lon, cells, chlaraphyil band, nucleus, strands of proto- plasm, and_ the granular wall layer of protoplasm. threads or plants of spirogyra, if we choose to calla threada plant, multiply, or increase. In this breaking ofa thread the cell wall which separates any two cells splits. If we should examine several species of spirogyra we would probably find threads which present two types as regards the character of the walls at the ends of the cells. In fig. 85 we see that the ends are plain, that is, the cross walls are all straight. But in some other species the inner wall of the cells presents a peculiar appearance. This inner wall at the end of the cell is at first straight across. But it soon becomes folded back into the interior of its cell, just as the end of an empty glove finger may be pushed in. Then the infolded end is pushed partly out again, so that a peculiar figure is the result. 222. How some of the threads break.—In the separation of the cells of a thread this peculiarity is often of advan- tage to the plant. The cell-sap within the protoplasmic membrane absorbs water and the pressure pushes on the ends of the infolded cell walls. The inner wall being so much longer than the outer wall, a pull is exerted on the latter at the junction of the cells. Being weaker at this point the outer wall is ruptured. The turgidity of the two cells causes these infolded inner walls to push out suddenly as the outer wall is ruptured, and the thread is snapped apart as quickly as a pipe-stem may be broken. 223. Conjugation of spirogyra.—Under cer- tain conditions, when vegetative growth and multiplication cease, a process of reproduction takes place which is of a kind termed sexual repro- duction. If we select mats of spirogyra which have lost their deep green color, we are likely to find different stages of this sexual process, which in the case of spirogyra and related plants is called conjugation. A few threads of such a mat we should examine with the microscope. If the material is in the right condition we see in certain of the cells an oval or elliptical body. If we note carefully the cells in which these oval bodies are situated, there will be seen a tube at one side which con- SPIROG YRA. 95 nects with an empty cell ofa thread which lies near as shown in fig. 86. If wesearch through the material we may see other threads connected in this ladder fashion, in which the contents of the cells are in various stages of collapse from what we have seen in the growing cell. In some the protoplasm and chlorophyll band have moved but little from the wall; in others it forms a mass near the center of the cell, and again in others we will see that the contents of the cell of one of the threads has moved partly through the tube into the cell of the thread with which it is connected. 224. This suggests to us that the oval bodies found in the cells of one thread of the ladder, while the cells of the other thread were empty, are formed by the union of the contents of the two cells. In fact that is what does take place. This kind of union of the contents of two similar or nearly similar cells is conjugation. The oval bodies which are the result of this conjugation are gygo/es, or zygospores. When we are examining living ma- terial of spirogyra in this stage it is possible to watch this process of con- jugation. Fig. 87 represents the differ- Fig. 86. ent stages of conjugation of spirogyra. Zygospores of spirogyra. 225. How the threads conjugate, or join.—The cells of two threads lying parallel put out short processes. The tubes from two opposite cells meet and join. The walls separating the con- tents of the two tubes dissolve so that there is an open communi- cation between the two cells. The content of each one of these cells which take part in the conjugation is a gamefe. The one which passes through the tube to the receiving cell is the supply- 096 MORPHOLOGY. mg gamete, while that of the receiving cell is the recemng gamele. 226. How the protoplasm moves from one cell to another.—Before any movement of the protoplasm of the supplying cell takes place we can see Fig. 87. Conjugation in spirogyra; from left to right beginning in the upper row is shown the gradual passage of the protoplasm from the supplying gamete to the receiving gamete. that there is great activity in its protoplasm. Rounded vacuoles appear which increase in size, are filled with a watery fluid, and swell up like a vesicle, and then suddenly contract and disappear. As the vacuole disap- pears it causes a sudden movement or contraction of the protoplasm around it to take its place. Simultaneously with the disappearance of the vacuole the membrane of the protoplasm is separated from a part of the wall. This is probably brought about by a sudden loss of some of the water in the cell- sap. These activities go on, and the protoplasmic membrane continues to slip away from the wall. Every now and then there is a movement by which the protoplasm is moved a short distance. It is moved toward the tube and finally a portion of it with one end of the chlorophyll band begins to move into the tube. About this time the vacuoles can be seen in an active condition in the receptive cell. At short intervals movement con- SPIROGYRA. 97 tinues until the content of the supplying cell has passed over into that of the receptive cell. The protoplasm of this one is now slipping away from the cell wall, until finally the two masses round up into the one zygospore. 227. The zygospore.—This zygospore now acquires a thick wall which eventually becomes brown in color. The chlorophyll color fades out, and a large part of the protoplasm passes intv an oily substance which makes it more resistant to conditions which would be fatal to the vegetative threads. The zygospores ure capable therefore of enduring extremes of cold and dry- ness which would destroy the threads. They pass through a ‘resting ” period, in which the water in the pond may be frozen, or dried, and with the oncoming of favorable conditions for growth in the spring or in the autumn they germinate and produce the green thread again. 228. Life cycle.—The growth of the spirogyra thread, the conjugation of the gametes and formation of the zygospore, and the growth of the thread from the zygospore again, makes what is called a complete Ze cycle. 229. Fertilization.—While conjugation results in the fusion of the two masses of protoplasm, fertilization is accomplished when the nuclei of the two cells come together in the zygospore and fuse into a single nucleus. The Fig. 88. Fertilization in spirogyra ; shows different stages of fusion of the two nuclei, with mature zygospore at right. (After Overton.) different stages in the fusion of the two nuclei of a recently formed zygospore are shown in figure 88. In the conjugation of the two cells, the chlorophyll band of the supplying cell is said to degenerate, so that in the new plant the number of chlorophyll bands in a cell is not increased by the union of the two cells. 230. Simplicity of the process.—In spirogyra any cell of the thread may form a gamete (excepting the holdfasts of some species). Since all of the cells of a thread are practically alike, there is no structural difference between a vegetative cell andacell about to conjugate. The difference is a physiological one. All the cells are capable of conjugation if the physiolog- ical conditions are present. All the cells therefure are potential gametes. (Strictly speaking the wall of the cell is the gametangium, while the content forms the gamete.) While there is sometimes a slight difference in size between the conjugat- 98 MORPHOLOGY. ing cells, and the supplying cell may be the smaller, this isnot general. We say, therefore, that there is no differentiation among the gametes, so that usually before the protoplasm begins to move one cannot say which is to be the supplying and which the receiving gamete. 231. Position of the plant spirogyra.—From our study then we see that there is practically no differentiation among the vegetative cells, except where holdfasts grow out from some of the cells for support. They are all alike in form, in capacity for growth, division, or multiplication of the threads. Each cell is practically an independent plant. There is no differ- entiation between vegetative cell and conjugating cell. All the cells are potential gametes. Finally there is no structural differentiation between the gametes. This indicates then a simple condition of things, a low grade of organization. 232. The alga spirogyra is one of the representatives of the lower alga belonging to the group called Conjugate. Zygnema with star-shaped chloro- plasts, mougeotia with straight or sometimes twisted chlorophyll bands, be- long to the same group. In the latter genus only a portion of the protoplasm of each cell unites to form the zygospore, which is located in the tube between the cells. Fig. gt. . Xanthidium. Fig. go. Micrasterias. Fig. 89. Fig. 92. Fig. 94. Closterium. Staurastrum, Euvastrum. Cosmarium. 233. The desmids also belong tothe same group. The desmids usually live as separate cells. Many of them are beautiful in form. They grow entangled among other algee, or on the surface of aquatic plants, or on wet soil. Sev- eral genera are illustrated in figures 89-94. CHAPTER XVI. CEDOGONIUM. 234. Cdogonium is also an alga. The plant is sometimes associated with spirogyra, and occurs in similar situations. Our attention was called to it in the study of chlorophyll bodies. These we recollect are, in this plant, small oval disks, and thus differ from those in spirogyra. 235. Form of cedogonium.—Like spirogyra, cedogonium forms simple threads which are made up-of cylindrical cells placed end to end. But the plant is very different from any member of the group to which spirogyra belongs. In the first place each cell is not the equivalent of an individual plant as in spirogyra. Growth is localized or confined to certain cells of the thread which divide at one end in such a way as to leave a peculiar overlapping of the cell walls in the form of a series of shallow caps or vessels (fig. 95), and this is one of the character- istics of this genus. Other differences we find in the manner of reproduction. 236. Fruiting stage of edogonium.—Material in the fruiting stage is quite easily obtainable, and may be preserved for study in formalin if there is any doubt about obtaining it at the time we need it for study. This condition of the plant is easily de- tected because of the swollen condition of some of the cells, or by the presence of brown bodies with a thick wall in some of the cells. 237. Sexual organs of edogonium. Oogonium and egg.— The enlarged cell is the oogonium, the wall of the cell being the wall of tne oogonium. (See fig.96.) The protoplasm inside, before 99 100 MORPHOLOGY. fertilization, istheegg cell. In those cases where the brown body with a thick wall is present fertilization has taken place, and this body is the fertilized egg, or oospore. It contains large quantities of an oily substance, and, like Fig. 95. Portion of thread of cedo- gonium, show- ing chlorophyll grains, and pe- culiar cap cell Fig. 96. walls. CEdogonium undulatum, with oogonia and dwarf males; the upper oogonium at the right has a mature oospore. the fertilized egg of spirogyra and vaucheria, is able to with- stand greater changes in temperature than the vegetative stage, and can endure drying and freezing for some time without injury. In the oogonium wall there can frequently be seen a rift near the middle of one side, or near the upper end. This is the EDOGONIUAM. IO! opening through which the spermatozoid entered to fecundate the egg. 238. Dwarf male plants.—In some species there will also be seen peculiar club-shaped dwarf plants attached to the side of the oogonium, or near it, and in many cases the end of this dwarf plant has an open lid on the end. 239. Antheridium.—The end cell of the dwarf male in such species is the azfheridium. In other species the spermatozoids are developed in different cells (antheridia) of the same thread which bears the oogonium, or on a different thread. 240. Zoospore stage of cedogonium.—The egg after a period of rest starts into active life again. In doing so it does not develop the thread-like plant directly as in the case of vaucheria and spirogyra. It first divides into four zouspores which are exactly like the zoogonidia in form. (See fig. 103.) These germinate and develop the thread form again. This is a quite re- markable peculiarity of cedogonium when compared with either vaucheria or spirogyra. It is the introduction of an intermediate stage between the fertilized egg and that form of the plant which bears the sexual organs, and should be kept well in mind. 241. Asexual reproduction.—Material for the study of this stage of cedo- gonium is not readily obtainable just when we wish it for study. But fresh plants brought in and placed ina quantity of fresh water may yield suitable material, and it should be examined at intervals for several days. This kind of reproduction takes place by the formation of soogonidia. The entire contents of a cell round off into an oval body, the wall of the cell breaks, and the zoogonidium escapes. It has a clear space at the small Fig. 97. Zoogonidia of ceedogonium escaping. At the right one is germinating and forming the holdfasts, by means of which these algz attach themselves to objects end, and around this clear space for support. (After Pringsheim.) is a row or crown of cilia as shown in fig. 97. By the vibration of these cilia the zoogonidium swims around for a time, then settles down on some object of support, and several slender holdfasts grow out in the form of short rhizoids which attach the young plant. 242. Sexual reproduction. Antheridia.—The antheridia are short cells which are formed by one of the ordinary cells dividing into a number of disk-shaped ones as shown in fig. 98. The protoplasm in each antheridium 102 MORPHOLOGY. forms two spermatozoids (sometimes only one) which are of the same form as the zoogonidia but smaller, and yeilowish instead of green. In some species a motile body intermedi- ate in size and color be- tween the spermatozoids and zoogonidia is first formed, which after swimming around comes to rest on the oogonium, or near it, and develops what is called a ‘‘ dwarf male plant” from which the real spermatozoid is produced. Fig. 98. Fig. 99. . Portion of thread Portion of thread of cedo- eas Gogunie. ae of cdogonium gonium showing upper half oogonia are formed di- showing antheridia of egg open, and a sperma- tozoid ready to enter. (After rectly from one of the Oltmans). vegetative cells. In most species this cell first enlarges in diameter, so that it is easily detected. The protoplasm inside is the egg cell. The oogonium wall opens, a bit of the protoplasm is emitted, and the spermatozoid then enters and fertilizes it (fig. 99). Nowa hard brown wall is formed around it, and, just as in spirogyra Fig 100. Fig. ror. Fig. 102. Male nucleus just entering Male nucleus fusing with The two nuclei fused, and egg at left side. female nucleus. fertilization complete. Figs. 100-102.—Fertilization in cedogonium. (After Oltmans). and vaucheria, it passes through a resting period. Atthe time of germination it does not produce the thread-like plant again directly, but first forms four zoospores exactly like the zoogonidia (fig. 103). | These zoospores then germinate and form the plant. 244. (Edogonium compared with spirogyra.—Now if we compare cedo- gonium with spirogyra, as we did in the case of vaucheria, we find here also that there is an advance upon the simple condition which exists in spiro- gyra. Growth and division of the thread is limited to certain portions. The sexual organs are differentiated. They usually differ in form and size from the vegetative cells, though the oogonium is simply a changed vegetative @DOGONIUM. 103 cell. The sexual organs are differentiated among themselves, the antheridium is small, and the oogonium large. The gametes are also differentiated in size, and the male gamete is motile, and carries in its body the nucleus which fuses with the nucleus of the egg cell. But a more striking advance is the fact that the fertilized egg does not Fig. 103. Fertilized egg of cedogonium after a period of rest escaping from the wall of the oogonium, and dividing into the four zoospores. (After Juranyi.) produce the vegetative thread of cedogonium directly, but first forms four zoospores, each of which is then capable of developing into the thread. On the other hand we found that inspirogyra the zygo- spore develops directly into the thread form of the plant. 245. Position of cedo- gonium.—(CEdogonium is one of the true thread-like alge, green in color, and the threads are divided Fig. 104. into distinct cells. It, Tuft of cheto- : - phora, natural along with many relatives, size. was once placed in the old genus conferva. These are all now placed in the group Confervoidee, that is, the conferva-like alge. Fig. 105. 246. Relatives of edogonium.—Many other genera Portion of chetophora are related to cedogonium. Some consist of simple ‘OWS branching. threads, and others of branched threads. An example of the branched forms is found in chetophora, represented in figures 104, 105. This plant grows in quiet pools or in slow-running water. It is attached to sticks, rocks, or to larger aquatic plants. Many threads spring from the same point of attachment and radiate in all directions. This. together with the branching of the threads, makes a small, compact, greenish, rounded mass, which is 104. MORPHOLOGY. held firmly together by a gelatinous substance. The masses in this species are about the size of a small pea, or smaller. Growth takes place in che- tophora at the ends of the threads and branches. That is, growth is api- cal. This, together with the branched threads and the tendency to form cell masses, is a great advance of the vegetative condition of the plant upon that which we find in the simple threads of cedogonium. CHAPTER XVII. VAUCHERIA. 247. The plant vaucheria we remember from our study in an earlier chapter. It usually occurs in dense mats floating on the water or lying on damp soil. The texture and feeling of these mats remind one of ‘‘felt,’’ and the species are sometimes called the ‘‘ green felts.’’ The branched threads are continuous, that is there are no cross walls in the vegetative threads. This plant multiplies it- self in several ways which would be too tedious to detail here. But when fresh bright green mats can be obtained they should be placed in a large vessel of water and set in a cool place. Only asmall amount of the alga should be placed in a vessel, since decay will set in more rapidly with a large quantity. For several days one should look for small green bodies which may be floating at the side of the vessel next the lighted window. Fig. 106. Portion of branched thread of vaucheria. 248. Zoogonidia of vaucheria.—If these minute floating green bodies are found, a small drop of water containing them should be mounted for exami- 105 106 MORPHOLOGY. nation. If they are rounded, with slender hair-like appendages over the surface, which vibrate and cause motion, they very likely are one of the kinds of reproductive bodies of vaucheria. The hair-like appendages are cilia, and they occur in pairs, several of them distributed over the surface. These rounded bodies are gontdia, and because they are motile they are called zoogonidia. By examining some of the threads in the vessel where they occurred we may have perhaps an opportunity to see how they are produced. Short branches are formed on the threads, and the contents are separated from those of the main thread by a septum. The protoplasm and other contents of this branch separate from the wall, round up into a mass, and escape through an opening which is formed in the end. Here they swim around in the water for a time, then come to rest, and germinate by growing out into a tube which forms another vaucheria plant. It will be observed that this kind of reproduction is not the result of the union of two different parts of the plant. It thus differs from that which is termed sexual reproduction. A small part of the plant simply becomes separated from it as a special body, and then grows inio a new plant. a sort of multiplication. This kind of re- production has been termed asexual reproduction. 249. Sexual reproduction in vaucheria.—The organs which are concerned in sexual reproduction in vaucheria are very readily obtained for study if one collects the material at the right season. They are found quite readily during the spring and autumn, and may be preserved in formalin for study at any season, if the material cannot be collected fresh at the time it is desired for study. Fine material for study often occurs on the soil of pots in greenhouses during the winter. While the zoogonidia are more apt to be found in material which is quite green and fresh- ly growing, the sexual organs are usually more abundant when the threads appear some- what yellowish, or yellow green. 250. Vaucheria sessi- lis; the sessile vauche- Young antheridium and oogonium of Vaucheria ses- silis, before separation from contents of thread by a ria.—In this plant the septum, Vig. 107. sexual organs are sessile, that is they are not borne ona stalk as in some other species. The sexual organs usually occur several ina group. Fig. 107 represents a portion of a fruiting plant. ee VAUCHERIA. 107 251. Sexual organs of vaucheria. Antheridium.—The antheridia are short, slender, curved branches from a main thread. A septum is formed which separates an end portion from the stalk, This end cell is the an/heridium. Frequently it is collapsed or empty as shown in fig. 108. The protoplasm in Fig 108. Vaucheria sessilis, one antheridium between two oogonia. the antheridium forms numerous small oval bodies each with two slender lashes, the cilia. When these are formed the antherid- ium opens at the end and they escape. It is after the escape of these spermatozoids that the antheridium is collapsed. Each spermatozoid is a male gamete. 252. Oogonium.—The oogonia are short branches also, but they become large and somewhat oval. The septum which separates the protoplasm from that of the main thread is as we see near the junction of the branch with the main Fig. 109. Vaucheria sessilis; oogonium opening and emit- = 7 ting a bit of protoplasm; spermatozoids; sperma- as shown in the figure, 18 tozoids entering oogonium. (After Pringsheim and usually turned somewhat Goebel.) thread. The oogonium, to one side. When mature the pointed end opens and a bit of the protoplasm escapes. The remaining protoplasm forms the large rounded egg cell which fills the wall of the oogonium., In some of the oogonia which we examine this egg is surrounded by a thick brown wall, with starchy and oily contents. This is the 108 MORPHOLOGY. fertilized egg (sometimes called here the oospore). It is freed from the oogonium by the disintegration of the latter, sinks into Fig. 110. Fertilization in vaucheria. 777, male nucleus ;_/7, female nucleus. Male nucleus entering the egg and approaching the female nucleus. (After Oltmans.) the mud, and remains here until the following autumn or spring, when it grows directly into a new plant. 253. Fertilization.—Fertilization is accomplished by the spermatozoids swimming in at the open end of the oogonium, Fertilization of vaucheria. /x, female nucleus; #2”, male nucleus. The different figures show various stages in the fusion of the nuclei. when one of them makes its way down into the egg and fuses with the nucleus of the egg. 254. The twin vaucheria (V. geminata).—Another specics of vaucheria is the twin vaucheria. This is also a common one, and may be used for study instead of the sessile vaucheria if the latter cannot be obtained. The sexual organs are borne at the end of a club-shaped branch. ‘There are usually two oogonia, and one antheridium between them which terminates the branch. In a closely related species, instead of the two oogonia there is a whorl of them with the antheridium in the center. 255. Vaucheria compared with spirogyra.—In vaucheria we have a plant which is very interesting to compare with spirogyra in several respects. VAUCHERIA,. 109 Growth takes place, not in all parts of the thread, but is localized at the ends of the thread and its branches. This represents a distinct advance on such a plant as spirogyra. Again, only specialized parts of the plant in vaucheria form the sexual organs. These are short branches. Farther there is a great difference in the size of the two organs, and especially in the size of the gametes, the supplying gametes (spermatozoids) being very minute, while the receptive gamete is large and contains all the nutriment for the fertilized egg. In spirogyra, on the other hand, there is usually no differ- ence in size of the gametes, as we hive seen, and each contributes equally in the matter of nutriment for the fertilized egg. Vaucheria, therefore, rep- resents a distinct advance, not only in the vegetative condition of the plant, but in the specialization of the sexual organs. Vaucheria, with other related algze, belongs toa group known as the Szphonea, so called because the plants are tube-like or siphon-like. CHAPTER XVIII. COLEOCH/ETE, 256. Among the green algz coleochete is one of the most interesting. Several species are known in this country. One of these at least should be examined if it is possible to obtain it. It occurs in the water of fresh lakes and ponds, attached to aquatic plants. 257. The shield-shaped coleochete.—This plant (C. scutata) a P Fig. 112. Stem of =) aquatic plant e ‘a showing co- i" [} leochete, natural size. Kt f Xx Fig. 113. Thallus of Coleochzte scutata. is in the form of a flattened, circular, green plate, as shown in fig. 112. It is attached near the center on one side to rushes 110 COLEOCH.ETE. Ill and other plants, and has been found quite abundantly for sev- eral years in the waters of Cayuga Lake at its southern extremity. As will be seen it consists of a single layer of green cells which radiate from the center in branched rows to the outside, the cells lying so close together as to form a continuous plate. The plant started its growth from a single cell at the central point, and grew at the margin in all directions. Sometimes they are quite irregu- lar in outline, when they lie quite closely side by side and inter- fere with one another by pressure. If the surface is examined carefully there will be found long hairs, the base of which is en- closed in a narrow sheath. It is from this character that the genus takes its name of coleochzte (sheathed hair). 258. Fruiting stage of coleochete.—It is possible at some seasons of the year to find rounded masses of cells situated near the margin of this green disk. These have developed from a fertilized egg which remained attached to the plant, and prob- ably by this time the parent plant has lost its color. 259. Zoospore stage.—This mass of tissue does not develop directly into the circular green disk, but each of the cells forms a zoospore. Here then, as in cedogonium, we have an- other stage of the plant in- terpolated between the fer- tilized egg and that stage of the plant which bears the gametes. But in coleochete we have a distinct advance in this stage upon what is pres- Figs ti4, of ortign of thallus = st i Portion of thallus of Co- scutata, showing ent In cedogonium, for in leochzte scutata, showing four antheridia ili empty cells from which formed from one coleochete the fertilized zoogonidia have escaped, thallus cell; a sin- i i one fromeach cell; zoogo- __gle spermatozoidat egg develops first into a nidia at the left.’ (After the right’ (After several-celled mass of tissue Pringsheim.) Pringsheim.) before the zoospores are formed, while in cedogonium only four zoospores are formed directly from the egg. Hig 260. Asexual reproduction.—In asexual reproduction any of the green cells on the plant may form zoogonida. The contents of a cell round off and 112 MORPHOLOGY. form a single zoogonidium which has two cilia at the smaller end of the oval body, fig. 114. After swimming around for a time they come to rest, ger- minate, and produce another plant. 261. Sexual reproduction.—Oogonium.—The oogonium is formed by the enlargement of a cell at the end of one of the threads, and then the end of the Fig. 116. Coleochate soluta; at left branch bearing oogonium (cog); antheridia (ax); egg in oogonium and surrounded by enveloping threads; at center three antheridia open, and one spermatozoid ; at right sporocarp, mature egg inside sporocarp wall. cell elongates into a slender tube which opens at the end to form a channel through which the spermatozoid may pass down to the egg. The egg is formed of the contents of the cell (fig. 116). Several oogonia are formed on one plant, and in such a plant as C. scutata they are formed in a ring near the margin of the disk. 262. Antheridia.—In C. scutata certain of the cells of the plant divide into four smaller cells, and each one of these becomes an antheri- Two sporocarps \ still Sporocarp ruptured b dium. In C, soluta the an- surrounded by thallus. growth of egg to form cell theridia grow out from the Thallus finally decays and mass. Cells of ‘this sporo- i . F sets sporocarp free. phyte forming zoospores. end of terminal cells in the Figs. 117, 118, C. scutata, form of short flasks, some- times four in number or less (fig. 116). A single spermatozoid is formed from the contents. It is oval and possesses two long cilia. After swim- COLEOCH ATE. 113 ming around it passes down the tube of the oogonium and fertilizes the egg. 263. Sporocarp.—After the egg is fertilized the cells of the threads near the egg grow up around it and form a firm covering one cell in thickness. This envelope becomes brown and hard, and serves to protect theegg. This is the ‘‘fruit’’ of the coleochate, and is sometimes called a sporocarp (spore fruit). The development of the cell mass and the zoospores from the egg has been described above: Some of the species of coleochzete consist of branched threads, while others form circular cushions several layers in thickness. These forms together with the form of our plant C. scutata make an interesting series of transi- tional forms from filamentous structures to an expanded plant body formed of a mass of cells. MORPHOLOGY. 114 x “s][29 JO ‘umr1uoSo0o spunoaims sseW ® WLIO: speaiy} Surdojaaua oy sMmod jO [eM uoTezTVAI09) pure. sap Jay “sdajua ploz 1d “s}sey “ummrpriey}|-oyeursads yoryam Jo “(ay Ayd “ue Yova wo1jaU0|Zuruado YZno1yy aqn}y *1]99 ‘3aa ‘unipru03 sureSe aseyd “Saa|- 0,9 we 3 ‘Ie 339)‘ proz oj eutads|Suoy yyM ‘[]99 "aa palapsurs wos [eIaAas 10|-ooza[SuIS v WAOF *saqe[d avpno sdojaaap = asods/uro ay [femasieq jayeyioiq ‘[eAQ. |-saejua ‘wnwos0Q =jAnoy ‘eipuayyuy jAeu [[a9 Auy -419 yeduroo -00Z ‘a10dsooz/Aq papunos “RITTD OM} YIM) ‘TeuULseUI 10/10 ‘speazyy)-azeyo Be suuoy yoeq j-ins) 33q “payenuasayiq, “payenuaiayiq: viptuosooz Aq |yeuruiay | payouerg -023[09, “wMIppayjue “sayeul yora wo1y omy) ieee ° JIVMp UO saUTTaWOS “winipru0s “urese aseyd “aa “BIT LO JO uMmOI|}Iq sya pue suado]"][ao aayejasaa au0]-ooza[Surs v ULIOY sdojaaap = yoy an *T[99 38alyIIM splrozoy ‘Yee BANRIVFIA palwioay peLaAas ‘padeys|Avur [pao Auy “peazyy “s]]22 ‘um aiodsooz sulioj ‘sysoqyjadiey |-euueds yeag |-suevyo ‘wniuos0g $ |-yxstp wipuayuy |-e1pt19 Jo uUMOIDJO suo Ly yeoupury Ao -o30py) yova { stjao anoj)"(a10dso00 YIM ‘erpluo3-sod ureyasljo © speaiy3 OyuL sapiaiq |10) 33q “payeljuarayiq. “payenuaiayiq: -00z [eAo Ag joy payuny ja jdwis suse[do} -oid jo y1q sywa pue ‘sptoz susdo ‘youriq [eI “say suo ‘]]22 B8a}-oyeutads — paye -ads uo‘{[ao papunol -ueiq [erads uo s[jad|-r0d = yeutut1a} “sayouelq “eu “sysoyjasiey [-y-omz emg jasiey ‘wmuos0Q jsapusys eipuayWUY jurogy ‘s[[a9 tayiO|pue spraiyy *snonun|-ayone a, “‘Apesp aseyd)-(ar0dsoo0 pue ‘eipiuogs00z|yo0 s pudal-uoo ‘speaiy) ‘Baa sdojaaaq 10) 33q *payenusragiq: “‘payenuarayiq: . /BeVHow Ag jo} paywryT jpayouesg *s[]P0 [199 Bur “M018 |TeoL Ip ups “Ay~earp aseyd *sysaqy|-e3n{uo0d Jo sjua}U09 a1} ‘aqny Aq a}e3nluoz “speaiy} jo dn/pue aptarp jo sproit3| e143 Boa sdopaaaq jesodso3sZ |-uq = ‘palenuesayipuy, |'peeityy jo [poo Auy “payenuesayipugq |suryeorq Ag js[pe2 Ty japduis -oudg “LINN ‘SHLEWV) ‘SNVDUO TVAXaS “NOIL¥D ‘ aSVHQ SAIL “dadO1dAa(T SI J -11dIL10 HLMOU) | eon eas soiods sieagq NOMS sae TEARS W NaOH so a8VHq = (ALAHd “STA MOH -OUOdS (-e1praogd pure suesi0 yenxes ayy siveq) §“@] LAHAOLANV9 ‘ALW HOOTOO ‘WOINODOGD ‘VINAHONVA ‘VUADONIdS WOA ATAVL AALLVUVANOD ‘b9S CHAPTER XIX. BROWN AND RED ALG. 265. If it is desired to extend the study of the alge to other groups, especially to some of the marine forms, examples of the brown algze and of the red algee may be obtained. These are accessible at the seashore, and for inland laboratories material thay be preserved in formalin (21% @). 266 The brown alge (Pheophycex).*—A good representative of one division of the brown algze and one often used for study is the genus fzczs. 267. Form and occurrence of fucus.—This plant is a more or less branched and flattened thallus or “frond.” One of them, illustrated in fig. II9g, measures I5—30c7 (6-12 inches) in length. It is attached to rocks and stones which are more or less exposed at low tide. From the base of the plant are developed several short and more or less branched expansions called ‘‘holdfasts,’’ which, as their name implies, are organs of attachment. Some species (F. vesiculosus) have vesicular swellings in the thallus. The fruiting portions are somewhat thickened as shown in the figure. Within these portions are numerous oval cavities opening by a circular pore, which gives a punctate appearance to these fruiting cushions. Tufts of hairs frequently project through them. 268. Structure of the conceptacles.—On making sections of the fruiting portions one finds the walls of the cavities covered with outgrowths. Some of these are short branches which bear a large rounded terminal sac, the oogonium, at maturity containing eight egg cells. More slender and much branched threads bear narrowly oval antheridia. In these are developed several two-ciliated spermatozoids. 269. Fertilization.—At maturity the spermatozoids and egg cells float out- side of the oval cavities where fertilization takes place. The spermatozoid sinks into the protoplasm of the egg cell, makes its way to the nucleus of the egg, and fuses with it as shown in fig. 125. The fertilized egg then grows into a new plant. Nearly all the brown algz are marine. * The members of the group possess chlorophyll, but it is obscured by a brown pigment. 115 116 MORPHOLOGY. 270. The red alge (Rhodophycex).—The larger number of the so-called red algze occur in salt water, though a few genera occur in fresh water. Fig. 121. Oogonium of fucus with ripe eggs. Fig. 119. Fig. 120. Portion of plant of fucus showing Section of conceptacle of fucus, showing conceptacles in enlarged ends; and oogonia, and tufts of antheridia. below the vesicles (Fucus vescicu- losus). (Lemanea grows only in winter in turbulent water of quite large streams. Batrachospermum grows in rather slow-running water of smaller streams. Both of these inhabit fresh water.) The plants of the group possess chloro- phyll, but it is usually obscured by a reddish or purple pigment. 271. Gracillaria.—Gracillaria is one of the marine forms, and one species is illustrated in fig. 126. It measures 15-20cvz or more long, and is pro- fusely branched in a palmate manner. The parts of the thallus are more or less flattened. The fruit is a cystocarp, which is characteristic of the rhodo- BROWN AND RED ALG. 1I7 phycex (florideze). In gracillaria these fruit bodies occur scattered over the thallus. They are somewhat flask-shaped, are partly sunk in the gcwdes = Fig. 122. Fig. 123. Fig. 124. Antheridia of fucus, on Antheridia of fucus with Egg of fucus surrounded branched threads. escaping spermatozoids. by spermatozoids. thallus, and the conical end projects strongly above the surface. The car- pospores are grouped in radiating threads within the oval cavity of the Fig. 125. Fertilization in fucus ;_/, female nucleus; 7, male nucleus; 7, nucleolus. In the ieft figure the male nucleus is shown moving down through the cytoplasm of the egg; in the remaining figures the cytoplasm of the egg is omitted. (After Strasburger.) cystocarp. These cystocarps are developed as a result of fertilization. Other plants bear gonidia in groups of four, the so-called ¢etraspores. 272. Rhabdonia.—This plant is about the same size as the gracillaria, though it possesses more filiform branches. The cystocarps form prominent elevations, while the carpospores lie in separated groups around the periph- ery of a sterile tissue within the cavity. (See figs. 128, 129.) Gonidia in the form of tetraspores are also developed in rhabdonia. 118 MORPHOLOGY. Fig. 126. Fig. 127. Gracillaria, portion of frond, Gracillaria, section of cystocarp showing position of cysto- showing spores. carps. 273. The principal groups of the alge are the following: ( Protococcoidez (the protococcus (Pleurococ- cus vulgaris); the red-snow plant (Spheerella nivalis), etc. Chlorophycee. | Conjugate (spirogyra, zygnema, mougeotia, Green alge. desmids, etc.). Siphonez (vaucheria). Confervoidez (cedogonium, cheetophora, cole- [ ocheete). Cyanophycee (nostoc, oscillatoria, etc.). The blue-green alge. Pheophycee (fucus, etc.). The brown algze, BROWN AND RED ALG. TIlg Rhodophycee (rhabdonia, gracillaria, callithamnion, champia, etc.). The red alge. 274. Some of the protococcoidez are believed to lie very near some of the lower animals like the flagellates. They are mostly single-celled plants; some of them are motile during the vegetative stage, and others are not motile, while others are Fig. 128. : Rhabdonia,branched Fig. 129. : : portion of frond show- Section of cystocarp of rhabdonia, showing ing cystocarps. spores. may be obtained by scraping the red-looking matter out of the bottom of dry shallow basins in the rocks, close by fresh-water streams or lakes. es § ®, By placing some of this material in a vessel of or water for a few days the motile stage may be FIBs 130. 5 Pleurococcus (pro- obtained. The protococcus, or Pleurococcus vul- tococcus) vulgaris. garis, may be obtained on the north side of trees, rocks, and walls, in damp places. . motile during certain stages. The red-snow plant > © © CHAPTER XX. FUNGI: MUCOR AND SAPROLEGNIA. Mucor. 275. In the chapter on growth, and in our study of proto- plasm, we have become familiar with the vegetative condition of mucor. We now wish to learn how the plant multiplies and re- produces itself. For this study we may take one of the mucors. Any one of several species willanswer. Thisplant may be grown by placing partially decayed fruits, lemons, or oranges, from which the greater part of the juice has been removed, in a moist cham- ber; or often it occurs on animal excrement when placed under similar conditions. In growing the mucor in this way we are likely to obtain Mucor mucedo, or another plant sometimes known as Mucor stolonifer, or Rhizopus nigricans, which is illus- trated in fig. 132. This latter one is sometimes very injurious to stored fruits or vegetables, especially sweet potatoes or rutaba- gas. Fig. 131 is from a photograph of this fungus on a banana. 276. Asexual reproduction.—On the decaying surface of the vegetable matter where the mucor is growing there will be seen numerous small rounded bodies borne on very slender stalks. These heads contain the gonidia, and if we sow some of them in nutrient gelatine or agar in a Petrie dish the material can be taken out very readily for examination under the microscope. Or we may place glass slips close to the growing fungus in the moist chamber, so that the fungus will develop on them, though cultures in a nutrient medium are much better. Or we may take the material directly from the substance on which it is growing. 120 FUNGI: MUCOR. 121 After mounting a small quantity of the mycelium bearing these heads, if we have been careful to take it where the heads appear quite young, it may be possible to study the early stages of their Fig. 131. 2 Portion of banana with a mould (Rhizopus nigricans) growing on one end. development. We shall probably note at once that the stalks or upright threads which support the heads are stouter than the threads of the mycelium. These upright threads soon have formed near the end a cross wall which separates the protoplasm in the end from the remain- der. This end cell now enlarges into a vesicle of considerable size, the head as it appears, but to which is applied the name of sporangium (sometimes called gonidangium), because it encloses the gonidia. At the same time that this end cell is enlarging the cross wall is arching up into the interior. This forms the columella. All the protoplasm in the sporangium now divides into gonidia. These are small rounded or oval bodies. The wall of the spo- 122 MORPHOLOGY. rangium becomes dissolved, except a small collar around the stalk which remains attached below the columella (fig. 133). Fig. 132. Group of sporangia of a mucor (Rhizopus nigricans) showing rhizoids and the stolon extend- ing from an older group. By this means the gonidia are freed. These gonidia germinate and produce the mycelium again. 277. Sexual stage.—This stage is not so frequently found, but may some- times be obtained by growing the fungus on bread. Conjugation takes place in this way. Two threads of the mycelium which lie near each other put out each a short branch which is clavate in form. The ends of these branches meet, and in each a septum is formed which cuts off a portion of the protoplasm in the end from that of the rest of the my- celium. The meeting walls of the branches now dissolve and the protoplasm of each gamete fuses into one mass. A thick wall is now formed around this mass, and the outer layer becomes rough and brown. This is the zygote or zygospore. ‘The mycelium dies and it becomes free often with the suspensors, as the stalks of these sexual branches are called, still attached. This zygo- spore passes through a period of rest, when with the entrance of favorable conditions of growth it germinatcs, and usually produces directly a sporan- gium with gonidia. This completes the normal life cycle of the plant. 278. Gemme.—Gemme, as they are somctimes called, are often formed on the mycelium. A short cell with a stout wall is formed on the side of a FUNGI: SAPROLEGNIA. 123 thread of the mycelium. In other cases large portions of the threads of the mycelium may separate into chains of cells. Both these kinds of cells are Fig. 133. A mucor (Rhizopus nigricans); at left nearly mature sporangium with columella showing within; in the middle is ruptured sporangium with some of the gonidia clinging to the colu- mella; at right two ruptured sporangia with everted columella. capable of growing and forming the mycelium again. They are sometimes called chlamydospores. Water Moulds (Saprolegnia). 279. The water moulds are very interesting plants to study because they are so easy to obtain, and it is so easy to observe a type of gonidium here to which we have referred in our studies of thealgze, the motile gonidium, or zoogonidium, (See appen- dix for directions for cultivating this mould.) 280. Appearance of the saprolegnia.—In the course of a few days we are quite certain to see in some of the cultures deli- cate whitish threads, radiating outward from the body of the fly in the water. A few threads should be examined from day to day to determine the stage of the fungus. 281. Sporangia of saprolegnia.—The sporangia of saprolegnia can be easily detected because they are much stouter than the 124 MORPHOLOGY. ordinary threads of the mycelium. Some of the threads should be mounted in fresh water. Search for some of those which Fig. 134. Sporangia of saprolegnia, one showing the escape of the zoogo- nidia show that the protoplasm is divided up into a great number of small areas, as shown in fig. 134. With the low power we should watch some of the older ap- pearing ones, and if after a few minutes they do not open, other preparations should be made. 282. Zoogonidia of saprolegnia.—The sporangium opens at Fig. 135. Branch of saprolegnia showing oogonia with oospores, eggs matured parthenogenetically. the end, and the zoogonidia swirl out and swim around for a short time, when they come to rest. With a good magnifying FUNGI: SAPROLEGNIA. 125 Fig. 136. Fertilization in saprolegnia, tube of antheridium carrying in the nucleus of the sperm cell to the egg. In the eee figure a smaller sperm nucleus is about to fuse with the nucleus of the egg. (After Humphrey and Trow.) Fig. 138. Branching hypha of Peronospora alsinearum. Branched hypha of downy mildew of grape showing peculiar branching (Plasmopara viticola). 126 MORPHOLOGY. power the two cilia on the end may be seen, or we may make them more distinct by treatment with Schultz’s solution, draw- ing some under the cover glass. The zoogonidium is oval and the cilia are at the pointed end. After they have been at rest “AM? LO es b = wae NY Fig. 139. Fig. r4o. Downy mildew of grape (Plasmopora viti- Phytophthora infestans showing pe- cola), showing tuft of gonidiophores bearing culiar branches; gonidia below. gonidia, also intercellular mycelium. (After Millardet.) for some time they often slip out of the thin wall, and swim again, this time with the two cilia on the side, and then the zoogonidium is this time more or less bean-shaped or reniform, 283. Sexual reproduction of saprolegnia.—When such cultures are older we often see large rounded bodies either at the end of a thread, or of a branch, which contain several smaller rounded bodies as shown in fig. 135. These are the oogonia (unless the plant is attacked by a parasite), and the round bodies inside are the egg cells, if before fertilization, or the eggs, if FUNGI: SAPROLEGNIA. 127 after this process has taken place. Sometimes the slender antheridium can be seen coiled partly around the oogonium, and one end entering to come in contact with the egg cell. But in some species the antheridium is not present, and that is the case with the species figured at 135. In this case if Q Fig. 14r. Fig. 142. po apnies and gonidia of potato poe (Phytophthora in- Gonidia of potato festans). 6, an older stage showing how the branch enlarges where blight forming zoogo- it grows beyond the older gonidium. (After de Bary.) nidia. ,After de Bary.) the eggs mature without fertilization. This maturity of the egg without fertilization is called parthenogenesis, which occurs in other plants also, but is a rather rare phenomenon. 284. In fig. 136 is shown the oogonium and an antheridium, and the antheridium is carrying in the male nucleus to the egg cell. Spermatozoids Fig. 143. Fertilization in Peronospora alsinearum; tube from antheridium carrying in the sperm nucleus in figure at the left, female nucleus near; fusion of the two nuclei shown in the two other figures. (After Berlese.) are not developed here, but a nucleus in the antheridium reaches the egg cell. It sinks in the protoplasm of the egg, comes in contact with the nu- cleus of the egg, and fuses with it. Thus fertilization is accomplished. 128 MORPHOLOGY. Downy Mildews. 285. The downy mildews make up a group of plants which are closely related to the water moulds, but they are parasitic on land plants, and some species produce very serious diseases. The mycelium grows between the cells of the leaves, stems, etc., of their liosts, and sends haustoria into the cells to take up nutriment. Gonidia are formed on threads which grow through the stomates to the outside and branch as shown in figs. 137-140. The gonidia are borne on the tips of the branches. The kind of branching bears some relation to the different genera. Fig. 137 is '\ from Peronospora alsinearum on leaves of cerastium; figs. 138 and 139 are Plasmopara viticola, the grape mildew, while figs. 140 and 141 are trom Phytophthora infestans, which causes a disease known as potato blight. The gonidia of peronospora germinate by a germ tube, those of plasmop- ara first form zoogonidia, while in phytophthora the gonidium Fig 144. may either germinate forming a Ripe oospore of Peronospora alsinearum. thread, or each gonidium may first form several zoogonidia as shown in fig. 142. 286. In sexual reproduction oogonia and antheridia are developed on the mycelium within the tissues. Fig. 143 represents the antheridium entering the oogonium, and the male nucleus fusing with the female nucleus in fertili- zation. The sexual organs of Phytophthora infestans are not known. 287. Mucor, saprolegnia, peronospora, and their relatives have few or no septa in the mycelium. In this respect they resemble certain of the alge like vaucheria, but they lack chlorophyll. They are sometimes called the alga-like fungi and belong to a large group called Phycomycetes. CHAPTER XXI. FUNGI CONTINUED (RUSTS AND SAC FUNGI). “Rusts” (Uredinez.. 288. The fungi known as ‘‘rusts’’ are very important ones to study, since all the species are parasitic, and many produce serious injuries to crops. 289. Wheat rust (Puccinia graminis).—The wheat rust is one of the best known of these fungi, since a great deal of study has been given to it. One form of the plant occurs in long Fig. 145. Fig. 146. Fig. 147. Fig. 148. Fig. 149. Wheat leaf with red Portion of leaf Natural size. Enlarged. Single trust, natural size. enlarged to show sorus. sori. Figs. 145, 146.—Puccinia graminis, red-rust stage (uredo stage). Figs. 147-149.—Black rust of wheat, showing sori of teleutospores. reddish-brown or reddish pustules, and is known as the ‘‘ red rust’’ (figs. 145, 146). Another form occurs in elongated black pustules, and this form is the one known as the ‘black rust”’ 129 130 MORPHOLOGY. (figs. 147-150). These two forms occur on the stems, blades, etc., of the wheat, also on oats, rye, and some of the grasses. 290. Teleutospores of the black-rust form.—If we scrape off some portion of one of the black pustules (sori), tease it out Teleutospores of wheat rust, showing two cells and the pedicel. t } Fig. 150. Fig. 152. Head of wheat showing black rust spots Uredospores of wheat rust, one on the chaff and awns. showing remnants of the pedicel. in water on a slide, and examine with a microscope, we see numerous gonidia, composed of two cells, and having thick, brownish walls as shown in fig. 151. Usually there is a slender brownish stalk on one end. ‘These gonidia are called /eleuto- spores. They are somewhat oblong or elliptical, a little con- stricted where the septum separates the two cells, and the end cell varies from ovate to rounded. The mycelium of the fungus FUNGI: RUSTS. 131 courses between the cells, just as is found in the case of the carnation rust, which belongs to the same family (see Part III). 291. Uredospores of the red-rust form.—If we make a simi- lar preparation from the pustules of the red-rust form we see that instead of two-celled gonidia they are one-celled. The walls are thinner and not so dark in color, and they are covered with minute spines. They have also short stalks, but these fall away very easily. These one-celled gonidia of the red-rust form are called ‘‘uredospores.’’ The uredospores and teleutospores are sometimes found in the same pustule. It was once supposed that these two kinds of gonidia belonged to different plants, but now it is known that the one-celled form, the uredospores, is a form developed earlier in the season than the teleutospores. 292. Cluster-cup form on the barberry. —On the barberry is found still another form of the wheat rust, the ‘‘ cluster cup’’ stage. The pustules on the under side of the barberry leaf are cup-shaped, the cups being partly sunk in the tissue of the leaf, while the rim is more or less curved back- ward against the leaf, and split at several places. These cups occur in clusters on the affected spots of the barberry Fig. 153. leaf as shown Barberry leaf with two Single spot Two cluster jn fig. 154. diseased ‘spots, natural showing cluster cups more en- ers size. cups enlarged. larged, showing \Vithin the split margin. Figs. 153-155.—Cluster-cup stage of wheat rust. cups numbers of one-celled gonidia (orange in color, called aecidiospores) are borne in chains from short branches of the mycelium, which fill the base of the cup. In fact the wall of the cup (peridium) 132 MORPHOLOG ¥. is formed of similar rows of cells, which, instead of separating into gonidia, remain united to form a wall. These cups are usually borne on the under side of the leaf. 293. Spermagonia.—Upon the upper side of the leaves in the same spot occur small, orange-colored pustules which are flask-shaped. They bear inside, minute, rod-like bodies on the ends of slender threads, which ooze SPE ee aes OR a i 4 leet Ne Ll . Os ISS \: aa S X cS) CH Fig. 156. Section of an azcidium (cluster cup) from barberry leaf. (After Marshall-Ward.) out on the surface of the leaf. These flask-shaped pustules are called spermagonia, and the minute bodies within them sfermatia, since they were once supposed to be the male element of the fungus. Their function is not known. They appear in the spots at an earlier time than the cluster cups. 293. How the cluster-cup stage was found to be a part of the wheat rust. —The cluster-cup stage of the wheat rust was once supposed also to bea dif- ferent plant, and the genus was called @c¢dium. The occurrence of wheat rust in great abundance on the leeward side of affected barberry bushes in England suggested to the farmers that wheat rust was caused by barberry rust. It was later found that the zcidiospores of the barberry, when sown on wheat, germinate and the thread of mycelium enters the tissues of the wheat, forming mycelium between the cells. This mycelium then bears the uredospores, and later the teleutospores. FUNGI: RUSTS. 133 294. Uredospores can produce successive crops of uredospores.—Tise uredo- spores are carried by the wind to other wheat or grass plants, germinate, Fig. 157. Section through leaf of barberry at point affected with the cluster-cup stage of the wheat rust; spermagonia above, zcidia below. (After Marshall-Ward.) form mycelium in the tissues, and later the pustules with a second crop of uredospores. Several successive crops of uredospores may be developed in Fig. 158. A, section through sorus of black rust of wheat, showing teleutospores. 2, mycelium bearing both teleutospores and uredospores. (After de Bary.) one season, so this is the form in which the fungus is greatly multiplied and widely distributed. : 134 MORPHOLOG ¥. 295. Teleutcspores the last stage of the fungus in the season.—The teleu- tospores are developed late in the season, or late in the development of the host plant (in this case the wheat is the host). They then rest during the winter. In the spring under favor- able conditions each cell of the teleutospore germi- nates, producing a short mycelium called a promy- celium, as shown in figs. 161, 162. This promy- celium is usually divided into four cells. From each cell a short, pointed pro- cess is formed called a “ sterigma.’’ Through this the protoplasm moves and Bigs 159: Figi/160. forms a small gonidium on Germinating uredospore of Germ tube entering the é wheat rust. (After Marshall- leaf through a stoma. the end, sometimes called Ward.) a sporidium. 296. How the fungus gets from the wheat back to the barberry.—If these sporidia from the teleutospores are carried by the wind so that they lodge on \ ys Fig. ror. Fig. 162. Fig. 163. Teleutospore germi- — Promycelium of ger- Germinating sporidia entering leai nating, forming promy- minating teleutospore, of barberry by mycelium, celium, forming sporidia. Figs. 161-163.—Puccinia graminis (wheat rust). (After Marshall-Ward.) FUNGI: RUSTS. 135 the leaves of the barberry, they germinate and produce the cluster cup again. The plant has thus a very complex life history. Because of the presence of several different forms in the life cyle, it is called a polymorphic fungus. The presence of the barberry does not seem necessary in all cases for the development of the fungus from one year to another. 297. Synopsis of life history of wheat rust. Cluster-cup stage on leaf of barberry. Mycelium between cells of leaf in affected spots. Spermagonia (sing. spermagonium), small flask-shaped bodies sunk in upper side of leaf; contain ‘‘ spermatia.’’ ZEcidia (sing. ecidium), cup-shaped bodies in under side of leaf. Wall or peridium, made up of outer layer of fungus threads which are divided into short cells but remain united. At maturity bursts through epidermis of leaf; margin of cup curves outward and downward toward surface of leaf. Central threads of the bundle are closely packed, but free. Threads divide into short angular cells which separate and become ecidiospores, with orange-colored content. ‘Ecidiospores carried by the wind to wheat, oats, grasses, etc. Here they germinate, mycelium enters at stomate, and forms mycelium between cells of the host. Uredo stage (red rust) on wheat, oats, grasses, etc. Mycelium between cells of host. Bears uredospores (1-celled) in masses under epidermis, which is later ruptured and uredospores set free. Uredospores carried by wind to other individual hosts, and new crops of uredospores formed. Teleutospore stage (black rust), also on wheat, etc. Mycelium between cells of host. Bears teleutospores (2-celled) in masses (sori) under epidermis, which is later ruptured. Teleutospores rest during winter. In spring each cell germi- nates and producesa promycelium, a short thread, divided into four cells. 136 MORPHOLOGY. Promycelium bears four sterigmata and four gonidia (or spo- ridia), which in favorable conditions pass back to the bar- berry, germinate, the tube enters between cells into the intercellular spaces of the host to produce the cluster cup again, and thus the life cycle is completed. 298. Higher fungi divided into two seriez.—Of the higher fungi there are two large series. One of these is represented by the mushrooms, a good example of which is the common mushroom (Agaricus campestris). (For the study of the mushrooms see Part III, Ecology.) The large group of fungi to which the mushroom belongs is called the basidiomycetes because in all of them a structure resembling a club, or basid- ium, is present, and bears a limited number of spores, usually four, though in some genera the number is variable. Some place the rusts (uredineze) in the same series (basidium series) because of the short promycelium, and four sporidia developed from each cell of the teleutospore. Sac Fungi. 299. The other large series of the higher fungi may be rep- resented by what are popularly called the ‘‘ powdery mildews."’ Fig. 164 is from a photograph of two willow leaves affected by one of these mildews. The leaves are first partly covered witha whitish growth of mycelium, and numerous chains of colorless gonidia are borne on short erect threads. The masses of gonidia give the leaf a powdery appearance. The mycelium lives on the outer surface of the leaf, but sends short haustoria into the epi- dermal cells. 300. Fruit bodies of the willow mildew.—On this same mycelium there appear later numerous black specks scattered over the affected places of the leaf. These are the fruit bodies (perithecia). If we scrape some of these from the leaf, and mount them in water for microscopic examination, we shall be able to see their structure. Examining these first with a low power of the microscope, each one is seen to be a rounded body, from which radiate numerous filaments, the appendages. Each one of these appendages is coiled at the end into the form ofa little hook. Because of these hooked appendages this genus is called uncinula. This rounded body is the peri/hecium. FUNGI: SAC FUNGI. 137 301. Asci and ascospores.—While we are looking at a few of these through the microscope with the low power, we should Fig. 164. Leaves of willow showing willow mildew. The black dots are the fruit bodies (perithecia) seated on the white mycelium. press on the cover glass with a needle until we see a few of the perithecia rupture. If this is done carefully we see several small ovate sacs issue, each containing a number of spores, as shown in fig. 166. Such a sac is an ascus, and the spores are ascospores. 138 MORPHOLOG ¥Y. 302. The sac fungi or ascomycetes.—The large group of fungi to which this uncinula belongs is known as the sac fungi, or ascomycetes. While Fig. 165. Willow mildew; bit of mycelium with erect conidiophores, bearing chain of onidia ; gonidium at eft germinating. Fig. 166. Fruit of willow mildew, showing hooked ap- pendages. Genus uncinula. Figs. 166, 167.—Perithecia (perithecium) of two powdery mildews, showing escape of asci containing the spores from the crushed fruit bodies. Fig. 167. Fruit body of an- other mildew with dichotomous appen- dages. Genus microsphera. many of the powdery mildews have a variable number of spores in an ascus, a large majority of the ascomycetes have just 8 spores in an ascus, while Fig. 168. Contact of an- theridium and carpogonium (carpogonium the larger cell); the beginning of fertilization. Fig. 169. Disappear- ance of contact walls of anthe- ridium and Wg. 170. carpogonium, Fertilized egg surrounded by and fusion of the enveloping threads which the two nuclei. grow up around it. Figs. 168-170.—Fertilization in sphzrotheca; one of the powdery mildews. (After Harper.) some have 4, others 16, and some an indefinite number. The complex struc- ture of the fruit body, as well as the usually definite and limited number of FUNGI: CLASSIFICA TION. 139 spores in an ascus, places these fungi on a higher scale than the mucors, saprolegnias, and their relatives, where the number of gonidia ina sporangium is always indefinite. 303. Leaf curl of the peach, black knot of the plum and cherry, ergot of the rye and grasses, and many other fungi are members of the ascomycetes. The majority of the lichens are ascomycetes, while a few are basidiomycetes. 304. Classification of the fungi.—Those who believe that the fungi repre- sent a natural group of plants arrange them in three large series related to each other somewhat as follows: The Basidium Type or Series. The number of gonidia on a basi- dium is limited and definite, and The Gonidium Type or Series. The | the basidium is a characteristic number of gonidia in the sporangium | structure; ex. uredinez (rusts), is indefinite and variable. It may be | mushrooms, etc. very large or very small, or even only The Ascus Type or Series. The one in a sporangium. To this series | number of spores in an ascus is belong the lower fungi; ex., mucor, | limited and definite, and the ascus saprolegnia, peronospora, etc. is a characteristic structure; ex. leaf curl of peach (exoascus), pow- dery mildews, black knot of plum, black rot of grapes, etc. L 305. Others believe that the fungi do not represent a natural group, but that they have developed off from different groups of the alge by becoming parasitic. As parasites they no longer needed chlorophyll, and consequently lost it. They thus derive their carbohydrates from organic material manu- factured by the green plants. According to this view the lower fungi have developed off from the lower alge (saprolegnias, mucors, peronosporas, etc., being developed off from siphonaceous algz like vaucheria), and the higher fungi being developed off from the higher algze (the ascomycetes perhaps from the rhodophycez). CHAPTER XXII. LIVERWORTS (HEPATIC). 306. We come now to the study of representatives of another group of plants, a few of which we examined in studying the organs ofassimilation and nutrition. I refer to what are called the liver- worts. ‘I'wo of these liverworts belonging to the genus riccia are illustrated in figs. 58, 171. Riccia. 307. Form of the floating riccia (R. fluitans).—The gen- eral form of floating riccia is that of a narrow, irregular, flattened, ribbon-like object, which forks repeatedly, in a dichotomous manner, so that there are several lobes to a single plant. It receives its name from the fact that at certain seasons of the year it may be found floating on the water of pools or lakes. When the water lowers it comes to rest on the damp soil, and rhizoids are developed from the under side. Now the sexual organs, and later the fruit capsule, are developed. 308. Form of the circular riccia (R. crystallina).—The circular riccia is shown in fig. 171. The form of this one is quite different from the floating one, but the manner of growth is much thesame. The branching is more compact and even, so that acir- cular plant is the result. This riccia inhabits muddy banks, lying flat on the wet surface, and deriving its soluble food by means of the little rootlets (rhizoids) which grow out from the under surface. Here and there on the margin are narrow slits, which extend 140 LIVERWORTS: RICCTA. I4I nearly to the central point. They are not real slits, however, for they were formed there as the plant grew. Each one of these V-shaped portions of the thal- lus is a Jobe, and they were formed in the young condition of the plant by a branching in a forked manner. Since growth took place in all direc- tions radially the plant be- came circular in form. These large lobes we can see are forked once or twice again, as shown by the seeming shorter slits in the margin. Fig. 171. 309. Sexual organs, — In Thallus of Riccia crystallina. order to study the sexual organs we must make thin sections through one of these lobes lengthwise and perpendicular to the thallus surface. These sections are mounted for examination with the microscope. 310. Archegonia.—We are apt to find the organs in various stages of de- velopment, but we will select one of the flask-shaped structures shown in fig. 172 for study. This flask-shaped body we see is'entirely sunk in the tissue of the thallus. This structure is the female organ, and is what we term in these plants the avchegonium. It is more complicated in structure than the cogonium. The lower portion is enlarged and bellied out, and is the venter of the archegonium, while the narrow portion is the neck, We here see it in section. The wall is one cell layer in thickness. In the neck is a canal, and in the base of the venter we see a large rounded cell with a distinct and large nucleus. This cell is the egg cell. 311. Antheridia.—The antheridia are also borne in cavities sunk in the tissue of the thallus. There is here no illustration of the antheridium of this riccia, but fig. 178 represents an antheridium of another liverwort, and there is not a great difference between the two kinds. Each one of those little rect- angular sperm mother cells in the antheridium changes into a swiftly moving body like a little club with two long lashes attached to the smaller end By the violent lashing of these organs the spermatozoid is moved through the water, or moisture which is on the surface of the thallus. It moves through the canal of the archegonium neck and into the egg, where it fuses with the nucleus of the egg, and thus fertilization is effected. 142 MORPHOLOGY. 312. Embryo.—In the plants which we have selected thus far for study, the egg, immediately after fecundation, we recollect, passed into a resting state, and was enclosed by a thick protecting wall. But in riccia, and in the other plants of the group which we are now studying, this is not the case. Fig. 172. Fig. 173. Archegonium of riccia, showing neck, Young embryo (sporogoni- venter, and the egg; archegonium is partly um) of riccia, within the venter surrounded by the tissue of the thallus. of the archegonium ; the latter (Riccia crystallina.) has now two layers of cells. (Riccia crystallina.) The egg, on the other hand, after acquiring a thin wall, swells up and fills the cavity of the venter. Then it divides by a cross wall into two cells. These two grow, and divide again, and so on until there is formed a quite large mass of cells rounded in form and still contained in the venter of the archegonium, which itself increases in size by the growth of the cells of the wall. 313. Sporogonium of riecia.—The fruit of riccia, which is developed from the fertilized egg in the archegonium, forms a rounded capsule still enclosed in the venter of the archegonium, which grows also to provide space for it. Therefore a section through the plant at this time, as described for the study of the archegonium, should show this capsule. The capsule then is a rounded mass of cells developed from the egg. A sin- gle outer layer of cells forms the wall, and therefore is sterile. LIVERWORTS: RICCIA. 143 All the inner cells, which are richer in protoplasm, divide into four cells each. Each of these cells becomes a spore with a thick wall, and is shaped like a triangular pyramid whose sides are of the same extent as the base (tetrahedral). These cells formed in Fig. 175. Riccia glauca; archegonium containing nearly mature spo- rogonium. sg, spore-producing Fig. Tae 48 cells surrounded by single layer Nearly mature sporogonium of Riccia crystallina ; of sterile cells, the wall of the mature spore at the right. sporogonium. fours are the spores. At this time the wall of the spore-case dis- solves, the spores separate from each other and fill the now en- larged venter of the archegonium. When the thallus dies they are liberated, or escape between the loosely arranged cells of the upper surface. 314. A new phase in plant life.—Thus we have here in the sporogonium of 77ccia a very interesting phase of plant life, in which the egg, after fertilization, instead of developing directly into the same phase of the plant on which it was formed, grows into a quite new phase, the sole function of which is the development of spores. Since the form of the plant on which the sexual organs are developed is called the gamefophyte, this new phase in which the spores are developed is termed the sforo- phyte. Now the spores, when they germinate, develop the game/o- pAyie, or thallus, again. So we have this very interesting condi- 144 MORPHOLOGY. tion of things, the thallus (gametophyte) bears the sexual organs and the unfertilized egg. The fertilized egg, starting as it does from a single-celled stage, develops the sporogonium (sporo- phyte). Here the single-cell stage is again reached in the spore, which now develops the thallus. 315. Riccia compared with coleochete, edogonium, ete.—We have said that in the sporogonium of riccia we have formed a new phase in plant life. If we recur to our study of coleochzte we may see that there is here possibly a state of things which presages, as we say, this new phase which is so well formed in riccia. We recollect that after the fertilized egg passed the period of rest it formed a small rounded mass of cells, each of which now forms a zoospore. The zoospore in turn develops the normal thallus (gametophyte) of the coleochete again. In coleochaete then we have two phases of the plant, each having its origin in a one-celled stage. Then if we go back to cedogonium, we remember that the fertilized egg, before it developed into the cedogonium plant again (which is the gametophyte), at first divides into four cells which become zoospores. These then develop the cedogonium plant. Note. Too much importance should not be attached to this seeming ho- mology of the sporophyte of cedogonium, coleochzete, and riccia, for the nu- clear phenomena in the formation of the zoospores of cedogonium and coleo- cheete are not known. They form, however, a very suggestive series. Marchantia. 816. The marchantia (M. polymorpha) has been chosen for study because it is such acommon and easily obtained plant, and also for the reason that with comparative ease all stages of development can be obtained. It illustrates also very well cer- tain features of the structure of the liverworts. The plants are of two kinds, male and female. The two dif- ferent organs, then, are developed on different plants. In appearance, however, before the beginning of the structures which bear the sexual organs they are practically the same. The thallus is flattened like nearly all of the thalloid forms, and branches in a forked manner. The color is dark green, and through the middle line of the thallus the texture is different from that of the margins, so that it possesses what we term a LIVERWORTS: MARCHANTIA. 145 midrib, as shown in figs. 176, 180. The growing point of the thallus is situated in the little depression at the free end. If we examine the upper surface with a hand lens we see diamond-shaped areas, and at the center of each of these areas are the openings known as the stomates. 317. Antheridial plants.—One of the male plants is figured at 176. It bears curious structures, each held aloft by a short stalk. These are the an- theridial recep- tacles (or male gametophores). Each one is cir- . wea cular, thick, and 4 shaped = some- Fig, 176. what like a bi- Male plant of marchantia bearing antheridiophores. convex lens. The upper surface is marked by radiating fur- rows, and the margin is crenate. Then we note, on careful examination of the upper surface, that there are numerous minute openings. If we make a thin section of this structure perpen- Fig. 177. Section of antheridial receptacle from male plant of Marchantia polymorpha, showing cavities where the antheridia are borne. dicular to its surface we shall be able to unravel the mystery of its interior. Here we see, as shown in fig. 177, that each one of these little openings on the surface is an entrance to quite 146 MORPHOLOGY. a large cavity. Within each cavity there is an oval or ellip- tical body, supported from the base of the cavity on a short stalk. This is an antheridium, and one of them is shown still more enlarged in fig. 178. This shows the structure of the antheridium, and that there are within several angular areas, which are divided by numerous straight cross-lines into countless tiny cuboidal cells, the sperm mother cells. Each of these, as stated in the former chapter, changes into a swiftly moving body resembling a serpent with two long lashes attached to its tail. 318. The way in which one of these sperm mother cells changes into this spermatozoid is very curious. We first note that a coiled spiral body is appear- f Fig. 178. : Fig. 179. Section of antheridium of mar- Spermatozoids of marchantia, chantia, showing the groups of uncoiling and one extended, show- sperm mother cells. ing the two cilia. ing within the thin wall of the cell, one end of the coil larger than the other. The other end terminates in a slender hair-like outgrowth with a delicate vesi- cle attached to its free end. This vesicle becomes more and more extended until it finally breaks and forms two long lashes which are clubbed at their free ends as shown in fig. 179. 319. Archegonial plants.—In fig. 180 we see one of the female plants of marchantia. Upon this there are also very curious structures, which remind one of miniature umbrellas. The general plan of the archegonial receptacle (or female LIVERWORTS: MARCHANTTA. 147 gametophore), for this is what these structures are, is similar to that of the antheridial receptacle, but the rays are more pro- nounced, and the details of structure are quite different, as we shall see. Underneath the arms there hang down delicate fringed curtains. If we make sections of this in the same direc- Fig. 180. Marchantia polymorpha, female plants bearing archegoniophores. tion as we did of the antheridial receptacle, we shall be able to find what is secreted behind these curtains. Such a section is figured at 184. Here we find the archegonia, but instead of being sunk in cavities their bases are attached to the under 148 MORPHOLOGY. surface, while the delicate, pendulous fringes afford them pro- tection from drying. An archegonium we see is not essentially different in marchantia from what it is in riccia, and it will be interesting to learn whether the sporogonium is essentially dif- ferent from what we find in riccia. CHAPTER XNIII. LIVERWORTS CONTINUED. 320. Sporogonium of marchantia.—If we examine the plant shown in fig. 181 we shall see oval bodies which stand out be- Fig. 181. sipotte oUt ne dieeniner ereieeta pubtiie ete srasen ie ottodlicd (a the receptacle underneath the curtain. In the left figure two of the capsules have burst and the elaters and spores are escaping. tween the rays of the female receptacle, supported on short stalks. These are the sporogonia, or spore-cases. We judge at once that they are quite different from those which we have studied in riccia, since those were not stalked. We can see that some of the spore-cases have opened, the wall splitting down from the apex in several lines. This is caused by the drying of the wall. These tooth- like divisions of the wall now curl backward, and we can see the yellowish mass of the spores in slow motion, 149 150 MORPHOLOG Y. falling here and there. It appears also as if there were twisting threads which aided the spores in becoming freed from the capsule. Section of archegonial receptacle of Marchantia polymorpha; ripe sporogonia. One is Opens scattering spores and elaters; two are still enclosed in the wall of the archegonium. ‘The junction of the stalk of the sporogonium with the receptacle is the point of attach- ment of the sporophyte of marchantia with the gametophyte. 321. Spores and elaters.—If we take a bit of this mass of spores and mount it in water for examination with the microscope, we shall see that, besides the spores, there are very peculiar thread-like bodies, the markings of which remind (> one of a twisted rope. These Ge) are very long cells from the inner part of the spore-case, and their walls are marked by spi- ral thickenings. This causes them in drying,and also when they absorb Ri : Fig. 183. moisture, to twist Elater and spore of marchantia. sf, spore ; sec, mother-cell of C spores, showi rtly formed i and curl in all? aaa aac sorts of ways. ‘They thus aid in pushing the spores out of the capsule as it is drying. 322. Sporophyte of marchantia compared with riccia.— We must recollect that the sporogonium in marchantia is larger than in riccia, and that it is also not lying in the tissue of the thallus, but is only attached to it at one side by a slender stalk. LIVERWORTS.: MARCHANTTA. ISI This shows us an increase in the size and complex structure of this new phase of the plant, the spurophyfe. This is one of the very interesting things which we have to note as we go on in the study of the higher plants. Fig. 184. Marchantia polymorpha, archegonium at the left with egg: archegonium at the right with young sporogonium ; /, curtain which hangs down around the archegonia ; e, egg; wv, venter of archegonium ; z, neck of archegonium; sf, young spo1ogonium. 323. Sporophyte dependent on the gametophyte for its nutri- ment.—We thussee that at no time during the development of the sporogonium is it independent from the gametophyte. This new phase of plants then, the sporophyte, has not yet become an in- dependent plant, but must rely on the earlier phase for sustenance. 324. Development of the sporogonium.—It will be interesting to note briefly how the development of the marchantia sporogonium differs from that of riccia. The first division of the fertilized egg is the same as in riccia, that is a wall which runs crosswise of the axis of the archegonium divides it into two cells. In marchantia the cell at the base develops the stalk, so that here there is a radical difference. The outer cell forms the capsule. But here after the wall is formed the inner tissue does not all go to make spores, as is the case with riccia. But some of it forms the elaters. While in riccia only the outside layer of cells of the sporogonium remained sterile, in marchantia the basal half of the egg remains completely sterile and 152 MORPHOLOG Y. develops the stalk, ana in the outer half the part which is formed from some of the inner tissue is also sterile. 4 <2 oe oT a7 sae: xn LR eZ $y Ee 23 <9 FES Fig. 185. Section of developing sporogonia of marchantia; 2/, nutritive tissue of gametophyte; s¢, sterile tissue of sporophyte; sf, fertile part of sporophyte; va, enlarged venter of arche- gonium., 325. Embryo.—In the development of the embryo we can see all the way through this division line between the basal half, which is completely sterile, and the outer half, which is the fertile part. In fig. 185 we see a young embryo, and it is nearly circular in section although it is composed of numerous cells. The basal half is attached to the base of the inner surface of the archegonium, and at this time the archegonium still surrounds it. The archegonium continues to grow then as the embryo grows, and we can see the remains of the shrivelled neck. The portion of the embryo attached to the base of the archegonium is the sterile part and is called the ‘ foot,” and later develops the stalk. The sporogonium during all the stages of its development derives its nourishment from the gametophyte at this point of LIVERWORTS: MARCHANTIA. 153 attachment at the base of the archegonium. Soon, as shown in fig. 185 at the right, the outer portion of the sporogonium begins to differentiate into the cells which form the elaters and those which form spores. These lie in radiating lines side by side, and form what is termed the archesporium. Each fertile cell forms four spores just as in riccia. They are thus called the mother cells of the spores, or spore mother cells. 826. How marchantia multiplies.—New plants of marchantia are formed by the germination of the spores, and growth of the same to the thallus. The plants may also be multiplied by parts of the old ones breaking away by the action of strong currents of water, and when they lodge in suitable places grow into well-formed plants. As the thallus lives from year to year and continues to grow and branch the older portions die off, and thus sepa- rate plants may be formed from a former single one. 327. Buds, or gemme, of marchantia.—But there is another way in which marchantia multiplies itself. If we examine the upper surface of such a Fig. 186. Marchantia plant with cupules and gemmz; rhizoids below. plant as that shown in fig. 186, we shall see that there are minute cup- shaped or saucer-shaped vessels, and within them minute green bodies. If we examine a few of these minute bodies with the microscope we see that they are flattened, biconvex, and at two opposite points on the margin there is an indentation similar to that which appears at the growing end of the old marchantia thallus. These are the growing points of these little buds. When they free themselves from the cups they come to lie on one 154 MORPHOLOGY. side. It does not matter on what side they lie, for whichever side it is, that will develop into the lower side of the thallus, and forms rhizoids, while the upper surface will develop the stomates. Leafy-stemmed liverworts. 328. We should now examine more carefully than we have done formerly a few of the leafy-stemmed liverworts (called foliose liverworts). 329. Frullania (Fig. 60).—This plant grows on the bark of logs, as well as on the bark of standing trees. It lives in quite dry situations. If we examine the leaves we will see how it is able to do this. We note that there are two rows of lateral leaves, which are very close together, so close in fact that they overlap like the shingles on a roof. Fig. 187. Then, as the Section of thallus of marchantia. 4, through the middle portion ; ’ fo sane ese eae Aiewieeatee side (Goebel). lie very close to the bark of the tree, these overlapping leaves, which also hug close to the stem and bark, serve to retain moisture which trickles down the bark during rains. If we examine these leaves from the under side as shown in fig. 62, we see that the lower or basal part of each one is produced into a peculiar lobe which is more or less cup-shaped. This catches water and holds it during dry weather, and it also holds moisture which the plant absorbs during the night and in damp days. FOLIOSE LIVERWORTS. 155 There is so much moisture in these little pockets of the under side of the leaf that minute animals have found them good places to live in, and one frequently discovers them in this retreat. There is here also a third row of poorly developed leaves on the under side of the stem. 330. Porella.—Growing in similar situations is the plant known as porella. Sometimes there are a few plants in a group, and at other times large mats occur on the bark of a trunk. This plant, porella, also has closely overlapping leaves in rows on opposite sides of the stem, and the lower margin of each leaf is curved under somewhat as in frullania, though the pocket is not so well formed. The larger plants are female, that is they bear archego- nia, while the male plants, those which bear antheridia, are smaller and the an- theridia are borne on small lateral branches. The an- theridia are borne in the axils of the leaves. Others of the leafy-stemmed liverworts live in Pig abs: ; Thallus of a thalloid liverwort (blasia) showing lobed damp situations. margin of the frond, intermediate between thalloid and Some of these, as fohose plant: Cephalozia, grow on damp rotten logs. Cephalozia is much more delicate, and the leaves are farther apart. It could not live in such dry situations where the frullania is sometimes found. If possible the two plants should be compared in order to see the adaptation in the structure and form to their environment. 331. Sporogonium of a foliose liverwort.—The sporogonium of the leafy-stemmed liverworts is well represented by that of several genera, We may take for this study the one illustrated 156 MORPHOLOG ¥. in fig. 192, but another will serve the purpose just as well. We note here that it consists of a rounded capsule borne aloft on a long stalk, the stalk being much longer proportionately than in -marchantia. At maturity the capsule splits down into four Fig. 190. Antheridium of a foliose liverwort (jun- germannia). Fig. 189. Fig. rgr. Foliose liverwort, male plant showing anthe- Foliose liverwort, female pant with ridia in axils of the leaves (a jungermannia). rhizoids. quadrants, the wall forming four valves, which spread apart from the unequal drying of the cells, so that the spores are set free, as shown in fig. 194. Some of the cells inside of the capsule de- velop elaters here also as well as spores, These are illustrated in fig. 196. 332, In this plant we see that the sporophyte remains attached FOLIOSE LIVERWORTS. 157 to the gametophyte, and thus is dependent on it for sustenance. This is true of all the plants of this group. The sporophyte never becomes capable of an independent existence, and yet we see that it is becoming larger and more highly differentiated than in the simple riccia. Fig. 193. Opening capsule showing escape of spores and elaters. iN). Fig. 194. Capsule pee down to the stalk. Vig. 192. Fruiting plant of a foliose liver- ig. 1905. ie: eh wort Ganeermannia), Leafy part Fig. 195 Fig. 196 is the gametophyte; stalk and cap- Four spores from Elaters, at left showing the two suleis the sporophyte (sporogonium mother cell held in spiral marks, at right a branched in the bryophytes). _ a group. elater. Figs. 193-196.—Sporogonium of liverwort (jungermannia) opening by splitting into four parts, showing details of elaters and spores. CHAPTER XXIV. MOSSES (MUSCI). 333. We are now ready to take up the more careful study of the moss plant. There are a great many kinds of mosses, and they differ greatly from each other in the finer details of struc- ture. Yet there are certain general resemblances which make it convenient to take for study almost any one of the common species in a neighborhood, which forms abundant fruit. Some, however, are more suited to a first study than others. (Polytri- chum and funaria are good mosses to study.) 334, Mnium.—We will select here the plant shown in fig. 197. This is known as a mnium (M. affine), and one or another of the species of mnium can be obtained without much difficulty, The mosses, as we have already learned, possess an avis (stem) and leaf-like expansions, so that they are leafy-stemmed plants also. Certain of the branches of the mnium stand upright, or nearly so, and the leaves are all of the same size at any given point on the stem, as seen in the figure. There are three rows of these leaves, and this is true of most of the mosses. 335. The mnium plants usually form quite extensive and pretty mats of green in shady moist woods or ravines. Here and there among the erect stems are prostrate ones, with two rows of promi- nent leaves so arranged that it reminds one of some of the leafy- stemmed liverworts. If we examine some of the leaves of the mnium we see that the greater part of the leaf consists of a single layer of green cells, just as is the case in the leafy-stemmed liverworts. But along the middle line is a thicker layer, so that it forms a distinct midrib. This is characteristic of the leaves 158 MOSSES. 159 of mosses, and is one way in which they are separated from the leafy-stemmed liverworts, the latter never having a midrib. 336. The fruiting moss plant.—In fig. 197 isa moss plant ‘‘in fruit,’’ as we say. Above the leafy stem a slender stalk bears the capsule, and in this capsule are borne the spores. The capsule then belongs to the sporophyte phase of the moss plant, and we should inquire whether the entire plant as we see it here is the sporophyte, or whether part of it is gametophyte. If a part of it is gametophyte and a part sporophyte, then where does the one end and the other begin? If we strip off the leaves at the end of the leafy stem, and make a longisection in the middle line, we should find that the stalk which bears the capsule is simply stuck into the end of the Portion of moss plant of Mnium affine, showing two sporogonia from one branch. Capsuleat left has just shed the cap or operculum ; capsule at right is shedding spores, and the teeth are bristling at the mouth. Next to the right is a young capsule with calyptra still attached; next are two spores enlarged. leafy stem, and is not organically connected with it. This is the dividing line, then, between the gametophyte and the sporo- phyte. We shall find that here the archegonium containing 160 MORPHOLOG Y. the egg is borne, which is a surer way of determining the limits of the two phases of the plant. 337. The male and female moss plants.—The two plants of mnium shown in figs. 198, I99 are quite different, as one can easily see, and yet they belong to the same species. One is a female plant, while the other is a male plant. The sexual organs then in mnium, as in many others of the mosses, are borne on separate plants. The archegonia are borne at the end of the stem, and are protected by somewhat narrower leaves which closely overlap and are wrapped together. They are similar to the archegonia of the liverworts. Fig. 198. Vig. 199. Female plant (gametophyte) of a moss Male plant (gametophyte) of a moss (mnium), showing rhizoids below, and the (mnium) showing rhizoids below and the tuft of leaves above which protect the arche- antheridia at the center above surrounded by gonia. the rosette of leaves. The male plants of mnium are easily selected, since the leaves at the end of the stem form a broad rosette with the antheridia, and some sterile threads packed closely together in the center. The ends of the mass of antheridia can be seen with the naked eye, as shown in fig. 199. When the antheridia MOSSES. 161 are ripe, if we make a section through a cluster, or if we merely tease out some from the end with a needle in a drop of water on the slide, then prepare for examination with the microscope, we can see the form of the antheridia. They are somewhat clavate or elliptical in outline, as seen in fig. 201. Be- tween them there stand short threads composed of several cells containing chlorophyll grains. These are sterile threads (paraphyses). 338. Sporogonium.—lIn fig. 197 we see illustrated a sporogonium of mnium, which is of course developed from the fertilized egg cell of the archegonium. There isa nearly cylindrical capsule, bent downward, and supported ona long sr ait se2 enue) crt y sae LNCIRN CLANS ies se = Soe SE - em CoN eee i BS am ete aE SS e, ¢ ie ee FSi ee ee By, Su am SS Ririg i ogee ew DEERE D>, ae, ie, oS woe Ss ' re ORS = {2 5 TA, Ry Ye ara Pon re 7 a, 2 a ees rg oe EZ S Fig. 201. Antheridium of mnium Fig. 200. Section through end of stem of female plant of mnium, show- with jointed paraphysis ing archegonia at the center. One archegonium shows the egg. at the left; spermato- On the sides are sections of the protecting leaves. zoids at the right. slender stalk. Upon the capsule is a peculiar cap,* shaped like a ladle or spatula. This is the remnant of the old archegonium, which, for a time sur- rounded and protected the young embryo of the sporogonium, just as takes place in the liverworts. In most of the mosses this old remnant of the arche- gonium is borne aloft on the capsule as a cap, while in the liverworts it is thrown to one side as the sporogonium elongates. 339. Structure of the moss capsule.—At the free end on the moss capsule * Called the calyptra. 162 MORPHOLOG Y. as shown in the case of mnium in Fig. 197, after the remnant of the arche- gonium falls away, there is seen a conical lid which fits closely over the end. When the capsule is ripe this lid easily falls away, and can be brushed off so that it is necessary to handle the plants with care if it is desired to preserve this for study. 340. When the lid is brushed away as the capsule dries more we see that the end of the capsule covered by the lid appears ‘‘frazzled.”’ If we examine this end with the micro- scope we see that the tissue of the capsule here is torn with great regularity, so that there are two rows of narrow, sharp teeth which project outward in a ring around the opening. If we blow our ‘‘breath”” upon these teeth they will be seen to move, and as the moisture disappears and reappears in the teeth, they close and open the mouth of the capsule, so sensi- tive are they to the changes in the humidity of the air. In this way all of the spores are prevented to some extent from escaping from the capsule at one time. 841. Note. If we make a sec- tion longitudinal of the capsule of mnium, or some other moss, we find that the tissue which develops the spores is much more restricted than in the capsule of the liver- worts which we have studied. The spore-bearing tissue is confined to a single layer which extends around the capsule some distance from the Fig. 202. outside of the wall, so that a central Two different stages of young sporogonium of cylinder is left of sterile tissue. a moss, still within the archegonium and wedg- 4s . ‘ ing their way into the tissue of the end of the stem. a is the columella, and is pres 4, neck of archegonium ; /, young sporogonium. ent in nearly all the mosses. Each aie we pore re ria SETHE Doren? of the cells of the fertile layer divides into four spores. 342. Development of the sporogonium.—The egg cell after fertilization divides by a wall crosswise to the axis of the archegonium. Each of these cells continues to divide for a time, so that a cylinder pointed at both ends is formed. The lower end of this cylinder of tissue wedges its way down through the base of the archegonium into the tissue of the end of the moss stem as shown in fig. 202. This forms the fvot through which the nutrient MOSSES. 163 materials are passed from the gametophyte to the sporogonium. The upper part continues to grow, and finally the upper end differentiates into the mature capsule. 343. Protonema of the moss.—When the spores of a moss germinate they form a thread-like body, with chlorophyll. This thread becomes branched, and sometimes quite extended tangles of these threads are formed. This is called the protonema, that is fst ¢hread. The older threads become finally brown, while the later ones are green. From this protonema at certain points buds appear which divide by close oblique walls. From these buds the leafy stem of the moss plant grows. Threads similar to these protonemal threads now grow out from the leafy stem, to form the rhizoids. These supply the moss plant with nutriment, and now the protonema usually dies, though in some few species it persists for long periods. MORPHOLOGY. 164 Cumruosayore (eur e jo yuruuat si ¥ F -[evads weeace umyuodorods ue sued ee a bare pure Pee lat ‘oa } *sarodg|"*:: sdoyaaap| ‘ aye “qy90} § TT “eTTour PROF vaydayed) OTE 40 es oe -qodo010ds uada)-auojoid dates ue uo WAHD T taiiiiaties at -nyoo okay: eas (uma yuvyd spewayjpua we ‘SPlOZ! 1 isoavay ‘stxe aui0 “(emueMsadun{| -1YLATOg iN se ate 09 a atnsdeo t i eni|-oSor0ds sdo|UO ‘399 YIM Yora|-oyeattads AY g Susti0} 0} ets) saavay jo “aawNa 4 mana ee 1eHS ated. st eanatieos pal-jaaeq) *33a ‘eyuoSayory |erpraeyqyuy | og aa ymoid Aq smor f ‘sIxe AES. WAIN] -AeppeoupurpAn § |-yyeys Joutedaytie3g = /paztyy498 7 “squrid yuaiayip uQ ‘suryoueiq Aq |-iedde yy jurlg “sassojy yuri) “sjurrd aeway pue *sia}e[a pue $13} SIEM 230! “Sena IRIN Saul ovr nd (019 ‘v1 ssatodal:sttreees ss ae -eja ‘siaXey [eraAas (uma ‘yueyd apeuray uoljo sxe ut ‘sproz phe SAey siyeui|Aeste, Sue 2 -paap (umuods|jo arnsdeo yo {TeM)\-oSo10ds sdo ‘B88 UA Mee royeutsads UHM jo a ‘ ee -o1vP aay -ayaue) amnsdea|*y[eys st amsdeo pol-jaaact) “88a/ PPUOSeuItV |r praeqquy ‘syed zapjo jo/pue seavay yuared| 10) vINNVIV jo red jenuag = [-yyeisyo wed apuiaig | pezipnsey “sjuryd juarayip ud Aeme 3urfp Ag |-de yum jued yw -4agONn ‘330 ue} ~saroydojoureS Uy yore ‘(a1oydlapeur 10 ‘saroyd, -oruosayore|-O1rprrayyue “s1a}e]9 pue 10) a1oydojawmes)uo ausroq ‘sproz loud ‘satodgy'*''' ae ssdo| ‘s1ajeya ‘s1akey] [era (Cunt (ease auioq roveutiads TAN -ojoure? rvaq uci -[2Aop__(wunprods}-as Jo ajnsdeo Jo t[em -oFo10ds sdo) PEFOPPTSAW VPIPITOMIUW | oonnas kq pueapeuray pue afeur -ayoae) — ausdea/‘yyeIs st afusdeo pa/-jaasq “330 ‘syurjd yusseytp |‘syed_ srapfo jo|‘paysoy ‘ayty-aoqqur| ‘vit joped peyuag = |-yeIs goyedapuays § |paziyn4a7 uo sajoejdaser [eeds uoauiog = [Aeme Surdp Ag |‘pauayey snireyy -NVHDYV]T = “yore “Sploz at 2 yyal-oyeunads = yy ier *sad0dg] +++ ++++-- sdopaaap “s]ao ere a ‘eyuosayory |‘erpraeyjuy jo cone pas “aepnoaty ATAwaU 10 (unt1odsayore)|takey-auo yo “ummu|-[243(q) “330 “snTTeIY JO Yor prem |pue Surouvsq ‘paysoy “oyt]-uoqqu 2 sseur yenuad |-oSo10ds jo [eA pazyyieg —|-dn ‘Surpunozims Aq pasrauuy = |Aq saumauog |‘pauayey snqteyL ‘VIDDIY “HLAHd “NOIL “a ‘ALAHdOL | LUVg aTILYag| ‘“LUVgd AMYALS -ONOdS 4O “SNVYDYQ TVAXES -VOITGILIDYY cMevLaeay, “NVQ dO ONINNIOS HAILVLaDa A ° ONINNIOAG JUIUIYSLIMNOU IOJ It uO yUapuadap pue Pr bese 0} payppeny) ALAHdMONOdS (-aouasixe yuapuadepur uv spray "ued ayy yo pred yuaummorg) “TL AHAOLANVD SASSOTL CGNV SLUOMUAATT AHL NI ALAHdOUWOdS ANV ALAHAOLANVYS AO NOILLVIAM ONLMOHS WIAVL “Pts CHIAPTER XXV. | FERNS. 345. In taking up the study of the ferns we tind plants which are very beautiful objects of nature and thus have alwaysattracted the interest of those who love the beauties of nature. But they are also very interesting to the student, because of certain re- markable peculiarities of the structure of the fruit bodies, and especially because of the intermediate position which they occupy within the plant kingdom, representing in the two phases of their development the primitive type of plant life on the one hand, and on the other the modern type. We will begin our study of the ferns by taking that form which is the more promi- nent, the fern plant itself. 346. The Christmas fern.—One of the ferns which is very common in the Northern States, and occurs in rocky banks and woods, is the well-known Christmas fern (Aspidium acrostichoides) shown in fig. 203. The leaves are the most prominent part of the plant, as is the case with most if not all our native ferns. The stem is very short and for the most part under the surface of the ground, while the leaves arise very close together, and thus form a rosette as they rise and gracefully bend outward. The leaf is elongate and reminds one somewhat of a plume with the pinn extending in two rows on opposite sides of the midrib. ‘These pinne alternate with one another, and at the base of each pinna is a little spur which projects upward from the upper edge. Such a leaf is said to be pinnate. While all the leaves have the same general outline, we notice that certain ones, especially those toward the center of the rosette, are much narrower from the 165 166 MORPHOLOGY. middle portion toward the end. This is because of the shorter pinne here. 347. Fruit “dots” (sorus, indusium).—If we examine the under side of such short pinnz of the Christmas fern we see that there are two rows of small circular dots, one row on either side of the pinna. These are called the ‘é fruit dots,’’ or sori (a single one is asorus). If we examine it with a low power of the mi- croscope, or with a pocket lens, we see that there is a circular disk which covers more or fi f less com- pletelyvery minute objects, usual- ly the ends of the latter projecting just be- yond the edge if they are mature. This circular disk is what is called the indu- sium, and it is a special outgrowth of the epidermis of the leaf here for the protection of the spore- cases. These minute ob- Christmas fern ree acrostichoides). jects underneath ate ‘the fruit bodies, which in the case of the ferns and their allies are called sporangia. This indusium in the case of the Christmas fern, and also in some others, is attached to the leaf by means of a short slender stalk FERNS. 167 which is fastened to the middle of the under side of this shield, as seen in cross section in fig. 209. 348. Sporangia. —If we section through the leaf at one of the fruit dots, or if we tease off some of the sporangia so that the Ff iy stalks are still attached, and ‘y 4 i, ‘ At, ‘ ; : examine them with the mi- My by croscope, we can see the hi form and structure of these peculiar bodies. Different ij | views of a sporangium are shown in fig. 210. The slender portion is the stalk, and the larger part is the spore-case proper. We should examine the structure of this spore-case quite care- fully, since it will help us to understand better than we otherwise could the remark- able operations which it performs in scattering the spores. 349. Structure of a spo- ESS SMe? Mo a, oy tS a = (Pa ZS t= ZS =e < \ <3 \\ ; rangium. —If we examine i one of the sporangia in side , view as shown in fig. 210, Fig. 204. we note a prominent row of Rhizome with bases of leaves, and roots of the cells which extend around Christmas fern. the margin of the dorsal edge from near the attachment of the stalk to the upper front angle. The cells are prominent because of the thick inner walls, and the thick radial walls which are perpendicular to the inner walls. The walls on the back of this row and on its sides are very thin and membranous. We should make this out carefully, for the structure of these cells is especially adapt- ed to a special function which they perform, This row of cells 168 MORPHOLOG ¥. is termed the annulus, which means a little ring. While this is not a complete ring, in some other ferns the ring is nearly complete. 350. In the front of the sporangium is another peculiar group Fig. 205. Rhizome of sensitive fern (Onoclea sensibilis). of cells. Two of the longer ones resemble the lips of some crea- ture, and since the sporangium opens between them they are sometimes termed the lip cells. These lip cells are connected with the upper end of the annulus on one side and with the upper end of the stalk on the other side by thin-walled cells, which may be termed connective cells, since they hold each lip cell to its part of the opening sporangium. ‘The cells on the side of the sporangium are also thin-walled. If we now examine a sporangium from the back, or dorsal Fig. 206. Under side of pinnaof Aspidium edge as we say, it will appear as in the spinulosum showing fruit dots (sori). left-hand figure. Here we can see how very prominent the annulus is. It projects beyond the surface of the other cells of the sporangium, The spores are contained inside this case, FERNS. 169 351. Opening of the sporangium and dispersion of the spores.—If we take some fresh fruiting leaves of the Christmas fern, or of any one of many of the species of the true ferns just at the ripening of the spores, and place a portion of it ona piece of white paper in a dry room, in a very short time we shall see that the paper is being dusted with minute brown objects which fly out from the leaf. Now if we take a portion of the same leaf and place it under the low power of the microscope, so that the full rounded sporangia can be seen, in a short time we note that the sporangium opens, the upper half curls backward as Fig. 207. Four pinnz of adiantum, showing recurved margins which cover the sporangia. shown in fig. 211, and soon it snaps quickly, to near its former position, and the spores are at the same time thrown for a consid- erable distance. This movement can sometimes be seen with the aid of a good hand lens. 352. How does this opening and snapping of the sporan- gium take place ?—We are now more curious than ever to see just how this opening and snapping of thesporangium takes place, We should now mount some of the fresh sporangia in water and cover with a cover glass for microscopic examination. A drop of glycerine should be placed at one side of the cover glass on the slip so that the edge of the glycerine will come in touch with the water. Now as one looks through the microscope to watch the 170 MORPHOLOGY. sporangia, the water should be drawn from under the cover glass with the aid of some bibulous paper, like filter paper, placed at the edge of the cover glass on the opposite side from the glycerine. As the glycer- ine takes the place of the water around the sporangia it draws the water out of the cells of the annulus, just as it took the water out of the cells of the spirogyra as we learned some time ago. As the water is drawn out of these cells there is produced a pressure from without, the atmospheric pressure upon the glycerine. This causes the walls of these cells of the annulus to bend in- ward, because, as we have Fig. 208. already learned, the glycer- wiceing” ack? ate? of cpontgtnn aaice ine does not pass through upeeiular capiate hate, the walls nearly so fast as the water comes out. 358. Now the structure of the cells of this annulus, as we have seen, is such that the inner walls and the perpendicular Fig. 209. Section through sorus and shield-shaped indusium of aspidium. walls are stout, and consequently they do not bend or collapse when this pressure is brought to bear on the outside of the cells, FERNS. 171 The thin membranous walls on the back (dorsal walls) and on the sides of the annulus, however, yield readily to the pressure and bend inward. This, as we can readily see, pulls on the ends of each of the perpendicular walls drawing them closer together. This shortens the outer surface of the annulus and causes it to first assume a nearly straight position, then curve backward until it quite or nearly becomes doubled on itself. The sporangium hy Fig. 210. Rear, side, and front views of fern sporangium. a, e, annulus; a, lip cells. opens between the lip cells on the front and the lateral walls of the sporangium are torn directly across. The greater mass of spores are thus held in the upper end of the open sporangium, and when the annulus has nearly doubled on itself it suddenly snaps back again in position. While treating with the glycerine we can see all this movement take place. Each cell of the annulus acts independently, but often they all act in concert. When they do not all act in concert, some of them snap sooner than others, and this causes the annulus to snap in segments. 354. The movements of the sporangium can take place in old and dried material.—If we have no fresh material to study 172 MORPHOLOGY. the sporangium with, we can use dried material, for the move- ments of the sporangia can be well seen in dried material, pro- vided it was collected at about the time the sporangia are mature, that is at maturity, or soon afterward. We take some of the dry sporangia (or we may wash the glycerine off those which we have just studied) and mount them in water, and quickly examine vs irs Fig. 201. Dispersion of spores from sporangium of Aspidium acrostichoides, showing different stages in the opening and snapping ot the annulus. them with a microscope. We notice that in each cell of the annulus there is a small sphere of some gas. The water which bathes the walls of the annulus is absorbed by some substance inside these cells. This we can see because of the fact that this sphere of gas becomes smaller and smaller until it is only a mere FERNS. 173 dot, when it disappears ina twinkling. The water has been taken in under such pressure that it has absorbed all the gas, and the farther pressure in most cases closes the partly opened sporangium more completely. 355. Now we should add glycerine again and draw out the water, watching the sporangia at the same time. We see that the sporangia which have opened and snapped once will do it again. And so they may be made to go through this operation several times in succession. We should now note carefully the annulus, that is after the sporangia have opened by the use of glycerine. So soon as they have snapped in the glycerine we can see those minute spheres of gas again, and since there was no air on the outside of the sporangia, but only glycerine, this gas must, it is reasoned, have been given up by the water before it was all drawn out of the cells. 356. The common polypody.—We may now take up a few other ferns for study. Another common fern is the polypody, one or more species of which have a very wide distribution. The stem of this fern is also not usually seen, but is covered with the leaves, except in the case of those species which grow on the surface of rocks. The stem is slender and prostrate, and is covered with numerous brown scales, The leaves are pinnate in this fern also, but we find no difference between the fertile and sterile leaves (except in some rare cases). The fruit-dots occupy much the same positions on the under side of the leaf that they do in the Christmas fern, but we cannot find any indusium, In the place of an indusium are club-shaped hairs as shown in fig. 208. The en- larged ends of these clubs reaching beyond the sporangia give some protection to them when they are young. 357. Other ferns.—\e might examine a series of ferns to see how different they are in respect to the position which the fruit dots occupy on the leaf. The common brake, which sometimes covers extensive areas and becomes a trouble- some weed, hasa stout and smooth underground stem (rhizome) which is often 12 to 20 cm beneath the surface of the soil. There is a long leaf stalk, which bears the lamina, the latter being several times pinnate. The margins of the fertile pinnee are inrolled, and the sporangia are found protected underneath in this long sorus along the margin of the pinna, The beautiful maidenhair fern and its relatives have obovate pinnz, and the sori are situated in the same posi- tions as in the brake. In other ferns, as the walking fern, the sori are borne along by the side of the veins of the leaf. 358. Opening of the leaves of ferns.—The leaves of ferns open in a peculiar manner. ‘The tip of the leaf is the last portion developed, and the growing 174 MORPHOLOGY. leaf appears as if it was rolled up as in fig. 204 of the Christmas fern. As the leaf elongates this portion unrolls, 359. Longevity of ferns.—Most ferns live from year to year, by growth adding to the advance of the stem, while by decay of the older parts the stem shortens up behind. The leaves are short-lived, usually dying down each year, and a new set arising from the growing end of the stem. Often one can see just back or below the new leaves the old dead ones of the past season, and farther back the remains of the petioles of still older leaves. 360. Budding of ferns. — A few ferns produce what are called bulbils or bulblets on the leaves. One of these, which is found throughout the greater part of the eastern United States, is the bladder fern (Cystop- teris bulbifera), which grows in shady rocky places. The long graceful delicate leaves form in the axils of the pinne, especially near the end of the leaf, small oval bulbs as shown in fig. 212, If we examine one of these bladder-like bulbs we see that the bulk of it is made up of short thick fleshy leaves, smaller ones ap- pearing between the outer ones at the smaller end of the bulb. This bulb contains a stem, young root, and several pairs of these fleshy leaves. They easily fall to the ground or rocks, where, with the abundant moisture usually present in localities where the fern is found, the bulb Fig. 212. Cystopteris bulbifera, young plant growing STOWS until the roots attach the plant from bulb. At right is young bulb in axil of t4 the sil ‘or dn the. érevices: ‘of the pinna of leaf. rocks. A young plant growing from one of these bulbils is shown in fig. 212. 361. Greenhouse ferns.—Some of the ferns grown in conservatories have similar bulblets. Fig. 213 represents one of these which is found abundantly on the leaves of Asplenium bulbiferum. These bulbils have leaves which are very similar to the ordinary leaf except that they are smaller. The bulbs are also much more firmly attached to the leaf, so that they do not readily fall away. 362. Plant conservatories usually furnish a number of very interesting ferns, and one should attempt to make the acquaintance of some of them, for FERNS. 175 here one has an opportunity during the winter season not only to observe these interesting plants, but also to obtain material for study. In the tree ferns which often are seen growing in such places we see examples of the massive trunks and leaves of some of the tropical species. 363. The fern plant is a sporophyte.—We have now studied the fern plant, as we call it, and we have found it to represent the spore-bearing phase of the plant, that is the sporophyle (cor- responding to the sporogonium of the liverworts and mosses). 364. Is there a ga- metophyte phase in ferns ?—But in the spor- ophyte of the fern, which we should not forget is the fern plant, we have a striking advance upon the sporophyte of the liverworts and mosses. In the latter plants the sporophyte remained attached to the gameto- phyte, and derived its nourishment from it. In the ferns, as we see, the sporophyte has a root of its own, and is Hed attached to the soil. Bulbil growing from leaf of asplenium (4, bulbiferum). Through the aid of root : hairs of its own it takes up mineral solutions. It possesses also a true stem, and true leaves in which carbon conversion takes place. It is able to live independently, then. Does a gametophyte phase exist among the ferns? Or has it been lost? If it does exist, what is it like, and where does it grow? From what we have already learned we should expect to find the gametophyte begin with the germination of the spores which are developed on the sporophyte, that is on the fern plant itself. We should investigate this and see. CHAPTER XXVI. FERNS CONTINUED. Gametophyte of ferns. 365. Sexual stage of ferns.—We now wish to see what the sexual stage of the ferns is like. Judging from what we have found to take place in the liverworts and mosses we should infer Fig. arg. Prothallium of fern, under side, showing rhizoids, antheridia scattered among and near them, and the archegonia near the sinus. that the form of the plant which bears the sexual organs is de- veloped from the spores. This is true, and if we should examine old decaying logs, or decaying wood in damp places in the near 176 FERNS. 177 vicinity of ferns, we should probably find tiny, green, thin, heart- shaped growths, lying close to the substratum. These are also found quite frequently on the soil of pots in plant conservatories where ferns are grown. Gardeners also in conservatories usually sow fern spores to raise new fern plants, and usually one can find these heart-shaped growths on the surface of the soil where they have sown the spores. We may call the gardener-to our aid in finding them in conservatories, or even in growing them for us if we cannot find them outside. In some cases they may be grown in an ordinary room Fig. 215. by keeping the surfaces where they are inte uoeng Ge thie ' Ee ~ : rayed elevation along growing moist, and the air also moist, by _ the side of which the : : spore wall cracks during placing a glass bell jar over them. germination. 366. In fig. 214 is shown one of these growths enlarged. Upon the under side we see numerous thread-like outgrowths, the rhizoids, which attach the plant to the substratum, and which act as organs for the absorption of nourishment. ‘The sexual organs are borne on the under side also, and we will study them later. This heart-shaped, Figs Sat: sigan flattened, thin, Spore of Aspidium Spore crushed to remove exospore and green plant is acrostichoides with show endospore. 3 winged exospore. the prothallium of ferns, and we should now give it more careful study, be- ginning with the germination of the spores. 367. Spores.—We can easily obtain material for the study of the spores of ferns. The spores vary in shape to some extent. Many of them are shaped like a three-sided pyramid. One of these is shown in fig. 215. The outer wall is roughened, and on one end are three elevated ridges which radiate from a given 178 MORPHOLOGY. point. A spore of the Christmas fern is shown in fig. 216. The outer wall here is more or less winged. At fig. 217 is a spore of the same species from which the outer wall has been crushed, showing that there is an inner wall also. If possible we should study the germi- nation of the spores of some fern. 368. Germination of the spores. —After the spores have been sown for about one week to ten days we should Fig. 218. Spores of asplenium; exospore re- moved from the one at the right. mount a few in water for examination with the microscope in order to study the early stages. If germination has begun, we find that here and there are short slender green threads, in many cases attached to brownish bits, the old walls of the — spores. Often one will sow the 3} sporangia along with the spores, and in such cases there may be found a number of spores. still within the old sporan- gium wall that are ger- minating, when they will appear as in fig. 219. 369. Protonema.— These short green threads are cited protonemal threads, or profonema, which means a first thread, and it here signifies that this short thread only pre- cedes a larger growth of the same object. In figs. 219, 220 are shown several stages of ; germination of different spores. Soon after Fig, 219. Germinating spores of the short germ tube emerges from the is aquilina still in t : ee she RE a sulin the Crack in the spore wall, it divides by the FERNS. 179 formation of a cross wall, and as it increases in length other cross walls are formed. But very early in its growth we see that a slender outgrowth takes place from the cell nearest the old spore wall. ‘This slender thread is colorless, and is not divided into cells. It is the first rhizoid, and serves both as an organ of attachment for the thread, and for taking up nutriment. 370. Prothallium.—Very soon, if the sowing has not been so crowded as to prevent the young plants from obtaining nutriment sufficient, we will see that the end of this protonema is broadening, as shown in fig. 220. This is done by the formation of the cell walls in different directions. It now continues to grow in this way, the end becoming broader and broader, and new rhizoids are formed from the under surface of the cells. The growing point remains at the mid- dle of the advancing margin, and the cells which are cut off from either side, as they become old, ; widen out. In this way: the Young asian ot a fern (nipho- ‘‘wings,’? or margins of the bel). little, green, flattened body, are in advance of the growing point, and the object is more or less heart-shaped, as shown in fig. 214. Thus we see how the prothallium of ferns is formed. : 371. Sexual organs of ferns.—If we take one of the prothal- lia of ferns which have grown from the sowings of fern spores, or one of those which may be often found growing on the soil 180 MORPHOLOGY. of pots in conservatories, mount it in water on a slip, with the under side uppermost, we can then examine it for the Fig. 221. Male prothallium of a fern (niphobolus), in form of an alga or protonema. Spermato- zoids escaping from antheridia. sexual organs, for these are borne in most cases on the under side. 372. Antheridia.—If we search among the rhizoids we see small rounded elevations as shown in fig. 214 or 222 scat- Fig. 222. Male prothallium of fern (niphobolus), showing opened and unopened antheridia ; section of unopened antheridium , spermatozoids escaping ; spermatozoids which did not escape from the antheridium, FERNS. 181 tered over this portion of the prothallium. These are the an- theridia. If the pro- thallia have not been watered for a day or so, we may have an opportunity of see- ing the spermato- zoids coming out of the antheridium, for when the prothallia Section of antheridia a ee cells, and spermato- are freshly placed jn zoids in the one at the right. water the cells of the antheridium ab- sorb water. This presses on the con- tents of the antheridium and bursts the cap cell if the antheridium is ripe, and all thé spermatozoids are shot out. We can see here that each one is ‘peel shaped like a screw, with the coils at Different views of spermatozoids; first close. But as the spermatozoid 42, 43, in a quiet condition; 44, in a = ‘ motion (Adiantum concinnum). begins to move this coil opens some- what and by the vibration of the long cilia which are on the smaller end it whirls away. In such preparations one may often see them spinning around for a long while, and it is only when they gradually come to rest that one can make out their form. 373. Archegonia.—If we now examine closely on the thicker part of the under surface of the prothallium, just back of the ee : “‘sinus,’? we may see longer gente Ove eee feet te ieee Gal cae cell, and in the canal of the neck are two stout projections from the surface nuclei of the canal cell. of the prothallium. These are shown in fig. 214. They are 182 MORPHOLOGY. the archegonia. One of them in longisection is shown in fig. 225. It is flask-shaped, and the broader portion is sunk in the Fig. 226. Mature and open archegonium of fern (Adiantum cuneatum) with spermatozoids making their way down through the slime to the egg. tissue of the prothallium. The egg isin the larger part. The spermatozoids when they are swimming around over the under surface of the pro- thallium come near the neck, and here they are caught in the viscid substance which has oozed out of the canal of the arche- gonium. From here they slowly swim down the canal, and finally one sinks into Fig. 227. the egg, fuses with the nucleus of the latter, fertilization in a fem and the egg is then fertilized. It is now (Marattia). sf, spermato- id fusing with the nu- : pice ee (After Teady to grow and develop into the fern ci li plant. This brings us back to the sporo- phyte, which begins with the fertilized egg. Sporophyte. 874. Embryo.—The egg first divides into two cells as shown in fig. 228, then into four. Now from each one of these quandrants of the embryo a definite part of the plant develops, from one the first leaf, from one the stem, from one the root, and from the other the organ which is called the foot, and which FERNS. 183 attaches the embryo to the prothallium, and transports nourishment for the embryo until it can become attached to the soil and lead an independent ex- istence. During this time the wall of the archegonium grows somewhat to accommodate the increase in size of the embryo, as shown in figs. 229, 230. But soon the wall of the archegonium is ruptured and the embryo emerges, the root attaches itself to the soil, and soon the prothallium dies. The embryo is first on the under side of the prothallium, and the first leaf Fig. 228. Two-celled embryo of Pteris serrulata. Remnant of archegonium neck below. and the stem curves upward between the lobes of the heart-shaped body, and then grows upright as shown in fig. 231. Usually only one embryo is formed on a single prothallium, but in one case I found a prothallium with two well- formed embryos, which are figured in 232. 375. Comparison of ferns with liverworts and mosses.—In the ferns then we have reached a remarkable condition of things as compared with that which we found in the mosses and liverworts. In the mosses and liverworts 184 MORPHOLOGY. the sexual phase of the plant (gametophyte) was the prominent one, and consisted of either a thallus or a leafy axis, but in either case it bore the sexual organs and led an independent existence; that is it was capable of ob- taining its nourishment from the soil or water by means of organs of absorp- tion belonging to itself, and it also performed the office of carbon conversion. 376. The spore-bearing phase (sporophyte) of the liverworts and mosses, on the other hand, is quite small as compared with the sexual stage, and it is Fig. 229. Young embryo of fern (Adiantum concinnum) in enlarged venter of the archegonium. 5S, stem; L, first leaf or cotyledon; 2, root; /, foot. completely dependent on the sexual stage for its nourishment, remaining at- tached permanently throughout all its development, by means of the organ called a foot, and it dies after the spores are mature. 877. Now in the ferns we see several striking differences. In the first place, as we have already observed, the spore-bearing phase (sporophyte) of FERNS. 185 the plant is the prominent one, and that which characterizes the plant. It also leads an independent existence, and, with the exception of a few cases, does not die after the development of the spores, but lives from year to year and develops successive crops of spores. There is a distinct advance here in the stze, complexity, and permanency of this phase of the plant. 378. On the other hand the sexual phase of the ferns (gametophyte), while it still is capable of leading an independent existence, is short-lived (with very few exceptions). It is also much smaller than most of the liverworts and Fig. 230. Embryo of fern (Adiantum concinnum) still surrounded by the archegonium, which has grown in size, forming the ‘‘ calyptra.”” Z, leaf; S, stem; A, root; /, foot. mosses, especially as compared with the size of the spore-bearing phase. The gametophyte phase or stage of the plants, then, is decreasing in size and durance as the sporophyte stage is increasing. We shall be interested to see if this holds good of the fern allies, that is of the plants which belong to the same group as the ferns. And as we come later to take up the study of the higher plants we must bear in mind to carry on this comparison, and see if this progression on the one hand of the sporophyte continues, and if the retrogression of the gametophyte continues also, 186 MORPHOLOG ¥. Fig. 232. Two embryos from one prothallium of attached to prothallium. Adiantum cuneatum. Fig. 231. Young plant of Pteris serrulata still CHAPTER XXVIL. HORSETAILS. 879. Among the relatives of the ferns are the horsetails, so called because of the supposed resem- blance of the branched stems of some of the species to a horse’s tail, as one might infer from the plant shown in fig. 237. They do not bear the least re- semblance to the ferns which we have been study- ing. But then relationship in plants does not depend on mere resemblance of outward form, or of the promi- nent part of the plant. 380. The field equisetum. Fertile shoots.—Fig. 233 represents the common horsetail (Equisetum ar- vense). It grows in moist sandy or gravelly places, and the fruiting portion of the plant (for this species is dimorphic), that is the portion which bears the spores, appears above the ground early in the spring. It is one of the first things to peep out of the recently frozen ground. ‘This fertile shoot of the plant does not form its growth this early in the spring. Its development takes place under the ground in the autumn, so that with the advent of spring it pushes up without delay. This shoot is from 10 to 20 cm high, and at quite regular intervals there are slight enlargements, the nodes of the stem. The cylindrical portions between the nodes are the _ internodes. If we examine the region of the inter- pore ¢ fertile plant of nodes carefully we note that there are thin mem- ¢guisetum ar- branous scales, more or less triangular in outline, and Y4nsqshowing leaves and the connected at their bases into a ring around the stem. fruiting spike. 187 188 MORPHOLOG Y. Curious as it may seem, these are the leaves of the horsetail. The stem, if we examine it farther, will be seen to possess numer- ous ridges which extend lengthwise and which alternate with furrows. Farther, the ridges of one node alternate with those of the internode both above and below. Likewise the leaves of one node alternate with those of the nodes both above and below. 381. Sporangia.—The end of this fertile shoot we see pos- sesses a cylindrical to conic enlargement. ‘This is the /eri/e spike, and we note that its surface is marked off into regular areas if the spores have not yet been disseminated. If we dissect off a few of these por- tions of the fertile spike, and examine one of them with a low magnifying power, it will appear like the : fig. 234. We see here that the angular area is a Fig. 234. disk-shaped body, with a stalk attached to its inner Pettate eect surface, and with several long sacs projecting from phyll of equisetum jside view) show its inner face parallel with the stalk and surrounding ing sporangia on mader SIS; the same. These elongated sacs are the sporangia, and the disk which bears them, together with the stalk which attaches it to the stem axis, is the sporophy//, and thus belongs to the leaf series. These sporophylls are borne in close whorls on the axis. 382. Spores.—When the spores are ripe the tissue of the sporangium becomes dry, and it cracks open and the spores fall out. Ifwe look at fig. 235 we see that the spore is covered with a very singular coil which lies close to the wall. When the spore dries this uncoils and thus rolls the spore about. Merely breathing upon these spores is sufficient to make them perform very curious evolutions by the twisting of these four coils which are attached to one place of the wall. ‘They are formed by the splitting up of an outer wall of the spore. 383. Sterile shoot of the common horsetail.—When the spores are ripe they are soon scattered, and then the fertile shoot dies down. Soon afterward, or even while some of the fertile shoots are still in good condition, sterile shoots of the HORSETAILS. 189 plant begin to appear above the ground. One of these is shown in fig. 237. This has a much more slender stem and is pro- Spore of equisetum Spore of equisetum with elaters un- with elaters coiled up. coiled. vided with numerous branches. If we ex- amine the stem of this shoot, and of the branches, we see that the same kind of leaves are present and that the markings on the stem are similar. Since the leaves of the horsetail are membranous and not green, the stem is green in color, and this per- forms the function of carbon conversion. These green shoots live for a great part of the season, building up material which is carried down into the underground stems, where it goes to supply the forming fertile shoots in the fall. On digging up some of these plants we see that the underground stems are often of great extent, and that both fertile and sterile shoots are attached to one and the same. 384. The scouring rush, or shave grass. —Another common species of horsetail in the Northern States grows on wet banks, or in sandy soil which contains moisture along railroad embankments. It is the scouring rush (E. hyemale), so called because it was once used for polishing purposes. This plant like Fig. 237. ; ; terile plant of horsetai i. all the species of the horsetails has Pea nee orselail (Equs 190 MORPHOLOGY. underground stems. But unlike the common horsetail, there is but one kind of aerial shoot, which is green in color and fertile. The shoots range as high as one meter or more, and are quite stout. The new shoots which come up for the year are un- branched, and bear the fertile spike at the apex. When the spores are ripe the apex of the shoot dies, and the next season small branches may form from a number of the nodes. 385. Gametophyte of equisetum.—The spores of equisetum have chloro- phyll when they are mature, and they are capable of germinating as soon as mature. The spores are all of the same kind as regards size, just as we found in the case of the ferns. But they develop prothallia of different sizes, according to the amount of nutriment which they obtain. Those which obtain but little nutriment are smaller and develop only antheridia, while those which obtain more nutriment become larger, more or less branched, and develop archegonia. This character of an independent pro- thallium (gametophyte) with the characteristic sexual organs, and the also independent sporophyte, with spores, shows the relationship of the horsetails with the ferns. We thus see that these characters of the reproductive organs, and the phases and fruiting of the plant, are more essential in deter- mining relationships of plants than the mere outward appearances. CHAPTER XXVIII. CLUB MOSSES. 386. What are called the ‘‘ club mosses’’ make up another group of interesting plants which rank as allies of the ferns. They are not of course true mosses, but the general habit of some of the smaller species, and especially the form and size of the leaves, suggest a resem- blance to the larger of the moss plants. 387. The clavate lycopodium.—Here is one of the club mosses (fig. 238) which has a wide distribution and which is well entitled to hold the name of club because of the form of the up- right club-shaped branches. As will be seen from the illustration, it has a prostrate stem. This stem runs for considerable distances on the surface of the ground, often partly buried in the leaves, and sometimes even buried beneath the soil. The leaves are quite small, are flat- tened-awl-shaped, and stand thickly over the stem, arranged in a spiral manner, which is the usual arrangement of the leaves of the club mosses. Here and there are upright branches which are forked several times. The end of one or more of these branches becomes pro- ‘ duced into a slender upright stem which is siete pti nearly leafless, the leaves being reduced to jim branch bearite twa = sporophyll with open mere scales. The end of this leafless branch Caregins stare then terminates in one or several cylindrical sPote ner it heads which form the club. gl 192 MORPHOLOGY. 388. Fruiting spike of Lycopodium clavatum.—This club is the fruiting spike or head (sometimes termed a s/roddlus). Here the leaves are larger again and broader, but still not so large as the leaves on the creeping shoots, and they are paler. If we bend down some of the leaves, or tear off a few, we see that in the axil of the leaf, where it joins the stem, there is a somewhat rounded, kidney-shaped body. This is the spore-case or spo- rangium, as we can see by an examination of its contents. There is but a single spore-case for each of the fertile leaves (sporophyll). When it is mature, it opens by a crosswise slit as seen in fig. 238. When we consider the number of spore-cases in one of these club- shaped fruit bodies we see that the number of spores developed ina large plant is immense. In mass the spores make a very fine, soft powder, which is used for some kinds of pyrotechnic material, and for various toilet purposes. Z 389. Lycopodium lucidulum.—Another com- AX mon species is figured at 239. This is Lycopo- * iN dium lucidulum. The habit of the plant is quite ‘Al a different. It grows in damp ravines, woods, and ZS moors. The older parts of the stem are prostrate, A ~~ while the branches are more or less ascending. It branches in a forked manner, The leaves are larger than in the former species, and they are all of the same size, there being no appreciable difference between the sterile and fertile ones. The characteristic club is not present here, but the SSA) N ISS 3% 5 LS YG spore-cases occupy certain regions of the stem, as shown at 239. Ina Yy; LN single season one region of the stem § iz may bear spore-cases, and then a ks sterile portion of the same stem is era loped, which later b h eLcopodium lucidulum, bulbils in axils of developed, which later bears another eaves near the top, sporangia in axils of leaves series of spore-cases highe 5 below them. At right is a bulbil enlarged. Sao agit (ae 390. Bulbils on Lycopodium lucidulum.—There is one curious way in which this club moss multiplies. One may see frequently among the upper leaves small wedge-shaped or heart- shaped green bodies but little larger than the ordinary leaves, These are little a LITTLE CLUB MOSSES. 193 buds which contain rudimentary shoot and root and several thick green leaves, When they fall to the ground they grow into new lycopodium plants, just as the bulbils of cystopteris do which were described in the chapter on ferns, 391. Note.—The prothallia of the species of lycopodium which have been studied are singular objects. In L. cernuum a cylindrical body sunk in the earth is formed, and from the upper surface there are green lobes, In L. phlegmaria and some others slender branched, colorless bodies are formed which according to Treub grow as a saphrophyte in decayed bark of trees. Many of the prothallia examined have a fungus growing in their tissue which is supposed to play some part in the nutrition of the prothallium. The little club mosses (selaginella). 392. Closely related to the club mosses are the selaginellas. These plants resemble closely the general habit of the club mosses, but are generally smaller and the leaves more delicate. Some species are grown in conservatories for ornament, the leaves of Fig. 240. Fig. 241. Fig. 242. Fig. 243. Selaginella with Fruiting spike Large spo- Small spo- three fruiting spikes. showing large and rangium. rangium. (Selaginella apus.) small sporangia. such usually having a beautiful metallic lustre. The leaves of some are arranged as in lycopodium, but many species have the leaves in four to six rows. Fig. 240 represents a part of a selaginella plant (S. apus). The fruiting spike possesses similar leaves, but they are shorter, and their arrangement gives to the spike a four- sided appearance. 194 MORPHOLOG ¥. 393. Sporangia.—On examining the fruiting spike, we find as in lycopodium that there is but a single sporangium in the axil of a fertile leaf. But we see that they are of two different kinds, small ones in the axils of the upper leaves, and large ones in the axils of a few of the lower leaves of the spike. The mzcro- spores are borne in the smaller spore-cases and the macrospores in the larger ones. Figures 241-243 give the details. There are many microspores in a single small spore-case, but 3-4 ma- crospores in a large spore-case. 394. Male prothallia.—The prothallia of selaginella are much reduced structures. The microspores when mature are already divided into two cells. When they grow into the mature pro- thallium a few more cells are formed, and some of the inner ones form the spermatozoids, as seen in fig. 244. Here we see that Fig. 244. Details of microspore and male prothallium of selagine!la; rst, microspore ; 2d, wall re- moved to show small prothallial cell below; 3d, mature male prothallium still within the wall; 4th, small cell below is the prothallial cell, the remainder is antheridium with wall and four sperm cells within; 5th spermatozoid. After Beliaieff and Pfeffer. the antheridium itself is larger than the prothallia. Only an- theridia are developed on the prothallia formed from the microspores, and for this reason the prothallia are called male prothallia. In fact a male prothallium of selaginella is nearly all antheridium, so reduced has the gametophyte become here. 395. Female prothallia.—The female prothallia are devel- oped from the macrospores. The macrospores when mature have a rough, thick, hard wall. The female prothallium begins to develop inside of the macrospore before it leaves the sporangium. The protoplasm is richer néar the wall of the spore and at the LITTLE CLUB MOSSES. 195 upper end. Here the nucleus divides a great many times, and finally cell walls are formed, so that a tissue of considerable ex- tent is formed inside the wall of the spore, which is very different from what takes place in the ferns we have studied. As the prothallium matures the spore is cracked at the point where the three angles meet, as shown in fig. 246. The archegonia are developed in this exposed surface, and several can be seen in the illustration. 396. Embyro,—After fertilization the egg divides in such a way that along cell called « suspensor is cut off from the upper side, Fig. 245. : Section of mature macrospore Mature female prothallium of Fig. 247- of selaginella, showing female selaginella, just bursting open Seedling of sela- prothallium and archegonia, the wall of macrospore, exposing ginella still attached After Pfeffer. archegonia. After Pfeffer. to the macrospore. After Campbell. which elongates and pushes the developing embyro down into the center of the spore, or what is now the female prothallium. Here it derives nourish- ment from the tissues of the prothallium, and eventually the root and stem emerge, while a process called the ‘‘ foot ’’ is still attached to the prothallium, When the root takes hold on the soil the embyro becomes free. Vig. 248. CHAPTER XXIX. QUILLWORTS (ISOETES). 397. The quillworts, as they are popularly called, are very curious plants. They grow in wet marshy places. They receive their name from the supposed resemblance of the leaf to a quill. Fig. 248 represents one of these ,quillworts (Isoetes engelmannii). / The leaves are the prominent part of the plant, and they are about all that can be seen except the roots, without removing the leaves, Each leaf, it will be - seen, is long and needle-like, ex- cept the basal part, which is expanded, not very unlike, in out- line, a scale of an onion. These expanded basal portions of the leaves closely overlap each other, and the very short stem is com- pletely covered at all times. Fig. 250 is from a longitudinal sec- tion of a quillwort. It shows the form of the leaves from this view (side view), and also the Tsoetes, mature plant, sporophyte stage. general outline of the short stem, which is triangular. The stem is therefore a very short object. 196 QUILLWORTS. 197 398. Sporangia of isoetes.—If we pull off some of the leaves of the plant we see that they are somewhat spoon-shaped as in fig. 249. In the inner surface of the expanded base we note a circular depression which seems to be of a different text- Fig. 24 Fig. 250. Base of leaf of isoetes, Section of plant of Isoetes engelmanii, showing cup- showing sporangium with shaped stem, and longitudinal sections of the sporan- macrospores. ({soetes en- gia in the thickened bases of the leaves. gelmannii.) ure from the other portions of the leaf. This is a sporangium. Beside the spores on the inside of the sporangium, there are strands of sterile tissue which extend across the cavity. This is peculiar to isoetes of all the members of the class of plants to which the ferns belong, but it will be remembered that sterile strands of tissue are found in some of the liverworts in the form of elaters. 899. The spores of isoetes are of two kinds, small ones (microspores) and large ones (macrospores), so that in this respect it agrees with selaginella, though it is so very different in other respects. When one kind of spore is borne in a sporan- 198 MORPHOLOG Y. gium usually all in that sporangium are of the same kind, so that certain sporangia bear microspores, and others bear macrospores. But it is not uncommon to find both kinds in the same sporan- gium. When a sporangium bears only microspores the number is much greater than when one bears only macrospores. 400. If we examine some of the microspores of isoetes we see that they are shaped like the quarters of an apple, that is they are of the bilateral type as seen in some of the ferns (asplenium). 401. Male prothallia.—lIn isoetes, as in selaginella, the microspores de- velop only male prothallia, and these are very rudimentary, one division of the spore having taken place before the spore is mature, just as in selagi- nella. 402. Female prothallia.—These are developed from the macrospores. The latter are of the tetrahedral type. The development of the female prothal- lium takes place in much the same way as in selaginella, the entire prothal- lium being enclosed in the macrospore, though the cell divisions take place after it has left the sporangium. When the archegonia begin to develop the macrospore cracks at the three angles and the surface bearing the arche- gonia projects slightly as in selaginella. Absorbing organs in the form of rhizoids are very rarely formed. 403. Embryo.—The embryo lies well immersed in the tissue of the pro- thallium, though there is no suspensor developed as in selaginella. CHAPTER XXX. COMPARISON OF FERNS AND THEIR RELATIVES. 404. Comparison of selaginella and isoetes with the ferns.—On compar- ing selaginella and isoetes with the ferns, we see that the sporophyte is, as in the ferns, the prominent part of the plant. It possesses root, stem, and leaves. While these plants are not so large in size as some of the ferns, still we see that there has been a great advance in the sporophyte of selagi- nella and isoetes upon what exists in the ferns. There is a division of labor between the sporophylls, in which some of them bear microsporangia with microspores, and some bear macrosporangia with only macrospores. In the ferns and horsetails there is only one kind of sporophyll, sporangium, and spore ina species. By this division of labor, or differentiation, between the sporophylls, one kind of spore, the microspore, is compelled to form a male prothallium, while the other kind of spore, the macrospore, is compelled to form a female prothallium. This represents a progression of the sporophyte of a very important nature. 405. On comparing the gametophyte of selaginella and isoetes with that of the ferns, we see that there has been a still farther retrogression in size from that which we found in the independent and large gametophyte of the jiverworts and mosses. In the ferns, while it is reduced, it still forms rhizoids, and leads an independent life, absorbing its own nutrient materials, and assimilating carbon. In selaginella and isoetes the gametophyte does not escape from the spore, nor does it form absorbing™ organs, nor develop assimilative tissue. The reduced prothallium develops at the expense of food stored by the sporophyte while the spore is developing. Thus, while the gametophyte is separate from the sporophyte in selaginella and isoetes, it is really dependent on it for support or nourishment. 406. The important general characters possessed by the ferns and their so-called allies, as we have found, are as follows: The spore-bearing part, which is the fern plant, leads an independent existence from the prothallium, and forms root, stem, and leaves. The spores are borne in sporangia on the leaves. The prothallium also leads an independent existence, though in isoetes and selaginella it has become almost entirely dependent on the sporo- 199 200 MORPHOLOGY. phyte. The prothallium bears also well-developed antheridia and arche- gonia. The root, stem, and leaves of the sporophyte possess vascular tissue. All the ferns and their allies agree in the possession of these char- acters. The mosses and liverworts have well-developed antheridia and archegonia, and the higher plants have vascular tissue. But no plant of either of these groups possesses the combined characters which we find in the ferns and their relatives. The latter are, therefore, the fern-like plants, or pteridophyla. The living forms of the pteridophyta are classified as fol- lows into families or orders. 407. Pteridophyta. Ophioglossacez. Marattiaceze. ? Heterosporous (Isoetaceze (Isoetes). Osmundacez. Schizeeaceze. a Gleicheniacez. Class I. Filicales. J Hymenophyl- laceze. Cyatheaceze. Polypodiacee. Polypodium, Ono- Leptosporangiatz. clea, Aspidium, etc. Salviniaceze. Marsiliaceze. Eusporangiate.... | Peano geen Homosporous. | Ieterosporous. | z Equisetacez. Class II. Equisetales. | ponte Lycopodiaceze (Lycopodium). Hommsparons: i Psilotaceze (tropical forms). Class III. Lycopodiales. | Heterosporous. (Selaginellaceze (Selaginella). 201 COMPARISON OF PTERIDOPHYTA. *eisuer -odsosotur_tvaq sauo aaddn ‘eysuerodso19 ‘BHa) -sprozoyeuriods A vo “WNL UPPLMUUI Tp Lo UU aydydorods uo = Juapuadap pue wmriuriods UL T[QS app pa sumipuriods Ut [[us aTYyM [fad purdipur pure ‘po ye a sah MOR Wendie obig OE GAG JRO suv eutoad peas) ypao peqyeyoad|-dopaaacy — apeurypeuas Oy padoyaaac | sorodsosoe nae Seu sae os Uh aie a eee SSALLO]OD[EAG [suis uLU sas AL] -ay ‘say oduv'y |-apeun ‘sau [peu “sasodsosoryy }****uiejU0d sauo pur aqy uo padnoadjo yur sdoafs? adlt MEMOS Ta WED tat “spur, OMT, “May jpeuy) spupy omy sarvoy Turmwaq-arods |-jaaacy) ‘33a}PUOTE MOT FEUER 94 hnq a0 ‘sproznya ou Gem arods yo apis} vaTAN yo wSuvaody [year ‘ways Yooy |pozyn.y ‘vypey ord yuasayip uc) “GY §][99 JO ssvUT papuNs ‘sso[L0[0 NVA arkydosods) -erduriodsoso1ur “splovoy ei) wo arousosseU) wuniguesods ur [ys souo touut ‘erSuesods *839)-1ads TEM Wnipl ur pasoys UAL apy [Jao purdsyyUL, -o19 BUI aeaq, Aqpensn WA yea fumiy)-ayy ay “PpAof-nu wos pado}pue “ao pet Jeyyoad sarodsouaeyy [reese urylsaavay sano aseq -[eqjoad oyewray eure) do “PaacL _“ayeway||peuts oyut padojaaacy -uog sauo adie, [ye saniavs ar wBuer] (yuypd saza]"SS?H40[09 yee ayy ury aa souo adav yz fropew tsauo [pews *sasodsosd1 yy ureyu09 souol-ods © yvaq ‘saavay|-ost ojut sdo|5® xadv ut ‘viuod/y on HO GP SPuULy OMT, ‘aay yng 40 ‘spioz {euty “spappomy|y20ys Ara wayg]-podacy) “SsayP Ute MFT FOBUE AUC) lau ou ATpensn ‘vm axods yo apisut jo eSuewodg [yea] furays yoo, jpazipqsayy VIT[LY OIC yuasagFIP UC) ‘s[[99 JO ssvuL popunos ‘ssap1o[o) *SaLaosy "339 uv YIM *splozoy Llu ‘satodg|- sees surey yora ‘eypeqpoad|-sads yy erp eyy, -uo9 uNTsuriody ‘puly auo jo ty stpAydorods uo widuvtody *sazodg |" *sureyuoo winut -uvsody “puny aUuo JOT jeay uo wdurtody “LUV ONILIAN of “year ‘ways ‘JOOX. *yeay ‘ways ‘JOOYy “LUV AAILVLAOTA (jury wanjas -mbaojut sdo -ppAay) *33a pazy G29 uday oyu sdo para) 33a Pez [AeoL “LANA -ONOdS AO ONINNIDS GT aywulay Jadivy uol-o1d ayeur [pews ‘vigodayoiy = luo ‘erpuayjuy "erypeyqoad yua -layip uo spury OM} 94} ATpens~) “sprozoyemuiads YIM PIPL yyy sunTeqyoad aures ay} UO spun (0g ATTENSE) “339 IM yove ‘eluoda yoy ‘SNVDYQ TvAXxXaS “sploziya Yim “Mord peqo, ‘pepuedxa ‘uryy ‘uaaid vv “WALASTNOST “SplLOzIyA YM ‘yyMoId padeys -yeay ‘papuedxa ‘un ‘usa y (*Vaovip -oddjog) “SNAG “LUV ] DAILV LAID A *HLAHdOL -awyy to |Apiey azow pur DNINNIDYE [Ue] (Cyeruuasad Aypensy) go Juapuadapuy sayhydoyoured ay ‘ued yur way aq. ayy jo yced yoda p> OLLAHdTOMOdS Cahydosods ay} uo yuspuadap Surur0saq saya0st pue eyauseyjas uy “yuapuadapur Apsour ‘aazjeMs Burwossg) “TLAHCOLANVS ‘SHALANGOURULLI SILL NI SLAMIdONOdS UNV ALAUCOLANVO JO NOLLVIAM ONIMOHS WIEVL ‘80F CHAPTER XXXI. GYMNOSPERMS. The white pine. 409. General aspect of the white pine.—The white pine (Pinus strobus) is found in the Eastern United States. In favorable situations in the forest it reaches a height of about 50 meters (about 160 feet), and the trunk a diameter of over 1 meter. In well-formed trees the trunk is straigkt and towering; the branches where the sunlight has access and the trees are not crowded, or are young, reaching out in graceful arms, form a pyramidal outline to thetree. In oldand dense forests the lower branches, because of lack of sunlight, have died away, leaving tall, bare trunks for a considerable height. 410. The long shoots of the pine.—The branches are of twokinds. Those which we readily recognize are the long branches, so called because the growth in length each year is considerable. The terminal bud of the long branches, as well as of the main stem, continues each year the growth of the main branch or shoot; while the lateral long branches arise each year from buds which are crowded close together around the base of the terminal bud. The lateral long branches of each year thus appear to be ina whorl. The distance between each false whorl of branches, then, represents one year’s growth in length of the main stem or long branch. 411. The dwarf shoots of the pine.—The dwarf branches are all lateral on the long branches, or shoots. They are scattered over the year’s growth, and each bears «a cluster of five long, needle-shaped, green Icaves, which remain on the tree for several years. At the base of the grven leaves are a number of chaff-like scales, the previous bud scales. While the dwarf branches thus bear green leaves, and scales, the long branches bear only thin scale-like leaves which are not green. 202 GYMNOSPERMS.: WHITE PINE, 203 412. Spore-bearing leaves of the pine.—The two kinds of spore-bearing leaves of the pine, and their close relatives, are so different from anything which we have yet studied, and are so unlike the green leaves of the pine, that we would scarcely recognize them as belonging to this category. Indeed there is great uncertainty regarding their origin. 413. Male cones, or male flowers.—The male cones are borne in clusters as shown in fig. 251. Each compact, nearly cylindri- Ni Fig. 251. Spray of white pine showing cluster of male cones just before the scattering of the pollen. cal, or conical mass is termed a cone, or flower, and each arises in place of a long lateral branch. One of these cones is shown 204 ° MORPHOLOGY. considerably enlarged in fig. 252. The central axis of each cone is a lateral branch, and belongs to the stem series. The stem axis of the cone can be seen in fig. 253. It is completely covered by stout, thick, scale-like outgrowths. These scales are obovate in outline, and at the inner angle of the upper end Fig. 252. Fig. 253. Fig. 254. Staminate cone of white Section of staminate Two sporo- pine, with bud scales re- cone, showing sporangia. phylls removed, moved on one side. showing open- ing of sporangia. there are several rough, short spines. They are attached by their inner lower angle, which forms a short stalk or petiole, and continues through the inner face of the scale as a ‘‘ mid- rib.’? What corresponds to the lamina of the scale-like leaf bulges out on each side below and makes the bulk of the scale. These prominences on the under side are the sporangia (micro- sporangia). There are thus two sporangia on a sporophyll (microsporophyll). When the spores (microspores), which here are usually called pollen grains, are mature each sporangium, or anther locule, splits down the middle as shown in fig. 254, and the spores are set free. 414. Microspores of the pine, or pollen grains.—A mature pollen grain of the pine is Fig. 255. : : 8 é Pollen’ grain of Shown in fig. 255. It is a queer-looking object, white pine. ? “ 3 possessing on two sides an air sac, formed by the upheaval of the outer coat of the spore at these two points. GYMNOSPERMS: WHITE PINE. 205 When the pollen is mature, the moisture dries out of the scale (or stamen, as it is often called here) while ‘it ripens. When a limb, bearing a cluster \ \ i of male cones, is jarred by the hand, or by Ny) currents of air, the split suddenly opens, and \ we a cloud of pollen bursts out from the numer- Wil ous anther locules. The pollen is N thus borne on the wind and some of it falls on the female flowers. Fig. 256. White pine, branch with cluster of mature cones shedding the seed. A few young cones four months old are shown on branch at the left. Drawn from photograph. 415. Form of the ma- ture female cone.—A cluster of the white- . pine cones is shown in ® fig. 256. These are mature, and the scales have spread as they do when mature and becoming dry, in order that the seeds may be set at liberty. The general out- Mature cone of white pine at time of scattering of the seed, nearly natural size. 206 MORPHOLOGY. line of the cone is lanceolate, or long oval, and somewhat curved. It measures about 1o-15cm long. If we remove one Fig. 258. Fig. 259. Fig. 260. Fig. 261. Fig. 262. Sterile scale. Scale with Seeds have Back of scale Winged Seeds undevel- well-developed split off from with small cover seed free from oped. seeds. scale. scale. scale. Figs. 258-262.—White pine showing details of mature scales and seed. of the scales, just as they are beginning to spread, or before the seeds have scattered, we shall find the seeds at- tached to the upper surface at the lower end. There are two seeds on each scale, one at each lower angle. They are ovate in outline, and shaped somewhat likea biconvex lens. At this time the seeds easily fall away, and may be freed by jarring the cone. As the seed is detached from the scale a strip of tissue from the latter is peeled off. This formsa ‘‘ wing ”’ for the seed. It is attached to one end and is shaped something lke a knife blade. On the back of the scale is a small appendage known as the cover scale. 416. Formation of the female pine cone.—The female flowers begin their development rather late in the spring of the year. They are formed from terminal buds of the higher branches of the tree. In this way the cone may terminate the main shvot of a branch, or of the lateral shoots ina whorl. Alter growth has procceded Female cones of the for some time in the spring, the terminal portion begins pine at time of pollina- : tion, about natural size. to assume the appearance of a young female cone or GYMNOSPERMS.: WHITE PINE. 207 flower. These young female cones, at about the time that the pollen is escaping from the anthers, are long ovate, measuring about 6-1omm long. They stand upright as shown in fig. 263. 417. Form of a “scale” of the female flower.—If we remove one of the scales from the cone at this stage we can better study it in detail. It is flattened, and oval in outline, with a staut ‘“‘rib,’’ if it may be so called, running through the middle line and terminating in a point. The scale is in two parts as shown in fig. 266, which is a view of the under side. The small ‘‘ out- growth’’ which appears as an appendage is the cover scale, for while it is smaller in the pine than the other portion, in some of the relatives of the pine it is larger than its mate, and being on the outside, covers it. (The inner scale is sometimes called the ovu- liferous scale, because it bears the ovules. ) 418. Ovules, or macrosporangia, of the pine.—At each of the lower angles of the Fig. 264. Fig. 265. Fig. 266. Section of female cone Scale of white pine with the Scale uf white pine seen of white pine, showing two ovules at base of ovulif- from the outside, showing the young ovules (macrospo- _erous scale. cover scale. rangia) at base of the ovu- liferous scales. scale is a curious oval body with two curved, forceps-like pro- cesses at the lower and smaller end. These are the macro- sporangia, or, as they are called in the higher plants, the ovules. These ovules, as we see, are in the positions of the seeds on the 208 MORPHOLOGY. mature cones. In fact the wall of the ovule forms the outer coat of the seed, as we will later see. 419. Pollination.—At the time when the pollen is mature the female cones are still erect on the branches, and the scales, which during the earlier stages of growth were closely pressed against one another around the axis, are now spread apart. As the clouds of pollen burst from the clusters of the male cones, some of it is wafted by the wind to the female cones. It is here caught in the open scales, and rolls down to their bases, where some of it falls between these forceps-like processes at the E lower end of the ovule. At Fig. 267. Branch of white pine showing young female cones at time of pollination on the ends of the branches, and one-year-old cones below, near the time of fertilization. this time the ovule has exuded a drop of a sticky fluid in this depression between the curved processes at its lower end. The pollen sticks to this, and later, as this viscid substance dries up, it pulls the pollen close up in the depression against the lower GYMNOSPERMS: WHITE PINE. 209 end of the ovule. This depression is thus known as the pollen chamber. ; 420. Now the open scales on the young female cone close up again, so tightly that water from rains isexcluded. What is also very curious, the cones, which up to this time have been standing erect, so that the open scale could catch the pollen, now turn so that they hang downward. This more certainly excludes the rains, since the overlapping of the scales forms a shingled surface. Quantities of resin are also formed in the scales, which exudes and makes the cone practically impervious to water. 421. The female cone now slowly grows during the summer and autumn, increasing but little in size during this time. During the winter it rests, that is, ceases to grow. With the coming of spring, growth commences again and at an accelerated rate. The increase in . ‘ : Fig. 268, size is more rapid. The cone reaches Macrosporangium of pine F . (ovule), z¢, integument; 7, nu- maturity in September. We thus see cellus; #z, macrospore. ” (After that nearly eighteen months elapse from offmeister.) the beginning of the female flower to the maturity of the cone, and about fifteen months from the time that pollination takes place. 422. Female prothallium of the pine.—To study this we must make careful longitudinal sections through the ovule (better made with the aid of a micro- tome). Such a section is shown in fig. 269. The outer layer of tissue, which at the upper end (point where the scale is attached to the axis of the cone) stands free, is the ovular coat, or zzéegument. Within this integument, near the upper end, there is a cone-shaped mass of tissue, which farther down continues along next the integument in a thinner strip. This mass of tissue is the zzcellus, or the macrosporangium proper. The elliptical mass of tissue within this, shown in fig. 271 is the female prothallium, or what is usually here called the endosperm. The conical portion of the nucellus fits over the 210 MORPHOLOGY. prothallium, and is called the nucellar cap. Only one end of the endosperm (prothallium) is shown in fig. 271. 423. Archegonia.—In the upper end of the endosperm (prothallium) are several archegonia, and they aid us in determining what portion is the female prothallium. The nucellus is of course formed before the prothallium. 0 ok Ls oe gee The latter arises from a cell (macro- aay spore) near the center of the nucellus. isn This cell is larger, and has a larger Sa nucleus than its fellows (see fig. 268). The prothallium here is formed much in the same way as in selaginella, where we recollect it begins to de- velop before the macrospore has Fig. 269. Fig. 270. Section of ovule of white pine. 7x¢, integ- | Upper portion of nucellus of white pine. ument; fc. pollen chamber; //, pollen tube; Ag, pollen-grain remains ; sfc, sperm cells ; n, nucellus; 7, macrospore cavity. vn, vegetative nucleus; #7, pollen tube. reached its full size, and where the archegonia begin to form before it leaves the macrosporangium. : 424. Male prcthallia.—By the time the pollen is mature the male pro- thallum is already partly formed. In fig. 255 we can see two well-formed cells. Other cells are said to be formed earlicr, but they become so flattened that it is difficult to make them out when the pollen grain is mature. At this stage of development the pollen grain is lodged at the mouth of the ovule, and is drawn up into the pollen chamber. 425. Farther growth of the male prothallium.—During the summer and autumn the male prothallium makes some farther growth, but this is slow. The larger cell, called the vegetative cell, elongates by the formation of a tube, furming a sac, known as the pollen tube. It is either simple or branched. Inside of this sac the cells of the prothallium are protected, and farther GYMNOSPERMS: WHITE PINE. 211 division of the cells takes place here, just as the female prothallium develops in the cavity of the nucellus, from the macrospore. The nucleus of the vege- tative cell passes down the cavity of this tubularsac. The antherid cell, which is the smaller cell of the pollen grain, in the pine, divides by a cross wall into a so-called stalk cell, and a mother sperm cell, the latter corresponding to the central cell of the an- Fig. 271. Section through upper part of nucellus and Fig. 272. endosperm of white pine, showing upper por- Last division of the egg in the white tion of archegonium, the entering sperm cells, pine cutting off the ventral canal cell and track of pollen tube; xc, nucellus: /¢, at the apex ofthearchegonium. xd, pollen tube; sfc, sperm cells. endosperm; Arch, archegonium. theridium, there being no wall formed. The sperm mother cell also passes down the tubular sac, and divides again into two sperm cells, as shown in fig. 270. About this time, or rather a little earlier, with the pollen tube part way through the nucellar cap, winter overtakes it, and all growth ceases until the following spring. 426. Fertilization.—In the spring the advance of the pollen tube con- tinues, and it finally passes through the nucellar cap about the time that the archegonia are formed and the egg cell is mature, as shown in fig. 271. The pollen tube now opens and the sperm cells escape into the archegonium, and later one of them fuses with the egg nucleus. The fertilized egg is now ready to develop into the embryo pine. 427. Homology of the parts of the female cone.—Opinions are divided as to the homology of the parts of the female cone of the pine. Some consider the entire cone to be homologous with a flower of the angiosperms. The en- 212 MORPHOLOGY. tire scale according to this view isa carpel, or sporophyll, which is divided into the cover scale and the ovuliferous scale. This division of the sporophy]1 is considered similar to that which we have in isoetes, where the sporophyll Archegonium of Picea Archegonium of Picea) Embryo of Pine seedling just vulgaris, sperm cell ap- vulgaris showing fusion white pine re- emerging from the proaching the nucleus of of sperm nucleus with moved from ground. egg cell. egg nucleus. seed, showing several coty- ledons. Figs. 273, 274.—Fertilization in picea. (After Strasburger.) has a ligule above the sporangium, or as in ophioglossum, where the leaf is divided into a fertile and a sterile portion. A more recent view regards each cone scale as a flower, the ovuliferous scale composed of three united carpels arising in the axil of a leaf, the cover scale. Two of the carpels are reduced to ovules, and the outer integument is expanded into the lateral portion of the scale, while the central carpel is sterile and ends in the point or mucro of the scale. GYMNOSPERMS: WHITE PINE. “oO” oe tten god NZS wee By, ad fee ee EL EAM” pee pan 2g-, em Doge Tees ae Fig. 277. White-pine seedling casting seed coats. 213 CHAPTER XXXII. FURTHER STUDIES ON GYMNOSPERMS. Cycas. 428. In such gymnosperms as cycas, illustrated in the front- ispiece, there is a close resemblance to the members of the fern group, especially the ferns themselves. This is at once suggested by the form of the leaves. The stem is short and thick. The leaves have a stout midrib and numerous narrow pinne. In the center of this rosette of leaves are numerous smaller leaves, closely overlapping like bud scales. If we remove one of these at the time the fruit is forming we see that in general it conforms to the plan of the large leaves. There are a midrib anda number of narrow pinne near the free end, the entire leaf being covered with woolly hairs. But at the lower end, in eat ok Gee place of the pinne, we see oval bodies. revoluta. These are the macrosporangia (ovules) of cycas, and correspond to the macrosporangia of selaginella, and the leaf is the macrosporophyll. 429. Female prothallium of cycas.—TIn figs. 279, 280 are shown mature ovules, or macrosporangia, of cycas. In 280, which is aroentgen-ray photograph of 279, the oval prothallium can be seen. So in cycas, as in selaginella, the female prothallium is 214 FURTHER STUDIES ON GYMNOSPERMS. 218 developed entirely inside of the macrosporangium, and derives the nutriment for its growth from the cycas plant, which is the [Ren ea ay 27 ise Fig. 279. Macrosporangium of Cycas revoluta sporophyte. cells. This aids us in deter- mining that it is the prothal- liunt. In cycas it is also called endosperm, just as in the pines. 430. If we cut open one of the mature ovules, we can see the en- dosperm (prothallium) as a whitish mass of tissue. Immediately sur- rounding it at maturity is a thin, papery tissue, the remains of the nucellus (macrosporangium), and outside of this are the coats of the ovule, an outer fleshy one and an inner stony one. 431. Microspores, or pollen, of cycas.—The cycas plant illustrated in the frontispiece is a female plant. . Male plants also exist which have : ‘oups on the under side. small leaves in the center that bear epee sporangia. Fig. 280. Roentgen photograph of same, show- ing female prothallium. Archegonia are developed in this internal mass of Fig. 281. A sporophyll (stamen) of cycas; sporangia in 6, group of sporangia ; (From Warming.) : 2 210 MORPHOLOG Y. only microsporangia. These leaves, while they resemble the ordinary leaves, are smaller and correspond to the stamens. Upon the under side, as shown in fig. 281, the microspo- rangia are borne in groups of three or four, and these contain the microspores, or pollen grains, The ar- rangement of these microsporangia on the under side of the cycas leaves bears a strong resemblance to the arrangement of the sporangia on the under side of the leaves of some ferns. : 432. The gingko tree is another very interesting plant belonging to this same group. It is a relic of a genus which Fig. 282. yur Zamia inte- i | \ grifolia, show- ing thick stem, fern-like leaves, and cone of male flowers. flourished in the remote past, and it is interesting also because of the re- semblance of the leaves to some of the ferns like adiantum, which sug- gests that this form of the leaf in gingko has been inherited from some fern-like ancestor. 433. While the resem- blance of the leaves of someof the gymnosperms to those of the ferns sug- gests fern-like ancestors for the members of this group, there is stronger evidence of such ances- try in the fact that a pro- thallium can well be de- Fig. 283. Two spermiatozeids in end of pollen tube of cycas. (After termined in the ovules. drawing by Hirase and Ikeno. The endosperm with its well-formed archegonia is to be considered a prothallium. 434, Spermatozoids in some gymnosperms.—But within the past two years it has been discovered in gingko, cycas, and zamia, all belonging to this FURTHER STUDIES ON GYAMNOSPERMS. 217 group, that the sperm cells are well-formed spermatozoids. In zamia each one is shaped somewhat like the half of a biconvex lens, and around the con- vex surface are several coils of cilia. After the pollen tube has grown down through the nucellus, and has reached a depression at the end of the prothallium (endosperm) where the archegonia are formed, the spermatozoids are set free from the pollen tube, swim around in a liquid in this depression, and later fuse with the egg. In gingko and cycas these spermatozoids were first discovered by Ikeno and Hirase in Japan, and later in zamia by Webber in this country. In figs. 283-286 the details of the male prothallia and of fertilization are shown. 435. The sporophyte in the gymnosperms.— In the pollen grains of the gymnosperms we easily recognize the characters belonging to the spores in the ferns and their allies, as well as in Fig. 284. the liverworts and mosses. They belong to the Pekeil aalt ae same series of organs, are borne on the same larger female nucleus of the egg. ; ‘ . The egg protoplasm fills the phase or generation of the plant. and are practi- archegonium. (From drawings cally formed in the same general way, the by Hivase and Ikeno.) variations between the different groups not being greater than those within a single group. These spores we have recognized as being the product of the sporophyte. We are able then to identify the sporophyte as that phase or generation of the plant formed from the fertilized egg and bearing ultimately the spores. We see from this that the sporophyte in the gymnosperms is the prominent part of the plant, just as we found it to be in the ferns. The pine tree, then, Fig 285. as well as the gingko, cycas, yew, hemlock- _ Spermatozoid of gingko, show- spruce, black spruce, the giant redwood of Cali. ing cilia at one end and tail at . the other. (After drawings by fornia, etc., are sporophytes. Hirase and Ikeno.) While the sporangia (anther sacs) of the male flowers open and permit the spores (pollen) to be scattered, the sporangia of the female flowers of the gymnosperms rarely open. The macrospore is developed within sporangium (nucellus) to form the female prothallium (endosperm). 436. The gametophyte has become dependent on the sporophyte.— In this respect the gymnosperms differ widely from the pteridophytes, though we see suggestions of this condition of things in isoetes and selaginella, where the female prothallium is developed within the macrospore, and even in sela- ginella begins, and nearly completes, its development while still in the spo- rangium, 218 MORPHOLOGY. In comparing the female prothallium of the gymnosperms with that of the fern group we see « remarkable change has taken place. The female pro- Fig. 286. Gingko biloba. 4, mature pollen grain; 3, germinating pollen grain, the branched tube entering among the cells of the nucellus; 4.x, exine (outer wall of spore); 7, pro- thallial cell; /,, antheridial cell (divides later to form stalk cell and generative cell); 3, vegetative cell; /“a, vacuoles ; Ne, nucellus. (After drawings by Hirase and Ikeno.) Fig. 287. thallium of the gymno- sperms is very much reduced in size. Espe- cially, it no longer leads an independent existence from the sporophyte, as is the case with nearly all the fern group. It remains enclosed within the macrosporangium (in cycas if not fertilized it sometimes grows outside of the macrosporangium and becomes green), and derives its nourishment through it from the sporo- phyte, to which the latter remains organically con- nected. This condition of the female prothallium of the gymnosperms necessitated a special adaptation of the male prothallium in order that the sperm cells may reach and fertilize the egg cell. Gingko biloba, diagrammatic representation of the relation of pollen tube to the arche- gonium in the end of the nucellus. Az, pollen tube; 0, archegonium. (After drawing by Hirase and Ikeno.) 437. Gymnosperms are naked seed plants.—The pine, as we have seen, has naked seeds. That is, the seeds are not enclosed within the carpel, but FURTHER STUDIES ON GYMNOSPERMS. 219 are exposed on the outer surface. All the plants of the great group to which the pine belongs have naked seeds. For this reason the name “‘ gymnosperms” has been given to this great group. 438. Classification of gymno- sperms.—The gingko tree has until recently been placed with the pines, yew, etc., in the class conifer, but the discovery of the spermatozoids in the pollen Fig. 288. Fig. 289. in Spermatozoids of Spermatozoid of zamia tube suggests that it is mot zamia in pollen tube showing spiral row of closely allied with the coniferee, eee ae Ghee” Sane WeEeees and that it represents a class | Webber.) coordinate with them. Engler arranges the living gymnosperms as follows : Class 1. Cycadales; family Cycadaceze. Cycas, zamia, etc. Class 2. Gingkoales ; family Gingkoaceze. Gingko. Class 3. Coniferze; family 1. Taxaceee. Taxus, the common yew in the eastern United States, and Torreya, in the western United States, are examples. family 2, Pinaceze, Araucaria (redwood of California), firs, spruces, pines, cedars, cypress, etc, Class 4. Gnetales. Welwitschia mirabilis, deserts of southwest Africa ; Ephedra, deserts of the Mediterranean and of West Asia. Gnetum, climbers (Lianas), from tropical Asia and America. [ juowmsayuy SUT[PIUNT wiodsopusy ogy JUBUINSaJUI puv snjpeonu ut O