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PEN Y PCRS 2 ¥Erdss pyr retires: er eee gers het we pes” *“* tf OVO ere rye oes i 2 ‘ites ove “we ae ey * ere rv te Sherer er, ddl te Dees BO ar 72% we i ° ores €F PtP Hs 6" Sarg te . e : TF ewvee 4 Sew ice e ar Pe% wa, ts res ° : i a eee e Pervreven, adr . eee. ° 7 . oo: F ~ > ca , °*¢ ‘ ve i? 5 Ccniearay > free E fs nw as , ‘ ‘Ff t #4 ‘ , ve -* #eeces . se . #6 Ne ¥ Ori 66 « . ’ . é pera F ‘ - > "s “ *» *e« © Oe Glas SK } — Book Bay: Copyright N° COPYRIGHT DEPOSIT. - 3 3c) ao ING AUT lee, : aaa ty aa sie © Vay Nias ‘ h ‘ if J i Sal to } ‘ Pt - ih “if fi Bae "3 ‘ . 6 4 . ‘ i 4 a i i ¢ y M ’ i ‘ y iy f? 5 i ee He al _ = . r v ; . a ’ 2 ‘ - 1 A un q = 1 , f i “ P , . i ’ A j : ; : : fF : ric Be F e . igs “it : , * = a : a, 4 x ; 2 = : 2 ‘ > ; , “ = + % ay ier — - 7 ? * - He A ; c > h i 2 y é ‘ Jung < , r sole 3 ; \ : > eS P c ‘ - : 4 ty 5 ae re a 4 3 3 Hes, ' 5 a ; + % “ 4 : < led ze A ce 5 ani be ae . ; ae is ' oh ome “4 (TCs etek . 5 ys os - ' és y a j ; - 5 = j ? : ** * > - * Z % 4 5 : F = vie %, ao he: a es P he 2 es ae i a> cc al ce ((22a2YS1,U044 ) “(118 e8ed 99s) VLATOARA SVIAD ELEMENTARY BOTANY BY GaOwGr FRANCIS: ATKINSON,, PH.B. Professor of Botany in Cornell Untverstty THIRD EDITION, REVISED NEW YORK HENRY HOLT AND COMPANY se ee Copyright, 1898, 1905 BY HENRY HOLT AND COMPANY ROBERT DRUMMOND, PRINTER, N2W YORK PREPACE: THE present book is the result of a revision and elaboration of the author’s ‘“‘Elementary Botany,’ New York, 1898. The general plan of the parts on physiology and general morphology remains unchanged: A number of the chapters in the physio- logical part are practically untouched, while others are thoroughly revised and considerable new matter is added, especially on the subjects of nutrition and digestion. ‘The principal chapters on general morphology are unchanged or only slightly modified, the greatest change being in a revision of the subject of the morphology of fertilization in the gymnosperms and angiosperms in order to bring this subject abreast of the discoveries of the past few years. One of the greatest modifications has been in the addition of chapters on the classification of the alge and fungi with studies of additional examples for the benefit of those schools where the time allowed for the first year’s course makes desirable the examination of a broader range of representative plants. The classification is also carried out with greater definite- ness, so that the regular sequence of classes, orders, and families is given at the close of each of the subkingdoms. ‘Thus all the classes, all the orders (except a few in the alge), and many of the families, are given for the alge, fungi, mosses, liverworts, pteridophytes, gymnosperms, and angiosperms. But by far the greatest improvement has been in the complete reorganization, rewriting, and elaboration of the part dealing with ecology, which has been made possible by studies of the past few years, so that the subject can be presented in a more logical and coherent form. As a result the subject-matter of iii lV PREFACE, the book falls naturally into three parts, which may be passed in review as follows: Part I. Physiology. This deals with the life processes of plants, as absorption, transpiration, conduction, photosynthesis, nutrition, assimilation, digestion, respiration, growth, and _ irritability. Since protoplasm is fundamental to all the life work of the plant, this subject is dealt with first, and the student is led through the study of, and experimentation with, the simpler as well as some of the higher plants, to a general understanding of protoplasm and the special way in which it enables the plant to carry on its work and to adjust itself to the conditions of its existence. This study also serves the purpose of familiarizing the pupil with some of the lower and unfamiliar plants. i Some teachers will prefer to begin the study with general morphology and classification, thus studying first the represen- tatives of the great groups of plants, and others will prefer to dwell first on the ecological aspects of vegetation. ‘This can be done in the use of this book by beginning witk Part II or with Part III. But the author believes that morphology can best be com- prehended after a general study of life processes and functions of the different parts of plants, including in this study some of the lower forms of plant life where some of these processes can more readily be observed. ‘The pupil is then prepared for a more intelligent consideration of general and comparative morphology and relationships. Even more important is a first study of physiology before taking up the subject of ecology. The great value to be derived from a study of plants in their relation to environment lies in the ability to interpret the dif- ferent states, conditions, behavior, and associations of the plant, and for this physiology is indispensable. It is true that a con- siderable measure of success can be obtained by a good teacher in beginning with either subject, but the writer believes that measure of success would be greater if the subjects were taken up in the order presented here. Part II. Morphology and lije history of representative plants. PREFACE. Vv This includes a rather carefu] study of representative examples among the alge, fungi, liverworts, mosses, ferns and _ their allies, gymnosperms and angiosperms, with especial emphasis on the form of plant parts, and a comparison of them in the different groups, with a comparative study of development, reproduction, and fertilization, rounding out the work with a study of life histories and noting progression and retrogression of certain organs and phases in proceeding from the lower to the higher plants. Thus, in the alge a first critical study is made of four examples which illustrate in a marked way progressive stages of the plant body, sexual organs, and reproduction. Addi- tional examples are then studied for the purpose of acquiring a knowledge of variations from these types and to give a broader basis for the brief consideration of general relationships and classification. A similar plan is followed in the other great groups. The processes of fertilization and reproduction can be most easily observed in the lower plants like the alge and fungi, and this is an additional argument in favor of giving emphasis to these forms of plant life as well as the advantage of proceeding logic- ally from simpler to more complex forms. Having also learned some of these plants in our study of physiology, we are following another recognized rule of pedagogy, i.e., proceeding from known objects to unknown structures and processes. Through the study of the organs of reproduction of the lower plants and by general comparative morphology we have come to an under- standing of the morphology of the parts of the flower, and of the true sexual organs of thé seed plants, and no student can hope to properly interpret the significance of the flower, or the sexual organs of the seed plants who neglects a careful study of the general morphology of the lower plants. Part III. Plant members in relation to environment. ‘This part deals with the organization of the plant body as a whole in its relation to environment, the organization of plant tissues with a discussion of the principal tissues and a descriptive synopsis of the same. This is followed by a complete study from a biological vi PREFACE. standpoint of the different members of the plant, their special function and their special relations to environment. ‘The stem, root, leaf, flower, etc., are carefully examined and their ecological relations pointed out. ‘This together with the study of physiology and representatives in the groups of plants forms a thorough basis for pure plant ecology, or the special study of vegetation in its relation to environment. There is a study of the factors of environment or ecological factors, which in general are grouped under the physical, climatic, and biotic factors. ‘This is followed by an analysis of vegeta- tion forms and structures, plant formations and societies. ‘Then in order are treated briefly forest societies, prairie societies, desert societies, arctic and alpine societies, aquatic societies, and the special societies of sandy, rocky, and marshy places. Acknowledgments. ‘The author wishes to express his grate- fulness to all those who have given aid in the preparation of this work, or of the earlier editions of Elementary Botany; -to his associates, Dr. E. J. Durand, Dr. K. M. Wiegand, and Professor W. W. Rowlee, of the botanical department, and to Professor B. M. Duggar of the University of Missouri, Professor J. C. Arthur of Purdue University, and Professor W. F. Ganong of Smith College, for reading one or more portions of the text; as well as to all those who have contributed illustrations. Illustrations. ‘The large majority of the illustrations are new (or are the same as those used in earlier editions of the author’s Elementary Botany) and were made with special reference to the method of treatment followed in the text. Many of the photographs were made by the author. Others were contributed » by Professor Rowlee of Cornell University; Mr. John Gifford of New Jersey; Professor B. M. Duggar, University of Missouri; Professor C. E. Bessey, University of Nebraska; Dr. M. B. Howe, New York Botanical Garden; Mr. Gifford Pinchot, Chief of the Bureau of Forestry; Mr. B. T. Galloway, Chief of the Bureau of Plant Industry; Professor Tuomey of Yale University; and Mr. E. H. Harriman, who through Dr. C. H. Merriam of the National Museum allowed the use of several of his copy- PREFACE. Vil righted photographs from Alaska. To those who have con- tributed drawings the author is indebted as follows: to Professor ‘Margaret C. Ferguson, Wellesley College; Professor Bertha Stoneman of Huguenot College, South Africa; Mr. H. Hassel- bring of Chicago; Dr. K. Miyake, formerly of Cornell University and now of Doshisha College, Japan; and Professors Ikeno and Hirase of the Tokio Imperial University. The author is also indebted to Ginn & Co., Boston, for the privilege to use from his “First Studies of Plant Life” the following figures: 2eeO AO TAS, AQ, 50, 62, 60, 67, 87, 102, 103, 422-426, 420, 430, 438-440, 443, 444, 448, 449, 452, 472-475. A few others are acknowledged in the text. CORNELL UNIVERsITy, April, 1905. Ds ae aT i irae TABLE OF CONTENTS. PART mee HYSIOLOGY. CHAPTERS. PAGE We A SI 6G ee RE eS a Sa I CHAPTER?IE Peerana | TE PUSION, OSMOSE« . ~~... <2 26 v's 0009, s00.9-0, sigayeleemers 13 CHAPTER. cE, eee OBTAIN: WATERS | ...5.000 gs wees once sts oe awesele's ale e220 CHAPTER IV. TRANSPIRATION, OR THE Loss OF WATER BY PLANTS... ....eece0e 35 CHAPTER V. PAtereOm IVLOVEMENT OF WATER. IN PLANTS; .cu..ccocectnccccccce 48 CHAPTER -VI. Poem SHS OF WATER. . 0.0. sce a ccc es eleecdevecveecuesss 56 CHAPTER VII. ee UR FORMATION Gs ces c csc decenbeneeseeuetcecunce 60 SMR (OUCCHNEG iyi het ccels ene e sas e ce ee caw eeeawe we 60 Er ITO TS FORMU aw cies». «as ee odes ec aseeeceeese'es 64 feeenrorophyll and the Formation of Starch. .......0..s.eesee0: 67 CHAPTER WII. STARCH AND SUGAR CONCLUDED; ANALYSIS OF PLANT SUBSTANCE.... 73 es Ca WON, Ol OLALC Ms gual ce ce aiineieie ow sisi ss class eu da soe Vf Pee ead JUCESION Of StareNe sce Cade sie wav cee wig wales 75 erough Analysis of Plant Substance. 16... cee cbse pee ees 79 x TABLE OF CONTENTS. CHAPTER: Ie PAGE How PLANTS ‘OBTAIN THEIR OOD, Tec. 4.95. sees... Se eee 81 Lr. Sourcesiof Plant (Hood-g--24s., 8.85 seitiensuens oon eee 81 2; Parasites:and Saprophytes:.. 2a c.se. sca Geetcs ae le 83 3, How Pungi~ Obtain: their Food.) 250 Steen eee eee 86 Asi IVEY COTMIZ AS? ocho. oo Siegen ee ee ee aeRO nade eae 4 Oo QI 5. Nitrogen-gatherers.:. Jaren < civis sisi ches semen es eee Oe g2 Ox LACHEnS... SS esisSs Sinte d wide sw cto eacke ee me ean Cee 93 CHAPTER X. HOW PLANTS “OBTAIN: THEIR HOOD ilies a4. oc we eee ee eee 97 Seedlings.97. ~ Digestion) 1074 Assimilation..2.)....5ose hee 109 CHAPTER a. TRIES PTINA TION. “s,s elisssuie tieile seas sastons ailete aicete «eke eecerss oie er re rece let eee IIo CHAPRER aI: GRO WEE). 5c.6. 5 0's) SS 5 be Bie etinhes Dee et Oe Prepon ner Ie rete ee 118 CHARTER Sai. TRRUTAB ELT Voie; ate veraies os o's, 0701 ono clevepate olet orale ls ove olelole “\okeloretelcks eta ean As PART Il, MORPHOLOGY AND» LIFE HiSst@ns OF REPRESENTATIVE PLANTS. CEAP Ree. SPUROG NRA iso eb oS eh oi Wise yy en Say led ek nce TCO) a ka ips tee 136 WEATICHIERTA§ aide shank ean bis Soe ate age, Bi wince ae rete coals lat Oy eit es ee 142 (CGORPOCHAITE (0185 gaat ane otaan oh oho Sich te seileig, ov Weis t= ain. eae wel okoneheteneke eaten 153 CHAPTER XVIII. CLASSIFICATION AND ADDITIONAL STUDIES OF THE ALGZH.......... 158 CHAPTER XD Func] : MucoR AND SAPROLEGNIA. ..-.-+- reeresrercorsereresces E77 TABLE OFX CONT EN TS. xi CHAP TER) XX: PAGE PaemOCONTINUED (~ Rusts’? Uredine). i... 2.50. ceceseccsecuds 187 CHAPTER 2XI, Sm MPLAD EMBTEINGT. voi. 2 cya ete cetges css false cies ca cele wecneeseecseas 195 CHARTER, come U pivibcle wus seee es 410 SPLEPAL Ta CATINGHENOOLS HG. 6 12> a.< = onthe ome a ecelin wave Boe le © ose ele os 410 MMC ROBIROOLS eas ain 2 nsw Oo nea e es nae este eves 415 CHAPTER XLIT. PE ETP SETOOT oo oe cc an cys sn ew cle ee Be bois we nic ele eb ebeuees 419 Mebtemiaittsror tne PlOWEL.:5..5 ose es cena pecmescnas dese 419 Wet PNOWEIS.©. 2.5 oc bes gS e ee ele ne fe ae 421 III. Arrangement of Flowers, or Mode of Inflorescence........ 426 CHAPTER XLII POMUUN ATION 2.50 cce cs cess LER Ine Eich SOLA eS nee. a 433 CHAPTER. XLIV. “SEE P3705. 2 0 SE Ae a ae ee re 450 etme Me MEU Gr co 5.05 3S x rales os ox © hinsnmmlee Mnidar® ane. = evel Soe 450 MIE ARSE E UES. og sc a. aa mg Pow es 4 ole bons Be ware ee 451 RPM rire ELS @ ceie ae ss coe. eed 2 ks aid nce o Ot ae uae eee s 452 Men an JUICY ETiWits.. gee cc cele es ew ee eee dene ode 454 eetrcrmrorced. or Accessory, Frttits. 2.0.0.6. eect eee eee eee 455 Reel Mes MiG YMINOSPELMS. 2... ee ee ee eet vere ene 456 Seiemesenta Ot Ferns, MOSSES, CLC... ces es te ce secs ce stece 457 CHAPTER XLV. SRPMS ATE SU IE cea) cS Sya bois Gia Se hai Gc ene @ 8@a coe ecctepece 458 CHAPTER XLVI. VEGETATION IN RELATION TO ENVIRONMENT ....cccccces aenetars 464 CHAPTER XLVII. ime tne ATION OF ANGIOSPERMS... 2... 0s. ccc ecco ccecceccces 487 PAK aE Brie SLOL.OG ¥- CHAPTER 1. PROTOPLASM.* 1. In the study of plant life and growth, it will be found convenient first to inquire into the nature of the substance which we call the living material of plants. For plant growth, as well as some of the other processes of plant life, are at bottom » dependent on this living matter. This living matter is called in general profoplasm. 2. In most cases protoplasm cannot be seen without the help of a microscope, and it will be necessary for us here to em- ploy one if we wish to see protoplasm, and to satisfy ourselves by examination that the substance we are dealing with zs protoplasm. 3. We shall find it convenient first to examine protoplasm in some of the simpler plants ; plants which from their minute size and simple structure are so transparent that when examined with the microscope the interior can be seen. For our first study let us take a plant known as sf:rogyra, though there are a number of others which would serve the pur- pose quite as well, and may quite as easily be obtained for study. * For apparatus, reagents, collection and preservation of material, etc., see Appendix. 2 PHYSIOLOGY. Protoplasm in spirogyra. 4. The plant spirogyra.—This plant is found in the water of pools, ditches, ponds, or in streams of slow-running water. It is green in color, and occurs in loose mats, usually floating near the surface. The name ‘‘ pond-scum’’ is sometimes given to this plant, along with others which are more or less closely related. It is an a/ga, and belongs to a group of plants known as alge. If we lift a portion of it from the water, we see that the mat is made up of a great tangle of green silky threads. Each one of these threads is a plant, so that the number con- tained in one of these floating mats is very great. | Let us place a bit of this thread tangle on a glass slip, and examine with the microscope and we will see certain things about the plant which are peculiar to it, and which enable us to dis- tinguish it from other minute green water plants. We shall also wish to learn what these peculiar parts of the plant are, in order to demonstrate the protoplasm in the plant.* 5. Chlorophyll bands in spirogyra.—We first observe the presence of bands; green in color, the edges of which are usually very irregularly notched. ‘These bands course along in a spiral manner near the surface of the thread. There may be one or several of these spirals, according to the species which we happen to select for study. This green coloring matter of the band is chlorophyll, and this substance, which also occurs in the higher green plants, will be considered in a later chapter. At quite regular intervals in the chlorophyll band are small starch grains, grouped in a rounded mass enclosing a minute body, the pyrenoid, which is peculiar to many algee. 6. The spirogyra thread consists of cylindrical cells end to end.—Another thing which attracts our attention, as we examine a thread of spirogyra under the microscope, is that the thread is * If spirogyra is forming fruit some of the threads will be lying parallel in pairs, and connected with short tubes. In some of the cells there will be found rounded or oval bodies known as zygospores. ‘These may be seen in fig. 86, and will be described in another part of the book. PROTOPLASM. 3 made up of cylindrical segments or compartments placed end to end. We can see a distinct separating line be- tween the ends. Each one of these segments or compartments of the thread is a cell, and the boundary wall is in the form of a cylinder with closed ends. | 7. Protoplasm.—Having distinguished these parts of the plant we can look for the protoplasm. Meroeeurs within the cells. It is colorless (i.e., hyaline) and consequently requires close observa- tion. Near the center of the cell can be seen a rather dense granular body of an elliptical or irregular form, with its long diameter transverse to the axis of the cell in some species; or trian-_ gular, or quadrate in others. ‘This is the xucleus. Around the nucleus is a granular layer from which delicate threads of a shiny granular substance radiate in a starlike manner, and terminate in the chlorophyll band at one of the pyrenoids. A granular layer of the same substance lines the inside of the cell wall, and can be seen through the microscope if it is properly focussed. This granular substance in the cell is protoplasm. 8. Cell-sap in spirogyra.—The greater part of the interior space of the cell, that between the radiating strands of protoplasm, is occupied by a watery fluid, the ‘‘ cell-sap.’’ 9. Reaction of protoplasm to certain reagents. —We can employ certain tests to demonstrate that-this granular substance which we have seen is protoplasm, for it has been found, by repeated experiments with a great many kinds of plants, that protoplasm gives a definite reaction in re- sponse to treatment with certain substances called reagents. Let us mount a few threads of the Fig. x Thread of spiro- gyra, showing lon cells, chlorophyl band, nucleus, strands of proto- plasm, and_ the granular wall layer of protoplasm. spirogyra in a drop of a solution of iodine, and observe the 4 PHYSIOLOGY. results with the aid of the microscope. The iodine gives a yellowish-brown color to the protoplasm, and it can be more distinctly seen. The nucleus is also much more prominent since it colors deeply, and we can perceive within the nucleus one small rounded body, sometimes more, the nucleolus. The iodine here kills and stains the protoplasm. ‘The proto- plasm, however, in a living condition will resist for a time some other reagents, as we shall see if we attempt to stain it with a ONE, per cent aqueous solu- tion of a dye known as eos7n. Let us mount a few diving threads in such a solution of eosin, and after Fig. 2. Fig. 3. a time wash off Cell of spirogyra before treat- Cell of spirogyra after treatment = ment with iodine. with alcohol and iodine. the stain. The protoplasm remains uncolored. Now let us place these threads for a short time, two or three minutes, in strong alcohol, which kills the protoplasm. Then mount them in the eosin solution. The protoplasm now takes the eosin stain. After the proto- ‘plasm has been killed we note that the nucleus is no longer elliptical or angular in outline, but is rounded. ‘The strands of protoplasm are no longer in tension as they were when alive. 10. Let us now. take some fresh living threads and mount them in water. Place a small drop of dilute glycerine on the slip at one side of the cover glass, and with a bit of filter paper at the other side draw out the water. The glycerine will flow under the cover glass and come in contact with the spirogyra threads. Glycerine absorbs water promptly. Being in contact with the threads it draws water out of the cell cavity, thus caus- - PROTOPLASM. 5 ing the layer of protoplasm which lines the inside of the cell wall to collapse, and separate from the wall, drawing the chlorophyll band inward toward the cemeer also. ~The wall layer of proto- plasm can now be m@re distinctly seen and its gran- ular character ob- served. We have thus employed three tests to demon- strate that this sub- stance with which we are dealing shows the _ reac- tions which we A : Fig. 4. know by See Cell of spirogyra before Cells of spirogyra after treatment ence to be given treatment with glycerine. with glycerine. by protoplasm. We therefore conclude that this colorless and partly granular, slimy substance in the spirogyra cell is proto- plasm, and that when we have performed these experiments, and noted carefully the results, we have seen protoplasm. 11. Earlier use of the term protoplasm.—FEarly students of the living matter in the cell considered it to be alike in substance, but differing in density; so the term protoplasm was applied to all of this living matter. The nucleus was looked upon as simply a denser portion of the protoplasm, and the nucleolus as a still denser portion. Now it is believed that the nucleus is a distinct substance, and a permanent organ of the cell, The remaining por- tion of the protoplasm is now usually spoken of as the cytoplasm. In spirogyra then the cytoplasm in each cell consists of a layer which lines the inside of the cell wall, a nuclear layer, which surrounds the nucleus, and radiating* strands which connect the nucleus and wall layers, thus suspending the nucleus near the center of the cell. But it seems best in this elementary study to use the term protoplasm in its general sense, 6 PHYSIOLOGY. | \ Protoplasm in mucor. 12. Let us now examine in a similar way another of the. -simple plants with the special object in view of demonstrating the protoplasm. For this purpose we may take one of the plants belonging to the group of fungi. ‘These plants possess no chlorophyll. One of several species of mucor, a common mould, is readily obtainable, and very suitable for this study.* 13. Mycelium of mucor.—A few days after sowing in some gelatinous culture medium we find slender, hyaline threads, which are very much branched, and, radiating from a central point, form circular colonies, if the plant has not been too thickly sown, as shown in fig. 6. These threads of the fungus form the myce- ium. From these characters of the plant, which we can readily see without the aid of a microscope, we note how different it is from spirogyra. To examine for protoplasm let us lift carefully a thin block of gelatine containing the mucor threads, and mount it in water on a glass slip. Under the microscope we see only a small portion of the branched threads. In addition to the absence of chlo- rophyll, which we have already noted, we see that the myce- lium is not divided at short intervals into cells, but appears like a delicate tube with branches, which become successively smaller toward the ends. 14. Appearance of the protoplasm.—Within the tube-like thread now note the protoplasm. It has the same general ap- pearance as that which we noted in spirogyra. It is slimy, or semi-fluid, partly hyaline, and partly granular, the granules con- sisting of minute particles (the mzcrosomes). While in mucor the protoplasm has the same general appearance as in spirogyra, its arrangement is very different. In the first place it is plainly * The most suitable preparations of mucor for study are made by growing the plant in a nutrient substance which largely consists of gelatine, or, better, agar-agar, a gelatinous preparation of certain seaweeds. ‘This; after the plant is sown in it, should be poured into sterilized shallow glass plates, called Petrig dishes, PROROPLAS IM, i, continuous throughout the tube. We do not see the prominent radiations of strands around a large nucleus, but still the proto- Fig. 6. Colonies of mucor. plasm does not fill the interior of the threads. Here and there are rounded clear spaces termed vacuoles, which are filled with the watery fluid, cell-sap. The nuclei in mucor are very mi- nute, and cannot be seen except after careful treatment with special reagents. 15 Movement of the protoplasm in mucor.—While exam- ining the protoplasm in mucor we are likely to note streaming movements. Often a current is seen flowing slowly down one side of the thread, and another flowing back on the other side, or it may all stream along in the same direction. 16. Test for protoplasm.—Now let us treat the threads with a solution of iodine. The yellowish-brown color appears which is characteristic of protoplasm when subject to this reagent, 8 PHYSIOLOGY. If we attempt to stain the living protoplasm with a one per cent aqueous solution of eosin it resists it for a time, but if we first kill the protoplasm with strong alcohol, it reacts quickly to the application of the eosin. If we treat the living threads with glycerine the protoplasm is contracted away from the wall, as we found to be the case with spirogyra. While the color, Fig. 7. Thread of mucor, showing protoplasm and vacuoles. form and structure of the plant mucor is different from spiro. gyra, and the arrangement of the protoplasm within the plant is also quite different, the reactions when treated by certain re- agents are the same. We are justified then in concluding that the two plants possess in common a substance which we call protoplasm. Protoplasm in nitella. 17. One of the most interesting plants for the study of one remarkable peculiarity of protoplasm is (Vztel/a. ‘This plant belongs to a small group known as stoneworts. They possess chlorophyll, and, while they are still quite simple as compared with the higher plants, they are much higher in the scale than spirogyra or mucor. 18. Form of nitella—A common species of nitella is Wtella flextlis. It grows in quiet pools of water, The plant consists of a main axis, in the form of a cylinder. At quite regular intervals are whorls of several smaller thread-like outgrowths, which, because of their position, are termed ‘‘ leaves,’’ though they are not true leaves. These are branched in a characteristic fash- ion at the tip. The main axis also branches, these branches arising in the axil of a whorl, usually singly. The portions of the axis where the whorls arise are the zodes. Each node is made up of a number of small cells definitely arranged. ‘The portion of the axis between two adjacent whorls is an inter- PROTOPLASM. 9 node. These internodes are peculiar. They consist of but a single ‘< cell,’’ and are cylindrical, with closed ends. They are sometimes 5—I0 cm. long. 19. Internode of nitella.—For the study of an internode of nitella, a small one, near the end, or the ends of one of the ‘‘ leaves’’ is best suited, since it is more transparent. = the organs of absorption. If we take _ 2 for example a plant of mnium = LA B= (M. affine), which is illustrated in fig. SB &% Ze 36, wenote that it consists of a slend Ss ?> exe 630, We note that 1t consists of a slender © | Gung “2 (fee > : so om Z Oe / > i > Pp;

given off will be very few. This indicates that Bubbles of oxygen gas given off from elodeain q large part of the gas is furnished by the presence of sunlight. (Oels.) leaves. 125. 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 gas will be set free. Sunlight here also is necessary for the rapid escape of the gas. 126. 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 m 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. 127. 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. 62 PHYSIOLOGY. 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 usa 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. a ee a The gas will rise against the thumb. A dry lecting usa Se soft pine splinter should be then lighted, and (Petmer.) 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. 128. It is better to allow the apparatus to stand several days in the sunlight in order to catch a full tube of the gas. Or on a sunny day carbon } dioxide gas can be led into the water in the jar from a generator, such an one as is used for the evolution of CO,. The CO, can be produced by the action of hydrochloric acid on: bits: of marble, “the ae should not be run below the fun- nel. The test-tube should be fastened so that the light oxygen gas will not raise it off the fun- nel. With the tube full of gas the test for oxygen can be made by lifting the tube with one hand and Fig. €6. Ready to see what the gas is. STARCH FORMATION.—THE GASES. 63 quickly thrusting the glowing end of the splinter in with the other hand. If properly handled, the splinter will flame again. If it is neces- sary to keep the appa- ratus standing for more oo Fig. 67. than one day Tt. 1S well The splinter lights again in the presence of to add fresh water in the oxygen gas. place of most of the water in the jar. Do not use leaves of land plants in this experiment, since the bubbles which rise when these leaves are placed in water are not evidence that this process is taking place. 129. Oxygen given off by green land plants also.—If we should extend our experiments to land piants 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 it 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. 130. 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. If we boil spring water or hydrant water which comes from a stream containing oxygen and carbon dioxide, for about 20 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. 64 PHYSIOLOGY. 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 witn the water. Now place the plant again in the water, set in the sunlight, and in several minutes observe the result. No oxygen or but little is given off. There must be then some other requisite for the evolution of the oxygen. 132. The gases are interchanged in the plants.—We will now introduce carbon dioxide again in the water. This can be done by leading CO, from a gas generator into the water. Broken bits of marble are placed in the generator, acted upon by hydro- chloric acid, and the gas is led over by glass tubing. 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. 133. 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. 134. Gases as well as 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. 2. Where Starch is Formed. We have found by these simple experiments that some chemical change takes 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 -- STARCH: PHOTOSYNTHESIS. 65 at hand we should set up others in order to make this examina- tion. 135. Starch formed as a result of this process—We may take spirogyra which has been standing in water in the bright sun- light 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 fotas- sium 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. 136. 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 few days 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 of CO, and giving off of oxygen), and that starch is a product of that chemical change. 137. 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 an alcoholic tincture of iodine. The threads of spi- rogyra 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. 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. 66 PHYSIOLOGY. The leaves are made transparent by the chloral hydrate so that the starch reaction from the iodine is easily detected. The following is a convenient and safe method of extract- ing chlorophyll from leaves. Fill a large pan, preferably a dishpan, half full of hot water. This may be kept hot by a small flame. On the water float an evaporating dish partly filled with alcohol. The leaves should be first immersed in the hot water for several minutes, then placed in the alcohol, which will quickly remove the chlorophyll. Now immerse the leaves in the iodine solution. 138. 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 Fig. 68. Fig. 60. Leaf of coleus showing green and white Similar leaf treated with iodine, the starch areas, before treatment with iodine. reaction only showing where the leaf Was green. 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 STARCH AND SUGAR: CHLOROPHYLL. 67 leaves of plants which have stood for some time in the dark, starch is absent. We reason from this that starch is the product of the chemical change which takes place in the green cells under these conditions. The CO, which is absorbed by the plant mixes with the water (H,O) in the cell and immediately forms carbonic acid. The chlorophyll in the leaf absorbs radi- ant energy from the sun which splits up the carbonic acid, and its elements then are put together into a more complex com- pound, starch. This process of putting together the elements of an organic compound is a synthesis, or a synthetic assimila- tion, since it is done by the living plant. It is therefore a syn- thetic assimilation of carbon dioxide. Since the sunlight sup- plies the energy it is also called photosynthesis, or photosynthetic assimilation. We can also say carbon dioxide assimilation, or CO, assimilation (see paragraph on assimilation at close of Chapter Io). 139. 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. 68 is from a photograph of such a leaf. We should first boil jit 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. 69, which is from a photograph of another coleus leaf treated with the iodine solution. 8. Chlorophyll and the Formation of Starch. 140. In our experiments thus far 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. 68 PHYSIOLOGY. 141. 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 photosyn- thesis 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. 142. Photosynthesis cannot take place in etiolated plants.— Moreover photosynthesis is usually confined to the green plants, and if by any means one of the ordinary green plants loses its green color this process cannot take place in that plant, even when brought into the sunlight, until the green color has ap- peared 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 efolated. 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 on a green color, and then we find that carbon dioxide assimila- tion begins. , 143. 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 chlorophyll, — 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. 144, Form of the chlorophyll bodies.—Chlorophyll bodies vary in form in some different plants, especially in some of the ~ : | ee a ee os STARCH AND SUGAR: CHLOROPHYLL. 69 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 alge, illustrated in fig. 144, the chlorophyll bodies Fig. 69a. _ 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. 138, the chlorophyll s bodies are oval in outline. ‘These two plants, cedogonium and 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, or 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. 145. 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 haye been placed for some time in alcohol los¢ 79 PH YSIOLOG Y. 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 trom that of the chloroplastid. 146. Chlorophyll absorbs energy from sunlight for photosynthesis.—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 A7metic energy, acts on the molecules of CH,O,, separating them into molecules of C, H, and O. (When the CO, from the air enters the plant cell it immediately unites with some of the water, forming carbonic acid = CH,O,.) After a series of complicated chemical changes starch is formed by the union cf carbon, oxygen, and hydrogen. In this process of the reduction of the CH,O, and the formation of starch there is a surplus of oxygen, which accounts for the giving off of oxygen during the process. 147, Rays of light concerne1 in photosynthesis. — 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 portious of the spectrum. These bands Le in the red, orange, yellow, green, blue, and violet, but the Lands 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 transformed into potential energy. That is, the molecule of CH,O, is broken up, and then by a different combination of certain elements starch is formed, * 148. Starch grains formed in the chloroplasts.—During photosynthesis the starch formed is deposited generally in small grains within the green chloro- olast 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 cf tle prothallia of ferns, etc. Starch grains may also be formed in the chloro- plasts from starch which was formed in some other part of the plant, but * In the formation of starch during photosynthesis the separated mole- _ cules from the carbon dioxide and water unite in such a way that carbon, hydrogen, and oxygen are united into a molecule of starch. ‘This result is usually represented by the following equation: CO,-+H,O=CH,O+0,. Then by polymerization 6(CH,O) = C,H,,O, = grape sugar. Then C,H,;0; — HZO = C,H,:0, =. starch. It is believed, however, that the process is much more complicated than this, that several different com- pounds are formed before starch finally appears, and that the formula for starch is much higher numerically than is represented by C,H,)0,. eadysCl. AND WSUGALS:. CHLOROPA VLE. 71 which has passed in solution. Thus the functions of the chloroplast are twofold, that of photosynthesis and the formation of starch grains. 149. 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 /eucoplasts, and those possessing other colors, as red and yellow, in floral leaves. the root of the carrot, etc., are called chromoplasts. 150. Photosynthesis in other than green plants.—While carbohydrates are usually only formed by green plants, there are some exceptions. Ap- parent exceptions are found in the blue-green alge, like oscillatoria, nostoc, or in the 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. 151. Influence of light on the movement of chlorophyll bodies.—Jn 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 hori- zontal 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 2 oe =. ee Asey s,s tac Fie a) ve OPT VSS Fig. 70. Fig. 71. Cell exposed to weak diffused light Same cell exposed to strong light, showing chlorophyll bodies along the showing chlorophyll bodies have horizontal walls. moved to perpendicular walls. Figs. 70, 71.—Cell of prothallium of fern. arranged along the surfaces of the perpendicular walls, and instead of hay- ing 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, 72 PH VSIOLOGY. 70, 71.) ‘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 sur- faces are exposed to the incidence of the rays of light, so that the chloro- phyll will 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 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. - VIET. STARCH AND SUGAR CONCLUDED. ANALYSIS OF PLANT SUBSTANCE. 1. Translocation of Starch. 152. Translocation of starch.—It has been found that leaves of many 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 suggests 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. To test this let us perform an experiment which is often made. We may take a plant such as a garden tropzolum or a clover plant, or other land plant in which it is easy to test for the presence of starch. Pin a piece of circular cork, which is smaller than the area of the leaf, on either side of the leaf, as in fig. 72, but allow E free circulation of air between Pig. 72. 5 Leafoftropeolum Leaf oftropzolum treated the cork and the under side of with portion covered with iodine after removal of with corks to pre- cork, to show that starch is the leat. Place the plant vent the formation removed from the leaf dur- where it will be in the sunlight. eres (After ing the night. On the afternoon of the fol- lowing day, if the sun has been shining, test the entire leaf for starch. The part covered by the cork will not give the reaction for starch, 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 during the night, and then during the following day, the parts being covered from the light, no starch was formed in them. 73 74 PHYSIOLOGY. 153. 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 photosynthesis. From the leaves it is transferred in solution to the underground 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. 154. Form of starch grains.—Where starch is stored asa 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. If we scrape some of the cut surface of the potato tuber into a pulp and mount a smaii quantny 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 layers, the dilute layers containing more water than the dense ones; others think that the successive layers from the hilum outward are 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 (or glucose) is the basis for the formation of other organic substances in the plant. Without such organic substances green plants cannot make any appreciable increase of plant substance, though a considerable increase in size of the plant may take place. Notr.—The organic compounds resulting from photosynthesis, 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 propor- SAK CHE LAN SLOCA LION. 75 tion as in water, are called carbohydrates. ‘The most common carbo- hydrates are sugars (cane sugar, C,,H,,O,,, for example, in beet roots, sugar cane, sugar maple, etc.), starch, and cellulose. 155. Vaucheria.—The result of carbon dioxide assimilation in the threads of Vaucheria is not clearly understood. Starch is absent or diffi- cult to find in all except a few species, while oil globules are present in most species. These oil globules are spherical, colorless, globose and highly refringent. Often small ones are seen lying against chlorophyll bodies. Oil is a hydrocarbon (containing C, H, and O, but the H and O are in different proportions from what they are in H,O) and until recently it was supposed that this oil in Vaucheria was the direct result of photo- synthesis. But the oil does not disappear when the plant is kept for a long time in the dark, which seems to show that it is not the direct prod- uct of carbon dioxide assimilation, and indicates that it comes either from a temporary starch body or from glucose. Schimper found glucose in sev- eral species of Yaucheria, and Waltz says that some starch is present in Vaucheria sericea, while in V. tuberosa starch is abundant and replaces the oil. To test for oil bodies in Vaucheria treat the threads with weak osmic acid, or allow them to stand for twenty-four hours in Fleming’s solution (which contains osmic acid). Mount some threads and examine with microscope. ‘The oil globules are stained black. 2. Sugar, and Digestion of Starch.* 156. It is probable that some form of sugar is always produced as the result of photosynthesis. ‘The sugar thus formed may be stored as such or changed to starch. In general it may be said that sugar is most com- mon in the green parts of monocotyledonous plants, while starch is most frequent in dicotyledons. Plant sugars are of three general kinds: cane sugar abundant in the sugar cane, sugar beet, sugar maple, etc.; glucose and fruit sugar, found in the fruits of a majority of plants, and abundant in some, as in apples, pears, grapes, etc.; and maltose, a variety produced in germinating seeds, as in malted barley. 157. Test for sugar.—A very pretty experiment may be made by taking two test tubes, placing in one a solution of commercial grape sugar (glucose), in the other one of granulated cane sugar, and adding to each a few drops of Fehling’s solution. After these tubes have stood in a warm place for * Paragraphs 156-160 were prepared by Dr. E. J. Durand. + Make up three stock solutions as follows: (1) Papiete SUD NAc eo. ate ige ee ala aus ees « 9 grams WRUCT s°ely > acces LS “SRE calle Hes enced 08 aaa Se Se 250 CC, 76 PHYSIOLOGY. half an hour, it will be found that a bright orange brown or cinnabar- colored precipitate of copper and cuprous oxide has formed in the tube containing grape sugar, while the other solution is unchanged. Grape sugar or glucose, therefore, reduces Fehling’s solution, while cane sugar as such has no effect upon it. Cane sugar may be changed or converted to glucose by being boiled for a short time with a dilute acid, or by adding Fehling’s solution to the sugar solution and boiling. In the latter case the change is brought about by the alkali and the precipitate of copper and cuprous oxide forms. 158. Tests for sugar in plant tissue.—(a) Scrape out a little of the tissue from the inside of a ripe apple or pear, place it with a little water in a test tube, and add a few drops of Fehling’s solution. After standing half an hour the characteristic precipitate of copper and cuprous oxide appears, showing that grape sugar is present in quantity. Make thin sections of the apple and mount in a drop of Fehling’s solu- tion on a slide. After half an hour examine with the microscope. ‘The granules of cuprous oxide are present in the cells of the tissue in great abundance. (b) Cut up several leaves of a young vigorous corn seedling, cover with water in a test tube and boil for a minute. After the decoction has cooled add the Fehling’s solution and allow to stand. The precipitate will ap- pear. For comparison take similar corn leaves, remove the chlorophyll with alcohol and test with iodine. No starch reaction appears. ‘The car- bohydrate in corn leaves is therefore glucose and not starch. If now the corn seed be examined the cells will be found to be full of starch grains which give the beautiful blue reaction with iodine. This experiment shows that grape sugar is formed in the leaves of the corn plant, but is changed to starch when stored in the seed. (c) Take two leaves of bean seedling or coleus, test one for sugar and the other for starch. Both are present. (d) Procure some maple sap in the spring, or in the winter months make a decoction of the broken tips of young branches of the sugar maple by boiling them in water in a test tube. To the sap or cool decoction add Fehling’s solution. No precipitate appears after standing. Now heat (2) @alistic POtasil. Sec ste sess epee ee eee 30 grams Waterco 0% sic ce eiro Oe aus eal cana ot ee ees ee eee 25 Ope: (3) Rochellé ‘salts.@ ah... Pic c.cckie wee eRe eee 49 grams WIESE. ce She eras a; setctn ots OLE ae, eee et Sie eee 250°C! For Fehling’s solution take one volume of each of (1), (2), and (3), and to the mixture add two volumes of water, NOGAM DIGHSTION, OF STARCH. Gs the same solution to the boiling-point, and the precipitate forms, showing the presence of cane sugar in the maple sap which was converted to glu- cose and fruit sugar by boiling in the presence of an alkali. (e) Scrape out some of the tissue from a sugar beet root, cover with water in a test tube and add Fehling’s solution. No change takes place after standing. Boil the same solution and the precipitate forms, showing the presence of cane sugar, inverted to grape sugar and fruit sugar by the hot alkali. 159. How starch is changed to sugar. —We have seen that in many plants the carbohydrate formed as the result of carbon dioxide assimilation is stored as starch. This substance being insoluble in water must be changed to sugar, which is soluble before it can be used as food or transported to other parts of the plant. This is accomplished through the action of cer- tain enzymes, principally diastase. This substance has the power of act- ing upon starch under proper conditions of temperature and moisture, causing it to take up the elements of water, and so to become sugar. This process takes place commonly in the leaves where starch is formed, but especially in seeds, tubers (during the sprouting, etc.), and other parts which tke plant uses as storehouses for starch food. It is probable that the same conditions of temperature and moisture which favor germination or active growth are also favorable to the production of diastase. yp. Experiments to show the action of diastase.—(a) Place a bit of starch half as large as a pea in a test tube, and cover with a weak solution * (about 7 per cent) of commercial taka diastase. After it has stood in a warm place for five or ten minutes test with Fehling’s solution. The pre- cipitate of cuprous oxide appears showing that some of the starch has been changed to sugar. By using measured quantities, and by testing with iodine at frequent intervals, it can be determined just how long it takes a given quantity of diastase to change a known quantity of starch. In this connection one should first test a portion of the same starch with Fehling’s solution to show that no sugar is present. (b) Repeat the above experiment using a little tissue from a potato, and some from a corn seed. (c) Take 25 germinating barley seeds in which the radicle is just appear- ing. Grind up thoroughly in a mortar with about three parts of water. After this has stood for ten or fifteen minutes, filter. Fill a test tube one- third full of water, add a piece of starch half the size of a pea or less, and boil the mixture to make starch-paste. Add the barley extract. Put ina warm place and test from time to time with iodine. The first samples so treated will be blue, later ones violet, brown, and finally colorless, showing * This solution of taka diastase should be made up cold. If it is heated to 60° C. or over it is destroyed. 78 PHYSIOLOGY. that the starch has all disappeared. This is due to the action of the dias- tase which was present in the germinating seeds, and which was dissolved out and added to the starch mixture. The office of this diastase is to change the starch in the seeds to sugar. Germinating wheat is sweet, and it is a matter of common observation that bread made from sprouted wheat is sweet. (d) Put a little starch-paste in a test tube and cover it with saliva from the mouth. After ten or fifteen minutes test with Fehling’s solution. A strong reaction appears showing how quickly and effectively saliva acts in converting starch to sugar. Successive tests with iodine will show the gradual disappearance of the starch. 161. These experiments have shown us that diastase from three different sources can act upon starch converting it into sugar. The active principle in the saliva is an animal diastase (ptyalin), which is necessary as one step in the digestion of starch food in animals. The /aka diastase is derived from a fungus (Eurotium oryzz) which feeds on the starch in rice grains converting it into sugar which the fungus absorbs for food. The malt dias- tase and /eaj diastase are formed by the seed plants. That in seeds con- verts the starch to sugar which is absorbed by the embryo for food. That in the leaf converts the starch into sugar so that it can. be transported to other parts of the plant to be used in building new tissue, or to be stored again in the form of starch (example, the potato, in seeds, etc.). The starch is formed in the leaf during the daylight. The light renders the leaf diastase inactive. But at night the leaf diastase becomes active and converts the starch made during the day. Starch is not soluble in water, while the sugar is, and the sugar in solution is thus easily transported throughout the plant. In those green plants which do not form starch in their leaves (sugar beet, corn, and many monocotyledons), grape sugar and fruit sugar are formed in the green parts as the result of photosynthesis. In some, like the corn, the grape sugar formed in the leaves is transported to other parts of the plant, and some of it is stored up in the seed as starch. In others like the sugar beet the glucose and fruit sugar formed in the feaves flow to other parts of the plant, and much of it is stored up as cane sugar in the beet root. ‘The process of photosynthesis probably proceeds in the same way in all cases up to the formation of the grape sugar and fruit sugar in the leaves. In the beet, corn, etc., the process stops here, while in the bean, clover, and most dicotyledons the process is carried one step farther in the leaf and starch is formed. ANALYSIS OF PLANT SUBSTANCE. 79 8S. Rough Analysis of Plant Substance. 162. Some simple experiments to indicate the nature of plant substance.— After these building-up processes of the plant, it is instructive to perform some simple experiments which indicate roughly the nature of the plant substance, and serve to show how it can be separated into other substances, some of them being reduced to the form in which they existed when the plant took them as food. For exact experiments and results it would be necessary to make chemical analyses. 163. The water in the plant.—-Take fresh leaves or leafy shoots or other fresh plant parts. Weigh. Permit them to remain in a dry room until they are what we call ‘‘dry.”” Now weigh. The plants have lost weight, and from what we have learned in studies of transpiration this loss in weight we know to result from the loss of water from the plant. 164. The dry plant material contains water.—Take air-dry leaves, shay- ings, or other dry parts of plants. Place them in a test tube. With a holder rest the tube in a nearly horizontal position, with the bottom of the tube in the flame of a Bunsen burner. Very soon, before the plant parts begin to ‘‘burn,” note that moisture is accumulating on the inner surface of the test tube. ‘This is water driven off which could not escape by drying in air, without the addition of artificial heat, and is called ‘‘ hygroscopic water.” 165. Water formed on burning the dry plant material.—Light a soft-pine or bass-wood splinter. Hold a thistle tube in one hand with the bulb down- ward and above the flame of the splinter. Carbon will be deposited over the inner surface of the bulb. After a time hold the tube toward the win- dow and look through it above the carbon. Drops of water have accumu- lated on the inside of the tube. This water is formed by the rearrangement of some of the hydrogen and oxygen, which is set free by the burning of the plant material, where they were combined with carbon, as in the cellu- lose, and with other elements. 166. Formation of charcoal by burning.—Take dried leaves, and shav- ings from some soft wood. Place in a porcelain crucible, and cover about 3 cm. deep with dry fine earth. Place the crucible in the flame of a Bun- sen burner and let it remain for about fifteen minutes. Remove and empty the contents. If the flame was hot the plant material will be reduced to a good quality of charcoal. The charcoal consists largely of carbon. 167. The ash of the plant.—Place in the porcelain crucible dried leaves and shavings as before. Do not cover with earth. Place the crucible in the flame of the Bunsen burner, and for a moment place on the porcelain cover; then remove the cover, and note the moisture on the under surface from the escaping water. Permit the plant material to burn; it may even flame for atime. In the course of fifteen minutes it is reduced to a whitish 80 PHYSIOLOGY. powder, much smaller in bulk than the charcoal in the former experiment. This is the ash of the plant. 168. What has become of the carbon t—In this experiment the air was not excluded from the plant material, so that oxygen combined with carbon as the water was freed, and formed carbon dioxide, passing off into the air in this form. This it will be remembered is the form in which the plant took the carbon-food in through the leaves. Here the carbon dioxide met the water coming from the soil, and the two united to form, ultimately, starch, cellulose, and other compounds of carbon; while with the addition of nitrogen, sulphur, etc., coming also from the soil, still other plant sub- stances were formed. 169. The carbohydrates are classed among the non-nitrogenous sub- stances. Other non-nitrogenous plant substances are the organic acids like oxalic acid (H,C,O,), 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, aleuron, or proteid grains, found in seeds). ‘The proteids are the source of nitrogenous food for the seedling during germination. Of the amides, asparagin (C,H,N.O,) is an example of a nitrogenous substance; and of the alkaloids, nicotin (C,,H,,N,) 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, exam- ples of which are given above, and inorganic compounds. By burning this dry residue the organic substances are mostly changed into volatile prod- ucts, principally carbonic acid, water, and nitrogen. The inorganic sub- stances 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 percentage 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. | foe eee oO : ; ©: TOROR Ce 3 Ha! | We uo} So 34 =| ileus Coie | é | 25/22/84) 85) ¢ | & Ee Bal eae aa | BO | Oo | ad | ae < A, cat | Ee a Sea gees ieee a | os Clover, ia blossom] 68.3] 21.06] 1.39 24.06) 7.44] 0.72] 6.74] 2.06] 1.62), 2.66 Wheat, nrelivals Sees) ale 4 6.14] 0.44 0.66] 2.36] 0.26) 9.26) O07) ozAZ2\ to com Wheat, straw... .| 53.7 7.33! O.7A4 32).00] 1.33) O83) 12.50 te sei sOL eg Omao Potato tubers... . 1.37.7] 22.76] 9.90 ©.07) 1.77) ©. 45] 6. 53))/2. 45) (eo 6o) pene Appless scstevelss « 14.4 5-14] 3-76,<0.50| 1.26) 70.20] 1.06] 0. 838\Jocaone. wee Peas (the seed). ..| 27.3] I1.41 oS L.36]. 2. 170. FO) 9.105) O 205 | oeaa ont CEiAse TER EX: Mower SANTS OBTAIN THEIR: FOOD. _ I. 1. Sources of Plant Food. 170. The necessary constituents of plant food.—As indicated in Chap- ter 3, investigation has taught us the principal constituents of plant food. Some suggestion as to the food substances is derived by a chemical analysis of various plants. In Chapter 8 it was noted that there are two principal kinds of compounds in plant substances, the organic compounds and the inorganic compounds or mineral substances. ‘The principal elements in the organic compounds are hydrogen, carbon, oxygen and nitrogen. The elements in the inorganic compounds which have been found indispensable to plant growth are calcium,* potassium, magnesium, phosphorus, sulphur and iron. (See paragraphs 54-58, and complete observations on water cultures.) Other elements are found in the ash of piants; and while they are not absolutely necessary for growth, some } of them are beneficial in one way or another. 171. The carbohydrates are derived, as we have learned, from the CO, of the air, and water in the plant tissue drawn from the soil; though in the case of aquatic plants entirely submerged, all the constituents are absorbed from the surrounding water. 172. Food substances in the soil.—Land plants derive their mineral food from the soil, the soil received the mineral substances from dissolving and disintegrating rocks. Nitrogenous food is chiefly derived from the same source, but under a variety of conditions which will be discussed in later paragraphs, but the nitrogen comes primarily from the air. Some of the mineral substances, those which are soluble as well as some of the nitrog- enous sukstances, are found in solution in the soil. These are absorbed by the plant, as needed, along with water, through the root hairs. * Calcium is not essential for the growth of the fungi. + For example, silicon is used by some plants in strengthening supporting tissues. Buckwheat thrives better when supplied with a chloride. 81 82 PHYSIOLOGY. 173. Absorption of soluble substances.—Since these substances are dis- solved in the water of the soil, it is not necessary for us to dwell on the process of absorption. This in general is dwelt upon in Chapter 3. It should be noted, however, that food substances in solution, during absorp- tion, 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. When the cells have absorbed a certain amount of a given substance, no more is absorbed until the concentration of the cell-sap in that particular substance is reduced. ‘This, however, does not interfere with the absorp- ~-tion of water, or of other substances in solution by the same cells. Plants have therefore a certain selective power in the absorption of food substances. 174. Action of root hairs on insoluble substances. Acidity of root hairs.—If we take a seedling which has been grown ina 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 excrete certain acid sub- stances. This acid property of the root hairs serves a very im- portant 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 par- ticles, 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. Carbonic acid and other acids are also formed in the soil, and aid in bringing these substances into solution. 175. This corrosive action of the roots can be shown by the weil-known experiment of growing a plant on a marble plate which is covered by soil In lieu of the marble plate, the peas may be plantedin clam or oyster shells, which are then buried in the soil of the pot, so that the roots of the seedlings will come in contact with the smooth surface of the shell. 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 sys- tem. 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 phenom- a PARASITES AND SAPROPHYTES. 83 ena. The acid salts are the substances which are most actively concerned in reddening the blue litmus paper. They do not directly aid in the corro- sion 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 phosphate) which is most actively concerned in reddening the blue litmus paper may act indirectly on these mineral sub- stances, 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. 176. Nore.—It is a general rule that plants cannot take solid food into their bodies, but obtain all food in either a liquid or gaseous state. The only exception to this is in the case of the plasmodia of certain Myxomy- cetes (Slime Moulds), and also perhaps some of the Flagellates and other very low forms, which engulf solid particles of food. It is uncertain, how- ever, whether these organisms belong to the plant or animal kingdom, and they probably occupy a more or less intermediate position. 177. Action of nitrite and nitrate bacteria.—Many of the higher green plants prefer their nitrogenous food in the form of nitrates. (Example, nitrate of soda, potassium nitrate, saltpetre.) Nitrates are constantly eing formed in soil by the action of certain bacteria. The nitrite bacteria (Nitromonas) convert ammonia in the soil to nitrous acid (a nitrite), while at this point the nitrate bacteria (Nitrohacter) convert the nitrites into nitrates. The fact that this nitrification is going on constantly in soil is of the utmost importance, for while commercial nitrates are often applied to the soil, the nitrates are easily washed from the soil by heavy rains. These nitrite and nitrate bacteria require oxygen for their activity, and they are able to obtain their carbohydrates by decomposing organic matter in the soil, or directly by assimilating the CO, in the soil, deriving the energy for the assimilation of the carbon dioxide from the chemical process of nitrification. This kind of carbon dioxide assimilation is called chemo- synthetic assimilation. 2. Parasites and Saprophytes. 178. Parasites among the fungi.—A parasite is an organism which derives all or a part of its food directly from another living organism (its host) and at the latter’s expense. The larger number of plant parasites are found among the fungi (rusts, smuts, mildews, etc.). (See Nutrition of the Fungi, paragraph 185.) Some of these are not capable of develop- ment unless upon their host, and are called obligate parasites. Others can grow not only as parasites but at other times can also grow on dead organic matter, and are called facultative parasites, i.e. they can choose either a parasitic life or a saprophytic one. 179. Parasites among the seed ‘plants.—Cuscuta——There are, however, parasites among the seed plants; for example, the dodder (Cuscuta), para- 84 PH VSIOLOG Y. sitic on clover, and a great variety of other plants. There is food enough in the seed for the young plant to take root and develop a slender stem until it takes hold of its host. It then twines around the stem of its host send- ing wedge-shaped haustoria into the stem to obtain food. The part then in connection with the ground dies. The haustoria of the dodder form a complete junction with the vascular ~ bundles of its host so that through the vessels water and salts are obtained, ~ while through the junction of sieve tubes the elaborated organic food is Fig. 74. Dedder. obtained. The union of the dodder with its host is like that between a graft and the graft stock. The beech drops (Epiphegus) is another exam- ple of a parasitic seed plant. It is parasitic on the roots of the beech. 180. The mistletoe (Viscum album), which grows on the branches of trees, sends its roots into the branches, and only the vessels of the vascular system are fused according to some. If this is true then it probably ob- tains only water and salts from its host. But the mistletoe has green leaves and is thus able to assimilate carbon dioxide and manufacture its own | PARASITES AND SAPROPHYTES. 85 organic substances. It is claimed by some, however, that the host derives some food from the parasite during the winter when the host has shed its leaves, and if this is true it would seem that organic food could also be derived during the summer from the hest by the mistletoe. 181. Saprophytes.—-A saprophyte is a plant which is enabled to obtain - its food, especially its organic food, directly from dead animals or plants or from dead organic substances. Many fungi are saprophytes, as the moulds, mushrooms, etc. (See Nutrition of the Fungi.) 182. Humus saprophytes.—The action of fungi as described in the pre- ceding chapter, as well as of certain bacteria, gradually converts the dead plants or plant parts into the finely powdered brown substance known as humus. In general the green plants cannot absorb organic food from humus directly. But plants which are devoid of chlorophyll can live saprophytically on this humus. They are known as humus saprophytes. Many of the mushrooms and other fungi, as well as some seed plants which lack chlorophyll or possess only a small quantity, are able to absorb all their organic food from humus. It is uncertain whether any seed plants can obtain all of their organic food directly from humus, though it is be- lieved that many can so obtain a portion of it. But a number of sced plants, like the Indian pipe (Monotropa) and certain orchids, obtain organic food from humus. These plants lack chlorophyll and cannot therefore manufacture their own carbohydrate food. Not being parasitic on plants which can, as in the case of the dodder and beech drops mentioned above, they undoubtedly derive their organic food from the humus. But fungus mycelium growing in the humus is attached to their roots, and in some orchids enters the roots and forms a nutritive connection. The fungus mycelium can absorb organic food from the humus and in some cases at least can transfer it over to the roots of the higher plant (see Mycorhiza). 183. Autotrophic, heterotrophic, and mixotrophic plants—An auto- trophic plant is one which is self-nourishing, i.e. it is provided with an abundant chlorophyll apparatus for carbon dioxide assimilation and with absorbing organs for obtaining water and salts. Heterotrophic plants are not provided with a chlorophyll apparatus sufficient to assimilate all the carbon dioxide necessary, so they nourish themselves by other means. Mixotrophic plants are those which are intermediate between the other two, i.e. they have some chlorophyll but not enough to provide all the organic food necessary, so they obtain a portion of it by other means. Evidently there are all gradations of mixotrophic plants between the two other kinds (example, the mistletoe). 184. Symbiosis.—Symbiosis means a living with or living together, and is said of those organisms which live so closely in connection with each other as to be influenced for better or worse, especially from a nutrition standpoint. Conjunctive symbiosis has reference to those cases wherc 86 . PHYSIOLOGY. there is a direct interchange of food material between the two organisms (lichens, mycorhiza, etc.) Duzsjunctive symbiosis has reference to an inter life relation without any fixed union between them (example, the relations between flowers and insects, ants and plants, and even in a broad sense the relation between saprophytic plants in reducing organic matter to a con- dition in which it may be used for food by the green plants, and these in turn provide organic matter for the saprophytes to feed upon, etc.). Avtag- onistic symbiosis is shown in the relation of parasite to its host, reciprocal symbiosis, or mutualistic symbiosis 1s shown in those cases where both symbionts derive food as a result of the union (lichens, mycorhiza, etc.). 8. How Fungi Obtain their Food. 185. Nutrition of moulds.—In our study of mucor, as we have seen, the growing or vegetative part of the plant, the mycelium, lies within the substratum, which contains the food materials in solution, and the slender threads are thus bathed on all sides by them. The mycelium absorbs the watery solutions throughout the entire system of ramifica- tions. When the upright fruiting threads are devel- oped they derive the materials for their growth directly from the mycelium with which they are in connection. The moulds which grow on de- caying fruit or on other organic matter derive their nutrient materials in the same way. The portion of the mould which we usually see on the surface of these sub- stances is in general the fruit- ing part. The larger part of the mycelium lies hidden within the subtratum. 186. Nutrition of para- sitic fungi.—Certain of the Fig. 75. Carnation rust on leaf and flowerstem. From photo- , i Se graph. fungi grow on or within the higher plants and derive their food materials from them and at their ex- pense. Such a fungus is called a parasite, and there are a large number HOW PLANTS OBTAIN FOOD. 87 of these plants which are known as farasitic fungi. The plant at whose expense they grow is called the ‘“ host.”’ One of these parasitic fungi, which it is quite easy to obtain in green- houses or conservatories during the autumn and winter, is the carnation rust (Uromyces caryophyllinus), since it breaks out in rusty dark brown patches on the leaves and stems of the carnation (see fig. 75). If we make thin cross sections through one of these spots on a leaf, and place them for a Fig. 76. Several teleutospores, showing the variations in form. few minutes in a solution of chloral hydrate, portions of the tissues of the leaf will be dissolved. After a few minutes we wash the sections in water on a glass slip, and stain them with a solution of eosin. If the sections were care- Bie 77. Cells from the stem of a rusted carnation, showing the intercellular mycelium and haustoria. Object magnified 30 times more than the scale. fully made, and thin, the threads of the mycelium will be seen coursing be- tween the cells of the leaf as slender threads. Here and there will be seen short branches of these threads which penetrate the cell wall of the host and project into the interior of the cell in the form of an irregular knob. Such a branch is a austorium. By means of this haustorium, which is here 88 PHYSIOLOGY. only a short branch of the mycelium, nutritive substances are taken by the fungus from the protoplasm or cell-sap of the carnation. From here it passes to the threads of the mycelium. These in turn supply food material for the development of the dark brown gonidia, which we see form the dark- looking powder on the spots. Many other fungi form haustoria, which take up nutrient matters in the way described for the carnation rust. In tke case Fig. 78. Fig. 79. Cell from carnation leaf, showing Intercellular mycelium with haustoria entering haustorium of rust mycelium grasping the cells. 4, of Cystopus candidus (white rust); the nucleus of the host. 4, haustori- £4, of Peronospora calotheca. (De Bary.) um; z, nucleus of host. of other parasitic fungi the threads of the mycelium themselves penetrate the cells of the host, while in still others the mycelium courses only between the cells of the host (fungus of peach leaf-curl for example) and derives focd materials from the protoplasm or cell-sap of the host by the process of osmosis. 187. Nutrition of the larger fungi.—If we select some one of the larger fungi, the majority of which belong to the mush- room family and its relatives, which is growing on a decaying log or in the soil, we shall see on tearing open the log, or on remov- ing the bark or part of the soil, as the case may be, that the stem of the plant, if it have one, is connected with whitish strands. During the spring, summer, or autumn months, exam- ples of the mushrooms connected with these strands may usually be found readily in the fields or woods, but during the winter and ——— HOW PLANTS OBTAIN FOOD. 89 colder parts of the year often they may be seen in forcing houses, especially those cellars devoted to the propagation of the mush- room of commerce. 188. These strands are made up of numerous threads of the mycelium which are closely twisted and interwoven into a cord or strand, which is called a mycelium strand, or rhizomorph. These are well shown in fig. 236, which is from a photograph of the mycelium strands, or ‘‘spawn’’ as the grower of mushrooms calls it, of Agaricus campestris. ‘The little knobs or enlargements on the strands are the young fruit bodies, or ‘‘ buttons.’’ 189. While these threads or strands of the mycelium in the decaying wood or in the decaying organic matter of the soil are Fig. 80. Sterile mycelium on wood props in coal mine, 400 feet below surface. (Photographed by the author.) 90 PHYSIOLOGY. not true roots, they function as roots, or root hairs, in the ab- sorption of food materials. In old cellars and on damp soil in moist places we sometimes see fine examples of this vegetative part of the fungi, the mycelium. But most magnificent examples are to be seen in abandoned mines where timber has been taken down into the tunnels far below the surface of the ground to support the rock roof above the mining operations. I have visited some of the coal mines at Wilkesbarre, Pa., and here on the wood props and doors, several hundred feet below the surface, -and in blackest darkness, in an atmosphere almost completely saturated at all times, the mycelium of some of the wood-destroy- ing fungi grows in a profusion and magnificence which is almost beyond belief. Fig. 80 is from a flash-light photograph of a beautiful example 400 feet below the surface of the ground. This was growing over the surface of a wood prop or post, and the picture is much reduced. On the doors in the mine one can see the strands of the mycelium which radiate in fan-like figures at certain places near the margin of growth, and farther back the delicate tassels of mycelium which hang down in fantastic figures, all in spotless white and rivalling the most beautiful fabric in the exquisiteness of its construction. 190. How fungi derive carbohydrate food.—The fungi being devoid of chlorophyll cannot assimilate the CO, from the air. They are therefore dependent on the green plants for their carbohydrate food. Among the saprophytes, the leaf and wood destroying fungi excrete certain substances (known as enzymes) which dissolve the carbohydrates and certain other organic compounds in the woody or leafy substratum in which they grow. They thus produce a sort of extracellular digestion of carbohydrates, con- verting them into a soluble form which can be absorbed by the mycelium. The parasitic fungi also obtain their carbohydrates and other organic food from the host. The mycelium of certain parasitic, and of wood destroying fungi, excretes enzymes (cyfase) which dissolve minute perforations in the cell walls of the-host and thus aid the hypha during its boring action in penetrating cell walls. Note.—Certain wood destroying fungi growing in oaks absorb tannin directly, i.e. in an unchanged form. One of the pine destroying fungi (Trametes pint) absorbs the xylogen from the wood cells, leaving the pure cellulose in which the xylogen was filtrated; while Polyporus mollis absorbs the cellulose, leaving behind only the wood element. EEE a ee ee HOW PLANTS OBTAIN FOOD. gI 4. Mycorhiza. 191. While such plants as the Indian pipe (Monotropa), some of the orchids, etc., are humus saprophytes and some of them are possibly able to absorb organic food from the humus, many of them have fungus mycelium in close connection with their rocts, and these fungus threads aid in the absorption of organic food. ‘The roots of plants which have fungus myce- lium intimately associated in connection with the process of nutrition, are termed mycorhiza. There is a mutual interchange of food between the fungus and the host, a reciprocal symbtiosts. 192. Mycorhiza are of two kinds as regards the relation of the fungus to the root; ectotrophic (or epiphytic), where the mycelium is chiefly on the outside of the root, and endotrophic (or endophytic) where the mycelium is chiefly within the tissue of the root. 193. Ectotrophic mycorhiza.—Ectotrophic mycorhiza occur on the roots of the oak, beech, hornbean, etc., in forests where there is a great deal of humus from decaying leaves and other vegetation. The young growing roots of these trees become closely covered with a thick felt of the mycelium, so that no root hairs can develop. The terminal roots also branch pro- fusely and are considerably thickened. ‘The fungus serves here as the absorbent organ for the tree. It also acts on the humus, converting some of it into available plant food and transferring it over to the tree. 194. Endotrophic mycorhiza.—These aie found on many of the humus saprophytes, which are devoid of chlorophyll, as well as on those possess- ing little or even on some plants possessing an abundance, of chlorophyll. Examples are found in many orchids (see the coral root orchid, for exam- ple), some of the ferns (Botrychium), the pines, leguminous plants, etc. In endotrophic mycorhiza the mycelium is more abundant within the tissues of the root, though some of the threads extend to the outside. In the case of the mycorhiza on the humus saprophytes which have no chlorophyll, or but little, it is thought by some that the fungus mycelium in the humus assists in converting organic substances and carbohydrates into a form available for food by the higher plant and then conducts it into the root, thus aiding also in the process of absorption, since there are few or no root hairs on the short and fleshy mycorhiza. The roots, however, of some of these humus saprophytes have the power of absorbing a portion of their organic compounds from the humus. It is thought by some, though not definitely demonstrated, that in the case of the oaks, beeches, hornbeans, and other chlorophyll-bearing symbionts, the fungus threads do not absorb any carbohydrates for the higher symbiont, hut that they actually derive their carbohydrates from it.* But it is reasonably certain that the fungus * Evidence points to the belief that certain cells of the host form sub- stances which attract, chemitropically, the fungus threads, and that in these cells the fungus threads are more abundant than in others. Further- Q2 PHYSIVLOG Y. threads do assimilate from the humus certain unoxidized, or feebly oxi- dized, nitrogenous substances (ammonia, for example), and transfer them over to the host, for the higher plants with difficulty absorb these sub- stances, while they readily absorb nitrates which are not abundant in humus. This is especially important in the forest. It is likely therefore pe 5. Nitrogen gatherers. 195. How clovers, peas, and other legumes gather nitrogen.—It has long been known that clover plants, peas, beans, and many other leguminous plants are often able to thrive in soil where the cereals do but poorly. ~ Soil poor in nitrogenous plant food becomes richer in this substance where clovers, peas, etc., are grown, and they are often planted for the purpose of enriching the soil. Leguminous plants, espe- cially in poor soil, are almost certain to have en- largements, in the form of nodules, or ‘root tubercles.” A root of the common vetch with some of these root tubercles is shown in fig. 81. 196. A fungal or bacterial organism in these root tubercles.—If we cut one of these root tuber- cles open, and mount a small portion of the in- Bee terior in water for examination with the micro- Root of the common vetch, showing root tubercles. scope, we shall find small rod-shaped bodies, some of which resemble bacteria, while others are more or less forked into forms like the letter Y, as shown in fig. 82. These bodies are rich in nitrogenous substances, or proteids. They are portions of a minute organism, of a fungus or bacterial nature, which attacks the roots of leguminous plants Fig. 82. Fig. 83. Root-tubercle organism from vetch, old con- Root-tubercle organism from Medicago dition. - denticulata. and causes these nodular outgrowths. The organism (Phytomyxa legumi- nosarum) exists in the soil and is widely distributed where legumes grow. more in the vicinity of the nucleus of the host seems to be the place where these activities are more marked. HOW PLANTS OBTAIN FOOD. 93 197. How the organism gets into the roots of the legumes.—This minute organism in the soil makes its way through the wall of a root hair near the end. It then grows down the interior of the root hair in the form of a thread. When it reaches the cell walls it makes a minute perforation, through which it grows to enter the adjacent cell, when it enlarges again. In this way it passes from the root hair to the cells of the root and down to near the center of the root. As soon as it begins to enter the cells of the root it stimulates the cells of that portion to greater activity. So the root here develops a large lateral nodule, or ‘‘root tubercle.’’ As this ‘‘ root tubercle” increases in size, the fungus threads branch in all directions, entering many cells. The threads are very irregular in form, and from cer- tain enlargements it appears that the rod-like bodies are formed, or the thread later breaks into myriads of these small ‘‘ bacteroids.” 198. The root organism assimilates free nitrogen for its host.—This organism assimilates the free nitrogen from the air in the soil, to make the proteid substance which is found stored in the bacteroids in large quantities. Some of the bacteroids, rich in proteids, are dissolved, and the proteid sub- stance is made use of by the clover or pea, as the case may be. This is why such plants can thrive in soil with a poor nitrogen content. Later in the season some of the root tubercles die and decay. In this way some of the proteid substance is set free in the soil. The soil thus becomes richer in nitrogenous plant food. The forms of the bacteroids vary. In some of the clovers they are oval, in vetch they are rod-like or forked, and other forms occur in some of the other genera. 199. NotE.—So far as we know the legume tubercle organism does not assimilate free nitrogen of the air unless it is within the root of the legume. But there are micro6rganisms in the soil which are capable of assimilating free nitrogen independently. Example, a bacterium, Clostridium pasteur- tanum. Certain bacteria and alge live in contact symbiosis in the soil, the bacteria fixing free nitrogen, while in return for the combined nitrogen, the alge furnish the bacteria with carbohydrates. It seems that these bac- teria cannot fix the free nitrogen of the air unless they are supplied with carbohydrates, and it is known that Clostridium pasteurianum cannot assim- ilate free nitrogen unless sugar is present. 6. Lichens. 200. Nutrition of lichens.—Lichens are’very curious plants which grow on rocks, on the trunks and branches of trees, and on the soil. They form leaf-like expansions more or less green in color, or brownish, or gray, or they occur in the form of threads, or small tree-like formations. Sometimes the 04 PHYSIOLOGY. plant fits so closely to the rock on which it grows that it seems merely tq paint the rock a slightly different color, and in the case of many which occur on trees there appears to be to the eye only a very slight discoloration of the bark of the trunk, with here and there the darker colored points where fruit bodies Fig. 84. Frond of lichen (peltigera), showing rhizoids. are formed. The most curious thing about them is, however, that while they form plant bodies of various form, these bodies are of a ‘dual nature” as regards the organisms composing them. The plant bodies, in other words, are formed of two different organisms which, woven together, exist apparently as one. A fungus on the one hand grows around and encloses in the meshes of its mycelium the cells or threads of an alga, as the case may be. If we take one of the leaf-like forms known as peltigera, which grows on damp soil or on the surfaces of badly decayed logs, we see that the plant body is flattened, thin, crumpled, and irregularly lobed. The color is dull greenish on the upper side, while the under side is white or light gray, and mottled with brown, especially the older portions. Here and there on the under surface are quite long slender blackish strands. These are composed entirely of fungus threads and serve as organs of attachment or holdfasts, and for the purpose of supplying the plant body with mineral substances which are in solution in the water of the soil. Ifwe make a thin section of the leaf-like portion of a lichen as shown in fig. 85, we shall see that it is composed of a mesh of colorless threads which in certain definite portions contain entangled green cells. “The colorless threads are those of the fungus, while the green cells are those of the alga. These green cells of the alga per- form the function of chlorophyll bodies for the dual organism, while the threads of the fungus provide the mineral constituents of plant food. The alga, HOW PLANTS OBTAIN FOOD. - 95 while it is not killed in the embrace of the fungus, does not reach the per- fect state of development which it attains when not in connection with the fungus. On the other hand the fungus profits more than the alga by this association. It forms fruit bodies, and perfects spores in the special fruit bodies, which are so very distinct in the case of so many of the species of the lichens. These plants have lived for so long a time in this close associa- tion that the fungi are rarely found separate from the algz in nature, but in a number of cases they have been induced to grow in artificial cultures sep- SSss5 SEERA LN DOO VOISING aoe eCiR aioe Naa oleae ANS RENAN os y oy ‘ Wi > >. yes Fig. 85. Lichen (peltigera), section of thallus; dark zone of rounded bodies made up largely of the algal cells. Fungus cells above, and threads beneath and among the algal cells. arate from the alga. This fact, and also the fact that the alge are often found to occur separate from the fungus in nature, is regarded by many as an tndication that the plant body of the lichens is composed of two distinct or- ganisms, and that the fungus is parasitic on the alga. 201. Others regard the lichens as autonomous plants, that is, the two or- ganisms have by this long-continued community of existence become unified into an individualized organism, which possesses a habit and mode of life 96 PHYSIOLOG ¥. distinct from that of either of the organisms forming the component parts. This community of existence between two different organisms is called by some mutualism, or symbiosis. While the alga inclosed within the meshes of the fungus is not so free to develop, and probably does not attain the full development which it would alone under favorable conditions, still it is Ze ——— 7; LATA Poo iN) SONI ete Vis (\ Fig. 86. Section of fruit body or apothecium of lichen (parmelia), showing asci and spores of the fungus. very likely that it is often preserved from destruction during very dry periods, within the tough thallus, on the surface of bare rocks. es re aa tal te Ee 2 CHAPTER X. Bowe LEeANTS OBTAIN THEIR FOOD, II. Seedlings. 202. It is evident from some of the studies which we have made in con- nection with germination of seeds and nutrition of the plant that there is a period in the life of the seed plants in which they are able to grow if sup- plied with moisture, but may entirely lack any supply of food substance from the outside, though we understand that growth finally comes to a standstill unless they are supplied with food from the outside. In con- nection with the study of the nutrition of the plant, therefore, it will be well to study some of the representative seeds and seedlings to learn more accu- rately the method of germination and nutrition in seedlings during the ger- minating period. 203. To prepare seeds for germination.—Soak a handful of seeds (or more if the class is large) in water for 12 to 24 hours. Take shallow crockery plates, or ordinary plates, or a germinator with a fluted bottom. Place in the bottom some sheets of paper, and if sphagnum moss is at hand scatter some over the paper. If the moss is not at hand, throw the upper layer of paper into numerous folds. Thoroughly wet the paper and moss, but do not have an excess of water. Scatter the seeds among the moss or the folds of the paper. Cover with some more wet paper and keep in a room where the temperature is about 20° C. to 25°C. The germinator should be looked after to see that the paper does not become dry. It may be necessary to cover it with another vessel to prevent the too rapid evaporation of the water. The germinator should be started about a week before the seedlings are wanted for study. Some of the soaked seeds should be planted in soil in pots and kept at the same temperature, for comparison with those grown in the germinator. 204. Structure of the grain of corn.—Take grains of corn that have been 97 98 PHYSIOLOG Y. soaked in water for 24 hours and note the form and difference in the two sides (in all of these studies the form and structure of the seed, as well as the stages in germination, should be illustrated by the student). Make a longisection of a grain of corn through the middle line, if necessary making several in order to obtain one which shows the structures well near the smaller end of the grain. Note the following structures: 1st, the hard outer ‘‘wall’’ (formed of the consoli- — = Bo dated wall of the ovary with the in- E> teguments of the ovules—see Chap- Se ters 35 and 36); 2d, the greater mass Fig. 87. GS aatioal oF eonatscad Ae ppen eer of starch and other plant food (the each as the plantlet, next the cotyledon, at endosperm) in the centre; 3d, a some- left the endosperm. what crescent-shaped body (the scutellum) lying next the endosperm and near the smaller end of the grain; 4th, the remaining portion of the young embryo lying between the scutellum and the seed coat in the depression. When good sections are made one can make out the radicle at the smaller end of the seed, and a few successive leaves (the plumule) which lie at the opposite end of the embryo shown by sharply curved parallel lines. Observe the attachment of the scutellum to the caulicle at the point of junction of the plumule and the radicle. ‘The scutellum is a part of the embryo and represents a coty- ledon. The endosperm is also called albwmen, and such a seed is albumin- ous. Dissect out an embryo from another seed, and compare with that seen in the section. 205. In the germination of the grain of corn the endosperm supplies the food for the growth of the embryo until the roots are well established in the soil and the leaves have become expanded and green, in which stage the plant has become able to obtain its food from the soil and air and live independently. The starch in the endosperm cannot of course be used for food by the embryo in the form of starch. It is first converted into a solu- ble form and then absorbed through the surface of the scutellum or coty- ledon and carried to all parts of the embryo. An enzyme developed by the embryo acts upon the starch, converting it into a form of sugar which is in solution and can thus be absorbed. This enzyme is one of the so-called diastatic “‘ fermeuts’’ which are formed during the germination of all seeds which contain food stored in the form of starch. In some seedlings, this diastase formed is developed in much greater abundance than in others, for example, in barley. Examine grains of corn still attached to seedlings several weeks old and note that a large part of their content has been used up. The action of diastase on starch is described in Chapter 8. PAOWA PLANTS OGLAIN THEIR: FOOD. 99 206. Structure of the pumpkin seed.—The pumpkin seed has a tough papery outer covering for the protection of the embryo plant within. ‘This covering is made up of the seed coats. When the seed is opened by slitting off these coats there is seen Mimmimedne meat of the pumpkin seed. ‘This is nothing more than the embryo plant. ‘The larger part of this embryo consists of two flattened bodies which are more prominent than any other part of the plantlet at this time. These two flattened bodies are the two first leaves, usually called cotyledons. If we spread these cotyledons apart we see that they are connected at one end. Lying between them at this point of attachment is a small bud. ‘This is the plumule. ‘The plumule consists of the very young leaves at the end of the stem which will grow as the seed germinates. At the other end where the cotyledons are joined is a small projection, the young root, often termed the radicle. 207. How the embryo gets out of a pumpkin seed.—To see how the embryo gets out of the pumpkin seed we should examine seeds germinated in the folds of damp paper or on damp sphagnum, as well as some which have been germinated in earth. Seeds should be selected which represent several different stages of germination. Germinating seed of pumpkin, showing how the heel or ‘‘ peg ” catches on the seed coat to cast it off. 208. The peg helps to pull the seed coats apart.—The root pushes its way out from between the stout seed coats at the smaller end, and then turns downward unless prevented from so 100 PHYSIOLOGY. doing by a hard surface. After the root is 2-4cm long, and the two halves of the seed coats have begun to be pried apart, if we look in this rift at the junction of the root and stem, we shall see that one end of the seed sa coat 1s caught against hy a heel, or "Spec id DHA ipa Saf SZ \ which has grown out from the stem for this purpose. Now if we examine one which is a liitke more ad- vanced, we shall see this heel more distinctly, and also that the stem is arching out away from the seed coats. As the stem arches up its back in this way it pries with the cotyledons against Bee the upper seed coat, | Escape of the pumpkin seedling from the seed coats. but the lower seed coat is caught against this heel, and the two are pulled gradually apart. In this way the embryo plant pulls itself out from be- tween the seed coats. In the case of seeds which are planted deeply in the soil we do not see this contrivance unless we dig down into the earth. The stem of the seedling arches through the soil, pulling the cotyledons up at one end. Hhemigap straightens up, the green cotyledons part, and open out their inner faces to the sunlight, as shown in fig. go. If we dig into the soil we shall see that this same heel is formed on the stem, and that the seed coats are cast off into the soil. WOW PLANTS OBTAIN THEIR FOOD. IOI 209. Parts of the pumpkin seedling.— During the germination of the seed all parts of the embryo have enlarged. ‘This in- crease in size of a plant is one of the peculiarities of growth. The cotyledons have elongated and expanded somewhat, though not to such a great extent as the root and the stem. The cotyledons also have become green on exposure to the light. Very soon after the main root has emerged from the seed coats, other lateral roots begin to form, so that the root soon becomes very much branched. The main root with its branches makes up the root system of the seedling. Be- tween the expanded cotyledons is seen the plumule. This has enlarged some- what, but not nearly so much as the root, or the part of the stem which extends below the cotyledons. This part of the stem, i.e., that part below the f, ) ; cotyledons and . | extending to the Vi | beginning of the fi, mes LL | | root, is called in Fig. 90. all seedlings Ae Pumpkin seedling rising from the ground. hypocotyl, which means ‘‘ below the cotyledon. ’ -210. The common garden bean.—The common garden bean or the lima bean, may be used for study. The garden bean is not so flattened or broadened as the lima bean. It is rounded- compressed, elongate slightly curved, slightly concave on one side and convex on the other, and the ends are rounded. At the middle of the concave side note the distinct scar (the hilum) formed where the bean seed separates from its attachment to the wall of the pod. Upon one side of this scar is a slight prom- inence which is continued for a short distance toward the end of the bean in the form of a slight ridge. This is the raphe, and represents that part of the stalk of the ovule which is joined to the side of the ovule when the latter is curved around against it ? 102 wus STOLOG ¥. (see Chapter 36), and at the outer end of the raphe is the cha- laza, the point where the stalk is joined to the end of the ovule, best understood in a straight ovule. Upon the opposite side of the scar and close to it can be seen a minute depression, the micropyle. Under- neath the seed coat and lying between this point and the end of the seed is the embryo, which gives greater prominence to the bean at this point, but it is especially more prominent after the bean has been soaked in water. Soak the beans in water and as Fig. or. ‘ Garden bean, they are swelling note how the seed coats swell I hihmoc eae: faster than the inner portion of the seed, which he; ¢, poi > - Chere Ghalan,, causes them to wrinkle in a curious way, but finally ae the inner portion swells and fills the seed coat out smooth again. Sketch a bean showing all the external features both in side view and in front. Split one lengthwise and sketch the half to which the embryo clings, noting the young root, stem, and the small leaves which were lying between the cotyledons. ‘There is no endo- sperm here now, since it was all used up in the growth of the embryo, and a large part of its substance was stored up in the cotyledons. As the seed germinates the young plant gets its Piles: first food from that stored in the cotyledons. jee ae eis The hypocotyl elongates, becomes strongly et. arched, and at last straightens up, lifting the cotyledons from the soil. As the cotyledons become exposed to the light they assume a green color. Some of the stored food in them goes to nourish the embryo during germination, and they therefore become smaller, shrivel somewhat, and at last fall off. 211. The castor-o0il bean.—This is not a true bean, since it belongs to a very different family of plants (Euphorbiacee). In the germination of this seed a very interesting comparison can be made with that of the garden bean. As the ‘‘bean”’ swells the very hard outer coat generally breaks open at the free end and slips off at the stem end. The next coat within, which is ee oe Se ee en HOW PLANTS OBTAIN THEIR FOOD. 103 also hard and shining black, splits open at the opposite end, that is at the stem end. It usually splits open in the form of three ribs. Next within the inner coat is a very thin, whitish film (the remains of the nucellus, and corresponding to the perisperm) which shrivels up and loosens from the white mass, the endosperm, within. In the castor-oil bean, then, the endosperm is not all absorbed by the embryo during the formation of the seed. As the plant becomes older we should note that the fleshy endosperm be- comes thinner and thin- ner, and at last there is nothing but Fig. 93. How the garden bean comes out of the ground. First the looped hypocotyl, then the cotyledons pulled out, next casting off the seed coat, last the plant erect, bearing thick cotyledons, the expanding leaves, and the plumule between them. a thin. whitish film covering the green faces of the cotyledons. _ The endosperm has been gradually absorbed by the germinat- imz plant through its cotyledons and used for food. « Ariszema triphyllum.* 212. Germination of seeds of jack-in-the-pulpit.—The ovaries of jack-in-the-pulpit form large, bright red berries with a soft pulp enclosing one to several large seeds. The seeds are oval in form. ‘Their germination is interesting, and illustrates one type * In lieu of Arisema make a practical study of the pea. See paragraph 210d. 104 PHY STOLOGN: of germination of seeds common among monocotyledonous plants. If the seeds are covered with sand, and kept in a moist place, they will germi- nate readily. 213. How the embryo backs out of the seed.—The embryo lis within the mass of the endosperm; the root end, near the smaller end of the seed. The club-shaped cotyledon lies near the . ~~ ~ Fig. 94. Germination of castor-oil bean. middle of the seed, surrounded firmly on all sides by the endo- sperm. The stalk, or petiole, of the cotyledon, like the lower part of the petiole of the leaves, is a hollow cylinder, and contains the younger leaves, and the growing end of the stem or bud. When germination begins, the stalk, or petiole, of the cotyledon elongates. This pushes the root end of the embryo out at the small end of the seed. The free end of the embryo now enlarges somewhat, as seen in the figures, and becomes the bulb, or corm, of the young plant. At first no roots are visible; but in a short time one, two, or more roots appear on the enlarged : end. 214. Section of an embryo.—If we make a longisection of the embryo and seed at this time we can see how the club- shaped cotyledon is closely surrounded by the endosperm. Through the cotyledon, then, the nourishment from the endo- sperm is readily passed over to the growing embryo. In the hollow part of the petiole near the bulb can be seen the first leaf. PLANTS GBTAIN THEIR FOOD. 105 mf ?- | i ' = Fig. 95. Seedlings of castor-oil bean casting the seed coats. and showing papery remnant of the endosperm. Fig. 96. Seedlings of jack-in-the pulpit; embryo backing out vi the seed. : Fig. 97. Section of germinating embryos of jack-in-the-pulpit, showing young leaves inside the petiole of the cotyledon. At the left cotyledon shown surrounded by the endo- sperm in the seed, at right endo- sperm removed to show the club- shaped cotyledon. 106 PHYSIOLOG Y. 215. How the first leaf appears.—As the embryo backs out of the seed, it turns downward into the soil, unless the seed is so lying that it pushes straight , downward. On the upper side of the arch thus formed, in the petiole of the cotyledon, a slit appears, and through this opening the first leaf arches its way out. The loop of the petiole comes out first, and the leaf later, as shown in fig. 98. The petiole now gradually Fig. 98. Fig. 90. Fig. 100. Seedlings of jack-in-the- Embryos of jack-in-the-pulpit Seedling of jack-in- pulpit, first leaf arching still attached to the endosperm in the-pulpit; section out of the petiole of the seed coats, and showing the simple of the endosperm cotyledon. first leaf. and cotyledon. straightens up, and as it elongates the leaf expands. 216. The first leaf of the jack-in-the-pulpit is a simple one. —The first leaf of the embryo jack-in-the-pulpit is very different in form from the leaves which we are accustomed to see on mature plants. If we did not know that it came from the seed BOW PLEANTS OBTAIN THETR FOOD. IO7 of this plant we would not recognize it. It is simple, that is it consists of one lamina or blade, and not of three leaflets as in the compound leaf of the mature plant. The simple leaf is ovate and with a broad heart-shaped base. The jack-in-the- pulpit, then, as trilium, and some other monocotyledonous plants which have compound leaves on the mature plants, have simple leaves during embryonic development. The ancestral monocotyledons are supposed to have had simple leaves. Thus there is in the embryonic development of the jack-in-the-pulpit, and others with compound leaves, a sort of recapitulation of the evolutionary history of the leaf in these forms. 216a. Germination of the pea.—Compare with the bean. Note especially that the cotyledons are not lifted above the soil as in the beans. Compare germination of acorns. Digestion. 216b. To test for stored food substance in the seedlings studied.—The pumpkin, squash, and castor-oil bean are examples of what are called oily seeds, since considerable oil is stored up in the protoplasm in the cotyle- dons. ‘To test for this, remove a small portion of the substance from the cotyledon of the squash and crush it on a glass slip in a drop or two of osmic acid.* Put on a cover-glass and examine with a microscope. The black amorphous matter shows the presence of oil in the protoplasm. The small bodies which are stained yellow are aleurone grains, a form of protein or albuminous substance. Both the oil and the protein substance are used by the seedling during germination. ‘The oil is converted into an available food form by the action of an enzyme called Jipase, which splits up the fatty oil into glucose and other substances. Lipase has been found in the endosperm of the castor oil, cocoanut, and in the cotyledons of the pumpkin, as well as in other seeds containing oil as a stored product. The aleurone is made available by an enzyme of the nature of trypsin. Test the endosperm of the castor-oil bean in the same way. Make another test of both the squash and castor-oil seeds with iodine to show that starch is not present. Test the cotyledon of the bean with iodine for the presence of starch. If the endosperm of corn seed has not been tested do so now with iodine. The endosperm consists largely of starch. ‘The starch is converted to glu- * Dissolve a half gram of osmic acid in 50 cc. of water and keep tightly corked when not using. 108 PHYSIOLOGY. cose by a diastatic ‘‘ ferment’ formed by the seedling as it germinates. Make a thin cross-section of a grain of wheat, including the seed coat and a portion of the interior, treat with iodine and mount for microscopic exam- ination. Note the abundance of starch in the internal portion of endo- sperm. Note a layer of cells on the outside of the starch portions filled with small bodies which stain yellow. ‘These are aleurone grains. The cellulose in the cell walls of the endosperm.is dissolved by another enzyme called cytase, and some plants store up cellulose for food. For example, in the endosperm of the date the cell walls are very much thickened and pitted. The cell walls consist of reserve. cellulose and the seedling makes use of it for food during growth. 216c. Albuminous and exalbuminous seeds.—In seeds where the food is stored outside of the embryo they are called albuminous; examples, corn, wheat and other cereals, Indian turnip, etc. In those seeds where the food is stored up in the embryo they are called exalbuminous; examples, bean, pea, pumpkin, squash, etc. 217. Digestion has a well-defined meaning in animal physiology and relates to the conversion of solid food, usually within the stomach, into a soluble form by the action of certain gastric juices, so that the liquid food may be absorbed into the circulatory system. ‘The term is not often ap- plied in plant physiology, since the method of obtaining food is in general fundamentally different in plants and animals. It is usually applied to the process of the conversion of starch into some form of sugar in solution, as glucose, etc. This we have found takes place in the leaf, especially at night, through the action of a diastatic ferment developed more abundantly in darkness. As a result, the starch formed during the day in the leaves is digested at night and converted into sugar, in which form it is transferred to the growing parts to be employed in the making of new tissues, or it is stored for future use; in other cases it unites with certain inorganic sub- stances, absorbed by the roots and raised to the leaf, to form proteids and other organic substances. In tubers, seeds, parts of stems or leaves where starch is stored, it must first be ‘‘digested”’ by the action of some enzyme before it can be used as food by the sprouting tubers or germinating seeds. For example, starch is converted to a glucose by the action of a diastase. Cellulose is converted to a glucose by cytase. Albuminoids are converted into available food by a tryptic ferment. Fatty oils are converted into glucose and other products by lipase. Inulin, a carbohydrate closely related to starch, is stored up for food in solution in many composite plants, as in the artichoke, the root tuber of dahlia, etc. When used for food by the growing plant it is converted into glucose by an enzyme, inulase. Make a section of a portion of a dahlia tuber or artichoke and treat with alcohol. The inulin is precipitated inte sphero crystals. (See also paragraphs 156-161 and 2100.) - ee HOW PLANTS OBTAIN THEIR FOOD. 109 218. Then there are certain fungi which feed on starch or other organic substances whether in the host or not, which excrete certain enzymes to dissolve the-starch, etc., to bring it into a soluble form before they can _absorb it as food. Such a process is a sort of extracellular digestion, i.e., the organism excretes the enzyme and digests the solid outside, since it cannot take the food within its cells in the solid form. To a certain degree the higher plants perform also extracellular digestion in the action of root- hair excretion on insoluble substances, and in the case of the humus sapro- phytes. But for them soluble food is largely prepared by the action of acids, etc., in the soil or water, or by the work of fungi and bacteria as described in Chapter 9. 219. Assimilation —In plant physiology the term assimilation has been chiefly used for the process of carbon-dioxide assimilation (= photosyn- thesis). Some objections have been raised against the use of assimilation here as one of the life processes of the plant, since its inception stages are due to the combined action of light, an external factor, and chlorophyll in the plant along with the living chloroplastid. So long, however, as it is not known that this process can take place without the aid of the living plant, it does not seem proper to deny that it is altogether not a process of assimilation. It is not necessary to restrict the term assimilation to the formation of new living matter in the plant cell; it can be applied also to the synthetic processes in the formation of carbohydrates, proteids, etc., and called synthetic assimilation. The sun supplies the energy, which is absorbed by the chlorophyll, for splitting up the carbonic acid, and the living chloroplast then assimilates by a synthetic process the carbon, hydro- gen, and oxygen. This process then can be called photosynthetic assimi- lation. ‘The nitrite and nitrate bacteria derive energy in the process of nitrification, which enables them to assimilate CO, from the air, and this is called chemosynthetic assimilation. The inorganic material in the form of mineral salts, nitrates, etc., absorbed by the root, and carried up to the leaves, here meets with the carbohydrates manufactured in the leaf. Under the influence of the protoplasm synthesis takes place, and proteids and other organic compounds are built up by the union of the salts, nitrates, etc., with the carbohydrates. This is also a process of synthetic assimila- tion. These are afterward stored as food, or assimilated by the proto- plasm in the making of new living matter, or perhaps without the first process of synthetic assimilation some of the inorganic salts, nitrates, and carbohydrates meeting in the protoplasm are assimilated into new living matter directly. CHAPTER XI. eS, Syleme away i IUCN: 220. One of the life processes in plants which is extremely interesting, and which is exactly the same as one of the life proc- esses of animals, is easily demonstrated in several ways. 221. Simple experiment to demonstrate the evolution of CO, during germination.—Where there are a number of stu- Test for presence of carbon dioxide in ves- 1 with germinating 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 CO, in the bottle. Lower a lighted taper. It is extinguished because of the great quantity of CO,. If flower buds are accessible, place a small handful in each of several jars and treat the same as in the case of the peas. Young growing mushrooms are excellent also for this experiment, and serve to show that respiration takes place in the fungi. Ito eS Oe RESPIRATION. II! 222. If we now take some of the baryta water and blow our “breath”? 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 res- piration. ‘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-dioxide assimilation. ) 223. To show that oxygen from the air is used up while plants respire——Soak some wheat for 24 hours in water. Remove it from the water and place it in the folds of damp cloth or Paper in a moist vessel. Let. it remain until it begins to germinate. Fill the bulb of a thistle tube with the germinating wheat. By the aid of a stand and clamp, support the tube upright, as shown in fig. ro2. Let the small end of the tube rest in a strong solution of caustic potash (one stick caustic potash in two- thirds tumbler of water) to which red ink has been added to give a deep red color. Place a small glass plate over the rim of the bulb and seal it air-tight with an abundance of vaseline. ‘Two tubes can be set up in one vessel, or a second one Fig. 102. Bambeset up instrong baryta water ,...PPat2tts to show respiration of colored in the same way. 224. The result.—It will be seen that the solution of caustic potash rises slowly in the: tube; the baryta water will also, if that is used. The solution is colored so that it can be plainly 112 PHYSIOLOGY. seen at some distance from the table as it rises in the tube. In the experiment from which the figure was made for the accom- panying illustration, the solution had risen in 6 hours to the height shown in fig. roa. In 24 hours it had risen to the height shown in fig. 103. potash rises in the tube.—Since no air can get into the thistle tube from above or below, it must be that some part of the air which is inside of the tube is used up while the wheat is germinating. From our study of germinating peas, we know that a suffocating gas, carbon dioxide, is given off while respiration takes place. The caustic potash solution, or the baryta water, whichever is used, absorbs the car- bon dioxide. ‘The carbon dioxide is heavier than air, and so it settles down in the tube 2UE, BSS. where it can be absorbed. Apparatus to show : - een of germinat- 226. Where does the carbon dioxide come from ?—We know it comes from the growing seedlings. The symbol for carbon dioxide is CO,. The carbon comes from the plant, because there is not enough in the air. Nitrogen could not join with the carbon to make COp. Some oxygen from the air or from the protoplasm of the grow- ing seedlings (more probably the latter) joins with some of the carbon of the plant. These break away from their association with the living substance and unite, making CO g. The oxygen absorbed by the plant from the air unites with the living sub- stance, or perhaps first with food substances, and from these the plant is replenished with carbon and oxygen. After the demon- stration has been made, remove the glass plate which seals the thistle tube above, and pour in a small quantity of baryta water. The white precipitate formed affords another illustration that carbon dioxide is released. 225. Why the solution of caustic —— a. s.-:. 4 RESPIRATION. 113 227. Respiration is necessary for growth.—After performing experiment in paragraph 221, if the vessel has not been open too long so that oxygen has entered, 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 consumed. 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 covered 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 Fig. ro4. Pea seedlings; the one at the left had no oxygen and little growth took place, the one at the right in oxygen and growth Was evident. check. Damp folded filter paper should be supported above the water, Fig. ros. Experiment to show that growth takes place more rapidly in presence of oxygen than in absence of oxygen. The two tubes in the vessel represent the condition at the beginning of the experiment. At the close of the experiment the roots in the tube at the left were longer than those in the tube filled at the start with mercury. The tube outside of the vessel represents the condi- tion of things where the peas grew in ab- sence of oxygen; the carbon dioxide given off has displaced a portion of the mercury. This also shows anaerobic respiration. and on this should be placed one- half dozen peas with roots of the same length as those in the jar containing carbon dioxide. 228. In 24 hours examine and note how much growth has taken place. It will be seen that the roots have elongated but very little or none in the first jar, while in the second one we see that the roots have elongated consider- ably, if the experiment has been carried on carefully. Therefore in an atmosphere devoid of oxygen very little growth will take place, which shows that normal respira- tion with access of oxygen (aerobic respiration) isnecessary for growth. 229. Another way of perform- ing the experiment.—lIf we wish we may use the following experi- ment 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 mm long may be selected. Fill a test tube with mercury and carefully invert it in a vessel of mercury so that there will 114 PHVSIOLOG Y. 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. Remove the outer coats from the peas so that no air will be introduced in the tube filled with the mercury, and insert them one at a time under the edge of the tube beneath the mercury, six in each tube, having first measured the length of the radicles. Place in a warm room. In 24 hours measure the roots. ‘Those in the air will have grown considerably, while those in the other tube will have grown but little or none. : 230. Anaerobic respiration.—The last experiment is also an excellent one to show anaerobic respiration. In the tube filled with mercury so tha 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 carbon di- oxide. This evolution of carbon dioxide by living plants when there is no access of oxygen is anaerobic respiration (sometimes called intramolecular respiration). It occurs markedly in oily seeds and especially in the yeast plant. 231. 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. 232. Respiration 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 containing baryta water. A sim- ilar apparatus should be set up, but with no plant, to serve as acheck. 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 experiment. The bell jar containing the plant should be covered with a black cloth to prevent carbon assimilation. In the course of 10 or 12 hours, if everything has Fig. 106. Test for liberation of car- bon dioxide from lealy, plant worked properly, the baryta water under the jar i iration. BONG ae Boe geen Bee a with the plant will show the film of barium car- (Sachs. ) bonate, while the other one will show none. Res- piration, therefore, takes place ina leafy plant as well as in germinating seeds RESPIRATION. i15 233. Respiration in fungi.—If several large actively growing mushrooms are accessible, place them in a tall glass jar as described for determining respiration in germinating peas. In the course of 12 hours test with the lighted taper and the baryta water. Respiration takes place in fungi as well as in green plants. 234. 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 absence of oxygen. 235. 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. | 236. Fermentation of yeast—Take two fer- mentation tubes. Fill the closed tubular parts of each with a weak solution of grape sugar, or with potato decoction, leaving the open bulb nearly empty. Into the liquid of one of the tubes place a piece of compressed yeast as large as apea. If the tubes are kept in a warm place for 24 hours bubbles of gas may be noticed rising in the one in which the yeast was placed, while in the second tube no such bubbles appear, especially if the filled tubes are first sterilized. The tubes may be kept until the first is entirely filled with the gas. Now dissolve in the liquid a small piece of caustic potash. Soon the gas will begin to be absorbed, and the liquid will rise until it again fills the tube. The gas was carbon dioxide, which was chiefly pro- Fig. 107. duced during the anaerobic respiration of the Fermentation tube with culture of yeast. rapidly growing yeast cells. In bread making this gas is produced in considerable quantities, and rising through the dough fills it with numerous cavities containing gas, so that the bread “rises.” When it is baked the heat causes the gas in the cavities to ex- 116 PHYSIOLOGY. pand greatly. This causes the bread to “‘rise’”? more, and baked in this condition it is “‘light.”’ There are two special processes accom- panying the fermentation by yeast: rst, the evolution of carbon dioxide as shown above; and, 2d, the formation of alcohol. The best illus- tration of this second process is the brewing of beer, where a form of the same organism which is employed in “‘bread rising” is used to *‘ brew beotay 237. The yeast plant.—Before the caustic potash is placed in the tube some m the fermented liquid should be taken for study of the yeast plant, unless separate cultures are made for this pur- pose. Place a drop of the fermented liquid on a glass slip, place on this a cover-glass, and examine with the microscope. Note the min- ute oval cells with granular protoplasm. ‘These are the yeast plant. Note in some a small “bud”? at one side of the end. These buds increase in size and separate from the parent plant. The yeast plant is one celled, and multiplies by “‘budding”’ or. “sprouting. @ palace fungus, and some species of yeast like the present one do not form any my- celium. Under certain CED conditions, which are not very favorable for growth Fig. 108a. Yeast. | Saccharo- : ; myces cerivisee. @, grown in a weak nutrient small colony; 6, single 4 cell budding: c. single substance on a thin layer i ll forming an ascus ° Fig. 108. cell fo of a plaster Paris slab), Fermentation tube filled With four roan ee with CO, from action of | Spores free from the several spores are formed ERE UN SUS 0 Moe SSCES gece Seat many of the yeast cells. After a period of rest these spores. will sprout and produce the yeast plant again. Because of this peculiar spore formation some place the yeast among the sac fungi. (See classification of the fungi.) 238. Organized ferments and unorganized ferments.—An organism like the yeast plant which produces a fermentation of a liquid with evo- lution of gas and alcohol is sometimes called a ferment, or ferment or- ganism, or an organized ferment. On the other hand the diastatic fer- ments or enzymes like diastase, taka diastase; animal diastase (ptyalin in the saliva), cytase, etc., are wnorganized ferments. In the case of these it is better to say enzyme and leave the word ferment for the ferment (example, when the yeast is organisms. ——. ae ee eS RESPIRA TION. LE, 239. Importance of green plants in maintaining purity of air.—By respi- ration, especially of animals, the air tends to become ‘‘ foul’’ by the increase of CO,. Green plants, i.e., plants with chlorophyll, purify the air during photosynthesis by absorbing CO, and giving off oxygen. Animals absorb in respiration large quantities of oxygen and exhale large quantities of CO,,. Plants absorb a comparatively small amount of oxygen in respiration and give off a comparatively small amount of CO,. But they absorb during photosynthesis large quantities of CO, and give off large quantities of oxygen. In this way a balance is maintained between the two processes, so that the percentage of CO, in the air remains approximately the same, viz., about four-tenths of one per cent, while there are approximately 21 parts oxygen and 79 parts nitrogen 239a. Comparison of respiration and photosynthesis. Carbon dioxide is taken in by the plant and oxygen is liberated. Starch is formed asa result of the metabolism, or chemical change. The process takes place only in green plants, and in Starch formation or the green parts of plants, that is, in the presence Photosynthesis. of the chlorophyll. (Exception in purple bacte- rium.) The process only takes place under the influence of sunlight. It is a building-up process, because new plant sub- stance is formed. Oxygen is taken in by the plant and carbon dioxide is liberated. Carbon dioxide is formed as a result of the meta- bolism, or chemical change. The process takes place in all plants whether they Respiration. possess chlorophyll or not (exceptions in anaerobic bacteria). The process takes place in the dark as well as in the sunlight. It is a breaking-down process, because disintegra- tion of plant substance occurs. CHAPTER Xai GROWTH. 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. 240. 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. 241. Form of the gonidia.—lIt 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 have not been immersed in a moist medium. 242. 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- 118 CROW Tie 119 sion, thus drawing water forcibly through the protoplasmic mem- brane. Since it does not filter out readily, the increase in Fig. roo. 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. 243. 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 grow?h, or, more properly speaking, one of the phenomena of growth. 244, 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 from a 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. 245. Growth in length takes place only at the end of the thread.—If there were any branches on the mycelium when the 120 PHYSIOLOGY. 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. 246. 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. 247. 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. 248. 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 asin fig. 110. 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 to hours, if convenient, observe them and note the farther growth of the root. j | , 3 ; GROWTH. E21 249. The region of elongation.—While the root has elon- gated, the region of elongation zs nof at the tip of the root. Tt hes a little distance back from the tp, beginning at about 2mm from the tip and extending over an area represented by from 4~—5 of the milli- meter marks. The root shown in fig. rro Ee, was marked at Io A.M. on July 5. At 6 P.M. of the same day, 8 Fig. 110. 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 give 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. 50. 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. 251. Formative region.—If we make a longitudinal section of the tip of a growing root of the pumpkin or other seedling, and examine it with the mi- 122 PHY SIOLOG Y. 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. 252. 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 zzfernodes. _Weshould mark off several of these internodes, especially the younger ones, into sections about 57m 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 4ommin one internode. See also Chapters 38, 39. 253. 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. 254. 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 GROWTH. 123 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. 255. 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. 256. 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 (Winn on ran I 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, fail fire « Tri +48 orn a J ws f and the zone of maximum growth is coincident with that of the leaves. It would SS ge be instructive to note it Fig, 111. in the case of other plants Lever auxanometer Oels) for measuring elongation of and also in the case of the stem during growth. ; fruits. 257. 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 tuward the apex of the growing stem, this line of elongation of the cells which is 124 PHYSIOLOGY. traveling around the stem does so in a 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 mutation. 258. 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. [Se ee ee ee CHEAPER XT, Ren oieAr BL Lelie. 259. We should now examine the movements of plant parts iteirespomse 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. 260. 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 1a5 126 PHYVSIOLOG ¥. is progeotropism. ‘The lateral growth of secondary roots is da- geolropism. The stem, on the other hand, which was placed in a horizontal position has become again erect. ‘This turning of the stem in Fig. 112. Fig. 113. Germinating pea placed in a hori- In 24 hours gravity has caused the root to zontal position. turn downward. Figs. 112, 113.—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. 114. 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. : : | | ee ee eee IRRITABILITY. 127 Horizontal leaves and shoots can be shown to be subject to the same influence, and are therefore dzageotropic. 261. Influence of light.—Not only is light a very important factor for plants during photosynthesis, it exerts great influ- ence on plant growth and movement. 962. Growth in the absence of light.—Plants grown in the dark are subject toa number of changes. The stems are often longer, more slender and weaker since they contain a larger amount of water in proportion to building material which the plant obtains from car- bohydrates manu- factired “im . the light. On many plants the leaves are very small when cei in the Radish seedlings growninthe W dark. dark, long, slender, not green. 268. Influence of light on direction of \\\\\\\\\ growth.—While we are growing seedlings, \Q i x the pots or boxes of some of them should be mee placed so that the plants will have a one- _Radishseedlings grown in sided illumination. ‘This can be done by and ares Paes eet : A 3 retarded by light. placing them near an open window, in a room with a one-sided illumination, 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 heliotropism, a turning influenced by the sun or sunlight. / 264. Diaheliotropism.—Horizontal leaves and shoots are diaheliotropic as well as diageotropic. The general direction 128 PHYSIOLOGY. 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 ff stimulus of light. The leaves of plants witha one-sided illu- mination, as. ‘can be 5 Gel. iby: trial, are turned with Fig. 117. ir Seedting of castor-oil bean, before and after thei Cee 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 plant which has been used to illus- trate this is the sun- flower. Some of these plants, which Fig. 18. Dark chamber with opening at one side to show heliotropism. (After Schleichert.) IRRITABILITY. 129 were grown in a box, when they were about 35cm high were covered for nearly two days, so that the lght was excluded. At midday on the second day the box was removed, and the leaves on the covered plants are well represented by fig. 119, 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. 120. Now on leaving these plants, which had exhibited AYES, Fig. 120. PA an Ale j h Sunflower plant removed from Wie 7 ~~ darkness, leaves extending under if influence of ligh iaheliotro- uP fl f light (diahel hy pism.) induced ‘‘sleep’’ move- ments, exposed to the light they gradually assumed the horizontal position again. 265. Epinasty and hyponasty.—During the early 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 leaves grows more rapidly in a longitudinal direction than the upper side, so that the leaves are held upward close against the Fig. 110. bud at the end of the stem. This is termed Sunflower plant. Epinastic con- dition of leaves induced during the é day in darkness. hyponastic. Later the growth is more rapid hyponasty, or the leaves are said to be on the upper side and the leaves turn downward or away from the bud. This is termed efzzasty, or the leaves are said to be efznastic. This is shown by the night position of the leaves, or in the induced ‘‘sleep” of the sun- 130 PHYSIOLOGY. 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. 266. 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 SS SS SS Fig. 121. Fig. 122. Squash seedling. Position of cotyledons in Squash seedling. Position of cotyledons in light. the dark. the cotyledons of the pumpkin is more or less horizontal, as shown in fig. 121. At night, or if we darken the plant by covering with a tight box, the leaves assume the position shown in fig, 122. 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. 267. Leaves with a fixed diurnal position.—Leaves of some plants when they are developed have a fixed diurnal position and are not subject to IRRITABILITY. 131 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. 268. 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. 269. 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 Rm. 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. 270. Movement influenced by contact.—In the case of tendrils, twining leaves, or stems, the irritability to contact is shown in a move- Fig. 123. ment of the tendril, etc., 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 (see fig. 123), and that part coils 132 PHYSIOLOGY. 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 easing up the plant when subject to violent gusts of wind which might tear the plant from its support were it not for the yielding and springing motion of this coil. 271. Sensitive plants.—These plants are remarkable for the rapid response to stimuli. Mimosa pudica is an excellent plant to study for this purpose. 272. 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. 125, until all the leaflets on this pinna are closed, then the stimu- lus travels down the other pinne in a simi- lar manner, and Sensitive-plant leaf in normal position. Fig. 125. Pinne fold- ing up after stimulus. soon the pinne approximate each other and : Fig. 126. the leaf then drops doyeanane as shown IN ater talk Wee fig. 126... The normal position of the leaf %s *ei eS) KS Fig. 217. Section of an zcidium (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 sfervmatia, 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. 406. 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 @ctdium. 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 erters the tissues of the wheat, forming mycelium between the cells. This mycelium then bears the uredospores, and later the teleutospores. BUNGLE RUSTS. > IOI 407. Uredospores can produce successive crops of uredospores.—Tue uredo- spores are carried by the wind to other wheat or grass plants, germinate Fig. 218. 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 ‘, A Ln \ens Rus Pi Fig. 210. A, section through sorus of black rust of wheat, showing teleutospores. 8, 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. 192 MORPHOLOGY. 407a. 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 Fig. 220. Fig. 221. Germinating uredospore of Germ tube entering the wheat rust. (After Marshall- leaf through a stoma. Ward.) 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, 222, 223. 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 forms a small gonidium on the end, sometimes called a Ssporidium. 408. 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 Fig. 222. Pigs 223. Teleutospore germi- Promycelium of ger- Germinating sporidia entering leaf nating, forming promy- minating teleutospore, of barberry by mycelium. celium. forming sporidia. Figs. 222-224.—Puccinia graminis (wheat rust). (After Marshall-Ward.) Fig. 224. FUNGI: RUSTS. 193 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. 409. 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.’’ écidia (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 eecidiospores, with orange-colored content. fEécidiospores 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. 194 MORPHOLOG ¥. 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. 410. Other examples of the rusts.—Some of the rusts do great injury to fruit trees and also to forest trees. The ‘“‘cedar apples’’ are abnormal growths on the leaves and twigs of the cedar stimulated by the presence of the mycelium of a rust known as Gymnosporangium macropus. The teleutospores are two celled and are formed in the tissue of the “‘cedar _apple’’ or gall. The teleutosori are situated at quite regular intervals over the surface of the gall at small circular depressions, and can be easily seen in late autumn and during the winter. A quantity of gelatine is developed along with the teleutospores. In early spring with the warm spring rains the gelatinous substance accompanying the teleutospores swells greatly, and causes the teleutospores to ooze out in long, dull, orange-colored strings, which taper gradually to a slender point and bristle all over the “‘cedar apple.” Here the teleutospores germinate and produce the sporidia. The sporidia are carried to apple trees where they infect leaves and even the fruit, producing here the cluster cups. There are no uredospores. G. globosum is another species forming cedar apples, but the gelatinous strings of teleutospores are short and clavate, and the cluster cups are formed on hawthorns. G. nidusavis forms ‘‘witches brooms’’ or “‘birds nests’’ in the branches of the cedar. ‘The mycelium in the branches stimu- lates them to profuse branching so that numerous small branches are devel- oped close together. The teleutosori form small pustules scattered over the branches. G. clavipes affects the branches of cedar only slightly deform- ing them or not at all, and the cluster cups are formed cn fruits, twigs, and leaves of the hawthorns or quinces, the cluster cups being long, tubular, and orange in color. CHAPTER XXzI. Mie nH Eee HUNG 411. The series of the higher fungi.—Of these there are two large series. One of these is represented by the sac fungi, and the other by the mushrooms, a good example of which is the common mushroom (Agaricus campestris). Sac Fungi (Ascomycetes). 412. The sac fungi may be represented by the “‘powdery mil- dews”; examples, uncinula, microsphera, podosphera, etc. Fig. 225 is from a photograph of two willow leaves affected by one of these mildews. ‘The leaves are first partly covered with a 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. 413. Fruit bodies of the willow mildew.—On this same myce- lium there appear later numerous black specks scattered over the affected places of the leaf. ‘These are the fruit bodies (per- ithecia). 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 of a little hook. Because of these hooked appendages this genus is called uncinula. ‘This rounded body is the peritheciwm. 195 196 MORPHOLOGY. 414. Asci and ascospores.—While we are looking at a few of these through the microscope with the low power, we should if SSS Ex a Fig. 225. 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. 227. Such a sac is an ascus, and the spores are ascospores. FUNGI: SAC FUNGI. 197 415. Number of spores in an ascus.—The ascus is the most important character showing the general relationship of the members of the sac fungi. Fig. 226. Fig. 227. Fig. 228. Willow mildew; Fruit of willow mildew, showing hooked Fruit body of an- bit of mycelium appendages. Genus uncinula. other mildew with dichotomous ap- pendages. Genus microsphera. with erect conidio- phores, bearing chain of gonidia; gonidium at leit germinating. Figs. 227. 228.—Perithecia (perithe- cium) of two powdery mildews, showing escape of asci containing the spores from the crushed fruit bodies. While many of the powdery mildews have a variable number of spores in Fig. 220. Fig. 230. Contact of Disap pear- antheridium ance of contact and carpogo- walls of anthe- nium (carpogo- ridium and ; nium the larger carpogonium, Fig. 231. cell); begin- and fusion of Fertilized egg surrounded ning of fertili- the two nuclei. by the enveloping threads zation. whic grow up around it. Figs. 229-231.—Fertilization in pas Sp one of the powdery mildews. (After arper. an ascus, a large majority of the ascomycetes have just 8 spores in an 198 MORPHOLOGY. ascus, while some have 4, others 16, and some an indefinite number. The asci in a perithecium are more variable. In some ascomycetes there is no perithecium. 416. The black fungi.—These are very c.mmon on dead logs, branches, e Weed Fig. 2314. _Edible Morel. Morchella esculenta. The asci, forming hymenium, cover the pitted surface, leaves, ctc., and may be collected in the woods at almost any season. The perithecia are often numerous, scattered or densely crowded as in Rosel- FUNGI: MUSHROOMS. . 199 linia. Sometimes they are united to form a crust which is partly formed from sterile elements as in Hypoxylon, or they form black clavate or branched bodies as in Xylaria. The black knot of the plum and cherry is also an example. The lichens are mostly ascomycetes like the black fungi or cup fungi, while a few are basidiomycetes. | 417. The morels (Morchella).—’There are several species of morels which are common in early spring on damp ground. Either one of the species is suitable for use if it is desired to include this in the study. — Fig. 231a illustrates the Morchella esculenta. The stem is cylindrical and stout. The fruiting portion forms the “‘head,”’ and it is deeply pitted. The entire pitted surface is covered by the asci, which are cylindrical and eight spored. A thin section may be made of a portion for study, or a small piece may be crushed under the cover glass. 418. The cup fungi.—These fungi are common on damp ground or on rotting logs in the summer. ‘They may be preserved in 7o per cent alcohol for study. Many of them are shaped like broad open cups or saucers. The inner surface of the cup is the fruiting surface, and is covered with the cylindrical asci, which stand side by side. A bit of the cup may be sec- tioned or crushed under a cover glass for study. Mushrooms (Basidiomycetes). 419. 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 basidium, is present, and bears a limited number of spores, usually four, though in some genera the number is variable. Some place the rusts (Uredinez) in the same series (basidium series), because of the short pro- mycelium and four sporidia developed from each cell of the teleutospore. 420. The gill-bearing fungi (Agaricacee).—A good example for this study is the common mushroom (Agaricus campestris). This occurs from July to November in lawns and grassy fields. The plant is somewhat umbrella-shaped, as shown in fig. 232, ‘and possesses a cylindrical stem attached to the under side of the convex cap or pileus. On the under side of the pileus are thin radiating plates, shaped somewhat like a knife blade. These are the gills, or lamellz, and toward the stem they are rounded on the lower angle and are not attached to the stem. The longer ones extend from near the stem to the margin of the pileus, and the V-shaped spaces between them are occupied by successively 200 oe MORPHOLOGY. ; Fig. 232. Agaricus campestris. View of under side showing stem, annulus, gills, and margin of pileus. Fig. 233- Agaricus campestris. Longitudinal section through stem and pileus. a, pileus; 4, portion of veil on margin of pileus; c, gill; “4, fragment of annulus; ¢, stipe. FUNGI: MUSHROOMS. 201 shorter ones. Around the stem a little below the gills is a collar, termed the ring or annulus. 421, Fruiting surface of the mushroom.—The surface of these gills is the fruiting surface of the mushroom, and bears the gonidia of the mushroom, which are dark purplish brown when mature, and thus the gills when old are dark in color. If we make a thin section across a few of the gills, we see that each side of the gill is covered with closely crowded club-shaped bodies, each one of which is a dastdium. In fig. 234 a few of these are en- | larged, so that the structure of the gill can. be “seen... Hach basidium of the com- mon mushroom has Fig. 234. Vig. 235. Portion of section of lamella of Agaricus campestris. Portion of hymenium of Co- tr, trama; si, subhymenium; 4, basidium; s/, sterigma _ prinus micaceus, showing large ( p2. sterigmata) ; ¢, basidiospore. cystidium in the hymenium. two spinous processes at the free end. Each one is a s/erzg’ma (plural s/erig’ma/a), and bears a gonidium. Ina majority of the members of the mushroom family each basidium bears four spores. When mature these spores easily fall away, and a mass of them gives a purplish-black color to objects on which they fall, so that a print of the under surface of the cap showing the arrangement of the gills can be obtained by cutting off the stem, and placing the pileus on white paper for a time. | 422. How the mushroom is formed.—The mycelium of the MORPHOLOGY. 202 Agaricus campestris. Soil washed from 66 spawn” and “ buttons, th) Fig. 230. showing the minute young “‘ buttons ”’ attached to the strands of mycelium. FUNGI: MUSHROOMS 203 mushroom lives in the ground, end grows here for several months or even years, and at the proper seasons develops the mature mushroom plant. The mycelium lives on decaying organic mat- ter, and a large number of the threads grow closely together form- ing strands, or cords, of mycelium, which are quite prominent if they are uncovered by removing the soil, as shown in fig. 236. 423. From these strands the buttons arise by numerous threads growing side by side in a vertical direction, each thread growing independently at the end, but all lying very closely side by Fig. 237. Agaricus campestris ; sections of ‘‘ buttons”’ of different sizes, showing iormation of gills and veil covering them. side. When the buttons are quite small the gills begin to form on the under margin of the knob. They are formed by certain of the threads growing downward in radiating ridges, just as many of these ridges being started as there are to be gills formed. At the same time, threads of the stem grow upward to meet those at the margin of the button in such a manner that they cover up the forming gills, and thus enclose the gills in a minute cavity. Sections of buttons at different ages will show this, as is seen in fig. 237. This curtain of mycelium which is thus stretched across the gill cavity is the veil. As the cap expands more and more this is stretched into a thin and delicate texture as 204. MORPHOLOG ¥. shown in fig. 238. Finally, as shown in fig. 239, this veil is ruptured by the expansion of the pileus, and it either clings Fig. 238. Agaricus campestris; mearly mature plants, showing veil still stretched across the gill cavity. Fig. 239. Agaricus campestris ; under view of two plants just after rupture of veil, fragments of the latter clinging both to margin of pileus and to stem. 7 FUNGI: MUSHROOMS. 208 Fig. 240. Agaricus campestris ; plant in natural position just after rupture of veil, showing tendency to double annulus on the stem. Portions of the veil also dripping from margin of pileus. Fig. 2ar. Agaricus campestris; spore print. NG MORPHOLOG 206 ** Fairy ring Fig. 242. ” formed by Agaricus arvensis (photograph by B. M. Duggar). The mycelium spreads centrifugally each year, g graph by g ycelium, and thus the plants appear in a ring. consuming the available food, FUNGI: MUSHROOMS. 207 to the stem as a collar, or a portion of it remains clinging to the margin of the cap. When the buttons are very young the gills are white, but they soon become pink in color, and Fig. 243. Amanita phalloides; white form, showing pileus, stipe, annulus, and volva. very soon after the veil breaks the spores mature, and then the gills are dark brown. 424. Beware of the poisonous mushroom.—The number of species of mushrooms, or toadstools as they are often called, is very great. Besides the common mushroom (Agaricus campes- 208 MORPHOLOGY. tris) there are a large number of other edible species. But one should be very familiar with any species which is gathered for food, unless collected by one who certainly knows what the plant is, since carelessness in this respect sometimes results fatally from eating poisonous ones. 425, A plant very similar in structure to the Agaricus campes- tris is the Lepiota naucina, but the spores are white, and thus the gills are white, except that in age they become a dirty pink. This plant occurs in grassy fields and lawns often along with the Fig. 244. Amanita phalloides; plant turned to one side, after having been placed in a horizontal position, by the directive force of gravity. common mushroom. Great care should be exercised in collect- ing and noting the characters of these plants, for a very deadly poisonous species, the deadly amanita (Amanita phalloides) is perfectly white, has white spores, a ring, and grows usually in wooded places, but also sometimes occurs in the margins of lawns. In this plant the base of the stem is seated in a cup-shaped struc- ture, the volva, shown in fig. 243- One should dig up the stem carefully so as not to tear off this volva if it is present, for with the absence of this structure the plant might easily be mistaken for the lepiota, and serious consequences would result. FUNGI: MUSHROOMS. 200 426. Tube-bearing fungi (Polyporacez).—In the tube-bearing fungi, the fruiting surface, instead of lying over the surface of gills, lines the surface of tubes or pores on the under side of the cap. The fruit-bearing portion therefore is “‘honey-combed.”’ The sulphur polyporus (Polyporus sulphu- reus) illustrates one form. The tube-bearing fungi are sometimes called “‘bracket”’ fungi, or “‘shelf’’ fungi, because the pileus is attached to the Fig. 245. _Edible Boletus. Boletus edulis. Fruiting surface honey-combed on under side of cap. tree or stump like a shelf or bracket. One very common form in the woods is the plant so much sought by “‘artists,” and often called Polyporus ap- planatus. It is hard and woody, reddish brown, brown or grayish on the upper side, according to age, and is marked by prominent and large concentric ridges. (This form is probably P. leucophzus.) The under side is white and honey-combed by numerous very minute pores. This plant is peren- nial, that is, it lives from year to year. Each year a new layer is added to the under side, and several new rings usually to the margin. If a plant two or three years old is cut in two, there will be seen several distinct tube layers or strata, each one representing a year’s growth. In some of these bracket fungi, each ring on the upper surface marks a 210 . MORPHOLOG Y. year’s growth as in the pine polyporus (P. pinicola). In the birch poly- porus (P. fomentarius) the tubes are quite large. It also occurs on other trees. The beech polyporus (P. igniarius, also on other trees) often be- Fig. 246. Coral fungus. Hydnum coralloides, spines hanging down from branches. comes very old. I have seen one specimen over eighty years old. Not all the tube-bearing fungi are bracket form. Some have a stem and cap (see fig. 245). Some are spread on the surface of logs. 427. Hedgehog fungi (Hydnacee).—These plants are bracket in form or have a stem and cap, or are spread on the surface of wood; but the finest specimens resemble coral masses of fungus tissue (example, Hydnum, fig. 246). In most of them there are slender processes resembling teeth, spines or awls, which depend from the under surface (fig. 247). The fruiting surface covers these spines. WW 428. Coral fungi or fairy clubs (Clavariaceze).—These plants stand upright from the wood, leaves, or soil, on which they grow (example, Clavaria). The ‘‘coral’’ ones are branched, while the “‘fairy clubs’’ are simple. The fruiting surface covers the entire exposed surface of the plants (fig. 248). FUNGI: MUSHROOMS. 211 Fig. 247. Hydnum repandum, spines hanging down from under side of cap. 212 MORPHOLOG Y. Fig. 248. meee Clavaria botrytes. « CHAPTER. XXII. CEASSIFICATION OF THE FUNGI. 429, 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_ba- sidium is limited and definite, and the basidium is a characteris- tic structure; examples: uredinee (rusts), mushrooms, etc. The Ascus Type or Series. The number of spores in an ascus is limited and definite, and the ascus is a characteristic structure; examples: leaf curl of peach (exoascus), pow- dery mildews, black knot of plum, black rot of grapes, etc. The Gonidium Type or Series. The number of gonidia in the spo- rangium is indefinite and variable. It may be very large or very small, or even only one in a sporangium. To this series belong the lower fungi; examples: mucor, saprolegnia, peronospora, etc. 430. Others believe that the fungi do not represent a natural group, but that they have developed off from different groups of the algee by becoming parasitic. As parasites they no longer needed chlorophyll, and conse- quently lost it. 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). 481. A very general outline of classification,* according to the former of * Class Myxomycetes, or Mycetozoa.— To this class belong the “‘slime malds,”’ low organisms consisting of masses of naked protoplasm which flows among decaying leaves and in decaying wood, coming to the surface to fruit. The fruit in many cases resembles miniature puff-balls, and these plants were formerly classed with the puff-balls. The spores germinate by 213 214 MORPHOLOG Y. these views, might be presented here to show. the general relationships of the fungi studied, with the addition of a few more in orders not represented above. It should be borne in mind that the author in presenting this view of classification does not necessarily commit himself to it. It is based on that presented in Engler & Prantl’s Pflanzenfamilien. ‘There are three classes. I. Class Phycomycetes (Alga-like Fungi). 1. SUBCLASS OOMYCETES. 432. These are the egg-spore fungi. They include the water mold (Saprolegnia), the downy mildew of the grape (Plasmopara), the potato Fig. 240. Chytrids. A, Harpochytrium hedenii, parasitic on spirogyra threads; a, sickle- form plant; b, the sporangium part with escaping zoospores; ¢, old ‘plant pro- liferating by forming new sporangium in the old empty one, d, zoospore; 6, two young plants just beginning to grow. B, Rhizophidium globosum parasitic on spirogyra. Globose sporangium with delicate threads inside of the host, zoospores escaping from one. C, Olpidium pendulum, parasitic in spirogyra cell. Ellip- tical sporangium with ‘slender exit tube through which zoospores are escaping. D, Lagenidium rabenhorstii parasitic in spirogyra cell. Two slender sporangia with exit tubes through which protoplasm escapes forming a rounded mass at the end of tube, this protoplasm forming biciliate zoospores. forming swarm spores which unite to form a small plasmodium, which in turn grows to form a large plasmodium or protoplasmic mass. It is doubt- ful if they are any more plant than animal organisms. Examples: Trichia, Arcyria, Stemonitis, Physarum, Ceratiomyxa, etc., on rotten wood; Plas- modiophora brassice is a parasite causing club foot of cabbage, radishes, etc. It lives within the roots, causing large knots and swellings on the same. FUNGI CONTINUED. CLASSIFICA TION. 215 blight (Phytophthora), the white rust of cruciferous plants (Cystopus= Albugo), the damping-off fungus (Pythium), and many parasites of the alge known as chytrids, as Olpidium, Rhizophidium, Lagenidium, Chytri- dium, etc. The two following orders are sometimes placed in a separate subclass, Archimycetes. 433. Order Chytridiales (Chytridinez).—These include the lowest fungi. Many of them are parasitic on alge and lack mycelium, the swarm spore either with or without minute rhizoids, developing into a globose sporan- gium (Rhizophidium, Chytridium, Olpidium, etc., fig. 249), or the swarm spore attached to the wall of the host develops into a long sword-shaped body with a sterile base, which proliferates ae and forms a new sporangium in the old one (Harpochytrium), or with slight develop- ment of mycelium in aquatic plants (Cla- dochytrium). Some are parasitic in leaves and stems of land plants. Synchytrium decipiens is very common on the trailing legume, Amphicarpzea monoica. 434, Order Ancylistales (Ancylistinez). —The members of this order have a slight development of mycelium and many are parasitic in alge (Lagenidium, fig. 249). 435. Order Saprolegniales (Saproleg- niinez).—These include the water molds (Saprolegnia). See Chapter XIX. 436. Order Monoblepharidales (Mono- blepharidinez).—These are peculiar water molds, related to the Saprolegniales, but motile sperm cells are formed (Monoble- pharis, etc., fig. 250). Fig. 250. ae Monoblepharis insignis Thax- 437. Order Peronosporales (Peronospori fee Bak ok US olla betes OSes. nez).—These include the downy mildews nium (00g) and antheridium (ant) P Pl ee perms escaping from antheridium ( eronospora, asmopara, Phytopthora, and creeping up on the oogonium., etc.), and the white rust of crucifers and (4!ter Thaxter.) other plants (Cystopus= Albugo), Chapter XIX. 2. SUBCLASS ZYGOMYCETES., 438. These are the conjugating fungi. 439. Order Mucorales (Mucorinee).—This includes the black mold and its many relatives (Mucor, Rhizopus, etc.). Chapter XIX. 440. Order Entomophthorales (Entomophthorinee).— This order in- cludes the ‘‘fly fungus’’ (Empusa) and its many relatives parasitic on insects. 216 MORPHOLOGY. In the autumn and winter dead flies are often found stuck to window-panes, with a white ring of the conidia around each fly. Il. Class Ascomycetes. (The ascus series.) 1. SUBCLASS HEMIASCOMYCETES, 441. Order Hemiascales (Hemiascinee).—Fungi with a well developed, Fig. 251. Dipodascus albidus. A, thread with sexual organs, ascogonium and antheridium; B, fertilized ascogonium developing ascus; C, ascus with spores; D, conidia. (After Lagerheim.) 4, 16, or more). Mycelium often well developed septate mycelium, but with a sporangium-like ascus, i.e., a large and indefinite number of spores in the ascus. Ex- amples: Protomyces macrosporus in stems of Umbelliferee, or P. poly- sporus in Ambrosia tri- fida. These two are by some placed in the Usti- laginez. Dipodascus albidus grows in the exuding sap of Bromeli- acee in Brazil and the Sap of the beech wai Sweden. The ascus is developed as the result of the fertilization of an ascogonium with an an- theridium (see fig. 251). 2. SUBCLASS PROTOASCOMYCETES, 442. Theasci are well defined and usually with a limited and definite number of spores (usu- ally 8, sometimes 1, 2, and septate. Asci scat- tered on the mycelium, not associated in definite fields or groups. 443. Order Protoascales (Protoascinee).—The asci are separate cells, or are scattered irregularly in loose wefts of mycelium. No fruit body. (The yeast, Saccharomyces, see paragraph 237; and certain mold-like fungi, some of which are parasitic on mushrooms, as Endomyces, are examples.) eS a ee FUNGI CONTINUED: CLASSIFICATION. 217 3. SUBCLASS EUASCOMYCETES, Asci associated in surfaces forming a hymenium, or in groups or inter- mingled in the elements of a fruit body. Fruit body usually present. The following four or five orders comprise the Discomycetes, according to the usual classification. 444, Order Protodiscales (Protodiscinee).— The asci are exposed and form large and indefinite groups, but there is no definite fruit body. Ex- amples: leaf curl of peach, plum pocket, etc. (Exoascus). 445. Order Helvellales (Helvellinee).—The asci form large fields over the upper portion of the fruit body. ‘This order includes the morels (fig. 231d), helvellas, earth tongues (Geoglossum), etc. 446. Order Pezizales (Pezizinew).—The asci form a definite field or fruiting surface surrounded on the sides and below by a wall of fungus tis- sue, forming a fruit body in the shape of a cup. These are known as the cup fungi (Peziza, Lachnea, etc.). 447. Order Phacidiales (Phacidiinee).—Fungi mostly saprophytic, and fruit body similar to the cup fungi. Examples: Propolis in rotting wood, Rhytisma forming black crusts on leaves (maple for example), Urnula craterium, a large black beaker-shaped fungus on the ground. 448. Order Hysteriales (Hysteriinew).—Fungi with a more or less elon- gated fruit body with an enclosing wall opening by a long slit. In some forms the fruit body has the appearance of a two-lipped body; in others it is shaped like a clam shell, the asci being inside. Example, Hystero- graphium common on dry, dead, decorticated sticks. 449. Order Tuberales (Tuberinee).— The more or less rounded fruit bodies are usually subterranean. The most important fungi in this order are the truffles (Tuber). The mycelium of many species assists in the formation of mycorhiza on the roots of oaks, etc., and several species are partly cultivated, or protected, and collected for food. This is especially the case with Tuber brumale and its forms; more than a million francs worth of truffles are sold in France and Italy yearly. Dogs and pigs are employed in the collection of truffles from the ground. 450. Order Plectascales (Plectascinee).—The fruit body of these plants is more or less globose, and contains the asci distributed irregularly through the mycelium of the interior. Some are subterranean (Elaphomyces), while others grow in decaying plants, or certain food substances (Euro- tium, Sterigmatocystis, Penicillium). Penicillium in its conidial stage forms blue mold on fruit, bread, etc. The following four orders comprise the Pyrenomycetes, according to the usual classification. 451. Order Perisporiales.—The powdery mildews are good examples of this order (Uncinula, Microsphera, etc., Chapter XXI). 218 MORPHOLOGY. 452. Order Hypocreales.*—The fruit bodies are colorless, or bright colored and entirely enclose the asci, sometimes opening by an apical pore. Nectria cinnabarina has clusters of minute orange oval fruit bodies, and is common on dead twigs. Cordyceps with a number of species is parasitic on insects, and on certain subterranean Ascomycetes, especially Elapho- myces (of the order Plectascales= Plectascine@). 453. Order Dothidiales.*—Fungi with black stroma formed of mycelium in which are cavities containing the asci. The cavities are usually shaped like a perithecium, but there is no wall distinct from the tissue of the stroma (Dothidea, Phyllachora, on grasses). 454, Order Spheriales.*—These contain the so-called black fungi, with separate or clustered, oval, fruit bodies, black in color. The black wall ‘encloses the asci, and usually opens by an apical pore. Examples are found in the black knot of plum and cherry, black rot of grapes, and in Rosellinia, Hypoxylon, Xylaria, etc., on dead wood. 455, Order Laboulbeniales (Laboulbinezw),.— These are peculiar fungi attached to the legs and bodies of insects by a short stalk, and provided with a sac-like fruit body which contains the asci. Example, Laboulbenia. III. Class Basidiomycetes. (The basidium series.) 1. SUBCLASS HEMIBASIDIOMYCETES, 456. Order Ustilaginales (Ustilaginee).—This order includes the well- known smuts on corn, wheat, oats, etc. (Ustilago, Tilletia, etc.). 2. SUBCLASS ACIDIOMYCETES. 457. Order Uredinales +} (Uredinezw).— This order includes the parasitic fungi known as rusts. Examples: wheat rust (Chapter XX), the cedar apple, etc. The true Basidiomycetes include the following orders: 3. SUBCLASS PROTOBASIDIOMYCETES, 458. Order Auriculariales.;—This order includes trembling fungi in which the basidium is long and divided transversely into usually four cells (example, Auricularia), and similar forms. Pilacre petersil on dead wood represents an angiocarpous form. 459. Order Tremellales (Tremellinew), trembling or gelatinous fungi with the globose basidium divided longitudinally into four cells (Tremella). * As suborder in Engler and Prantl. + The Uredinales and Auriculariales in Engler and Prantl are placed in order, Auriculariinee. FUNGI CONTINUED: CLASSIFICA TION. 219 4. SUBCLASS EUBASIDIOMYCETES. 460. Order Dacryomycetales (Dacryomycetinee),— This order includes certain fungi of a gelatinous or waxy consistency, usually of bright colors. They resemble the Tremellales, but the basidia are slender and fork into two long sterigmata. (Example, Dacryomyces.) Gyrocephalus rufus is quite a large plant, 10-15 cm. high, growing on the ground in woods. 461. Order Exobasidiales (Exobasidiinee).—The fungus causing azalea apples is an example (Exobasidium). 462. Order Hymeniales (Hymenomycetineze),.—In this order the basidia are usually club-shaped and undivided, and bear usually four spores on the end (sometimes two or six). There are several families. 463. Family Thelephoracee.—The fruit bodies are more or less mem- branous and spread over wood or the ground, or somewhat leaflike, grow- ing on wood or the ground. The fruiting surface is nearly or quite even, and occupies the under side of the leaflike bodies (Stereum, Thelephora) or the outside of the forms spread out on wood (Corticium, Coniophora). 464, Family Clavariacee.—This order includes the fairy clubs, and some of the coral fungi. The larger number of species are in one genus (Clava- ria, fig. 248). 465. Family Hydnacee.—The fungi of this order are known as ‘“‘hedge- hog’’ fungi, because of the numerous awl-like teeth or spines over which the fruiting surface is spread, as in Hydnum (figs. 246, 247). 466. Family Polyporacee.—The tube-bearing fungi (Polyporus, Bole- tus, etc., fig. 245). 467. Family Agaricacee.—The gill-bearing fungi (Agaricus, Amanita, etc., see Chapter XXI). The above five orders, according to the earlier classification (still used at the present time by some), made up the order Hymenomycetes, while the following five orders made up the Gasteromycetes. The Hymenomycetes, according to this system, included those plants in which the fruiting portion (hymenium) is either exposed from the first, or if covered by a veil or volva (as in Agaricus, Amanita, etc.) this ruptures and exposes the fruiting sur- face before, or at the time of, the ripening of the spores, while the Gaster- omycetes included those in which the fruit body is closed until after the maturity of the spores. 468. Order Phallales (Phallinee).—The “‘stink-horn’’ fungi, or ‘‘buz- zard’s nose.’? Usually foul-smelling fungi, the fruiting portion borne aloft on a stout stalk, and dissolving (Dictyophora, Ithyphallus, etc.). 469. Order Hymenogastrales (Hymenogastrinex).—The basidia form a distinct hymenium which does not break down at maturity. Some of the plants resemble Boletus or Agaricus in the way the fruit bodies open (Seco- tium, etc.), while others open irregularly on the surface (Rhizopogon) or 220 ' MORPHOLOG Y. Zi like an earth star (Sclerogaster), or portions of the surface become gelatin- ized (Phallogaster). The last-named one grows ©n very rotten wood, while most of the others grow on the ground. 470. Order Lycoperdales (Lycoperdinee).— ‘These include the “puff- balls,”’ or ‘‘devil’s snuff-box’’ (Lycoperdon), and the earth stars (Geaster). The basidia form a distinct hymenium, but at maturity the entire inner por- tion of the plant (except certain peculiar threads, the capillitium) disinte- grates and with the spores forms a powdery mass. 471. Order Nidulariales (Nidulariinee).—These are known as bird-nest fungi. The fruit body when mature is cup-shaped, or goblet-shaped, and contains minute flattened circular bodies (peridiola) containing the spores. The intermediate portions of the fruit body disintegrate and set the peri- diola free, which then lie in the cup-shaped base like eggs in a nest. 472. Order Plectobasidiales (Plectobasidiinew).—The basidia do not form a definite hymenium, but are interwoven with the threads inside, or are collected into knot-like groups. (Examples: Calostoma, Tulostoma, Astrzus, Sphzrobolus, etc.) 472a. Lichens.—The plant body of the lichens (see paragraphs 200, 201) consists of two component parts, the one a fungus, the other an alga. The fructification is that of the fungus. ‘The fruit body shows the lichens to be related some to the Ascomycetes, others to the Hymenomycetes, and Gasteromycetes. They are usually classified as a distinct class or order from the fungi, but a natural arrangement would distribute them in sev- eral of the orders above. ‘Their special relationship with these orders has not been satisfactorily worked out. For the present they are arranged as follows: Ascolichenes. Pyrenocarpous lichens (those with a fruit body like the Pyrenomycetes). Gymnocarpous lichens (those with a fruit body like the Discomycetes), Hymenolichenes (those with a fruit body like the Hymenomycetes). Gasterolichenes (those with a fruit body like the Gasteromycetes). From a vegetative standpoint there are two types according to the dis- tribution of the elements. 1st. Where the fungal and algal elements are evenly distributed in the plant body the lichen is said to be homoiomerous. ‘There are two types of these: a. Filamentous lichens, example, Ephebe pubescens. b. Gelatinous lichens, example, Collema (with the alga nostoc), Physma (with the Chroococcacez). 2d. Where the elements are stratified, as in Parmelia, etc., the lichen is said to be heteromerous. In these there are three types: a. Crustaceous lichens, the plant body is in the form of a thin incrusta- tion on rocks, etc. — Pave) | CLASSIFICA TION. FUNGI CONTINUED: Parmelia, Peltigera, etc. b. Foliaceous lichens, the plant body is leaflike and lobed and more or less loosely attached by rhizoids 251d. Fig Rock lichen (Parmelia contigua) ke and filamentous or band- is the plant body ? c. Fruticose lichens branched, as in Usnea, la, etc. nia, € Clado CHAPTER XXIII. LIVERWORTS (HEPATIC). 473. We come now to the study of representatives of another group of plants, a few of which we examined in studying the organs of assimilation and nutrition. I refer to what are called the liver- worts. Two of these liverworts belonging to the genus riccia are illustrated in figs. 30, 252. Riccia. 474, 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 thesexual organs, and later the fruit capsule, are developed. 475. Form of the circular riccia (R. crystallina).—The circular riccia is shown in fig. 252. ‘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 a cir- 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 222 LIVERWORTS: RICCIA. 223 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. 476. Sexual organs. — In Thallus ee Sas ete 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. 477, 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. 253 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 archegonium. It is more complicated in structure than the oogonium. 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. 478. 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. 259 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. 224 MORPHOLOGY. 479, 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. Fiz. 253. Fig. 254. Archezgonium 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 Alls the cavity of the venter. Then it divides by a cross wall into two cells. These two grow, and divide again, and soon 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. 480. Sporogonium of riccia.—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 theegg. A sin- gle outer layer of cells forms the wall, and therefore is sterile. LIVERWORTS: RICCTA. 225 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. 256. Riccia glauca; archegonium containing neariy mature spo- rogonium. sg, spore-producing Fig. 255. 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, 481. A new phase in plant life.—Thus we have here in the sporogonium of zzccza 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 gamefo- phyte, or thallus, again. So we have this very interesting condi- 226 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. 482. Riccia compared with coleochete, cdogonium, etc.—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 coleochzete 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 coleochzte 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, coleocheete, and riccia, for the nu- clear phenomena in the formation of the zoospores of cedogonium and coleo- chete are not known. ‘They form, however, a very suggestive series. Marchantia. 483, 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: MARCHANTTIA. 227 midrib, as shown in figs. 257, 261. The growing point of the thallus is situated in the little depression at the free end. Ifwe 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. 484, Antheridial plants.—One of the male plants is figured at 257. It bears curious structures, each held aloft by a short stalk. These are the an- theridial recep- tacles (or male & gametophores). ~~ Pr iy Each one is cir- ~Y77 , GY KY cular, thick, and ¢ ~” p% shaped some- Fig. 257. 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- SRM? Za te { Fig. 258. 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. 258, that each one of these little openings on the surface is an entrance to quite 228 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. 259. This shows the structure: of thie 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. 485. 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- Fig. 250. Fig. 260. 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. 260. 486. Archegonial plants.—In fig. 261 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 TIVERWORTS: MARCHANTIA. 229 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. 261. _ 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 266. Here we find the archegonia, but instead of being sunk in cavities their bases are attached to the under 230 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. 487. Homology of the gametophore of marchantia.—To see the relation Fig. 262. Marchantia polymorpha, showing origin cf gametophore. of the gametophore to the thallus of marchantia take portions of the thallus bearing the female recepta- cle. On the under side note that the prominent midrib continues be- yond the thin lateral expansions and arches upward in the sinus or notch at the end, or at the side where the branch of the thallus has continued to grow beyond. The stalk of the gametophore is then a continuation of the midrib of the thallus. On the apex of this are organized sev- eral radial growing points which develop the digitate or ray-like receptacle. The gametophore is thus a specialized branch of the thallus. When young, or in many cases when nearly or quite mature, the gametophore, as one looks at the upper surface of the thallus, appears to arise from the upper surface, as in fig. 261. ‘This is because the thin lateral expansions of the thallus project forward and overlap in advance of the stalk. It is sometimes necessary to tear these overlapping edges apart to see the real origin of the gametophore. But in quite old plants these expanded portions are farther apart and show clearly that the stalk arises from the midrib below and arches upward in the sinus, as in fig. 262. CHAPTER XXIV. LIVERWORTS CONTINUED. 488. Sporogonium of marchantia.—If we examine the plant shown in fig. 181 we shall see oval bodies which stand out be- Fig. 263. Archegonial receptacles of marchantia bearing ripe sporogonia. The capsule of the sporogonium projects outside, while the stalk is attached to 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 Oy y, | 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 inseveral 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, 231 232 MORPHOLOGY. falling here and there. It appears also as if there were twisting threads which aided the spores in becoming freed from the capsule. Fig. 264. Section of archegonial receptacle of Marchantia polymorpha; ripe sporogonia. One is open, 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. 489. Spores and elaters.—lIf 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 (o> one of atwisted rope. These 34?) are very long cells from the a inner part of the spore-case, and their walls are marked by spi- ral thickenings. ~~ This causes them ¢ Y oa 14% : eae aS Cl XXVE FERNS. 529. In taking up the study of the ferns we find 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. 530. 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. 286. 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 pinnz extending in two rows on opposite sides of the midrib. ‘These pinnee 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 251 20D MORPHOLOGY. middle portion toward the end. ‘This is because of the shorter pinne here. 531. 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 (ogame dots,’’ or sori (a single one is asorus). If : we examine it with a low power of the mi- 7 OY croscope, ~~ “ Ne - or with a ~ e SY pore7k et | ses x lens -owe see that : there is a Y Gime Wilke of disk which 4" CLO Wes i more or a Ah £¢bdbee less com- ue ASH B* pletelyvery NN San) minute objects, usual- WX = ly the ends of the latter projecting just be- yond the edge if they are mature. This circular disk is what is called the zzdu- stum, and it is a special outgrowth of the epidermis of the leaf here forstue protection of the spore- cases. These minute ob- jects underneath are 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 Christmas fern (Aspidium acrostichoides). FERNS. 253 which is fastened to the middle of the under side of this shield, as seen in cross section in fig. 292. 532. 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 . 77 stalks are still attached, and examine them with the mi- croscope, we can see the form and structure of these peculiar bodies. Different views of a sporangium are shown in fig. 293. 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. 533. Structure of a spo- rangium. —If we examine one of the sporangia in side view as shown in fig. 293, Fig. 287. we note a prominent row of I ae bases of leaves, and roots of the cells which extend around 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 —e 254 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. 534. In the front of the sporangium is another peculiar group Spies Fig. 288. 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 hp 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. 280. : : 3 Under side of pinna of 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. De 535. 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 on a 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 Four pinne of adiantum, showing recurved margins which cover the sporangia. shown in fig. 294, 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. | 536. 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 the sporangium 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 256 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 Fig. 201. Section through sorus of Polypodium vulgare showing different stages of sporangium, and one multicellular capitate hair. as the water comes out. 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 soine ‘time ago. JAsmime 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 already learned, the glycer- ine does not pass through the walls nearly so fast 537. Now the structure of the cells of this annulus, as we have seen, is such that the inner walls and the perpendicular Fig. 292. 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. Dy) 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 fy Fig. 203. Rear, side, and front views of fern sporangium. 4d, e, annulus; 4, 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. 538. The movements of the sporangium can take place in old and dried material.—If we have no fresh material to study 258 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 = Sw A QA Fig. 204. : Dispersion of spores from sporangium of Aspidium acrostichoides, showing different stages in the opening and snapping of 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. 259 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. 539. 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. 540. 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, 291. The en- larged ends of these clubs reaching beyond the sporangia give some protection to them when they are young. 541. Other ferns.—We 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, has a 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. ‘[he margins of the fertile pinnze 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 pinne, 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. 542. 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 260. fi MORPHOLOGY. leaf appears as if it was rolled up as in fig. 287 of the Christmas fern. As the leaf elongates this portion unrolls, 543. 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. Re 544, Budding of ferns. — A few WZ ferns produce what are called bulbils aie or bulblets on the leaves. One of ONY 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 wf the pinne, especially near the end of w+ the leaf, small oval bulbs as shown ‘ in fig. 295. 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. 205: ; Cystopteris bulbifera, young plant growing STOWS until the roots attach the plant from bulb. At right is young bulb in axil of ¢, the soil or in the crevices of the pinna otf leaf. rocks. A young plant growing from one of these bulbils is shown in fig. 295. 545. Greenhouse ferns.—Some of the ferns grown in conservatories have similar bulblets. Fig. 296 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. 546. Plant conservatories usually furnish a number of very interesting ferns, and one should attempt to make the acquaintance of some of them, for d ; | ‘4 7 ¥ q i : FERNS. 2061 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. 547. 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 sporophyte (cor- responding to the sporogoniuin of the liverworts and mosses). 548. 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 Fig. 296. attached* to the soil. Bulbil growing from leaf of asplenium (A, bulbiferum). Through the aid of root hairs of its own it takes up mineral solutions. It possesses alse 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. CEEA PARE Ra Sox VEE FERNS CONTINUED. Gametophyte of ferns. 549. 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 eases = Pe. WD SOERIR AREAS Meme SEHD ARM on R e sets egunnedlinniscnss Sie RTE, ENS MTP Marstan (larity csesercertee PRES OAS StU atl Var azer means PETTY EET MATA Ap SESS OATS RY OY 5 ie esseE NAW al, WE Lt Ae a WRN SV ON See of Ye See NT GON > PREV TLL LAL EPA NY WBS BREA EY SK SSE BR SOE ESM SEC Oe RR NNO) seaee Tf SS eas i peseners Paez Copan Qegews Cr YO See ence: 5% rz r) Capa} ELAS pe Sererceri: ee 1 >. ey Ny, SWSN Saree’, Nea goe RH een ey ese TAO LD MC Sey BUEN (o4, Cy gsvhor? C] SO QA NL Eatd ly SSH ar eS Sema aees, Ne Fig. 207. 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 302 FERNS. 263 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. 208. Spore of Pteris serru- by keeping the surfaces where they are lata showing the three- 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. 550. In fig. 297 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 OEZaNS. are borne on the under side also, and we will study them ute ren © ks heart-shaped, flattened, thin, Fig. 290. Spore of Aspidium Spore crushed to remove exospore and green plant iS acrostichoides with show endospore. ‘ winged exospore. the prothallium of ferns, and we should now give it more careful study, be-. ginning with the germination of the spores. 551. 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. 298. The outer wall is roughened, and on one end are three elevated ridges which radiate from a given 264 MORPHOLOGY. point. A spore of the Christmas fern is shown in fig. 299. The outer wall here is more or less winged. At fig. 300 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. 552. Germination of the spores. —After the spores have been sown for about one week to ten days we should Fig. 301. 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. fs) Often one will sow the 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. 302. 553. Protonema. — These short green threads are called profonemal threads, or protonema, 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. 302, 303 are shown several stages of germination of different spores. Soon after Fig. 302. Germinating spores of the short germ tube emerges from the Pteris aquilina still in the : : Sl te Se eam crack in the spore wall, it divides by the FERNS. 265 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. 554. 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. 303. ‘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 Fig. 303. Young prothallium of a fern (nipho- wines, or margins of the Poles) little, green, flattened body, are in advance of the growing point, and the object is more or less heart-shaped, as shown in fig. 297. Thus we see how the prothallium of ferns is formed. 555. 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 266 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. 304. 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. 556. Antheridia.—If we search among the rhizoids we see small rounded elevations as shown in fig. 297 or 305 scat- Fig. 30s. 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. 267 tered over this portion of the prothallium. These are the an- theridia. Ifthe 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 é when the prothallia Section of antheridia eee cells, and spermato- are freshly placed in 20ids 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 the spermatozoids are shot out. We can see here that each one is shaped like a screw, with the coils at Fig. 307. Different views of spermatozoids; first close. But as the spermatozoid eae, ccccinnan). ae 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. 557. Archegonia.—If we now examine closely on the thicker part of the under surface of the prothallium, just back of the Big. 308. ie a Archegonium of fern. Large cell in the sinus, we may see longer venter is the egg, next is the ventral canal 5 : 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. 297. They are 268 MORPHOLOGY. the archegonia. One of them in longisection is shown in fig. 308. It is flask-shaped, and the broader portion is sunk in the Fig. 300. 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 is in 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. 310. the egg, fuses with the nucleus of the latter, Pra ete and the egg is then fertilized. It is now Le Bea es tee ready to grow and develop into the fern plant. This brings us back to the sporo- Campbell. ) phyte, which begins with the fertilized egg. Sporophyte. 558. 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 toot, and which ™ hata "= FERNS. 269 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. 312, 313. 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. 311. 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. 314. 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 315. 559. 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 270 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 photosynthesis. 560. 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. 312. Young embryo of fern (Adiantum concinnum) in enlarged venter of the archegonium. SS, © stem; J, first leaf or cotyledon; F, 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. 561. 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. 71 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 szze, complexity, and permanency of this phase of the plant. 562. 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 .cw exceptions). It is also much smaller than most of the liverworts and Cis Fig. 313. Embryo of fern (Adiantum concinnum) still surrounded by the archegonium, which has grown in size, forming the “‘ calyptra.’”? ZL, 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. 272 MORPHOLOGY. a " » Ki Bans: I “ANN \ : aan i \ \ i \ KN Tee a oe ——- et EE —t5 We eS Zea E; MY MW ry Wass, RNA \\ f) AI Y Ny 4 Aili a Xe oa Fig. 314. Young plant of Pteris serrulata still attached to prothallium. Nien, Shr 5 Two embryos from one prothallium of Adiantum cuneatum. CHAPTER XXVIII. DIMORPHISM OF FERNS. 563. In comparing the different members of the leaf series there are often striking illustrations of the transition from one form to another, as we have noted in the case of the trillium flower. This occurs in many other flowers, and in some, as in the water lily, these transformations are always present, here showing a transition from the petals to the stamens. In the bud scales of many plants, as in the butternut, walnut, currant, etc., there are striking gradations between the form of the simple bud scales and the form of the leaf. Some of the most interesting of these transformations are found in the dimorphic ferns. 564. Dimorphism in the leaves of ferns.—In the common polypody fern, the maidenhair, and in many other ferns, all the leaves are of the same form. That is, there is no difference be- tween the fertile leaf and the sterile leaf. On the other hand, in the case of the Christmas fern we have seen that the fertile leaves are slightly different from the sterile leaves, the former having shorter pinnz on the upper half of the leaf. The fertile pinnee are here the shorter ones, and perform but little of the function of carbon conversion. ‘This function is chiefly per- formed by the sterile leaves and by the sterile portions of the fertile leaves. This is a short step toward the division of labor between the two kinds of leaves, one performing chiefly the labor of carbon conversion, the other chiefly the labor of bearing the fruit. 565. The sensitive fern.—This division of labor is carried to an extreme extent in the case of some ferns. Some of our native 273 274A. MORPHOLOGY. ferns are examples of this interesting relation between the leaves like the common sensitive fern (Onoclea sensibilis) and the ostrich fern (O. struthiopteris) and the cinnamon fern (Osmunda cinnamomea). The sensitive fern is here shown in fig. 316. The sterile leaves are large, broadly expanded, and pinnate, the Fig. 316. Sensitive fern ; normal condition of vegetative leaves and sporophylls. pinne being quite large. The fertile leaves are shown also in the figure, and at first one would not take them for leaves at all. But if we examine them carefully we see that the general plan of the leaf is the same: the two rows of pinnze which are here much shorter than in the sterile leaf, and the pinnules, or smaller DIMORPHISM OF FERNS. 278 divisions of the pinne, are inrolled into little spherical masses which lie close on the side of the pinne. If we unroll one of these pinnules we find that there are several fruit dots within protected by this roll. In fact when the spores are mature these Fig. 317- Sensitive fern; one fertile leaf nearly changed to vegetative leaf. pinnules open somewhat, so that the spores may be dissemi- nated. There is very little green color in these fertile leaves, and what green surface there is is very small compared with that of the broad expanse of the sterile leaves. So here there is practi- cally a complete division of labor between these two kinds of 276 MORPHOLOG ¥. leaves, the general plan of which is the same, and we recognize each as being a leaf. 566. Transformation of the fertile leaves of onoclea to sterile ones.—It is not a very rare thing to find plants of the sensitive fern which show intermediate conditions of the sterile and the fertile leaf. A number of years ago it was thought by some that this represented a different species, but now it is known Fig. 318. Sensitive fern, showing one vegetative leaf and two sporophylls completely transformed. that these intermediate forms are partly transformed fertile leaves. It is a very easy matter in the case of the sensitive fern to pro- duce these transformations by experiment. If one in the spring, when the sterile leaves attain a height of 12 to 16 cm (8—-I0 inches), cuts them away, and again when they have a second time reached the same height, some of the fruiting leaves which develop later will be transformed. A few years ago I cut off the DIMORPHISM OF FERNS. 277 sterile leaves from quite a large patch of the sensitive fern, once in May, and again in June. In July, when the fertile leaves were appearing above the ground, many of them were changed partly or completely into sterile leaves. In all some thirty plants Fig. 310. Normal and transformed sporophyll of sensitive fern. showed these transformations, so that every conceivable gradation was obtained between the two kinds of leaves. 567. It is quite interesting to note the form of these changed leaves carefully, to see how this change has affected the pinnz and the sporangia. We note that the tip of the leaf as well as the tips of ali the pinnze are more expanded than the basal por- 278 MORPHOLOGY. tions of the same. This is due to the fact that the tip of the leaf develops later than the basal portions. At the time the stimulus to the change in the development of the fertile leaves reached them they were partly formed, that is the basal parts of the fertile leaves were more or less developed and fixed and could not change. ‘Those portions of the leaf, however, which were not yet completely formed, under this stimulus, or through correlation of growth, are incited to vegetative growth, and ex- pand more or less completely into vegetative leaves. 568. The sporangia decrease as the fertile leaf expands.— If we now examine the sporangia on the successive pinne of a partly transformed leaf we find that in case the lower pinne are not changed at all, the sporangia are normal. But as we pass to the pinnze which show increasing changes, that is those which are more and more expanded, we see that the number of sporangia decrease, and many of them are sterile, that is they bear no spores. Farther up there are only rudiments of sporangia, until on the more expanded pinnz sporangia are no longer formed, but one may still see traces of the indusium. On some of the changed leaves the only evidences that the leaf began once to form a fertile leaf are the traces of these indusia. In some of these cases the transformed leaf was even larger than the sterile leaf. 569. The ostrich fern.—Similar changes were also produced in the case of the ostrich fern, and in fig. 319 is shown at the left a normal fertile leaf, then one partly changed, and at the right one completely transformed. 570. Dimorphism in tropical ferns.—Very interesting forms of dimorphism are seen in some of the tropical ferns. One of these is often seen growing in plant conservatories, and is known as the staghorn fern (Platycerium alcicorne). ‘This in nature grows attached to the trunks of quite large trees at considerable elevations on the tree, sometimes surrounding the tree with a massive growth. One kind of leaf, which may be either fertile or sterile, is narrow, and branched in a peculiar manner, so that it resembles somewhat the branching of the horn of a stag. DIMORPHISM OF FERNS, 279 Below these are other leaves which are different in form and sterile. These leaves are broad and hug closely around the roots and bases of the other leaves. Here they serve to catch and Fig. 320. Ostrich fern, showing one normal sporophyll, one partly transformed, and one completely transformed. retain moisture, and they also catch leaves and other vegetable matter which falls from the trees. In this position the leaves decay and then serve as food for the fern. CHAPTER SOx xXe HORSETAILS: 571. 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. 325. 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. 5072. The field equisetum. Fertile shoots.—Fig. 321 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- Bee ee . fertile plant of nodes carefully we note that there are thin mem-pogeqae oe branous scales, more or less triangular in outline, and Mer eS connected at their bases into a ring around the stem. inne we 280 HORSETAILS. 281 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. 573. Sporangia.—The end of this fertile shoot we see pos- sesses a cylindrical to conic enlargement. ‘This is the fertile 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. 322. We see here that the angular area is a Fig.322, disk-shaped body, with a stalk attached to its inner Pee oueoro” surface, and with several long sacs projecting from phyll of equisetum {eide view) =o“ its inner face parallel with the stalk and surrounding ing sporangia on a 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 sforophyl/, and thus belongs to the leaf series. These sporophylls are borne in close whorls on the axis. 574. Spores.—When the spores are ripe the tissue of the sporangium becomes dry, and it cracks open and the spores fall Guteliewe look at fig. 323 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. 575. Sterile shoot of the common horsetail.—When the spores are ripe they are soon scattered, and then the fertile shoot dies dowm Soon afterward, or even while some of the fertile shoots are still in good condition, sterile shoots of the 282 MORPHOLOGY. plant begin to appear above the ground. One of these is shown in fig. 325. ‘This has a much more slender stem and is pro- Fig. 323. 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 photosynthesis. ‘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. 576. 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 =a@ called because it was once used for polishing purposes. This plant lke Fig. 325- ; Sterile plant of horsetail (Equi- all.the speciessof ahe thorsetails has) Geasaa ss) eae (Equi HORSETAILS. 283 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. 577. 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. CEUAPAMEIRS” XOX: CLUB MOSSES: 578. What are called the ‘‘ club mosses’’ make up another group of interesting plants which rank as allies of the ferns. general habit of They are not of course true mosses, but the 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. 579. The clavate lycopodium.—Here is one of the club mosses (fig. 326) 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 atrangement 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 nearly leafless, the leaves being reduced to mere scales. The end of this leafless branch Fig. 326. Lycopodium clava- tum, branch bearing two fruiting spikes; at right sporophyll with open sporangium; single then terminates in one or several cylindrical sPore 7ear +t. heads which form the club. 284 CLUB MOSSES. 285 580. Fruiting spike of Lycopodium clavatum.—This club is the fruiting spike or head (sometimes termed a s/rodilus). 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. 325. When we consider the number of spore-cases in one of these club- shaped fruit bodies we see that the number of spores developed in a large plant is immense. In mass the spores make a very fine, WW. soft powder, which is used for some mae kinds of pyrotechnic material, and for Wr ve various toilet purposes. 581. Lycopodium lucidulum.—Another com- mon species is figured at 327. This is Lycopo- dium lucidulum. The habit of the plant is quite different. It grows in damp ravines, woods, and moors. The older parts of the stem are prostrate, 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 spore-cases occupy certain regions of = the stem, as shown at 327. Ina 4 eS SIN S Sy Be J ee ¢ yy (7 WARN AAS single season one region of the stem :| may bear spore-cases, and then a sterile portion of the same stem is Fig. 327. Lycopodium lucidulum, bulbils in axils of leaves near the top, sporangia in axils of leaves series of spore-cases higher up. below them. At right is a bulbil enlarged. < 4 : 582. Bulbils on Lycopodium lucidulum.—There is one curious way in which this club moss multiplies. developed, which later bears another 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 286 MORPHOLOGY. 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. 583. 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). 584. 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. 328. Fig. 320. Fig. 330. Fig. 331. 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. 328 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. LILLE CLOB MOSSES. 237 585. 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 muzcro- spores are borne in the smaller spore-cases and the macrospores iine larger ones. Figures 329-331 give the details. There are many microspores in a single small spore-case, but 3-4 ma- crospores in a large spore-case. 586. 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. 332. Here we see that Fig. 332. Details of microspore and male prothallium of selagineila; 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 prothalha. In fact a male prothallium of selaginella is nearly all antheridium, so reduced has the gametophyte become here. 587. 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 near the wall of the spore and at the 288 MORPHOLOG VY. 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. 334. The archegonia are developed in this exposed surface, and several can be seen in the illustration. 588, Embyro.—After fertilization the egg divides in such a way that along cell called a suspensor is cut off from the upper side, Ms i 2 Ae agi ae Fig. 333. : Section of mature macrospore Mature female prothallium of Fig. 335+ 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. Isoetes, mature plant, sporophyte stage. CHAPTER XXXI. QUILLWORTS (ISOETES). 589. 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. 336 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. 338 is from a longitudinal sec- tion of a quillwort. It shows the form of the leaves from this view (side view), and also the general outline of the short stem, which is triangular, The stem is therefore a very short object. 289 290 MORPHOLOGY. 590. 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. 337. In the inner surface of the expanded base we note a circular depression which seems to be of a different text- Fig. 337. Fig. 338. 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. (lIsoetes 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. 591. 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- QUILLWORTS. 291 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. 592. 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). 593. Male prothallia.—In 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. 594. 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. 595. Embryo.—The embryo lies well immersed in the tissue of the pro- thallium, though there is no suspensor developed as in selaginella. CHAP TER Deed: COMPARISON OF FERNS AND THEIR RELAY ES: 596. 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 in a 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. 597. 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 liverworts 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. 598. 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- 292 COMPARISON OF FERNS. 293 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 pleridophyla. The living forms of the pteridophyta are classified as fol- lows into families or orders. (See page 295.) MORPHOLOGY. 294 *PISURL -odso1s1ur 1e9q souo joddn ‘eisur1odso10 sorodsorseyy | ~°° °° **** ure}|-eUT 1vaq Soo 1OMO'T -u0d souo asivy|‘eyxids e@ UL Wa}s JO *so10dsos01 Jy |*** *Ule}U0D sauUO|/pus oy} uo pednois [[eus spury omy|soAvoy Zutreeq-e10ds jo verisueiodg |‘jyeo, ‘ula}s “oO “e1suel0dso1OIUl souo Jauut ‘ersueiods -o1ovur 1eeq AT[ensn ‘ ulvy/SeAvI_ JoyNO +: aSeq -U0d soud aSieT |}e SOIARD UI eIsUeL “--uleyu0s sauo|-ods ivaq sSoAva'T [VWs ‘spurz,omy|y104S IAA UI}5 jo wrduriodg |‘yeoy “was ‘00x sorodso1seyyy | sss ttt oe *so10dsox9t yA ‘sor0ds e + ee eeeere SUIE} -uw09 wintsuR10ds ‘puUIy 9UO FO Itv ‘sj(Aydosods uo eisguer1ods *yea] ‘uI93}s “OOXy *sorods |** *suleju09 ints -uvi0ds ‘puly 0 (e) jo IV Jeo] uo eisuei0ds ‘yeay ‘u1ays “100% ‘LUV ; ONILINYN J LUVd FAILVLAOAA ‘A LAHAOL (-je1uuesed Ayjyens() -ANV5) 10 |Apiey o10ur pue ‘so yuspusdoepuy ONINNIONG |yuejd ay} jo yred ysad1eT) ‘ayAydoyoures aya ‘ueyy ‘ALAHdOUXOdS 234 do1ods uo juapuedep| ‘umrsuesods ut [Ns *339| ‘sprozoyeutieds'pue wmrsueriods ap1ym [20 priasyjue UWA YORI “UINI[|YPAUMIPMSYyJUW UL T[YS IIYM pa/pue “T7a0 yeypeyzosd (-queyd eyjoid = ayeures|"[[9o «- [eypeyio1d|-dojaasq — ay eur|[eus 0jut podoyjaaeq v[[autseyas ‘SSoTIOJOD [BAO | 2] SUIS ULY} Jas1[|-9j ‘souv adie] |'apeur ‘souo {[eUISg oyut sdols? xode ul ‘eluos|yonu ‘unipri ‘Spuly OM], ‘Moz -jaAaq) ‘38a/PT9t® MOT 1FeqiUe E4Q ing 10 ‘sproziyx ou ‘rem e1ods jo opis|‘-wITaN pezyuie 7 “elTyeyyOAd JussNTFIp UO -UI S[[99 JO sseuI papunor ‘ssa]10[05 - -IDW1ES syaydorods) | ‘Splozojzeur| uo01y o10dsor9eWM) ‘wnTsuRiods ut [[Ys ‘$39 |-10ds YIM WIMIpIA| UT pato}s yUoUTLy|aTTYM [Jeo prieyyUR YUM yoes “unit|-ayyaW ‘T[99|-nuU uto1y pedo/pue ‘199 eyreyzoad -jeyjoid §ayeuros [er[pey}o1d s[suts|-jaasq ‘aT eulay||;euIs 0jur podojaaaq (ued saye PaPaEse]03 Pens ay} URY} AVs1e[|‘souo aS1e yz frayeu ‘souo [Jews EOsTONUMSE @] Horo ent (EMU O-s Ep Ma IES prs "SpUIy OM], ‘May ynq JO ‘spr1oz BOAO sp oe eee ee ee ES eS OS rou ATensd aon sredaeto ses pezipu.8 4 Bly[eyjoad yussezFIp uC, ‘s]]29 JO sseul pepunor ‘ssajiojod || ‘SaLHOsy ‘380 UC Y}IM *splozo}eul yoes ‘erjjey}o1d|-1ods yim ‘eryyeuy (-queyd umjas |P1PUOy Josie] uo|-o1d oreur [[euIs -nbaoyut sdo| 24 Ose2yo1y |uo ‘eiproyjuy -JeAeq]) “339 “ely]eyyoid jue *“SPIOZIYI YIM “YWMOIs pezi[ 49,7 -loyfip WO spuly OM} ay} AT[eNS~Q) |peqo, ‘pepuedxe ‘uy, ‘useis vy ‘WOALHSINOE (ued ‘339 YjIM yore| ‘sp1ozozeurs1eds uxaz ojut sdo ‘eIUOSIYIIV [YPM eIplioyuYy (‘zoovrp -[eAIq) *330 “wintIT]eyyo1d *Sploziya YIM “YZMOIs podeys -od4jog) peziisea jeuies oy} UO spuly Yjoq Ajjensq |-yzvay ‘popuedxe ‘uly ‘uses *“SNUA “aLAHd -O%OdS 40 ‘SNVDUQ TVAXaS ‘LUV FAILVLAOT A ONINNIDE : (91Aydo.10ds ay} uo yuspuedep Sutur0seq saja0st i jueld Wey OULipue evyjaursejes uy ‘juspuadaput Aysour ‘“sa[jeuis Burwi0.0g) “| LAHAOLANVS ‘SSHLAHdAOGIYALd AHL NI ALAHdOWOdS AUNV YULAHdOLYNVD HO NOLLVTHY ONIMOHS ATAVL ‘669 / FERNS: CLASSIFICA TION. 295 Classification of the Pteridophytes. Of the living pteridophytes four classes may be recognized. CLASS FILICINEZ.* This class includes the ferns. Four orders may be recognized. 600. Order Ophioglossales. (One Family, Ophioglossacez).—This order includes the grapeferns (Botrychium), so called because of the large botryoid cluster of sporangia, resembling roughly a cluster of grapes; and the adder-tongue (Ophioglossum), the sporangia being embedded in a long tongue-like outgrowth from the green leaf. Botrychium and Ophioglos- sum are widely distributed. The roots are fleshy, nearly destitute of roct hairs, and contain an endophytic fungus, so that the roots are mycorhiza. The gametophyte is subterranean, and devoid of chlorophyll. In Botry- chium virginianum, an endophytic fungus has been found in the prothal- lium. Another genus (Helminthostachys) with one species is limited to the East Indies. 601. Order Marattiales (One Family, Marattiacee).—These are trop- ical ferns, with only four or five living genera (Marattia, Danza, etc.). They resemble the typical ferns, but the sporangia are usually united, sev- eral forming a compound sporangium, or synangium. The Ophioglossales and Marattiales are known as eusporangiate ferns, while the following order includes the leptosporangiate ferns. 602. Order Filicales.—This order includes the typical ferns. Fight families are recognized. Family Osmundacee.—Three genera are known in this family. Os- munda has a number of species, three of which are found in the Eastern United States; the cinnamon-fern (O. cinnamomea), the royal fern (O. regalis), and Clayton’s fern (O. claytoniana). No species of this family are found on the Pacific coast. Family Gleicheniacee.—These ferns are found chiefly in the tropics, and in the mountain regions of the temperate zones of South America. There are two genera, Gleichenia containing all but one of the known species. Family Matoniacee.— One genus, Matonia, in the Malayan region. Family Schizeacee.—These are chiefly tropical, but two species are found in eastern North America, Schizza pusilla and Lygodium palma- tum, the latter a climbing fern. Family Hymenophyllacee.—These are known as the filmy ferns because of their thin, delicate leaves. They grow only in damp or wet regions, mostly in the tropics, but a few species occur in the southern United States. Family Cyatheacee.—These are known as the tree-ferns, because of the ** As class Filicales in Engler and Prantl. 296 MORPHOLOG Y. large size which many of them attain. They occur chiefly in tropical moun- tainous regions, many of them palm-like and imposing because of the large trunks and leaves. Dicksonia, Cyathea, Cibotium, Alsophila, are some of the most conspicuous genera. . Family Parkeriacee.—There is a single species in this family (Cera- topteris thalictroides), abundant in the tropics and extending into Florida. It is aquatic. Family Polypodiacee.—This family includes the larger number of living ferns and many genera and species are found in North America. Exam- ples, Polypodium, Pteridium (= Pteris), Adiantum, etc. 603. Order Hydropterales (or Salviniales).—The members of this order are peculiar, aquatic ferns, some floating on the water (Azolla, Salvinia), while others are anchored to the soil by roots (Marsilia, Pilularia). They are known as water ferns. ‘The sporangia are of two kinds, one containing ~-large spores (macrospores) and the other small spores (microspores). They are therefore heterosporous ferns. Family Salviniacee.—There are two genera, Salvinia and Azolla. Family Marsiliacee.—Two genera, Marsilia and Pilularia. In this family the sporangia are enclosed in a sporocarp, which forms a pod-like structure. CLASS EQUISETINEZ.* 604. Order Equisetales.—The single order contains a single family, Equisetacee, among the living forms, and but a single genus, Equisetum. There are about twenty-four species, with fourteen in the United States (see Chapter XXIX). CLASS LYCOPODIINEZA.; - 605. Order Lycopodiales.—The first two families of this order include the homosporous Lycopodiinez, while the Selaginellacez are heterosporous. Family Lycopodiacee.—There are two genera. Lycopodium (club moss) includes many species, most of them tropical, but a number in tem- perate and subarctic regions. ‘The gametophyte of many species is tuber- ous, lacks chlorophyll, and in some there lives an endophytic fungus. Phy]l- loglossum with one species is found in Australia. Family Psilotacee.—There are two genera. Psilotum chiefly in the tropics has one species (P. triquetrum) in the region of Florida. Family Selaginellacee.—These include the little club mosses, with one genus, Selaginella (see Chapter XXX). ' CLASS ISOETINEZ. 606. Order Isoetales, with one family Isoetaceee and one genus Isoetes (see Chapter XXXI). There are about fifty species, with about sixteen in the United States. * As class Equisetales in Engler and Prantl. } As class Lycopodiales in Engler and Prantl. CHAPTER XXXIII. GYM MOS:-PERMS. The white pine. 607. 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 straight 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 tothe tree. In oldand dense forests the lower branches, because of lack of sunlight, have died away, leaving tall, bare trunks for a considerable height. 608. 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. 609. 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 leaves, which remain on the tree for several years. At the base of the green 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, 20] 298 MORPHOLOGY. 610. 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. ; 611. Male cones, or male flowers.— The male cones are borne in clusters as shown in fig. 339. Each compact, nearly cylindri- Fig. 330. 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 1 in place of a long lateral branch, One of these cones is shown q GYVUNOSPERMS: WHITE PINE. 299 considerably enlarged in fig. 340. 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. 341. 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. 340. Fig. 341. Fig. 342. 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 tneir 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. 342, and the spores are set free. ) 612. Microspores of the pine, or pollen grains.—A mature pollen grain of the pine is Fig. 343- : . F : Pollen grain of shown in fig. 343. It is a queer-looking object, white pine. : i i possessing on two sides an air sac, formed by the upheaval of the outer coat of the spore at these two points. 300 MORPHOLOG ¥. 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 of male cones, is jarred by the hand, or by currents of air, the spht suddenly opens, and a cloud of pollen bursts out from the numer- ous anther locules. The pollen is thus borne on the wind and some of i Hl it falls on the Wa female flowers. WY, = Fig. 344. White pine, branch with cluster uf mature cones shedding the seed. A few young cones four months old are shown on branch at the left. Drawn from photograph. 613. Form of the ma- ture female cone.—A ai ve Hy : N Op , a 1 q “p) EAN SSS c Fig. 345. ; i), SUN & cluster of the white- Mature cone of white pine WA S48 LOSs ; 7 at time of scattering of the y \ SS = Pine Cone shown in seed, nearly natural size. We) A RY fig 344 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- GYMNOSPERMS: WHITE PINE. 301 line of the cone is lanceolate, or long oval, and somewhat curved. It measures about 10o-15cm long. If we remove one Fig. 346. Pig. 347- Fig. 348. Fig. 340. Fig. 350. 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. 346-350.—White pine showing details of mature scales and seed. of the scales, just as they are beginning to spread, or before the o 3 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 like a knife blade. On the back of the scale is a small appendage known as the cover scale. 614. 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 shoot of a branch, or of the Fig. 351. lateral shoots ina whorl. After growth has proceeded 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 302 MORPTOLOGW= flower. These young female cones, at about the time that the pollen is escaping from the anthers, are long ovate, measuring about 6-107 long. They stand upright as shown in fig. 351. 615. 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 stout ‘‘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. 354, 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. ) 616. Ovules, or macrosporangia, of the pine.—At each of the lower angles of the Fig. 353- Fig. 354. Section of female cone Scale of white pine with the Scale of 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 GYMNOSPERMS: WHITE PINE. 303 mature cones. In fact the wall of the ovule forms the outer coat of the seed, as we will later see. 617. 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, ey £26 apres : if Wy some of it is wafted by the wind to the ee 7 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 At lower end of the ovule. 4 Fig. 355. 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 304 MORPHOLOG Y. end of the ovule. ‘This depression is thus known as the pollen chamber. 618. Now the open scales on the young female cone close up again so tightly that water from rains is excluded. 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, ow now turn so that they hang downward. ie oe a This more certainly excludes the rains, Pa 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. 619. The female cone now slowly grows during the summer and autumn, Fig. 356. increasing but little in size during this (oviyn Ge ee eee time. During the winter it rests, that Doe he bene ospore? 2 is, ceases to grow. With the coming of grain; @m aule jor pee spring, growth commences again and cee at an accelerated rate. The increase in size is more rapid. The cone reaches maturity in September. We thus see that nearly eighteen months elapse from the begin- ning of the female flower to the maturity of the cone, and about fifteen months from the time that pollination takes place. fay <7 ES Er 620. Female prothallium of the pine.—To study this we must make care- ful longitudinal sections through the ovule (better made with the aid of a microtome). Such a section is shown in fig. 358. The outer layer of tis- sue, which at the upper end (point where the scale is attached to the axis of the cone) stands free, is the ovular coat, or integument. Within this integu- ment, near the upper end, there is a cone-shaped mass of tissue. ‘This mass of tissue is the nucellus, or the macrosporangium proper. In the lower part of the nucellus in fig. 356 can be seen a rounded mass of “‘spongy tissue ”’ (spt), which is a special nourishing tissue of the nucellus, or spo- rangium, around the macrospore. Within this can be seen an axile row of three cells (aw: m). The lowest one, which is larger than the other two, is the macrospore. Sometimes there are four of these cells in the axile row. ‘This axile row of three or four cells is formed by the two successive GYMNOSPERMS : WHITE PINE. 305 divisions of a mother cell in the nucellus. So it would appear that these three or four cells are all spores. Only one of them, however, the lower one, develops; the ° ° 2 Bi ierk others are disorganized and 7" pkzSGe disappear. the macrospore now divides several times to form several free nuclei in the now enlarg- ing cavity, much as the nu- cleus of the macrospore in Selaginella and Isoetes divides . ing. The nucleus of Wks Fig. 357- Pollen grains of pine. One of them germinat- piand p2, the two disintegrated pvrothallial within the spore. The de- cells,= sterile part of male gametophyte; a.c., Ue a ie 1 central cell of antheridium; v.n., vegetative nu- velopment thus far takes place cleus or tube nucleus of the single-wall cell of during the first summer, and antheridium; s.g.,starch grains. (After Ferguson.) now with the approach of winter the very young female prothallium goes wv oy fe C cq) yO: arn = ecg Ur pease P18 Q ‘@ Fig. 358. Section of ovule of white pine. nt, in- tegument, pc, pollen chamber; ??, pollen tube: 2, nucleus; m, macrospore cavity. into rest about the stage shown in fig. 358. The conical portion of the nucellus which lies above is the nucellar cap. 621. Male prothallia.—By the time the pollen is mature the male prothallium is already partly formed. In fig. 343 we can see two well-formed cells. Two other cells are formed earlier, but they become so flattened that it is diffi- cult to make them out when the pollen grain is mature. These are shown in fig. 357, p! and p”, and they are the only sterile cells of the male prothallium in the pines. The large cell is the antheridium wall, its nucleus v.7. in fig. 357. The smaller cell, a.c., is the central cell of the antheridium. During the summer and autumn the male prothallium makes some farther growth, but this is slow. The larger cell, called the vegetative cell or tube cell, which is in reality the wall of the antheridium, elon- 306 MORPHOLOG VY. gates by the formation of a tube, forming a sac, known as the pollen tube. It is either simple or branched. It grows down into the tissue of the nu- cellus, and at a stage represented in fig. 358, winter overtakes it and it rests. At this time the central cell has divided into two cells, and the vegetative nucleus is in the pollen tube. | 622, The endosperm.—In the following spring growth of all these parts J Fig. 350. Section of nucellus and endosperm of white pine. The inner layer of cells of the integument shown just outside of nucellus; arch, archegonium; en, egg nu- cleus. In the nucellar cap are shown three pollen tubes. vn, vegetative nucleus or tube nucleus; sic, stalk cell; spu, sperm nuclei, the larger one in advance is the one which unites with the egg nucleus. The archegonia are in the endosperm or female gametophyte. (After Ferguson.) continues. The nuclei in the macrospore divide to form more, and event- ually cell walls are formed between them making a distinct tissue, known GYMNOSPERMS: WHITE PINE, 307 as the endosperm. ‘This endosperm continues to grow until a large part of the nucellus is consumed for food. _ 623. Female prothallium and archegonia.—The endosperm is the female prothallium. This is very evident from the fact that severa. archegonia are developed in it usually on the side toward the pollen chamber. The archegonia are sexual organs, and since the sexual organs are developed on the gametophyte, therefore, the endosperm is the female gametophyte, or prothallium. In fig. 359 are represented two archegonia in the endosperm and the pollen tubes are growing down through the nucellus. The arche- gonia are quite large, the wall is a sheath or jacket of cells which encloses the very large egg which has a large nucleus in the center. 624. Pollen tube and sperm cells.—While the endosperm (female pro- thallium) and archegonia are developing the pollen tube continues its growth down through the nucellar cap, as shown in fig. 359. At the same time the two cells which were formed in the pollen grain (antheridium) from the central cell move down into the tube. One of these is the “‘generative’’ cell, or ‘“‘body”’ cell, and the other is called the stalk cell, though it is more properly a sterile half of the central cell. The nucleus of the gener- ative cell, about the time the archegonium is mature, divides to form two nuclei, which are the sperm nuclei, and the one in advance is the larger, though it is much smaller than the egg nucleus. 625. Fertilization.—Very soon after the archegonia are mature (early in June in the northern United States) the pollen tube grows through into the archegonium and empties the two sperm nuclei, the vegetative nucleus and the stalk cell, into the proto- ‘plasm of the large egg. The larger of the two sperm nuclei at once comes in contact with the very large egg nucleus and sinks down into a depression of the same, as shown in fig. 361. These two nuclei, in the dj Fig. 360. pines, do not fuse into a resting nucleus, but Last division of the egs in the at once organi Lhe White pine cutting off the ventral See the nuclear figure for the canal cell at the apex of the first division of the embryo. Two nuclei ei Chegoniam: End, endosperm, aed rch, archegonium. are thus formed, and these divide to form 7 four nuclei which sink to the bottom of the archegonium and there organ- a 308 MORPHOLOGY. ize the embryo which pushes its way into the endosperm from which it derives its food (fig. 362). 626. 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 Fig. 361. Archegonium of white pine at stage of fertilization. en, egg nucleus; spn, sperm nucleus in conjugation with it; mb, nutritive bodies in cytoplasm of large egg; cpt, cavity of pollen tube; vm, vegetative nucleus or tube nucleus; sc, stalk cell: spn, second sperm nucleus: pr, portion of prothallium or endosperm; sg, starch grains in pollen tube. The sheath of jacket cells of the archegonium is not shown. (After Ferguson.) entire scale according to this view is a carpel, or sporophyll, which is divided into the cover scale and the ovuliferous scale. This division of the sporo- phyll is considered similar to that which we have in isoetes, where the spo- rophyll has a ligule above the sporangium, or as in ophioglossum, where the leaf is divided into a fertile and a sterile portion. Others believe that the ovuliferous scale is composed of two leaves situ- ated laterally and consolidated representing a shoot in the axis of the bract. There is some support for this in the fact that in certain abnormal cones which show proliferation a short axis appears in the axil of the bract and oe GYMNOSPERMS: WHITE PINE. 309 bears lateral leaves, and in some cases all gradations are present between these lateral leaves on the axis and their consolidation into an ovuliferous scale. In the normal condition of the ovuliferous scale the axis has disap- peared and the shoot is represented only by the consolidated leaves, which would represent then the macrosporophylls (or carpels) each bearing one macrospo- rangium (ovule). One of the most interesting and plausible views is that of Celakovsky. He believes that the axial shoot is reduced to two ovules, that the ovules RI ae gon x 2 m3 ~~ F Fig. 362. Pine seed, sectionof. sc, | Embryoof white Pine seedling just seed coat;”,remainsofnu- pine removed from emerging from the cellus; end, endosperm seed, showing ground. (=female gametophyte); several cotyle- emb, embryo=young spo- dons. rophyte. Seed coat and nucellus=remains of old sporophyte. have two integuments, but the outer integument of each has become pro- liferated into scales which are consolidated. In this proliferation of the outer integument it is thrown off from the ovule so that it only remains attached to one side and the larger part of the ovule is thus left with only one integument. This view is supported by the fact that in gingko, for example (another gymnosperm), the outer integument (the ‘‘collar’’) sometimes proliferates into a leaf. Ceiakovsky’s view is, therefore, not very different from the second one mentioned above. 310 MORPHOLOGY. ey Ee Ree ih, LLANE Bie By ita Fig. 365. White-pine seedling casting seed coats. CHAPTER XXXIV. BURIRER STUDIES ON GYMNOSPERMS. Cycas. 627. In such gymnosperms as cycas, illustrated in the front- - ispiece, there is a close resemblance to the members of the fern Fig. 366. Macrosporophyll of Cycas revoluta. 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 pinnz near the free end, the entire leaf being covered with woolly hairs. But at the lower end, in place of the pinnz, we see oval bodies. These are the macrosporangia (ovules) of cycas, and correspond to the macrosporangia of selaginella, and the leaf is the macrosporophyll. 628. Female prothallium of cycas.—In figs. 367, 368, are shown mature ovules, or macrosporangia, of cycas. In 368, which is a roentgen-ray photograph of 367, the oval prothallium can be seen. So in cycas, as in selaginella, the female prothallium is 311 Bue MORPHOLOGY. vs developed entirely inside of the macrosporangium, and derives the nutriment for its growth from the cycas plant, which is the Fig. 367. Fig. 368. Macrosporangium of Cycas revoluta. Roentgen photograph of same, show- sporophyte. Archegonia are cells. This aids us in deter- mining that it is the prothal- lium. In cycas it is also called endosperm, just as in the pines. 629. 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. 630. Microspores, or pollen, of eycas.—The cycas plant illustrated in the frontispiece is a female plant. Male plants also exist which have small leaves in the center that bear ing female prothallium. developed in this internal mass of OFb00 Ch 6” DOO O59 b ote? O- Or Q 0 COR ve ee OU) coRty.ce hig. 360. A sporophyll (stamen) of cycas; sporangia in groups on theunder side. 4, group of sporangia ; ¢,open sporangia. (From Warming.) FURTHER STUDIES ON GYMNOSPERMS. 313 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. 369, the microspo- / i) rangia are borne in groups of three or four, and these a! contain the microspores, or pollen grains. The ar- 7x rangement of these microsporangia on the under side of the cycas leaves bears a strong resemblance to the A arrangement of the sporangia on the under side of the leaves of some ferns. 631. The gingko tree is another very interesting plant = be'onging to this same group. Ze \ j It is a relic of a genus which d \ L] — eI Zamia inte- grifolia, show- ing thick stem, fern-like leaves, and cone of male flowers. Fig. 370. 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. 632. 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 oe /, SN tg. A Wy Wy oN MY Te ait ay D7 Ze group, there is stronger evidence of such ances- try in the fact that a pro- thallium can well be de- Fig. 371. Two spermatozoids 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. 633. Spermatozoids in some gymnosperms.—But within the past two years it has been discovered in gingko, cycas, and zamia, all belonging to this 314 MORPHOLOGY. 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 nucel- lus, and has reached a depression at the end of the prothallium (endosperm) where the arche- gonia 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 spermato- zoids were first discovered by Ikeno and Hirase in Japan, and later in zamia by Webber in this country. In figs. 371-374 the details of the male prothallia and of fertilization are shown. 634. The sporophyte in the gymnosperms. — In the pollen grains of the gymnosperms we - easily recognize the characters belonging to the BP er cycas, SPOTes in the ferns and their allies, as well as in small spermatozoid fusing the liverworts and mosses. They belong to the with the larger female nu- : cleus of the egg. The egg same series of organs, are borne on the same Oe ees te phase or generation of the plant, and are practi- Hirase and Ikeno.) cally formed in the same general way, the 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 fer- tilized 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, as well as the gingko, cycas, Fig. 373. NY \' yew, hemlock-spruce, black spruce, the giant Sore eenteted Ce redwood of California, etc., are sporophytes. ae see (After Ikeno and irase. 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 de- veloped within sporangium (nuccllus) to form the female prothallium (en- dosperm). 635. 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 fe- inale prothallium is developed within the macrospore, and even in Selaginella begins, and nearly completes, its development while still in the sporangium. HORAHER STUDIES ON GYMNOSPERMS. 315 In comparing the female prothallium of the gymnosperms with that of the fern group we see a remarkable change has taken place. The female pro- thalltam 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 Fig. 374. necessitated a _ special Gingko biloba. A, mature pollen grain; Perens adaptation of the male pollen grain, the branched tube entering among the cells : . of the nucellus; 4x, exine (outer wall of spore); 7, pro- prothallium in order that thallial cell; Pa; antheridial cell (divides later to form stalk the sperm cells may reach cell and generative cell); 73, vegetative cell; Va, vacuoles; eae Ne, nucellus. (After drawings by Hirase and Ikeno.) and fertilize the egg cell. Fig. 375. Gingko biloba, diagrammatic representation of the relation of pollen tube to the arche- gonium in the end of the nucellus. 7, pollen tube; 0, archegonium. (After drawing by Hirase and Jkeno.) 636. 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 316 MORPHOLOG Y. 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. 637. Classification of gymno- sperms.—The gingko tree has until recently been placed with : the pines, yew, etc., in the order Fig. 376. Fig. 377. - Pinales, but the discovery of Spermatozyiis of || Spermatozoid of za~ the spermatozoids in the pollen zami.i in pollen tube; mia showing spiral pg, pollen grain; a, a, row of cilia. (After tube suggests that it is not spermatozoids. (After Webber. ) Webber.) closely allied with the Pinales, and that it represents an order coordinate with them. Engler arranges the living gymnosperms somewhat as follows: Class Gymnosperme. Order 1. Cycadales; family Cycadaceze. Cycas, Zamia, etc. Order 2. Gingkoales; family Gingkoaceze. Gingko. Order 3. Pinales (or Conifers); family 1. Taxacee. Taxus, the common yew in the eastern United States, and Torreya, in the western United States, are examples. family 2. Pinaceze. Sequoia (redwood of California), firs, spruces, pines, cedars, cypress, etc. Order 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. ol7 FURTHER STUDIES ON GYMNOSPERMS. 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MORPHOLOGY OF THE .ANGIOSPERMS:) TRIREIORE DENTARIA. Trillium. 639. General appearance.—As one of the plants to illustrate this group we may take the wake-robin, as it is sometimes called, or trillum. There are several species of this genus in the United States; the commonest one in the eastern part is the ‘‘ white wake-robin ’’ (Trillium grandiflorum). This occurs in or near the woods. A picture of the plant is shown in fig. 378. There is a thick, fleshy, underground stem, or rhizome as it is usually called. This rhizome is perennial, and is marked by ridges and scars. ‘The roots are quite stout and possess coarse wrinkles. From the growing end of the rhizome each year the leafy, flowering stem arises. This is 20—30cm (8—12 inches) in height. Near the upper end is a whorl of three ovate leaves, and from the center of this rosette rises the flower stalk, bearing the flower at its summit. 640. Parts of the flower. Calyx.—Now if we examine the flower we see that there are several leaf-like structures. These are arranged also in threes just as are the leaves. First there is a whorl of three, pointed, lanceolate, green, leaf-like members, which make up the calyx in the higher plants, and the parts of the calyx are sepals, that is, each leaf-like member is a sepal. But while the sepals are part of the flower, so called, we easily recognize them as belonging to the /ea/ serves. 318 ANGIOSPERMS: TRILLIUM. 319 641. Corolla.—Next above the calyx is a whorl of white or pinkish members, in are also leaf-like in form, being usually somewhat make up what is the and each member of the they are parts of the their form and_ posi- also belong to the leaf 642. Andrecium. — tion of the corolla is of members which do not form. They are known As seen in fig. 379 each ament), and extending greater part of the length side. This part of the ridges form the anther Soon after the flower is ther sacs open also by a along the edge of the time we see quantities of \ SND Fig. 378. Trillium grandiflorum, which and broader than the sepals, broader at the free end. These corolla in the higher plants, corolla is a fef/al. But while flower, and are not green, tion would suggest that they series. Within and above the inser- found another tier, or whorl, at first sight resemble leaves in in the higher plants as s/amens. stamen possesses a stalk (= fil- along on either side for the are four ridges, two on each stamen is the anther, and the sacs, or lobes. Ca opened, these an- WR SS split in the wall ridge. At this yellowish powder or dust escaping from the Trillium grandiforum. ruptured anther locules. If we place some of this under the microscope we see 220 MORPHOLOG ¥. that it is made up of minute bodies which resemble spores; they are rounded in form, and the outer wall is spiny. Theyare in fact spores, the microspores of the trillium, and here, as in the gymnosperms, are better known as pollen. Big. S70 eRe . a oa Se Sepal, petal, stamen, and pisnl of TrlRam . 648. The stamen a sporo- phyll.—Since these pollen grains are the spores, we would infer, from what we have learned of the ferns and gym- nesperms, that this member of the flower which bears them is a sporophyll ; and this is the case. It is in fact what is called the microsporephvll, Then we see also that the anther sacs, since they enclose the spores, would Fig. 380. be the sporangia (microsporangia). From this Trilham gan- Qhoram, with the compound piwal expanded ito three leaf. Kke members. At the neh ~< these three are shown in Getail. it is Now quite clear that the stamens belong also to the leaf series. They are just Six in number, twice the number found in a whorl of leaves, or sepals, or corolla. It is believed, therefore, that there are two whorls of stamens in the flower of tollium. 644. Gynecium.—Next above the stamens and at the center of the flower is a stout, angular, ovate body which terminates in three long, slender, curved points. This is the pistil, and at ANGTOSPLR MS ¢ alii LL LOM, 321 present the only suggestion which it gives of belonging to the leaf series is the fact that the end is divided into three parts, the number of parts in each successive whorl of members of the flower. If we cut across the body of this pistil and examine it with a low power we see that there are three chambers or cavi- ties, and at the junction of each the walls suggest to us that this body may have been formed by the infolding of the margins of three leaf-like members, the places of contact having then become grown together. We see also that from fine imcurved margins of each division of the pistil there stand out in the cavity oval bodies. These are the ovules. Now the ovules we have learned from our study of the gymnosperms are the sporangia (here the macrosporangia). It isnow more evident that this curious body, the pistil, is made up of three leaf-like members which have fused together, each mem- ber being the equivalent of a sporophyll (here the macrosporo- phyll). This must be a fascinating observation, that plants of such widely different groups and of such different grades of complexity should have members formed on the same plan and belonging to the same series of members, devoted to similar functions, and yet carried out with such great modifications that at first we do not see this common meeting ground which a comparative study brings out so clearly. stamen of til. 045. Transformations of the flower of trillium.— eee ce Ie anything more were needed to make it clear that on the margin. the parts of the flower of trillium belong to the leaf series we could obtain evidence from the transformations which Abnormal trilllum. The nine parts of the perianth are green, and the outer whorls of stamens are expanded into petal - like members, ‘Transformed 329 MORPHOLOGY. the flower of trillium sometimes presents. In fig. 381 is a sketch of a flower of trillium, made from a photograph. One set of the stamens has expanded into petal-like organs, with the anther sacs on the margin. In fig. 380 is shown a plant of Trillium grandiflorum in which the pistil has separated into three distinct and expanded leaf-like structures, all green except portions of the margin. Dentaria. 646. General appearance.—For another study we may take a plant which belongs to another division of the higher plants, the common ‘‘ pepper root,’’ or ‘‘toothwort’’ (Dentaria diphylla) as it is sometimes called. This plant occurs in moist woods during the month of May, and is well distributed in the northeastern United States. A plant is shown in fig. 383. It has a creeping underground rhizome, whitish in color, fleshy, and with a few scales. Each spring the annual flower-bearing stem rises from one of the buds of the rhizome, and after the ripening of the seeds, dies down. The leaves are situated a little above the middle point of the stem. They are opposite and the number is two, each one being divided into three dentate lobes, making what is called a compound leaf. 647. Parts of the flower.—The flowers are several, and they are borne on quite long stalks (pedicels) scattered over the ter- minal portion of the stem. We should now examine the parts of the flower beginning with the calyx. This we can see, look- ing at the under side of some of the flowers, possesses four scale- like sepals, which easily fall away after the opening of the flower. They do not resemble leaves so much as the sepals of trillium, but they belong to the leaf series, and there are two pairs in the set of four. The corolla also possesses four petals, which are more expanded than the sepals and are whitish in color. The sta- mens are six in number, one pair lower than the others, and also ANGIOSPERMS: DENTARIA, 322 shorter. The filament is long in proportion to the anther, the latter consisting of two lobes or sacs, instead of four as in trillium. The pistil is composed of two carpels, or leaves fused together. So we find in the case of the pepper root that the parts of the flower are in twos, or multiples of two. Thus they agree in this respect with the leaves; and while we do not see such a strong resem- blance between the parts of the flower here and the leaves, yet from the pres- ence of the pollen Fig. 384. 1 lower ot the toothwort (Dentaria diphylla). Fig 383. Toothwort (Dentaria diphylla). 324 MORPHOLOGY. (microspores) in the anther sacs (microsporangia) and of ovules (macrosporangia) on the margins of each half of the pistil, we are, from our previous studies, able to recognize here that all the members of the flower belong to the leaf series. 648. In trillium and in the pepper root we have seen that the parts of the flower in each apparent whorl are either of the same number as the leaves in a whorl, or some multiple of that num- ber. This is true of a large number of other plants, but it is not true of all. A glance at the spring beauty (Claytonia virginiana, and at the anemone (or Isopyrum biternatum, fig. 563) will serve to show that the number of the different members of the flower may vary. ‘The trillium and the dentaria were selected as being good examples to study first, to make it very clear that the members of the flower are fundamentally leaf structures, or rather that they belong to the same series of members as do the leaves of the plant. 649. Synopsis of members of the sporophyte in angiosperms. Higher plant. eis { Foliage leaves, Sporophyte phase i JOG) ‘ Pp : | Shoot. Stem, | Perianth ees: (or modern phase). Leaf, J Spore-bearing leaves | with sporangia. Flower. (Sporangia sometimes on shoot.) CHAPTER XXXVI. GAMETOPHYTE AND SPOROPHYTE OF ANGIO- SPERMS. 650. Male prothallium of angiosperms.—The first division which takes place in the nucleus of the pollen grain occurs, in Fig. 385. : Nearly mature sion of the nucleus into two nuclei took place ollen grain of tril- és fum. The smaller soon after the formation of the four cells from cell is the genera- cs : tive cell. the mother cell. The nucleus divided in the young pollen grain is shown in fig. the case of trilium and many others of the angio- sperms, before the pollen grain is mature. In the case of some specimens of T. grandiflorum in which the pollen was formed during the month of October of the year before flowering, the divi- 385. After this takes place the wall of the pollen grain becomes stouter, and minute spiny projections are formed. 651. The larger cell is the vegetative cell of the prothallium, while the smaller one, since it later forms the sperm cells, is the generative cell. This generative cell then corresponds to the central cell of the antheridium, and the vegetative cell perhaps corresponds to a wall cell of the antheridium. If this is so, then the male prothallium of angiosperms has become reduced to a very simple antheridium. The farther growth takes place after fertilization. In some plants the generative cell divides into the two sperm cells at the maturity of the pollen grain. In other cases the generative Fig. 386. Germinating spores (pollen grains) of pel- tandra ; generative nucletis in one undi- vided, in other divided to form the two sperm nuclei; vegetative nu- cleus in each near the pollen grain. cell divides in the pollen tube after the germination of the pollen grain. For study of the pollen tube the pollen may be germinated in a weak solution of sugar, or on the cut surface 325 326 MORPHOLOGY. of pear fruit, the latter being kept in a moist chamber to prevent drying the surface. 652. In the spring after flowering the pollen escapes from the anther sacs, and as a result of pollination is brought to rest on the stigma of the pistil. Here it germinates, as we say, that is, it develops a long tube which makes its way down through the style, and in through the micropyle to the embryo sac, where, in accordance with , what takes place in other ¢% plants examined, one of the sperm cells unites with the egg, and fertilization of the egg is the result. 653. Macrospore and embryo sac. three carpels are united into one, two carpels are also united into one Simple pistils are found in many in the ranunculacee, the buttercups, These simple pistils bear a greater —In trillium the and in dentaria the compound pistil. plants, for example columbine, ete. resemblance to a leaf, the margins of which are folded ~ around so that they meet and enclose the ovules or spo- rangia. 654. If we cut across the com- pound pistil of tril- lium we find that the infoldings of the Fig. 387. three pistils meet to Section of pistil of tril- Fig. 388. 2 lium, showing position of Mandrake (Podo- form three partial ovules (macrosporangia). phyllum peltatum). partitions which extend nearly to the center, dividing off three spaces. In these spaces are the ovules which are attached to the infolded margins. If we make cross sections of a pistil of the May-apple (podo- GAUERTOTTEET E AND: SPOROPAYT EF. 327 phyllum) and through the ovules when they are quite young, we shall find that the ovule has a structure like that shown in fig. 380. At.m is a cell much larger than the surrounding ones. This is called the macrospore. The tissue surrounding it is called here the nucellus, but because it contains the macrospore it must be the macrosporangium. ‘The two coats or integuments of the ovule are yet short and have not grown out over the end of the nucellus. This macrospore increases in size, forming first a cavity or sac in the nucellus, the embryo sac. The nucleus divides several 2D> \s S50 SOP eOCOCNe ON SD— Ta eels a) 2 eae s ‘ *; S beset Te S RO eS OTT Se SY LX > bya K la )ejai> Fig. 380. Young ovule (macrosporangium) of podophyllum. x, nucellus containing the one- celled stage of the macrospore; 1.1mt, inner integument; o.imt, outer integument. times until eight are formed, four in the micropylar end of the embryo sac and four in the opposite end. In some plants it has been found that one nucleus from each group of four moves toward the middle of the embryo sac. Here they fuse together to form one nucleus, the endosperm nucleus or definitive nucleus shown in fig. 390. One of the nuclei at the micropylar end is the egg, while the two smaller ones nearer the end are the syner- 328 MORPHOLOG Y. gids. The egg cell is all that remains of the archegonium in this reduced prothallium. The three nuclei at the lower end are the anti podal cells. Fig. 390. Podophyllum peltatum, ovule containing mature embryo sac; two synergids, and eggs at left, endosperm nucleus in center, three antipodal cells at Tight. 655. Embryo sac is the young female prothallium.—In figs. 391-393 are shown the different stages in the development of the embryo sac in lilium. The embryo sac at this stage is the young female prothallium, and the egg is the only remnant of the female sexual organ, the arche- gonium, in this reduced gameto- phyte. 656. Fertilization—When the pollen tube has reached the em- aoe bryo sac (paragraph 652) it opens Macrospore (one-celled stage) of lilium. and the two sperm cells are emptied near the egg. The first sperm nucleus enters the protoplasm surrounding the egg nucleus and uniting with the latter brings about fertilization. The second sperm nucleus often unites with the endosperm nucleus (or with one or both of the “polar nuclei”), bringing about what some call a second fertilization. Where this takes place in addition to the union of the first sperm GAMETOPHYTE AND SPOROPHYTE. 329 nucleus with the egg nucleus it is called double fertilization. The sperm nucleus is usually smaller than the egg nucleus, but often grows to near or quite the size of the egg nucleus before union. See figs. 394 and 395. 657. Fertilization in plants is fundamentally the same as in animals.—In all the great groups of plants as represented by spirogyra, cedogonium, vaucheria, peronospora, ferns, gymno- Fig. 302. _Two- and four-celled stage of embryo-sac of lilium. The middle one shows division of nuclei to form the four-celled stage. (Easter lily.) sperms, and in the angiosperms, fertilization, as we have seen, consists in the fusion of a male nucleus with a female nucleus. Fertilization, then, in plants is identical with that which takes place in animals. 658. Embryo,—After fertilization the egg develops into a short row of cells, the suspensor of the embryo. At the free end the em- bryo develops. In figs. 397 and 398 is a young embryo of trillium. 659. Endosperm, the mature female prothallium.—During the development of the embryo the endosperm nucleus divides 330 MORPHOLOG Y. into a great many nuclei in a mass of protoplasm, and cell walls are formed separating them into cells. This mass of cells is the endosperm, and it surrounds the embryo. It is the mature female prothalhium, belated in its growth in the angiosperms, usually de- veloping only when fertilization takes place, and its use has been assured. 660. Seed.—As the embryo_ Mature embryo sac (young pro- Section through nucellus and upper part of embryo thallium) of lilium. 7, micropylar sac of cotton at time of entrance of pcllentube. &, end; S, synergids; £, egg; Px, egg; 5S, synergids; P, pollen tube with sperm cell in polar nuclei; Azz, antipodals. theend. (Duggar.) (Easter lily.) GAMETOPHVTE AND SPOROPAYTE. 331 is developing it derives its nourishment from the endosperm (or in some cases perhaps from the nucellus). At the same time Fertilization of cotton. /¢, pollen tube; Sz, synergids; £4, egg, with male and female nu- ‘ cleus fusing. (Duggar.) = the integuments increase SNC N in extent and harden as o-4 2 O\\ the seed is “Sumas : i y qs é cee 661" Perisperm. —In “|| SP. iid most plants the nucellus is “ Fe iy : all consumed in the devel- Hii, y . opment of the endosperm, p ZH Wiel ae so that only minute frag- Hs pk ments of disorganized cell A = a " walls remain next the in- RSH ner integument. Insome RS ie ei plants, however, (thewater- Fig. 300. lily family, the pep Pcs Diagrammatic section of ovary and ovule at time ily. 1 of fertilization in angiosperm. /, funicle of uvule; family, etc. ,) Cr portion of mn, nucellus; z, micropyle; 4, antipodal cells of the nucellus remains in- ¢™bryo sac; e, endosperm nucleus; 4, egg cell and synergids ; az, outer integument of ovule; 77, inner fact im the mature seed. ‘pemtpent. The track of the poem tbe is shove In such seeds the remain- ™¢ropylar end of the embryo sac. ing portion of the nucellus is the perzsperm. 662. Presence or absence of endosperm in the seed.—In many of the angiosperms all of the endosperm is consumed by the embryo during its growth in the formation of the seed. This is the case in the rose family, crucifers, composites, willows, oaks, legumes, etc., as in the acorn, the bean, pea and others. In some, as in the bean, a large part of the nutrient substance pass- 332 MORPHOLOGY. ing from the endosperm into the embryo is stored in the cotyle- dons for use during germination. In other plants the endosperm Fig. 307. Fig. 398. Section of one end of ovule of trillium, showing Embryo en- young embryo in endosperm. larged. is not all consumed by the time the seedis mature. Examples of this kind are found in the buttercup family, the violet, lily, palm, Fig. 300. Fig. 400. Section of fruit of pepper (Piper nigrum), showing small embryo lying in a small quantity of whitish endo- sperm at one end, the perisperm oc- . cupying the larger part of the interior, surrounded by pericarp. Seed of violet, external view, and section. The section shows the embryo lying in the endosperm. jack-in-the-pulpit, etc. Here the remaining endosperm in the seed is used as food by the embryo during germination. 663. Outer parts of the seed.—While the embryo is forming ANGIOSPERMS: SEED. a 5D within the ovule and the growth of the endosperm is taking place, where this is formed, other correlated changes occur in’ the outer parts of the ovule, and often in adjacent parts of the flower. These unite in making the “‘seed,’’ or the “‘ fruit.’’ Especially in connection with the formation of the seed a new growth of the outer coat, or integument, of the ovule occurs, forming the outer coat of the seed, known as the ¢es/a, while the inner integument is absorbed. In some cases the inner integument of the ovule also forms a new growth, making an inner coat of the seed (rosacez). In still other cases neither of the integuments develops into a testa, and the embryo sac lies in contact with the wall of the ovary. Again an additional envelope grows up around the seed; an example of this is found in the case of the red berries of the *‘ yew ’’ (taxus), the red outer coat being an extra growth, called an arvl. In the willow and the milkweed an aril is developed in the form of a tuft of hairs. (In the willow it is an outgrowth of the funicle, = stalk of the ovule, and is called a funicular aril; while in the milkweed it is an outgrowth of the micropyle, = the open end of the ovule, and is called a micropylar aril. ) 664. Increase in size during seed formation.—Accompany- ing this extra growth of the different parts of the ovule in the formation of the seed is an increase in the size, so that the seed is often much greater in size than the ovule at the time of fer- tilization. At the same time parts of the ovary, and in many plants, the adherent parts of the floral envelopes, as in the apple; or of the receptacle, as in the strawberry; or in the involucre, asin the acorn; are also stimulated to additional growth, and assist in making the fruit. 334 MORPHOLOGY. 665. Synopsis of the seed. Aril, rarely present. Ovular coats (one or two usually present), the testa. Funicle (stalk of ovule), raphe (portion of funicle when bent on to the side of ovule), micropyle, hilum (scar where seed was attached to ovary). Remnant of the nucellus (central part of ovule); sometimes nucellus remains as L Perisperm in some albuminous seeds. Endosperm, present in albuminous seeds. Embryo within surrounded by endosperm when this is present, or by the remnant of nucellus, and by the ovular coats which make the festa. In many seeds (example, bean) the endo- sperm is transferred to the cotyledons which become fleshy (exalbuminous seeds). 666. Parts of the ovule——In fig. gor are represented three different kinds of ovules, which depend on the position of the AG A, represents a straight (orthotropus) ovule of polygonum; B, the inverted (anatropous) ovule of the lily; and_C, the right-angled (campylotropus) ovule of the bean. j7, funicle; c, chalaza; k, nucellus; az, outer integument; 7, inner integument; m, micropyle; em, embryo sac. Ripened ovule. The seed. Bomy ig ovule with reference to its stalk. The funicle is the stalk of the ovule, the hilum is the point of attachment of the ovule with the ovary, the raphe is the part of the funicle in contact with the ovule in inverted ovules, the chalaza is the portion of the ovule where the nucellus and the integuments merge at the base of the ovule, and the micropyle is the opening at the apex of the ovule where the coats do not meet. FLOWER: MEMBERS AND ORGANS. 335 Comparison of Organ and Member. 667. The stamens and pistils are not the sexual organs.— Before the sexual organs and sexual processes in plants were properly understood it was customary for botanists to speak of the stamens and pistils of flowering plants as the sexual organs. Some of the early botanists, a century ago, found that in many plants the seed would not form unless first the pollen from the stamens came to be deposited on the stigma of the pistil. A little further study showed that the pollen germinated on the stigma and formed a tube which made its way down through the pistil and into the ovule. This process, including the deposition of the pollen on the stigma, was supposed to be fertilization, the stamen was looked on as the male sexual organ, and the pistil as the female sexual organ. We have found out, however, by further study, and especially by a comparison of the flowering plants and the lower plants, that the stamens and pistils are not the sexual organs of the flower. 668. The stamens and pistils are spore-bearing leaves.—The stamen is the spore-bearing leaf, and the pollen grains are not unlike spores; in fact they are the small spores of the angio- sperms. ‘The pistil is also a spore-bearing leaf, the ovule the sporangium, which contains the large spore called an embryo sac. In the ferns we know that the spore germinates and produces the green heart-shaped prothallium. The prothallium bears the sexual organs. Now the fern leaf bears the spores and the spore forms the prothallium. So it is in the flowering plants. The stamen bears the small spores—pollen grains—and the pollen grain forms the prothallium. The prothallium in turn forms the sexual organs. The process is in general the same as it is in the ferns, but with this special difference: the prothallium and the sexual organ of the flowering plants are very much reduced. 669. Difference between organ and member.—While it is not strictly correct then to say that the stamen is a sexual organ, 330 MORPHOLOGY. or male organ, we might regard it as a male member of the flower, and we should distinguish between organ and member. It is an organ when we consider pollen production, but it is not a sexual organ. When we consider /ertilization it is not a sexual organ, but a male member of the flower which bears the small spore. The following table will serve to indicate these relations. Stamen =spore-bearing leaf=male member of flower. Anther locule=sporangium. Pollen grain =small spore=reduced male prothallium and sexual organ. So the pistil is not a sexual organ, but might be regarded as the female member of the flower. Pistil = spore-bearing leaf= female member of flower. Ovule = sporangium. Embryo sac=large spore=female prothallium containing the egg. The egg =a reduced archegonium=the female sexual organ. Progression and Retrogression in Sporophyte and Gametophyte. 670. Sporophyte is prominent and highly developed.—In the angiosperms then, as we have seen from the plants already studied, the trillium, dentaria, etc., are sporophytes, that is they represent the spore-bearing, or sporophytic, stage. Just as we found in the case of the gymnosperms and ferns, this stage is the prominent one, and the one by which we characterize and recognize the plant. We see also that the plants of this group are still more highly special- ized and complex than the gymnosperms, just as they were more specialized and complex than the members of the fern group. From the very simple condition in which we possibly find the sporophyte in some of the algz like spirogyra, vaucheria, and coleochete, there has been a gradual increase in size, specialization of parts, and complexity of structure through the bryo- phytes, pteridophytes, and gymnosperms, up to the highest types of plant structure found in the angiosperms. Not only do we find that these changes have taken place, but we see that, from a condition of complete dependence of the spore-bearing stage on the sexual stage (gametophyte), as we find it in the liverworts and mosses, it first becomes free from the gametophyte in the mem- bers of the fern group, and is here able to lead an independent existence. The sporophyte, then, might be regarded as the modern phase of plant life, GAMETOPHVTE AND SPOROPARYTE. 337 since it is that which has become and remains the prominent one in later times. 671. The gametophyte once prominent has become degenerate.—On the other hand we can see that just as remarkable changes have come upon the other phase of plant life, the sexual stage, or gametophyte. There is reason to believe that the gametophyte was the stage of plant life which in early times existed almost to the exclusion of the sporophyte, since the characteristic thallus of the algze is better adapted to an aquatic life than is the spore-bearing state of plants. At least, we now find in the plants of this group as wellas in the liverworts, that the gametophyte is the prominent stage. When we reach the members of the fern group, and the sporophyte becomes independent, we find that the gametophyte is decreasing in size, in the higher members of the pteri- dophytes, the male prothallium consisting of only a few cells, while the fe- male prothallium completes its development still within the spore wall. And in selaginella it is entirely dependent on the sporophyte for nourishment. 672. As we pass through the gymnosperms we find that the condition of things which existed in the bryophytes has been reversed, and the gameto- phyte is now entirely dependent on the sporophyte for its nourishment, the female prothallium not even becoming free from the sporangium, which remains attached to the sporophyte, while the remnant of a male prothallium, during the stage of its growth, receives nourishment from the tissues of the nucellus through which it bores its way to the egg-cell. 678. Inthe angiosperms this gradual degradation of the male and female prothallia has reached a climax in a one-celled male prothallium with two sperm-cells, and in the embryo-sac with no clearly recognizable traces of an archegonium to identify it as a female prothallium, The development of the endosperm subsequent, in most cases, to fertilization, providing nourishment for the sporophytic embryo at one stage or another, is believed to be the last remnant of the female prothallium in plants. 674. The seed.—The seed is the only important character possessed by the higher plants (the gymnosperms and angiosperms) which is not pos- sessed by one or another of the lower great groups. With the gradual evo: lution of the higher plants from the lower there has been developed at cer- tain periods organs or structural characters which were not present in some of the lower groups. Thus the thallus is the plant body of the alge and fungi, so that these two groups of plants are sometimes called Thallophytes. In the Bryophytes (liverworts and mosses) the thallus is still present, but there is added the highly organized archegonium in place of the simple female gamete or oogonium, or carpogonium of the alge and fungi, and the sporophyte has become a distinct though still dependent structure. In the Pteridophytes the thallus is still present as the prothallium, archegoina are also present, and while both of these structures are retrograding the spo- rophyte has become independent and has organized for the first time a true 338 MORPHOLOGY. vascular system for conduction of water and food. In the gymnosperms and angiosperms the thallus is present in the endosperm; distinct, though reduced, archegonia are present in most gymnosperms and represented only by the egg in the angiosperms; the vascular system is still more highly developed while the seed for the first time is organized, and characterizes these plants so that they are called seed plants, or Spermatophytes. Variation, Hybridization, Mutation. 674a. Variation.—It is a well-known fact that plants as well as ani- mals are subject to variation. Under certain conditions, some of which are partly understood and others are unknown, the progeny of plants dif- fer in one or more characters from their parents. Some of these variations are believed to be due to the influence of environment (see Parts III and IV). Others are the result of the crossing of individuals which show greater or lesser differences In one or more characters, or the crossing of different species (hybridization). ‘The most profound variations are those which spring suddenly into existence (mutation). 674b. Hybridization.—Two different species are ‘‘crossed’’ where the egg-cell of one species is fertilized by the sperm of another species. The progeny resulting from such a cross is a hybrid. Hybrids sometimes resem- ble one parent, sometimes another, sometimes both. Where the parents: differ only in respect to one character of an organ or structure, there is a regular law in respect to the progeny if they are self-fertilized. In the first generation all the individuals are alike and resemble one of the parents, and the special differential character of that parent is called the dominant character. In the second generation 75% possess the dominant character, while 25% resemble the other original parent, and its differential charac- ter is called recessive. ‘These are pure recessives, since successive genera- tions, if self-fertilized, are always recessive. Of the 75% which show the dominant character in the second generation, one-third (or 25% of the whole number) are pure dominants if self-fertilization is continued, while 50% are really “cross breds”’ like the first generation, and if self-fertilized split up again into approximately 25 dominants, 50 cross breds, and 25 recessives. This is what is called Mendel’s law. Where the original par- ents differ in respect to more than one character, the result is more compli- cated (see Mendel’s Principles of Heredity; also de Vries, Das Spaltungs- gesetz der Bastarde, Ber. d. deutsch. bot. Gesell., 18, 83, 1900). 674c. Mutation.—This term is applied to those variations which appear so suddenly that some of the progeny of two like individuals differ from all the others to a marked degree. Some of these mutations are so different as to be regarded as new species. Some of the primroses show mutations, and (Enothera gigas is a mutation from ‘Enothera lamarkiana (see de Vries, Die Mutationstheorie, Leipzig) ; 339 GAMETOPHYVTE AND SPOROPHYTE. jo puv uniedsopus jo sulewot : “p2295 "snoyo -nu uiiadsopua jo SuOISIAIp Aueut Aq padoyaaap ‘wiodsopuy “snajonu wuodsopua Suryeul ‘pasny royonu avjod omy, ‘JQ WINS 10 ‘][9d [VUIOIVIY "oes OAIQUI, ‘ovs-oA quid JO 978} IvapONUIUL) Zz Jo x Aq paiaaod ‘sn{jesonN . Cae sid oydurts -2wsng io yedied ‘s][99 SATJVIOUIS IO ‘S[]Id [eULA}IVg "Oqn} YA Ure1s UsT[Og *]]99 DATBIDUIS "]J209 2aTVeIO59 A, ‘ulviIs Ud][Oq “Moj 10 OA} A]TeNsn ‘ovs UIT[Og uomelny | ‘Ioyuy | *sjodivd pue susWe}S ‘yueyd roystpy “SWAT, NOWWO’) Ud} ‘pods 94} = (vod Av[Nao pur ‘snyjeona ) ayfydorods pyo jo sand mou pues ayaydojawes jo sjuvumat Aq pepunoins ayAydorods Suno x aii naye Sah >) sri e Ree eie sO PATI TOTS pye jo YMos Mou pue ayAydojawes 9y} jo sjavd Aq popunoums 9}4ydo.sods Suno x = sjvoo Aq pepunouims (juesqe ayinb 10 Ajtvou qoye] sowmmetos) wuedsopua ut oAmquéy = “OA1q -UI9 WO} 0} SAPIAIp Bsa ‘55a Jo UOTFEpUNdI} JoIFW = wnyjeyqjoid speulay 9.ANjV I = wunreyjord jo yzed Surmory Il Il Sellclas! wuntyeyjoad ayewayz Sunof wuo0y 0} s[[I9 g O}UT saprarp aerodsosV = soSivpua AWAvd ‘9a1f BUIODDG JOU Sa0P ‘umiBuviodsoiovm jo pue ul [a0 ‘aiodso1ovyy { (uvSi0 yen $80 “umuoSoyaie Jo hy *ayAydojowes oem | = syeoo z 10 1 Aq padaaoo ‘umisuviodsosov yy eee eee eee eocee eect ee ee eee ay4ydoiods |Aqdosodsorv Jy J = s]j2o weds z ‘paprarp [[99 UNIpHayUy | = wnyjeqioid speur aanqye yy = (uvS10 [eNxas o[VU) WINIpltayj}Uue Fo [Jao yeaqua ayy st []29 e8avy, Jo wusv[dojoad ur Sunvoy ‘yyw ou ‘snapnu YA [Jeo [VUg “~ = aiods jo [je Aq papunoums snaponu sj yy “(¢ [pea. wMIpuayjue jo Wed) [Jao aswT “I wniyyeyjoard ts ayeut Sunod ile € 10 z jo Ayyensn Ayunjeu ye os1odsos9IpY wnisuviodsoss1yy ssecvecescoascoe sear {qdojouluG oP Aydorodsoxs1yy AE te ae tt armani) 7.003 Ce! Coos qyaed Sutrvaq a10dg ay4ydosodg “SHLAHdOCGINALG NI GaSN HSOHL OL SNIGNOdSHUNOD SNAAT “SNWUAdSOIDNV NI ALAHdOLANVD GNV ALAHdONOdS AO SAIDOTONOH ONIMOHS ATAVL “GLI CHAPTER XXXVII. MORPHOLOGY OF THE NUCLEUS AND Siena CANCE OF GAMETOPHYTE-AND SPOROPHYIE: 676. In the development of the spores of the liverworts, _mosses, ferns, and their allies, as well as in the development of the microspores of the gymnosperms and angiosperms, we have : observed that four spores are formed from a single mother cell. These Fig. 402. Fig. 403. Forming spores in mother Spores just mature and wall of cells (Polypodium vulgare). mother cell broken (Asplenium bul- biferum). mother cells are formed as a last division of the fertile tissue (archesporium) of the sporangium. In ordinary cell di- vision the nucleus always divides prior to the division of the cell. In many cases it is directly connected with the laying down of the dividing cell wall. 677. Direct division of the nucleus.—The nucleus divides in two different ways. Onthe one hand the process is very simple. The nucleus simply fragments, or cuts itself in two. This is direct division. 678. Indirect division of the nucleus.—On the other hand very complicated phenomena precede and attend the division of 340 GAMELOLPALV LTE. AND SPOROPH VIE: 341 the nucleus, giving rise to a succession of nuclear figures presented by a definite but variable series of evolutions on the part of the nuclear substance. This is zdirect division of the nucleus, or karyokinests. Indirect division of the nucleus is the usual method, and it occurs in the normal growth and division of the cell. The nuclear figures which are formed in the division of the mother cell into the four spores are somewhat different from those occurring in vegetative division, but their study will serve to show the general character of the process. 679. Chromatin and linin of the nucleus.—In figure 404 is represented a pollen mother cell of the May-apple (podophyl- Fig. 404. Fig. 405. Fig. 406, Pollen mother cell Spirem stage of nucleus. Forming _ spindle, of podophyllum, rest- 2, nuclear cavity; 2, nu- threads from _proto- ing nucleus. Chroma- cleolus; S/, spirem. plasm with several tin forming a net- poles, roping the work. chromosomes up to (Figures 404-406 after Mottier.) nuclear plate. lum). The nucleus is in the resting stage. There is a network consisting of very delicate threads, the “zz network. Upon this network are numerous small granules, and at the junction of the threads are distinct knots. The nucleolus is quite large and prominent. The numerous small granules upon the linin stain very deeply when treated with certain dyes used in differentiating the nuclear structure. This deeply staining substance is the chromain of the nucleus. 342 MORPHOLOGY. 680. The chromatin skein.—One of the first nuclear figures in the preparatory stages of division is the chromatin skem or spirem. ‘The chromatin substance unites to form this. The spirem is in the form of a narrow continuous ribbon, or band, woven into an irregular skein, or gnarl, as shown in figure 405. This band splits longitudinally into two narrow ones, and then each divides into a definite number of segments, about eight in the case of podophyllum. Sometimes the longitudinal splitting of the band appears to take place after the separation into the chro- matin segments. The segments remain in pairs until they separate at the nuclear plate. 681. Chromosomes, nuclear plate, and nuclear spindle.— ~ Each one of these rod-like chromatin segments is a chromosome. Fig. 407. Karyokinesis in pollen mother cells of podophyllum. At the left the spindle with the chromosomes separating at the nuclear plate; in the middle figure the chromosomes have reached the poles of the spindle, and at the right the chromosomes are forming the daughter nuclei. (After Mottier.) The pairs of chromosomes arrange themselves in a median plane of the nucleus, radiating somewhat in a stellate fashion, forming the nuclear plate, or monasier. At the same time threads of the protoplasm (kinoplasm) become arranged in the form of a spindle, the axis of which is perpendicular to the nuclear plate of chromo- somes, as shown in figure 407, at left. Each pair of chromosomes now separate in the line of the division of the original spirem, one chromosome of each pair going to one pole of the spindle, GAMETOPHVTE AND SPOKOPHYTE. 343 while the other chromosome of each pair goes to the opposite pole. The chromosomes here unite to form the daughter nuclei. Each of these nuclei now divide as shown in figure _ 409 (whether the chromo- somes in this second divi- sion in the mother cell split longitudinally or divide transversely has not been Fig. 408. definitely settled), and four Be cisocomns yeeros nuclei are formed in the Mottier ) In podophyllum. pollen mother cell. The protoplasm about each one of these four nuclei now surrounds itself with a wall and the spores are formed. The number of chromosomes usually the same in a given species throughout one phase of the plant.—In those plants which have been carefully studied, the number of chromosomes in the dividing nucleus has been found to be fairly constant in a given species, through all the divisions in that stage or phase of the plant, especially in the embryonic, or young growing parts. For example, in the prothallium, or gameto- phyte, of certain ferns, as osmunda, the number of chromosomes in the divid- ing nucleus is always twelve. ffs So in the development of |y M4 peas the pollen of lilium from }r4\\ 9 the mother cells, and in the divisions of the antherid cell to form the generative cells or sperm cells, there Fig. 409. Fig. 410. Second division of Chromosomes uniting _ nuclei in pollen mother at poles to form the 2 always twelve chromo cell of podophyllum, nuclei of the fourspores. somes so far as has been chromosomes at poles. (After Mottier.) found. In the development of the egg of lilium from the macrospore there are also twelve chromosomes. 344 MORPHOLOG Y. When fertilization takes place the number of chromosomes is doubled in the embryo.—In the spermatozoid of osmunda then, as well as in the egg, since these are developed on the game- tophyte, there are twelve chromosomes each. ‘The same is true in the sperm-cell (generative cell) of lium, and also in the egg- cell. When these nuclei unite, as they do in fertilization, the paternal nucleus with the maternal nucleus, the number of chro- mosomes in the fertilized egg, if we take hlium as an example, is twenty-four instead of twelve; the number is doubled. ‘The fertilized egg is the beginning of the sporophyte, as we have seen. Curiously throughout all the divisions of the nucleus in the em- bryonic tissues of the sporophyte, so far as has been determined, ~ up to the formation of the mother cells of the spores, the number of chromosomes is usually the same 682. Reduction of the number of chromosomes in the nu- cleus. —If there were no reduction in the number of chromosomes Fig. 411. Karyokinesis in sporophyte cells of podophyllum (twice the number of chromosomes here that are found in the dividing spore mother cells). at any point in the life cycle of plants, the number would thus become infinitely large. A reduction, however, does take place. GAMETOPHYTE AND SPOROPAYTE. 345 This usually occurs, either in the mother cell of the spores or in the divisions of its nucleus, at the time the spores are formed. In the mother cells a sort of pseudo-reduction is effected by the chromatin band separating into one half the usual number of nu- clear segments. So that in lilium during the first division of the nucleus of the mother cell the chromatin band divides into twelve segments, instead of twenty-four as it has done throughout the sporophyte stage. Soin podophyllum during the first division in the mother cell it separates into eight instead of into sixteen. Whether a qualitative reduction by transverse division of the spirem band, unaccompanied by a longitudinal splitting, takes place during the first or second karyokinesis is still in doubt. Qualitative reduction does take place in some plants according to Beliaieff and others. Recently the author has found that it takes place in Trillium grandiflorum during the second karyoki- nesis, and in Arisaema triphyllum the chromosomes divide both transversely and longitudinally during the first karyokinesis form- ing four chromosomes, and a qualitative reduction takes place here. 683. Significance of karyokinesis and reduction.—The pre. cision with which the chromatin substance of the nucleus is di- vided, when in the spirem stage, and later the halves of the chromosomes are distributed to the daughter nuclei, has led to the belief that this substance bears the hereditary qualities of the organisin, and that these qualities are thus transmitted with cer- tainty to the offspring. In reduction not only is the original number of chromosomes restored, it is believed by some that there is also a qualitative reduction of the chromatin, i.e. that each of the four spores possesses different qualitative elements of the chromatin as a result of the reducing division of the nucleus during their formation. The increase in number of chromosomes in the nucleus occurs with the beginning of the sporophyte, and the numerical reduc- tion occurs at the beginning of the gametophyte stage. The full import of karyokinesis and reduction is perhaps not yet known, but there is little doubt that a profound significance is to be attached to these interesting phenomena in plant life. 346 MORPHOLOGY. 684. The gametophyte may develop directly from the tissue of the sporophyte.—lIf portions of the sporophyte of certain of the mosses, as sections of a growing seta, or of the growing capsule, be placed on a moist substratum, under favorable condi- tions some of the external cells will grow directly into protonemal threads. In some of the ferns, as in the sensitive fern (onoclea), when the fertile leaves are expanding into the sterile ones, proto- nemal outgrowths occur among the aborted sporangia on the leaves of the sporophyte. Similar rudimentary protonemal growths sometimes occur on the leaves of the common brake (pteris) among the sporangia, and some of the rudimentary spo- rangia become changed into the protonema. In some other ferns, as in asplenium(A. filix-foemina, var. clarissima), prothallia are borne among the aborted sporangia, which bear antheridia and archegonia. In these cases the gametophyte develops from the tissue of the sporophyte without the intervention or necessity of the spores. ‘This is apospory. 685. The sporophyte may develop directly from the tissue of the gametophyte.—In some of the ferns, Pteris cretica for example, the embryo fern sporophyte arises directly from the tissue of the prothallium, without the intervention of sexual organs, and in some cases no sexual organs are de- veloped on such prothallia. Sexual organs, then, and the fusion of the spermato- zoid and egg nucleus are not here necessary for the development of the spo- rophyte. This is apogamy. Apogamy occurs in some Fig. 412. other species of ferns, and cas DL case i gli g'S = in other groups of plants as well, though it is in general a rare occurrence except in certain species, where it may be the general rule. GAMETOPHYVTE AND SPOROPHVTE. 347 686. Types of nuclear division—The nuclear figures in the vegetative cells are usually different from those in the spore mother cells. In the spore mother cells there are two types of nuclear division. (1) The first division in the mother cell is called heterotypic. The early stages of this division usually extend over a longer period than the second, and the figures are more complex. Before the chromosomes arrive at the nuclear plate they are often in the form of rings, or tetrads, or in the form of X, V, or Y, and the number is usually one half the num- ber in the preceding cells of the sporophyte. (2) The homo- typic division immediately follows the heterotypic and the figures are simpler, often the chromosomes being of a hook form, or sometimes much stouter than in the heterotypic division. In the vegetative cells (sometimes called somatic cells, or body cells in contrast with reproductive cells) there is another type, called by some the vegetative type. ‘The chromosomes here are often in the form of the letter U, and the figures are much sim- pler than in the heterotypic division. In the somatic cells of the sporophyte, as stated above, the number of chromosomes is double that found in the heterotypic and homotypic divisions of the mother cells and in the somatic cells of the gametophyte, Fig. 411 represents a late stage in the division of somatic cells in the sporophyte of podophyllum. The root tips of various plants as the onion, lily, etc., are excellent places in which to study nuclear division in the somatic cells of the sporophyte. 687. Comparison with animals.—In animals there does not seem to be anything which corresponds with the gametophyte of plants unless the sperm cells and eggs themselves represent it. Heterotypic and homotypic division with the accompanying reduction of the number of the chromosomes takes place in ani- mals usually in the mother cells of the sperms and eggs. At the time of fertilization the number of chromosomes is doubled, so that all the somatic cells (except in rare instances) from the fertilized egg to the mother cells of sperms and eggs have the doubled number of chromosomes. Reduction, therefore, takes place in animals just prior to the formation of the gametes, while 348 MORPHOLOGY. in plants it takes place just prior to the formation of the gameto- phytes. 688. Perhaps there is not a fundamental difference between gametophyte and sporophyte.—This development of sporophyte, or leafy-stemmed plant of the fern (parag. 685), from the tissue of the gametophyte is taken by some to indicate that there is not such a great difference between the gametophyte and sporophyte of plants as others contend. In accordance with this view it has been suggested that the leafy-stemmed moss plant, as well as the leafy stem of the liverworts, is homologous with the sporophyte or leafy stem of the fern plant; that it arises by budding from the protonema; and that the sexual organs are borne then on the sporophyte. PART Uf: PLANT MEMBERS IN RELATION TO ENVIRONMENT. CHAPTER XXXVIII. timer ORGANIZATION OF THE PLANT. I]. Crganization of Plant Members.* 689. It is now generally conceded that the earliest plants to appear in the world were very simple in form and structure. Perhaps the earliest were mere bits of naked protoplasm, not * Suggestions to the teacher, —Jn the studv of the flowering plants in the secondary school and in elementary courses three general topics are sug- gested. ist, the study of the form and members of the plant and their arrangement, as in Chapters XXXVIII-XLV. 2d, the study of a few plants representative of the more important families, in order that the members of the plant, as studied under the first topic, may be seen in corre- lation with the plant as a whole in a number of different types. 3d, the study of plants in their relation to environment, as in Chapter XLVI. The first and second topics can be conducted consecutively in the class- room and laboratory. ‘The third topic can be studied at opportune times during the progress of topics 1 and 2. For example, while studying topic 1 excursions can be made to study winter conditions of buds, shoots, etc., if in winter period, or the relations of leaves, etc., to environment, if in the growing period. While studying topic 2 excursions can be made to study flower relations, and also vegetation relations to environment (see Chapters XLVI-LVII of the author’s ‘‘College Text-book of Botany’’), It is believed that a study of these three general topics is of much more value to the beginning student than the ordinary plant analysis and deter- mination of species. : 349 350 RELATION TO ENVIRONMENT. essentially different from early animal life. The simplest ones which are clearly recognized as plants are found among the lower alge and fungi. ‘These are single cells of very minute size, roundish, oval, or oblong, existing during their growing period in water or in a very moist substratum or atmosphere. Examples are found in the red snow plant (Spherella nivalis), the Pleurococcus, the bacteria; and among small colonies of these simple organisms (Pandorina) or the thread-like forms (Spirogyra, Cidogonium, etc.). It is evident that some of the life relations of such very simple organisms are very easily ob- tained—that is, the adjustment to environment is not difficult. _All of the living substance is very closely surrounded by food material in solution. These food solutions are easily absorbed. Because of the minute size of the protoplasts and of the plant body, they do not have to solve problems of transport of food to distant parts of the body. When we pass to more bulky organ- isms consisting of large numbers of protoplasts closely com- pacted together, the problem of relation to environment and of food transport become felt; the larger the organism usually the greater are these problems. A point is soon reached at which there is a gain by a differentiation in the work of different proto- plasts, some for absorption, some for conduction, some for the light relation, some for reproduction, and so on. There is also a gain in splitting the form of the plant body up into parts so that a larger surface is exposed to environment with an economy in the amount of building material required. In this differentiation of the plant body into parts, there are two general problems to be solved, and the plant to be successful in its struggle for exist- ence must control its development in such a way as to preserve the balance between them. (1) A ready display of a large sur- face to environment for the purpose of acquiring food and the disposition of waste. (2) The protection of the plant from injuries incident to an austere environment. It is evident with the great variety of conditions met with in different parts of the same locality or region, and in different parts of the globe, that the plant has had very complex problems ORGANIZATION PLANT MEMBERS. 351 to meet and in the solution of them it has developed into a great variety of forms. It is also likely that different plants would in many cases meet these difficulties in different ways, sometimes with equal success, at other times with varied success. Just as different persons, given some one piece of work to do, are likely to employ different methods and reach results that are varied as to their value. While we cannot attribute consciousness or choice to plants in the sense in which we understand these qual- ities in higher animals, still there is something in their “consti- tution” or “character” whereby they respond in a different manner to the same influences of environment. This is, per- haps, imperceptible to us in the different individuals of the same species, but it is more marked in different species. Because of our ignorance of this occult power in the plant, we often speak of it as an “inherent” quality. ' Perhaps the most striking examples one might use to illustrate the dif- ferent line of organization among plants in two regions where the environ- ment is very different are to be found in the adaptation of the cactus or the yucca to desert regions, and the oak or the cucurbits to the land condi- tions of our climate. The cactus with stem and leaf function combined in a massive trunk, or the yucca with bulky leaves expose little surface in comparison to the mass of substance, to the dry air. They have tissue for water storage and through their thick epidermis dole it out slowly since there is but little water to obtain from dry soil. The cucurbits and the oak in their foliage leaves expose a very large sur- face in proportion to the mass of their substance, to an atmosphere not so severely dry as that of the desert, while the roots are able to obtain an abundant supply of water from the moist soil. The cactus and the yucca have differentiated their parts in a very different way from the oak or the cucurbits, in order to adapt themselves to the peculiar conditions of the environment. When we say that certain plants have the power to adapt themselves to certain conditions of environment, we do not mean to say that if the cucur- bits were transferred to the desert they would take on the form of the cactus or the yucca. They could do neither. They would perish, since the change would be too great for their organization. Nor do we mean, that, if the cactus or yucca were transferred from the desert to our climate, they would change into forms with thin foliage leaves. They could not. The fact is that they are enabled to live in our climate when we give them some care, but they show no signs of assuming characters like those of our vegetation. 352 RELATION TO ENVIRONMENT. What we do mean is, that where the change is not too great nor too sudden, some of the plants become slightly modified. This would indicate that the process of organization and change of form is a very slow one, and is there- fore a question of time—ages it may be—in which change in environment and adaptation in form and structure‘have gone on slowly hand in hand. 690. Members of the plant body.—The different parts into which the plant body has become differentiated are from one point of view, spoken of as members. It is evident that the sim- plest forms of life spoken of above do not have members. It is only when differentiation has reached the stage in which certain more or less prominent parts perform certain functions for the plant that members are recognized. In the alge 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 /rond. The Latin word for frond is thallus, and this name is applied to the plant body of all the lower plants, the alge and fungi. The algze and fungi together are sometimes called thallophytes, or thallus plants. ‘The word thallus is also sometimes applied to the flattened body of the liverworts. In the foliose liverworts and mosses there is an axis with leaflike 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. In the higher plants there is usually great differentiation of the plant body, though in many forms, as in the duckweeds, it is in the form of a frond. While there is a great variety in the form and function of the members of the plant body, they are all reducible to a few fundamental members. Some reduce these forms to three, the root, stem, leaj; while others to two, the root, and shoot, which is perhaps the best primary subdivision, and the shoot is then divided into stem and leaf, the leaf being a lateral outgrowth of the stem, and can be indicated by the fol- lowing diagram: ORGANIZATION PLANT MEMBERS. 353 Stem. Shoot. «% en Plant body..... ! Root. KINDS OF SHOOTS. 691. Since it is desirable to consider the shoot in its relation to environment, for convenience in discussion we may group shoots into four prominent kinds: (1) Foliage shoots; (2) Shoots with- out foliage leaves; (3) Floral shoots; (4) Winter conditions of shoots and buds. ‘Topic (4) will be treated in Chapter XXXIX, section IV. 692. (1st) Foliage shoots.—Foliage shoots are either aerial, when their relation is to both light and air; or they are aquatic, when their relation is to both light and water. They bear green leaves, and whether in the air or water we see that light is one of the necessary relations for all. Naturally there are several ways in which a shoot may display its leaves to the light and air or water. Because of the great variety of conditions on the face of the earth and the multitudinous me kinds of plants, there is the oes perennis. Foliage shoot and floral greatest diversity presented in the method of meeting these conditions. ‘There is to be con- sidered the problem of support to the shoot in the air, or in the water. The methods for solving this problem are funda- mentally different in each case, because of the difference in the density of air and water, the latter being able to buoy up the plant to a great degree, particularly when the shoot is provided with air in its intercellular spaces or air cavities. In the solu- 354 - RELATION TO ENVIRONMENT. tion of the problem in the relation of the shoot to aerial en- vironment, stem and leaf have in most cases codperated; * but in view of the great variety of stems and their modifications, as well as of leaves, it will be convenient to discuss them in separate chapters. 693. (2d) Shoots without foliage leaves._-These are subter- ranean or aerial. Nearly all subterranean shoots have also aerial shoots, the latter being for the display of foliage leaves (foliage shoots), and also for the display of flowers (flower shoots). The subterranean kinds bear scale leaves, i.e., the leaves not having a light relation are reduced in size, being small, and they lack chlorophyll. Examples are found in Solomon’s seal, man- Fig. 413a. Burrowing type, the mandrake, a ‘‘rhizome.”’ drake (fig. 413@), etc. Here the scale leaves are on the bud at the end of the underground stem from which the foliage shoot arises. Aerial shoots which lack foliage leaves are the dodder, Indian pipe-plant, beech drops, etc. These plants are sapro- phytes or parasites (see Chapter IX). Deriving their carbo- hydrate food from other living plants, or from humus, they do not need green leaves. The leaves have, therefore, probably been reduced in size to mere scales, and accompanying this there has been a loss of the chlorophyll. Other interesting ex- amples of aerial shoots without foliage leaves are the cacti where * It is interesting to note that in some foliage shoots the stem is entirely subterranean. See discussion of the bracken fern and sensitive fern in Chapter XXXIX. ORGANIZATION: PLANT MEMBERS. 355 the stem has assumed the leaf function and the leaves have become reduced to mere spines. The various modifications which shoots have undergone accompanying a change in their leaf relation will be discussed under stems in Chapter XX XIX. 694. (3d) Floral shoots.—The floral shoot is the part of the plant bearing the flower. As interpreted here it may consist of but a single flower with its stalk, as in Trillium, mandrake, etc., or of the clusters of flowers on special parts of the stem, termed flower clusters, as the catkin, raceme, spike, umbel, head, etc. In the floral shoot as thus interpreted there are several peculiarities to observe which distinguish it from the foliage shoot and adapt it to its life relations. The floral shoot in many respects is comparable to the foliage shoot, as seen from the following peculiarities: (z) It usually possesses, beside the flowers, small green leaves which are in fact foliage though they are very much reduced in size, because the function of the shoot as a foliage shoot is sub- ordinated to the function of the floral shoot. These small leaves on the floral shoot are termed bracts. (2) It may be (a) unbranched, when it would consist of a single flower, or (0) branched, when there would be several to many flowers in the flower cluster. (3) The flower bud has the same origin on the shoot as the leaf bud; it is either terminal or axillary, or both. (4) The members of the flower belong to the leaf series, i.e., they are leaves, but usually different in color from foliage leaves, because of the different life relation which they have to perform. Evidence of this is seen in the transition of sepals, petals, sta- mens, or pistils, to foliage leaves in many flowers, as in the pond lily, the abnormal forms of trillium, and many monstrosities in other flowers (see Chapter XXXIV). (5) The position of the members of the flower on its axis, though usually more crowded, in many cases follows the same plan as the leaves on the stem. The various kinds of floral shoots or flower clusters will be discussed in Chapter XLII, on the Floral Shoot. 356 RELATION TO ENVIRONMENT. I]. Organization of Plant Tissues. 695. A tissue is a group of cells of the same kind having a similar position and function. In large and bulky plants differ- ent kinds of tissue are necessary, not only because the work of the plant can be more economically performed by a division of labor, but also cells in the interior of the mass or at a distance from the source of the food could not be supplied with food and air unless there were specialized-channels for conducting food and specialized tissue for support of the large plant body. In these two ways most of the higher plants differ from the simple ones. The tissues for conduction are sometimes called collec- tively the mestome, while tissues for mechanical. support are called stereome. Division of labor has gone further also so that there are special tissues for absorption, assimilation, perception, reproduction, and the like. The tissues of plants are usually grouped into three systems: (1) The Fundamental System, (2) The Fibrovascular System, (3) The Epidermal System. Some of the principal tissues are as follows: . 1, THE FUNDAMENTAL SYSTEM. 696. Parenchyma.—Tissue composed of thin-walled cells which in the normal state are living. Parenchyma forms the loose and spongy tissue in leaves, as well as the palisade tissue (see Chapter IV); the soft tissue in the cortex of root and stem (Fig. 414), as well as that of the pith, of the pith rays or medullary rays of the stem; and is mixed in with the other elements of the vascular bundle where it is spoken of as wood parenchyma and bast parenchyma; and it also includes the undifferentiated tissue (meristem) in the growing tips of roots and shoots; also the “‘intrafascicular’? cambium (i.e., between the bundles, some also include the cambium within the bundle). 697. Collenchyma.—This is a strengthening tissue often found in the cortex of certain shoots. It also is composed of living cells. The cells are thickened at the angles, as in the tomato and many other herbs (fig. 414). 698. Sclerenchyma, or stone-tissue.—This is also a strengthening tissue and consists of cells which do not taper at the ends and the walls are evenly thickened, sometimes so thick that the inside (lumen) of the cell has nearly disappeared. Usually such cells contain no living contents at maturity. Sclerenchyma is very common in the hard parts of nuts, and underneath ORGANIZATION: PLANT TISSUES. 357 the epidermis of stems and leaves of many plants, as in the underground stems of the bracken fern, the leaves of pines (fig. 415), etc. es wien VOCROONe Cog 10>, EOS) HC ly (Qe n E Fig. 414. lara Alas Transverse section of portion of Margin of leaf of Pinus pinaster, transverse tomato stem. ep, epidermis; ch section. ¢, cuticularized layer of outer wall chlorophyll-bearing cells; co, collen- of epidermis; 7, inner non-cuticularized chyma; cp, parenchyma. layer; c’, thickened outer wall of marginal cell; g, 2’, hypoderma of elongated scle- renchyma; p, chlorophyll-bearing paren- chyma; pr, contracted protoplasmic con- tents. X80o0. (After Sachs.) 699. Cork.—In many cases there is a development of “‘cork’’ tissue underneath the epidermis. Cork tissue is cleveloped by repeated division of parenchyma cells in such a way that rows of parallel cells are formed toward the outside. These are in distinct layers, soon lose their proto- plasm and die; there are no intercellular spaces and the cells are usually of regular shape and fit close to each other. In some plants the cell walls are thin (cork oak), while in others they are thickened S@aea— (beech). The tissue giving JG0rSAS40 Span rise to cork is called “cork > Fa CLI OSe cambium,” or phellogen, and may occur in other parts of thew plant, For example, where plants are wounded the es Twa Hf \e> ¥ at living exposed parenchyma Woot OL Wy cells often change to cork J) a bad cambium and develop a pro- tective layer of cork. The Fig. 416. : _ Section through a lenticel of Betula alba show walls of cork cells contain a ing stoma at top, phellogen below producing rows substance termed suberin, of flattened cells, the cork. (After De Bary.) which renders them nearly waterproof. 1e 358 RELATION TO ENVIRONMENT. 700. Lenticels.—These are developed quite abundantly underneath stomates on the twigs of birch, cherry, beech, elder, etc. The phellogen underneath the stoma develops a cushion of cork which presses outward in the form of an elevation at the summit of which is the stoma (fig. 416). The lenticels can easily be seen. 2. THE FIBROVASCULAR SYSTEM. 701. Fibrous tissue.*—This consists of thick-walled cells, usually with- out living contents which are elongated and taper at the ends so that the cells, or fibers, overlap. It is common as one of the elements of the vas- cular bundles, as wood fibers and bast fibers. 702. Vascular tissue, or tracheary tissue.—This consists of the vessels or ducts, and tracheides, which are so characteristic of the vascular bundle (see Chapter V) and forms a conducting tissue for the flow of water. The vascular tissue contains spiral, annular, pitted, and scalariform vessels and tracheides according to the marking on the walls (figs. 58, 59). These are all without protoplasmic contents when mature. There are also thin- walled living cejls intermingled called wood parenchyma. In the conifers (pines, etc.) the tracheary tissue is devoid of true vessels except a few spiral vessels in the young stage, while it is characterized by tracheides with pecu- liar markings. ‘These marks on the tracheides are due to the ‘‘bordered”’ pits appearing as two concentric rings one within the other. ‘These can be easily seen in a longitudinal section of wood of conifers. 703. Sieve tissue.—This consists of elongated tubular cells connected at the ends, the cross walls being perforated at the ends. ‘These are in the phloem part of the bundle, and serve to conduct downwards the dissolved substances elaborated in the leaves. 704. Fascicular cambium.—This is the living, cell-producing tissue in the vascular bundle, which in the open bundle adds to the phloem on one side and the xylem on the other. 3. THE EPIDERMAL SYSTEM. 705. To the epidermal system belong the epidermis and the various out- growths of its cells in the form of hairs, or trichomes, as well as the guard cells of the stomates, and probably some of the reproductive organs, 706. The epidermis.—The epidermis proper consists of a single layer of external cells originating from the outer layer of parenchyma cells at the growing apex of the stem or root. These cells undergo various modifications of form. In many cases they lose their protoplasmic contents. In many cases the outer wall becomes thickened, especially ** Some fibers occur also very frequently in the Fundamental System, forming bundle-sheaths, or strands of mechanical tissue in the cortex. ORGANIZATION; PLANT TISSUES. 359 in plants growing in dry situations or where they are exposed to drying conditions. The epidermal cells generally become considerably flattened, and are usually covered with a more or less well developed water-proof cuticle, a continuous layer over the epidermis. In many plants the cuticle is covered with a waxy exudation in the form of a thin layer, or of rounded grains, or slender rods, or grains and needles in several layers. These Waxy coverings are sometimes spoken of as “‘bloom”’ on leaves and fruit. 707. Trichomes.—Trichome is a general term including various hair- like outgrowths from the epidermis, as well as scales, prickles, etc. These include root hairs, rhizoids, simple or branched hairs, glandular hairs, glandular scales, etc. Glandular hairs are found on many plants, as tomato, verbena, primula, etc.; glandular scales on the hop; simple-celled hairs on the evening primrose, cabbage, etc.; many-celled hairs on the primrose, pumpkin; branched hairs on the shepherd’s purse, mullein, etc., stellate hairs on some oak leaves. For stomates see Chapter IV. 4. ORIGIN OF THE TISSUES. 708. Meristem tissue.—The various tissues consisting of cells of dissimi- lar form are derived from young growing tissue known as meristem. Meri- stem tissue consists of cells nearly alike in form, with thin cell walls and rich in protoplasm. It is situated at the growing regions of the plants. In the higher plants these re- gions in general are three in number, the stem and root apex, and the cambium cyl- inder beneath the cortex. Tissues produced from the stem and root apex are called primary, those from the cam- bium secondary. In most cases the main bulk of the plant is secondary tissue, while in the corn plant it is all ar ea ; Fig. 417. | 709. Origin of stem tissues, Section through growing point of stem. d, —Just back of the apical] dermatogen, », plerome; periblem between. ‘ e 2 é After De Bary.) meristem in a longitudinal section of a growing point it can be seen that the cells are undergoing a change in form, and here are organized three formative regions. The outer layer of cells is called dermatogen (skin producer), because later it becomes the epidermis. The central group of elongating cells is the plerome (to fill). This later develops the central cylinder, or stele, as it is called 360 ’ RELATION TO ENVIRONMENT. (fig. 417). Surrounding the plerome and filling the space between it and the dermatogen is the third formative tissue called the periblem, which later forms the cortex (bark or rind), and consists of parenchyma, collenchyma, sclerenchyma, or cork, etc., as the case may be. It should be understood that all these different forms and kinds of cells have been derived from meristem by gradual change. In the mature stems, therefore, there are three distinct regions, the central cylinder or stele, the cortex, and the epidermis. 710, Central cylinder or stele—As the central cylinder is organized from the plerome it becomes differentiated into the vascular bundles, the pith, the pith rays (medullary rays) which radiate from the pith in the center between the bundles out to the cortex, and the pericycle, a layer of cells lying between the central cylinder and the cortex. The bundles then are farther organized into the xylem and phloem portions with their different ~—elements, and the fascicular cambium (meristem) separating the xylem and phloem, as described in Chapter V. Such a bundle, where the xylem and phloem portions are separated by the cambium is called an open bun- Fig. 418. Concentric bundle from stem of Polypodium vulgare. Xylem in the center, ee by phloem, and this by the endodermis. (From the author’s Biology of Ferns. dle (as in fig. 58). Where the phloem and xylem lie side by side in the same radius the bundle is a collateral one. Dicotyledons and conifers are char- acterized by open collateral bundles. This is why trees and many other ORGANIZATION: PLANT. TISSUES, 361 perennial plants continue to grow in diameter each year. The cambium in the open bundle forms new tissue each spring and summer, thus adding to the phloem on the outside and the xylem on the inside. In the spring and early summer the large vessels in the xylem predominate, while in late summer wood fibers and small vessels predominate and this part of the wood is firmer. Since the vascular bundles in the stem form a circle in the cylinder, this difference in the size of the spring and late summer wood produces the ‘‘annual”’ rings, so evident in the cross-section of a tree trunk. Branches originate at the surface involving epidermis, cortex, and the bundles. In monocotyledonous plants (corn, palm, etc.) the bundles are not regu- larly arranged to form a hollow cylinder, but are irregularly situated through the stele. There is no meristem, or cambium, left between the xylem and phloem portions of the bundle and the bundle is thus closed (as in fig. 60), since it all passes over into permanent tissue. In most monocotyledons there is, therefore, practically no annual increase in diameter of the stem. 711. Ferns.—In the ferns and most of the Pteridophytes an ee meri- stem tissue is wanting, its. place being taken by a single apical cell from the several sides of which cells are successively cut "off, though Isoetes and many species of Lycopodium have an apical meristem group. In most of the Pteridophytes also the bundles are concentric instead of col- lateral. Fig. 418 represents one of the bundles from the stem of the polypody jemiee) Phe xylem is in the center, this Fig. 4109. surrounded by the phloem, the phloem by Bee oe oe) ae the phloem sheath, and this in turn by sclerenchyma; a, thin - walled sclerenchyma; par, parenchyma. the endodermis, giving a concentric ar- rangement of the component tissues. A cross-section of the stem (fig. 419) shows two large areas of sclerenchyma, which gives the chief mechan- ical support, the bundles being comparatively weak. 712. Origin of root tissues.—A similar apical meristem exists in roots, but there is in addition a fourth region of formative tissue in front of the meristem called calyptrogen (fig. 420). This gives rise to the “root cap” which serves to protect the meristem. The vascular cylinder in roots is very different from that of the stem. There is a solid central cylinder in which the groups of xylem radiate from the center and groups of phloem alternate with them but do not extend so near the center (fig. 421). As the root ages, changes take place which obscure this arrangement more or less. Branches of the roots arise from the central cylinder. In fern roots the apical meristem is replaced by a single four-sided (tetrahedral) 362 RELATION TO ENVIRONMENT. apical cell, the root cap being cut off by successive divisions of the outer face, while the primary root tissues are derived from the three lateral faces. Fig. 420. Fig. 421. Median longitudinal section of the Cross-section of fibrovasculas bundle apex of a root of the barley, Hordeum in adventitious root of Ranunculus re- vulgare. k, calyptrogen; d, dermat- pens. w, pericycle; g, four radial plates ogen; ¢, its thickened wall; pr, peri- of xylem; alternating with them are blem; pl, plerome; en, endodermis; groups of phloem. This is a radial 2, intercellular air-space in process of bundle. (After De Bary.) formation; a, cell row destined to form a vessel; 7, exfoliated cells of the root cap. (After Strasburger.) Function of the root cap.—The root cap serves an important function in protecting the delicate meristem or cambium at the tip of the root. These cells are, of course, very thin-walled, and while there is not so much danger that they would be injured from dryness, since the soil is usually moist enough to prevent evaporation, they would be liable to injury from friction with the rough particles of soil. No similar cap is devefoped on the end of the stem, but the meristem here is protected by the overlapping bud- scales. One of the most striking illustrations of a root cap may be seen in the case of the Pandanus, or screw-pine, often grown in conservatories (see fig. 447). On the prop roots which have not yet reached the ground the root caps can readily be seen, since they are so large that they fit over the end of the root like a thimble on the finger. OLRGANIZALAON: PLANE TISSOES: 713. Descriptive Classification of Tissues. Epidermis. Simple hairs. Many-celled hairs. Branched hairs, often stellate. SySten, ./.. . Glandular hairs. Root hairs. Epidermal Trichomes. 1 Clustered, tufted hairs. | Prickles. Guard-cells of stomates. Spiral vessels. Pitted vessels Scalariform vesseis. Xylem (wood). + Annular vessels. Tracheides. | Wood fibers. Wood parenchyma. Fibrovascular System. .... Cambium (fascicular). Sieve-tubes. Phloem (bast). 4 Bast fibers. Companion cells. Bast parenchyma. Cork. | Collenchyma. Cortex... 7 Parenchyma. Fibers. | Milk tissue. Parenchyma. Stem and root. Parenchyma. Sclerenchyma. Fundamental Bundle-sheath. OYSIeEM. . ss. Endodermis. § Palisade tissue. eavesuee ees Spongy parenchyma. Reproductive Organs (mainly fundamental). 363 Intrafascicular cambium. 364 RELATION TO ENVIRONMENT. 714, Physiological Classification of Tissues. Formative Tissue. Thin-walled celis composing the meristem, capable of division and from which other tissues are formed. Protective Tissue. Tegumentary System.—Epidermis, periderm, bark protecting the plant from external contact. Mechanical System.—Bast tissue, bast-like tissue, collenchyma, scler- enchyma, afford protection against harmful bending, pulling, etc. Nutritive Tissues. Absorptive System.—Root hairs and cells, rhizoids, aerial root tissue, absorptive leaf glands, absorptive organs in seeds, haustoria of para- sites, etc. Assimilatory System.—Assimilating cells in leaf and stem. Conductive System.—Sieve tissue, tracheary tissue, milk tissue, conduct- ing parenchyma, etc. Food-storing System.—Water reservoir, water tissue, slime tissue, fleshy roots and stems, endosperm and cotyledons, etc. Aerating System.—Air spaces and tubes, special air tissue, air-seeking roots, stomates, lenticels, etc. Secretory and Excretory System.—Water ands, digestive glands, resin glands, nectaries, tannin, pitch and oil receptacles, etc. Apparatus and Tissues for Special Duties. Holdfasts. Tissues of movement, parachute hairs, floating tissue, hygroscopic tis- sue, living tissue. For perceiving stimuli. For conducting stimuli, etc. CHAPTER XXXIX. ae DOirhrRENT PYPES OF STEMS. WINTER SHOOTS: AND= BUDS: I. Erect Stems. 715. Columnar type.—The columnar type of stem may be simple or branched. When branching occurs the branches are usually small and in general subordinate to the main axis. The sunflower (Helianthus annuus) is an example. The foliage part is mainly simple. The main axis remains unbranched during the larger part of the growth period. The principal flowerhead terminates the stem. Short branches bearing small heads then arise in the axils of a few of the upper leaves. In dry, poor soil, or where other conditions are unfavorable, there may be only the single terminal flowerhead, when the stem is unbranched. The mullein is another columnar stem. The foliage part is rarely branched, though branches sometimes occur where the main axis has become injured or broken. The flower stem is terminal. The corn plant and the Easter lily are good illustra- tions also of the columnar stem. Among trees the Lombardy poplar (Populus fastigiata) is an excellent example of the columnar type. Though this is pro- fusely branched, the branches are quite slender and small in contrast with the main axis, unless by some injury or other cause two large axes may be developed. As the technical name indi- cates, the branching is fastigiate, i.e., the branches are crowded close together and closely surround the central axis. The royal palm and some of the tree ferns have columnar, simple stems, 365 366 RELATION TO ENVIRONMENT. but the large, wide-spreading leaves at the top of the stem give Fig. 422. Cylindrical stem of mullein. the plant anything but a cylin- drical habit. Some cedars and arbor-vite are also columnar. The advantages of the colum- nar habit of stem are three: (2) That the plant stands above other neighboring ones of equal fohage area and thus is enabled to obtain a more favorable light relation; (2) where large num- bers of plants of the same species are growing close together, they can maintain practically the same habit as where growing alone; (3) the advantage gained by other types in their neighbor- hood in less shading than if the type were spreading. ‘The cyl- indrical type can, therefore, grow between other types with less competition for existence. 716. The cone type.—This is well exampled in the larches, spruces, the gingko tree, some of the pines, cedars, and other gymnosperms. In the cone type, the main axis extends through the system of branches like a tall shaft, i.e., the trunk is excur- vent. The lower branches are wide-spreading, and the branches become successively _ shorter, usually uniformly, as one ascends the stem. The branching is of two types: (1) the branches are in false whorls; (2) the branches TYPES OF STEMS. 367 are distributed along the stem. To the first type belong the pines, Norway spruce, Douglas pruce, etc. The white pine is an exquisite example, and in young and middle-aged trees shows the style of branching to very good advantage. The branches are nearly horizontal, with a slight sigmoid graceful curve, while towards the top the branches are ascending. ‘This direction of the branches is due tovune tient relation. The few whorls at the top are ascending because of the strong light from above. ‘They soon become ex- tended in a horizontal direction as the main source of light is shifting to the side by the shad- ing of the top. The ascending piers direction first taken by the upper OG S28 (ent Gn. branches and their subsequent turning downward, while the ends often still have a slight ascending direction gives to the older branches their sigmoid curve. The young vernal shoots of the pines show some very interest- ing growth-movements. There are two growth periods: (1) the elongation of the shoot, and (2) the elongation of the leaves. The elongation of the shoot takes place first and is completed in about six weeks or two months’ time. The direction of the shoot in the first period seems to be entirely influenced by geot- ropism. It grows directly upward and stands up as a very conspicuous object in strong contrast with the dark green foliage of the more or less horizontal shoots. | When the second period of growth takes place, and the leaves elongate, the shoot bends downward and outward in a lateral direction. The rate of growth of the pines can be very easily observed since each whorl of branches (between the whorls of long shoots 368 RELATION TO ENVIRONMENT. there are short shoots bearing the needle leaves), whether on the main axis or on the lateral branches, marks a year; the new branches arising each year at the end of the shoot of the previous year. The rate of growth is sometimes as high as twelve to twenty-four inches or more per year. The spruces form a more perfect cone than the pines. The long branches are mostly in whorls, but often there are interme- diate ones, though the rate of growth per year can usually be easily determined. In the hemlock spruce, the branching is distributed. ‘The /arch has a similar mode of branching, but it is deciduous, shedding its leaves in the autumn, and it has a tall, — conical form. It would seem that trees of the cone type possessed certain advantages in some latitudes or elevations over other trees. (1) A conical tree, like the spruces and larches and the pines, and hemlocks also, before they get very old, meets with less injury during high winds than trees of an oval or spreading type. The slender top of the tree where the force of the wind is greatest presents a small area to the wind, while the trunk and short slender branches yield without breaking. Perhaps this is one reason why trees of this type exist in more northern latitudes and at higher elevations in mountainous regions, and why the spruce type reaches a higher latitude and altitude even than the pines. (2) The form of the tree is such as to admit light to a large foliage area, even where the trees are growing near each other. The evergreen foliage, persistent for several years, on the wide-spreading lower branches, probably affords some pro- tection to the trees since this cover would aid in maintaining a more equable temperature in the forest cover than if the trees were bare during the winter. (3) There is less danger of injury from the weight of snow since the greater load of snow would lie on the lower branches. ‘The form of the branches also, espe- cially in the spruces, permits them to bend downward without injury, and if necessary unload the snow if the load becomes too heavy. 717. The oval type.—This type is illustrated by the oak, chest- TYPES OF STEMS. 3690 nut, apple, etc. The trees are usually deciduous, i.e., cast their leaves with the approach of winter. The main axis is some- times maintained, but more often disappears (trunk is deliques- cent), because of the large branches which maintain an ascending direction, and thus lessen the importance of the central axis which is so marked in the cone type. ‘Trees of this type, and in fact all deciduous trees, exhibit their character or habit to better advantage during the winter season when they are bare. ‘Trees of this type are not so well adapted to conditions in the higher altitudes and latitudes as the cone type, for the reason given in the discussion of that type. ‘The deciduous habit of the oaks, etc., enables them to withstand heavy winds far better than if they retained their foliage through the winter, even were the foliage of the needle kind and adapted to endure cold. 718. The deliquescent type.—The elm is a good illustration of this type. The main axes and the branches fork by a false dichotomy, so that a trunk is not developed except in the forest. The branches rise at a narrow angle, and high above diverge in the form of an arch. The chief foliage development is lofty and spreading. Trees possess several advantages over vegetation less lofty. They may start their growth later, but in the end they outgrow the other kinds, shade the ground and drive out the sun-loving kinds. Il. Creeping, Climbing, and Floating Stems. 719. Prostrate type.—This type is illustrated by creeping or procumbent stems, as the strawberry, certain roses, of which a good type is one of the Japanese roses (Rosa wichuriana), which creeps very close to the ground, some of the raspberries, the curcubits like the squash, pumpkin, melons, etc. These often cover extensive areas by branching and reaching out radi- ally on the ground or climbing over low objects. The cucurbits should perhaps be classed with the climbers, since they are capa- ble of climbing where there are objects for support, but they are prostrate when grown in the field or where there are no ob- 370 RELATION TO ENVIRONMENT, jects high enough to climb upon. In the prostrate type, there is economy in stem building. The plants depend on the ground for support, and it is not necessary to build strong, woody trunks for the display of the foliage which would be necessary in the case of an erect plant with a foliage area as great as some of the Fig. 424. Prostrate type of the water fern (marsilia). prostrate stems. This gain is offset, at least to a great extent, by the loss in ability to display a great amount of foliage, which can be done only on the upper side of the stem. Other advantages gained by the prostrate stems are protec- tion from wind, from cold in the more rigorous climates, and some propagate themselves by taking root here and there, as in certain roses, the strawberry plant, etc. Some plants have erect stems, and then send out runners below which take root and aid the plant in spreading and multiplying its numbers. 720. The decumbent type.—lIn this type the stem is first erect, but later bends down in the form of an arch, and strikes root where the tip touches the ground. Some of the raspberries and blackberries are of this type. ee SS TYPES OF STEMS. 371 721. The climbing type.—The grapes, clematis, some roses, the ivies, trumpet creeper, the climbing bittersweet, etc., are climbing stems. Like the prostrate type, the climbers economize in the material for stem building. They climb over shrubs, up the trunks of trees and often reach to a great height and acquire the power of displaying a great amount of foliage by sending branches out on the limbs of the trees, sometimes devel- oping an amount of foliage sufficient to cover and nearly smother the foliage of large trees; while the main stem of the vine may be not over two inches in diameter and the trunk of the supporting tree may be three feet in diameter. 722. Floating stems.—These are necessarily found in aquatic plants. The stems may be ascending or horizontal. The stems are usually not very large, nor very strong, since the water bears them up. The plants may grow in shallow water, or in water 10-12 feet or more deep, but the leaves are usually formed at or near the surface of the water in order to bring them near the light. Various species of Potamogeton, MyriophylMum, and other plants common along the shores of lakes, in ponds, slug- gish streams, etc., are examples. Among the alge are exam- ples like Chara, Nitella, etc., in fresh water; Sargassum, Macro- cystis, etc., in the ocean. In these plants, however, the plant body is a thallus, which is divided into stem-like (cauledium) and leaf-like (phyllidium) structures. 723. The burrowing type, or rhizomes.—These are horizon- tal, subterranean stems. ‘The bracken fern, sensitive fern, the mandrake (see fig. 413a), Solomon’s seal, Trillium, Dentaria, and the like, are examples. The subterranean habit affords them protection from the cold, the wind, and from injury by certain animals. Many of these stems act as reservoirs for the storage of food material to be used in the rapid growth of the short-lived aerial shoot. In the ferns mentioned, the subterra- nean is the only shoot, and this bears scale leaves which are devoid of chlorophyll, and foliage leaves which are larger, and the only member of the plant body which is aerial. The foliage leaf has assumed the function of the aerial shoot. The latter is 372 RELATION TO ENVIRONMENT. not necessary since flowers are not. formed. The mandrake, Solomon’s seal, Trillium, etc., have scale leaves on the fleshy underground stems, while foliage leaves are formed on the aerial stems, the latter also bearing the flowers. Some or the advan- tages of the rhizomes are protection from injury, food storage for the rapid development of the aerial shoot, and propagation. Many of the grasses have subterranean stems which ramify for great distances and form a dense turf. For the display of foliage and for flower and seed production, aerial shoots are developed from these lateral upright branches. III. Specialized Shoots and Shoots for Storage of Food.* 724, The bulb.—The bulb is in the form of a bud, but the scale leaves are large, thick, and fleshy, and contain stored in them food products manu- factured in the green aerial leaves and transported to the underground bases of the leaves. Or when the bulb is aerial in its formation, it is developed as a short branch of the aerial stem from which the reserve food material is transported. Examples are found in many lilies, as Easter Fig. 425. lily, Chinese lilies, onion, tulip, Bulb of hyacinth. etc. The thick scale leaves are closely overlapped and surround the short stem within (also called a tunicated stem). In many lilies there is a sufficient * Besides these specialized shoots for the storage of food, food-substances are stored in ordinary shoots. For example, in the trunks of many trees starch is stored. With the approach of cold weather the starch is con- verted into oil, in the spring it is converted into starch again, and later as the buds begin to grow the starch is converted into glucose to be used for food In many other trees, on the other hand, the starch changes to sugar on the approach of winter. TVPES OF STEMS. 373 amount of food to supply the aerial stem for the development of flower and seed. There are roots, however, from the bulb and these acquire water for the aerial shoot, and when planted in soil additional food is obtained by them. 725. Corm.—A corm is a thick, short, fleshy, underground stem. A good example is found in the jack-in-the- pulpit (Arisaema). 726. Tubers.— These are thickened portions of the subterranean stems. The most generally known example is the potato tuber (“‘Irish”’ potato, not the sweet potato, which is a root). The “eyes” of the potato are buds on the stem from which the aerial shoots arise when the po- tato sprouts. The potato tuber is largely composed of starch which is used for food by the young sprouts. 726q. Phylloclades. ae Corm of Ee ees <7) These are trees, shrubs, or herbs in which the leaves are reduced to mere bracts and stems, are not only green and function as leaves, but some or all of the branches are flattened and resemble leaves in form as in Phyl- lanthus, Ruscus, Semele, Asparagus, etc. The flowers are borne directly on these flattened axes. The prickly pear cactus (Opuntia) is also a phylloclade. Examples of phylloclades are often to be found in greenhouses. 727. Undifferentiated stems are found in such plants as the duckweed, or duckmeat (Lemna, Wolffia, etc. See Chapter III). 374 RELATION TO ENVIRONMENT. IV. Annual Growth and Winter Protec=- tion of Shoots and Buds.* 728. Winter conditions.t— While herbs are subjected only to the damp warm atmosphere of summer, woody plants are also exposed dur- ing the cold dry winter, and must protect them- selves against such conditions. The air is dryer in winter than in summer; while at the same time root absorption is much retarded by the cold soil. Then, too, the osmotic activity of the dormant twig-cells being much reduced, the water-raising forces are at a minimum. It is easy to see, therefore, that a tree in winter is prac- tically under desert conditions. Moreover, it has been found by various investigators, contrary to the general belief, that cold in freezing is only indi- rectly the cause of death. The real cause is the abstraction of water from the cell by the ice crys- tals forming in the intercellular spaces. Death ensues because the water content is reduced below the danger-point for that particular cell. It was formerly thought that on freezing, the cells in the tissue were ruptured. ‘This is not so. Ice almost never forms within the cell, but in the spaces between. Freezing then is really a drying proc- ess, and dryness, not cold, causes death in winter. To protect themselves in winter, trees provide various waterproof coverings for the exposed sur- faces and reduce the activity of the protoplasm so that it will be less easily harmed by the loss of water abstracted by the freezing process. aay | 729. Protection of the twig.—Woody plants Fig. 427. protect the living cells within the twigs by the - -old twi : of nose chestnue production of a dull or rough corky bark, or by a showing buds and leaf-scars. (A twig : ; with a terminal bud * This topic was prepared by Dr. K. M. Wiegand. should have been se- lected for this figure.) | | See discussion of Tropophytes in Chapter XLVI, TYPES OF STEMS. 3 thick glossy epidermis over the entire surface. At intervals occur small whitish specks called lenticels, which here perform nearly the same function as do stomates in the leaf. 730. Bark of trunk.—A similar service is performed by the bark for the main trunk and branches of the tree. To admit of growth in diameter the old bark is constantly being thrown off in strips, flakes, etc., and replaced by a new but larger cylinder of young bark. The external appearance thus produced enables experienced persons to recognize many kinds of trees by the trunk alone. 731. Leaf-scars and bundle-scars——The presence of foliage leaves during the winter would greatly increase the transpiring surface without being of use to the plant; hence they are usually thrown off on the approach of winter. ‘The scars left by the fallen leaves are termed leaf-scars. The small dots on the leaf- scars left by the vascular bundles which extended through the petiole into the twig are termed bundle-scars. Sometimes stipule-scars are left on each side of the leaf-scar by the fallen stipules. 732. Nodes and internodes.—The region upon a stem where a leaf is borne is termed a node. The space between two nodes is an internode. 733. Phyllotaxy.—Investigation of a horse-chestnut or willow twig will show that the leaf-scars occupy definite positions which are constant for each plant but different for the two species. The arrangement of the leaves on the stem in any plant is termed phyllotaxy. In the horse- chestnut we find two scars placed at the same node, but on opposite sides of the stem. Somewhat higher up we find two more similarly placed, but in a position perpendicular to that of the first pair. Such phyllotaxy is termed opposite. If in any plant several leaves occur at a node, the phyl- lotaxy is whorled. If but one at each node, as in the willow, the phyllotaxy is alternate. The opposite and alternate types are very commonly met with. Closer observation will show that in the willow, if a line be drawn connecting the successive leaf-scars, it will pass spirally up the twig until at length a scar is reached directly over the one taken as a starting-point. Such spiral arrangement always accompanies alternate phyllotaxy. The section of the spiral thus delineated is termed a cycle. We express the nature of the cycle by the fractions 4, 4, 2, 3, 7s, etc., in which the 376 RELATION TO ENVIRONMENT. numerator denotes the number of turns around the stem in each cycle, and the denominator the number of leaf-scars in the same distance. In a general way we find in plants only such arrangements as are represented by the fractions given above. ‘These fractions show the curious condition that the numerator and de- nominator of each is equal to the sum of the numerator or denominator of the two preceding fractions. Much specula- tion has been indulged in regarding the significance of these definite laws of leaf- arrangement. In part they may be due to the desire that each leaf receive the maximum amount of light. Only certain definite geometrical conditions will insure this. More likely it is due to the economy of space alotted to the leaf-fundaments in the bud. Here, again, geometrical laws govern this economy. The phyllo- taxy is nearly constant for a given species. 734. Buds.—The growing point of the stem or branch together with its leaf or flower fundaments and protective structures is termed a bud. Winter buds on woody plants are terminal when inclosing the growing point of the main axis of the twig; lateral when the growing point is that of a branch of the main axis. Lateral buds are always axil- lary, i.e., situated on the upper angle between a leaf and the main axis. 735. Buds occupying special po- sitions. — Several species of trees Fig. 428. Fig. oe and shrubs produce more than one Fig. 428.—Shoot of butternut ° See a showing leaf-scars, axillary buds, bud in each leaf axil. The addi and adventitious buds (buds com- +E = SA) AL sug. from aibowe tie ale)! tional ones are termed accessory or whe ode” Shoot and bud of FOLIAGE LEAVES. 393 cells of this layer are narrow and long. This is often beauti- fully shown when comparing leaves of the same plant grown in strong light with those grown mimeene shade. The compass plant (Lactuca scariola) affords an interesting example. The leaves grown in the light are usually vertical, so that the light reaches both sides. Such leaves often have all of the mesophyll organized into palisade cells (fig. 435), while leaves grown in the deep shade may have no palisade 0s. cells. 764. (2) Protective covering. —Epidermis and cuticle-—The walls of the epidermal cells are much thickened in some plants. Sometimes this thickening occurs in the outer wall, or both walls may be thickened. Variation in i Fig. 435. this respect as well as the extent __ Structure of leaf of Lactuca scariola. ‘ 4 . Upper one grown in sunlight, palisade of the thickening occur in dif- cells on both sides. Lower one grown in shade, no palisade tissue. ferent plants and are often corre- lated with the extremes of conditions which they serve to meet. The cuticle, a waxy exudation from the thick wall of the epider- mis of many leaves, also serves as a protection against too great loss of water, or against the leaf becoming saturated with water during rains. The cabbage, carnation, etc., have a well-developed cuticle. The effect of the cuticle in shedding water can be nicely shown by spraying water on a cabbage leaf or by immersing it in water. Sunken stomata also retard the loss of water vapor. Covers of hair or scales—In many leaves certain of the cells of the epidermis grow out into the form of hairs or scales of various forms, and they serve a variety of purposes. When i! 394 RELATION TO ENVIRONMENT. the hairs form a felt-like covering as in the common mullein some antennarias, etc., they lessen the loss of water vapor be- cause the air-currents close to the surface of the leaf are retarded. Spines (see the thistles, etc.) also afford a protection against certain animals. 765. (3) Reduction of surface.—Reduction of leaf surface is brought about in a variety of ways. There are two general modes: (ist) Reduction of surface along with reduction of mass; (2d) Reduction of surface inversely as the mass. Ex- amples of the first mode are seen in the dissected leaves of many aquatic plants. In this finely dissected condition the mass of of the leaf substance is much reduced as well as the leaf surface, but the leaf is less liable to be injured by movement of the water. In addition it has already been pointed out that lobed and divided aerial leaves are much less liable to injury from violent movements of the air, than if a leaf with the same general out- line were entire. The needle leaves of the conifers are also examples, and they show as well structural provisions for pro- tection in the thick, hard cell-walls of the epidermis. To off- set the reduced surface there are numerous crowded leaves. Reduction of surface inversely as the mass, i.e., the mass of the leaf may not be reduced at all, or it may be more or less increased. In other words, there is less leaf surface in pro- portion to the mass of leaf substance. It is probable in many cases, example: the crowded, overlapping small scale leaves of the juniper, arbor vite, cypress, cassiope, pyxidanthera, etc., that there has been a reduction in the size of the leaf, and at the same time an increase in thickness. This with the crowding together of the leaves and their thick cell-walls greatly lessens the radiation of moisture and heat, thus protecting the leaves both in dry and cold weather. The succulents, like ‘‘live-for- ever,” have a small amount of surface in proportion to the mass of the leaf. In the yucca, though the leaves are often large, they are very thick and expose a comparatively small amount of surface to the dry air and intense sunlight of the desert regions. The epidermal covering is also hard and thick. In addition, FOLIAGE LEAVES. 395 such leaves, as well as those of many succulents, are so thick they provide water storage sufficient for the plants, which radi- ate so slowly from their surface. 766. (4) Elimination of the leaf—Perhaps the most striking illustration of the reduction of leaf surface is in those cases where Fig. 436. A ‘“‘Phylloclade,” leaves absent, stems broadened to function as leaves, on the edges numerous flowers are borne. the leaf is either completely eliminated as in certain euphorbias, or in certain of the cacti where the leaves are thought to be re- duced to spines. Whether the cactus spine belongs to the leaf series or not, the leaf as an organ for assimilation and trans- piration has been completely eliminated and the same is true in the phylloclades. The leaf function has been assumed by the stem. The stem in this case contains all the chlorophyll; is bulky, and provides water storage. III. Protective Positions. 767. In many cases the leaves are arranged either in relation to the stem, or to each other, or to the ground, in such a way as to give protection from too great radiation of heat or moisture. In the examples already cited the imbricated leayes of cassiope, 396 RELATION TO ENVIRONMENT pyxidanthera, juniper, etc., come also under this head. In the junipers the leaves spread out in the summer, while in the winter they are closely overlapped. An interesting example of protective position is to be seen in the case of the leaves of the white pine. During quite cold winter weather the needles are appressed to the stem, and sometimes the trees present a striking appear- ance in contrast with the spreading position of the needles in summer. On windy days in winter, the needles turn with the wind and become rigid in that position so that they remain in a horizontal position for some time, often until the wind dies down, or until milder weather. The following day, should there be a cold strong wind from the opposite direction, the needles again assume a leeward direction. In quiet weather appressed to the stem and in the form of a brush there is less radiation of heat than if they diverged. In strong winds by turning in the leeward direction the wind is not driven between the needle bases and scales. Some plants, especially many of those in arctic and alpine regions, have very short stems and the leaves are developed near the ground, or the rock. Lying close on the ground they do not feel the full force of the drying winds, there is less radiation from them, and the radiation of heat from the ground protects them. Many plants exhibit movement in response to certain stimuli which place them in a position for protection. Some of these examples have been discussed under the head of irritability (see Chapter XIII). The night position of leaves and cotyledons presented by many plants, but especially by many of the Leguminosz, is brought about by the removal of the light stimulus at evening. In many leaves, when the light influence is removed, the influence of growth turns the leaves downward, or the cotyledons of some plants upward. In this vertical position of the leaf-blade there is less radiation of heat during the cool night. The most strik- ing cases of protection movements are seen in the sensitive plant. As we have seen, the leaves of mimosa close in a verti- cal position at midday if the light and heat are too strong. Ex- cessive transpiration is thus prevented, At night the vertical tf aes FOLIAGE LEAVES. 397 position prevents excessive radiation of heat. The vertical or profile position of the leaves of the compass plant already re- ferred to not only lessens transpiration, but the intense heat and light of the midday sun is avoided. This profile position is characteristic of certain plants in the dry regions of Australia, and the topmost leaves of tropical forests. IV. Relation of Leaves to Light. 768. It is very obvious from our study of the function of the foliage leaf that its most important relation to environment is that which brings it in touch with light and air. It is necessary that light penetrate the leaf tissue that the gases of the air and Fig. 437 Mosaic form by trailing shoots of Panicum variegatum, “ribbon grass.” plant may readily diffuse and that water vapor may pass out of the leaf. ‘The thin expanded leaf-blade is the most economi- cal and efficient organ for leaf work. We have seen that leaves respond to light stimulus in such a way as to bring their upper sides usually to face the source of light, at right angles to it or nearly so (heliotropism, see Chapter XIII). How fully this is brought about depends on the kind of plant, as well as on other elements of the environment, for as we have seen in our study of leaf protection there is danger to some plants in any region, 398 RELATION TO ENVIRONMENT. and to other plants in certain regions that the intense light and heat may harm the protoplast, or the chlorophyll, or both. The statement that leaves usually face the light at right angles is to be taken as a generalized one. The source of the strongest illumination varies on different days and again at different times of the day. On cloudy days the zenith is the source of strongest illumination. ‘The horizontal position of a leaf, where there are no intercepting lateral or superior objects would receive its strongest light rays perpendicular to its surface. The fact is, however, that leaves on the same stem, because of taller or shorter adjacent stems, are so situated that the rays of greatest _ illuminating power are directed at some angle between the zenith and horizon. Many leaves, then, which may have their upper sides facing the general source of strongest illumination, no not necessarily face the sun, and they are thus protected from possible injury from intense light and heat because the direct rays of sunlight are for the most part oblique. This does not apply, of course, to those leaves which “follow the sun” during the day. Their specific constitution is such that intense illumination is beneficial. The leaf is adjusted as well as may be in different species of varying constitution, and under different conditions, to a certain balance in its relation to the factors concerned. The problem then is to interpret from this point of view the positions and grouping of leaves. Because of the specific constitution of dif- ferent plants, and because of a great variety of conditions in the environment, we see that it is a more or less complex question. 769. Day and night positions contrasted.—In many plants the day and night positions of the leaves are different. At night the leaves assume a position more or less vertical, known as the profile position. This is generally regarded as a pro- tective position, since during the cool of the night the radiation of heat is less than if the leaf were in a vertical position. In many of these plants, however, the leaves in assuming the night position become closely appressed which would also lessen the radiation. This peculiarity of leaves is largely possessed by ., i fT ae ae ee ee ee a i ~ FOLIAGE LEAVES, 399 the members of the family Leguminosez (clovers, peas, beans, etc.), and by the sensitive plants.* But it is also shared by some other plants as well (oxalis, for example). The leaves of these plants are usually provided with a mechanism which enables them to execute these movements with ease. There is a cushion (pulvinus) of tissue at the base of the petiole, and in the case of compound leaves, at the base of the pinnz and pin- nules which undergoes changes in turgor in its cells. The col- lapsing of the cells by loss of water into the intercellular spaces causes the leaf to droop. When the cells regain their turgor by the absorption of the water from the intercellular spaces the leaf is raised to the horizontal, or day position. The light stim, ulus induces turgor of the pulvinus, the disappearance of the stim- Fig. 438. Sunflower with young head turned toward morning sun. ulus is accompanied by a loss of turgor. It is a remarkable fact that in some sensitive plants, intense light stimuli are alarm signals which result in the same movement as if the light stim- * The most remarkable case is that of the ‘‘telegraph’’ plant (Des- modium gyrans). Aside from the day and night positions which the leaves assume, there is a pair of small lateral leaflets to each leaf which con- stantly execute a jerky motion, and swing around in a circle like the second hand of a watch. 400 RELATION TO ENVIRONMENT. ulus were entirely removed. As we know also contact or pres- sure stimulus, or jarring produces the same result in “‘sensitive” plants like mimosa, some species of rubus, etc. In many plants there is no well-developed pulvinus, and yet the leaves show similar movements in assuming the day and night positions. Examples are seen in the sunflower, and in the cotyledons of many plants. A little observation will enable any one interested to discover some of these plants.* In these cases the night position is due to epinastic growth, and while this influence is not removed during the day the lght stimulus overcomes it and the leaf is raised to the day position. 770. Leaves which rotate with the sun.—During the growth period the leaves of the sunflower as well as the growing end Fig. 430. Same sunflower plant photographed just at sundown. of the stem respond readily to the direct sunlight. The re- sponse is so complete that during sunny days the leaves toward the growing end of the stem are drawn close together in the form of a rosette and the entire rosette as well as the end of the * Seedlings are usually very sensitive to light and are good objects to study. FOLIAGE LEAVES. 401 stem are turned so that they face the sun directly. In the morn- ing under the stimulus of the rising sun the rosette is formed and faces the east. All through the day, if the sun continues to shine, the leaves follow it, and at sundown the rosette faces squarely the western horizon. For a week or more the young sunflower head will also face the sun directly and follow it all day as surely as the rosette of leaves. At length, a little while before the flowers in the head blossom, the head ceases to turn, Fig. 440. Same plant a little older when the head does not turn, but the stem and leaves do. but the rosette of leaves and the stem also, to some extent, con- tinue to turn with the sun. When the leaves become mature they also cease to turn. This is well shown in all three photo- graphs (figs. 438-439). The lower leaves on the stem being older have assumed the fixed horizontal position usually char- acteristic of the plant with cylindrical habit. It is not true, as is commonly supposed, that the fully opened sunflower head turns with the sun. But I have observed young heads four or five inches in diameter rotate with the sun all day. This is because the growing end of the stem as well as the young head responds to the light stimulus. So there is some truth as well as a great deal of fiction in the popular belief that the sun- 402 RELATION TO ENVIRONMENT, flower head follows the sun. The young head will follow the sun all day even if all the leaves are cut off, and the growing stem will also if all the leaves as well as the flower head are cut away. Young seedlings will also turn even if the cotyledons and plumule are cut off. This phenomenon of the rotation of leaves with the sun is much more general than one would infer, as may be seen from a little careful observation of rapidly growing plants on bright sunny days. In Alabama I have observed beautiful rosettes of Cassia marilandica rotate with the sun all day. ‘The peculiarity is very striking in the cotton plant, especially when the rows extend north and south. In the forenoon or afternoon it is most striking as the entire row shows the leaves tilted up facing the sun. There are many of our weeds and common flowers of field and garden which show this rotation of the leaves. Some of these form rotating rosettes; while in others the leaves rotate independently as in the sweet clover. 771. Fixed position of old leaves.—In many of the cases cited in the preceding paragraph, the rotation of the leaf only occurs on sunny days. During cloudy days the leaves of the sunflower, for example, are in a nearly horizontal position, or the lower ones may be somewhat oblique, since the stronger illumination on such a plant would be the oblique rays rather than the zenith rays. As the leaves reach maturity also the epinasitic growth is equalized by hyponastic growth so that the growth movements bring the leaf to stand in a nearly horizontal position, or that position in which it receives the best illumination. In age, then, many leaves have a fixed position and this corresponds with the position assumed on cloudy days. 772. Position on horizontal stems.—On horizontal stems the leaves have a horizontal position, and if such a stem is stood in an erect position the appearance is very odd. If the leaf arises directly from the horizontal stem, its petiole will be twisted part way around in order to bring the face of the leaf uppermost. It is interesting to observe the different relation of stem, petiole and blade and the amount of twisting as the horizontal stem or FOLIAGE LEAVES. 403 vine trails over irregularities in the surface, or climbs over and through other vegetation. 773. Position of leaflets on divided leaves.—An interesting comparison can be made with entire, lobed, divided and dis. sected leaves. The entire leaf usually lies in one plane, since usually the problem of adjustment is the same for the entire surface. So the lobes of a leaf usually lie all in the same plane as they would if the leaf were entire. We find the same is true usually of the compound leaf. It forms an incomplete mosaic. Some of the pieces having been removed allow much of the light to pass through to leaves beneath. Leaves, especially those of some size rarely lie in a flat plane. Some are more or less de- pressed. Some curve downward. Compound leaves often curve more or less and the leaflets often droop more or less in a graceful fashion. It is interesting, however, that these far-sepa- rated leaflets all lie in the same general plane. This is because the area of the leaf, if not too large, makes the problem of posi- tion with reference to light much the same as if the leaf were entire. The leaflets or divisions, though separated, are laminate, and they can work more efficiently facing the light. But suppose we extend our observation to the finely dissected capillary leaves of some of the parsley family (Umbellifere), or to the upper leaves of the fennel-leaved thoroughwort (Eupatorium fceni- culaceum) among the aerial plants, and to Myriophyllum among the aquatic plants. The divisions are threadlike or cylindrical. One side of the leaflet is just as efficient when presented to the light as another. As a result the leaflets are not arranged in the same plane, but stand out in many directions. Occasionally one finds a divided or compound leaf in such a position that one portion, because of being shaded above, receives the stronger light stimulus from the side, while the other portion is lighted from above. If this relation continues throughout the growth-period of the leaf the leaflets of one portion may lie in a different plane from those of the other portion. In such cases, some of the leaflets are permanently twisted to bring them into their proper light relation. 404. RELATION TO ENVIRONMENT. V. Leaf Patterns. MOSAICS, OR CLOSE PATTERNS, 774. Where the leaves of a plant, or a portion of a plant, are approximate and arranged in the form of a pattern, the leaves fitting together to form a more or less even and continuous sur- face, such patterns are sometimes termed “‘mosaics,”’ since the relation of leaves to one another is roughly like the relation of the pieces of a mosaic. A good illustration of a mosaic is pre- sented by a greenhouse plant Fittonia (fig. 441). The stems Fig. 441. _ Fittonia showing leaves arranged to form compact mosaic. The netted vena- tion of the leaf is very distinctly shown in this plant. (Photo by the Author.) are prostrate and the erect branches quite short, but it may have quite a wide system by the spreading of the runners; the branches of such a length that the leaves borne near the tips all fit together forming a broad surface of leaves so closely fitted together often that the stems cannot be seen. The advantage of a mosaic over a separate disposition of leaves at somewhat different levels is that the leaves do not shade one another. Were all the light rays coming down at right angles to the leaves, there would not be any shading of the lower ones, but the oblique rays of light would be cut off from many of the leaves. In the case of a mosaic all the rays of light play upon all the leaves. Some of the mosaics which can be observed are as follows: FOLIAGE LEAVES. a 405 775. Rosette pattern.—The rosette pattern is presented by many plants with “‘radial’”’ leaves, or leaves which arise in a cluster near the surface of the ground, and are thus more or less crowded in their arrangement on the stem. The pretty gloxinia often presents fine examples of a loose fesetie. lm the rosette pattern the petioles of the lower leaves are longer than the upper ones, and the blade is thus carried out beyond imiewmimners caves. . The leaves being so crowded in their attachment to the stem lie very nearly Fig. 442. in the same plane. Rosette pattern of leaves. 776. Vines and climbers.—Some of the most extensive mosaic patterns are shown in creeping and climbing vines. A very common example is that of the ivies trained on the walls of build- ings, covering in some instances many square yards of surface. Where the vines trail over the ground or clamber over other vegetation, it is interesting to observe the various patterns, and the distortion of petioles brought about by turning of the leaves. Of examples found in greenhouses, the Pellonia is excellent, and the trailing ribbon-grass often forms loose mosaics. 777. Branch patterns—These patterns are very common. They are often formed in the woods on the ends of branches by the leaves adjusting themselves so as to largely avoid shading each other. Figure 443 illustrates one of them from a maple branch. It is interesting to note the way in which the leaves fit themselves in the pattern, how in some the petioles have elongated, while others have remained short. Of course, it 406 RELATION TO ENVIRONMENT. Fig. 443. Spray of leaves of striped maple, showing different lengths of leafstalks. Fig. 444. Cedar of Lebanon, strong light only from one side of tree (Syria). FOLIAGE LEAVES. 407 should be understood that the pattern is made during the growth of the leaves. 778. The tree pattern.—Mosaics are often formed by the exterior foliage on a tree, though they are rarely so regular as some of those mentioned above. Still it is common to see in some trees with drooping limbs like the elm, beautiful and large mo- saics. The weeping elm sometimes forms a very close and quite even pattern over the entire outer surface. In most trees the leaf arrangement is not such as to form large patterns, but is more or less open. While the conifers do not form mosaics there are many interesting examples of grouping of foliage on branch systems into broadly expanded areas, as seen in the branches of white pine trees, especially in the edge of a wood, or as seen in the arbor vite. OTHER PATTERNS. 779. Imbricate pattern of short stems—This pattern is quite common, and differs from the rosette in that the leaves are dis- tributed further apart on the stem so that the cen- tral ones are consider- ably higher up than in the mosaic. The lower petioles are longer, as in the rosette, so that the outer lower leaves ex- tend further out. Some begonias show fine im- bricate patterns. 780. Spiral patterns. —They are very common . Fig. 445. aac the cylindrical Imbricate pattern of leaves; Begonia. type, which are unbranched, or but little branched. The sun- flower, mullein, chrysanthemum, as it is grown in greenhouses, the Easter lily, etc., are examples. The spiral arrangement of the leaves provides that each successive leaf on the stem, as one ascends the stem, is a little to one side so that it does not cast shade on the 408 RELATION TO ENVIRONMENT. leaf just below. In some stems, according to the leaf arrange- ment (or phyllotaxy), one would pass several times around in ascending the stem before a leaf would be found directly above another, which would be such a distance below that it would not be shaded to an appreciable extent. Interesting observations can be made on different plants to work out the relation of dis- tance of leaves on the stem to length of the upper and lower Fig. 446. Palm showing radiate arrangement of leaves and the petiole of the leaf func- tions as stem in lifting leaf to the light. leaves; the number of vertical rows on the stem compared to the width of the leaves; and the relation of these facts to the problem of light supply. Related to the spiral pattern is that of erect stems with opposite leaves. Here each pair is set at right angles to the direction of the pair above or below. 781. Radiate pattern.—This pattern is present in many grasses and related plants with narrow leaves and short stems. The leaves are often very crowded at the base, but by radiating in all directions from the horizontal to the vertical, abundant ex- BPOLTAGE LEAVES. 409 posure to light is gained with little shading. The dragon tree screw-pine, and plants grown in greenhouses also illustrate this Fig. 447. Screw pine (Pandanus) showing prop roots and radiate pattern of leaves. type. Itis also shown in cycads, palms, and many ferns, although these have divided leaves. 782. Compass plants.—These plants with vertical leaf arrange- ment, and exposure of both surfaces to the lateral rays of light have been mentioned in other sections (Lactuca scariola). 783. Open patterns.—Open patterns are presented by divided or “branched” leaves. Where the leaves are very finely dis- sected, they may be clustered in great profusion and yet admit sufficient light for some depth below. Where the leaflets are broader, the leaves are likely to be fewer in number and so arranged as to admit light to a great depth so that successive leaves below on the same or adjacent stems may not be too much shaded. On such plants, often the leaves lying next the ground are entire or less divided. | CHAPTER XLI. JUSS IROOW I. Function of Roots. 784. The most obvious function of the roots of ordinary plants are two: rst, To furnish anchorage and partial support, and 2d, absorption of liquid nutriment from the soil. The environ- mental relation of such roots, then, in broad terms, is with the soil. It is very clear that in some plants the root serves both functions, while in other plants the root may fulfil only one of these requirements. The problems which the plant has to solve in working out these relations are: (1) Permeation of the soil or substratum. (2) Grappling the substratum. (3) A congenial moisture or water relation. (4) Distribution of roots for the purpose of reaching’ food- laden soil. (5) Exposure of surface for absorption. (6) The renewal of the delicate structures for absorption. (7) Aid in preparation of food from raw material. (8) The maintenance of the required balance between the environment as a whole and the increasing or changing require- ments of the plant. 785. (1) Permeation of the soil or substratum.—The funda- mental divergence of character in the environmental relations of root and stem are manifest as soon as they emerge from the germinating seed. Under the influence of the same stimulus (gravity) the root shows its geotropic character by growing down- 410 ROOTS. 4iI ward, while the geotropic character of the stem is shown in its upward growth. The medium which the root has to penetrate offers consider- able resistance, and the form of the root as well as its manner of growth is adapted to overcome this difficulty. The slender, conical, penetrating root-tip wedges its way between the minute particles of soil or into the minute crevices of the rock, while the nutation of the root enables it to search for the points of least resistance. The root-tips having penetrated the soil, the older portions of the root continue this wedge action by growth in diameter, though, of course, elongation of the old parts of the root does not take place. It is the widening growth of the taper- ing root that produces the wedge-like action. The crevices -of the rock are sometimes broadened, but the resistance here is so great, the root is often greatly flattened out. 786. (2) Grappling the substratum.—The mere penetration of a single root into the soil gives it some hold on the soil and it offers some resistance to a “pull” since it has wedged its way in and the contact of soil particles offers resistance. The root-hairs formed on the first entering root growing laterally in great num- bers and applying themselves very closely to the soil particles, increase greatly the hold of the plant on the soil, as one can readily see by pulling up a young seedling. Lateral roots are soon formed, and as these continue to extend and ramify in all directions, the hold is increased until in the case of some of the larger plants the resistance their hold would offer would equal many tons. Even in some of the smaller shrubs and herbs the resistance is considerable, as one can easily test by pulling with the hand. To obtain some idea of the amount of resistance the roots of these smaller plants offer, they can be tested by pulling with the ordinary spring scales. 787. (3) A congenial moisture, or water relation.—In gen- eral, the roots seek those portions of the soil provided with a modi- cum of moisture. Usually a suitable moisture condition is present in those portions of the soil containing the plant food. But if por- tions of the soil are too dry and very nearby other portions con- 412 RELATION TO ENVIRONMENT. taining moisture, the roots grow mainly into the moist substratum (hydrotropism). If the soil is too wet, the roots grow away from it to soil with less water, or in som2 cases will grow to and upon the surface of the soil. The roots need aeration, and where the supply of water is too great, the air is shut out, and we know that corn, wheat, and many other plants become “sickly” in low and undrained soil in wet seasons. ‘This can only be said in the case of our ordinary dry land plants, i.e., those that occupy an intermediate position between water-loving plants and dry-conditioned plants. ‘This phase of the subject must be reserved for special treatment. (See Chapter XLVI.) 788. (4) Distribution of roots for the purpose of reaching food-laden soil.—This is one of the essential relations of the root in the case of the land plant, and probably accounts for the very extensive ramification of the roots. To some extent it also explains the different root systems in some plants. The pines, spruces, etc., usually grow in regions where the soil is very shal- low. The root system does not extend deeply into the soil. It spreads laterally and extends widely through the shallow surface soil and presents a very different aspect from the stem system in the air. ‘The root-system of the broad-leaved trees usually extends more deeply into the soil, while of course, extending laterally to great distances. ‘The hickory, walnut, etc., especially have strong tap roots which extend deeply into the soil, and the root system of such a tree is more comparable in aspect, if it were cntirely uncovered, to the stem system in the air. The tap-root is more pronounced in some trees than in others. It may be that in the hickory and walnut the deep tap-root is important in supplying the tree with water in dry seasons, especially when growing on dry, gravelly soil which does not retain moisture on the surface nor hold it within two or three feet of the surface. Experiment has demonstrated, by pot culture of plants, that where soil rich in plant food lies adjacent to poor soil, no matter in what part of the pot the rich soil is, the greatest growth and branching of roots is in the rich soil, | ROOTS. A413 789. (s) Exposure of root surface for absorption.—The prin- cipal part of root absorption takes place in the young root and the root hairs growing near the root-tip. The root-tips and root-hairs in their relation to the root systems on which they are borne are not to be compared morphologically with the leaves and stem system. But the root-tips and hairs are absorbing organs of the roots while the main root system supports them, brings them into relation with the soil and moisture, and con- ducts food and other substances to and from them. One of the important relations of the leaf is that of light, and since the source of light is restricted, i.e., it is not equally strong from all sides, an expanded and thin leaf-blade is more effective than an equal expenditure of plant material in the form of thread-like out- growths. It is different, however, with the plant food dissolved in the soil water. It is equally accessible on all sides. A greater surface for absorption is exposed with the same expenditure of material by multiplication of the organs and a reduction in their size. Numerous delicate root-hairs present a greater absorbing surface than if the same amount of material were massed into leaflike expansions. There is another important advantage also. Its slender roots and thread-like root-hairs allow greater freedom of circulation of water, food solutions, and air than if the absorbing organs of the roots were broadly expanded. 790. (6) The renewal of the delicate structures for absorp- tion.—The delicate root-hairs are easily injured. The thin cell-walls through which food solutions flow become more or less choked by the gradual deposit of substances in solution in the water, and continued growth of the root in diameter forms a firmer epidermis and cortex through which the solutions taken up by the root-hairs would pass with difficulty. For this reason new root-hairs are constantly being formed on the growing root- tip throughout the growing season, and in the case of perennial plants, through each season of their growth. 791. (7) Aid in preparation of food from raw materials.—For most plants the food obtained from the soil is already in solution in the soil water. But there are certain substances (examples, some 414 RELATION TO ENVIRONMENT. of the chemical compounds of potash, phosphoric acid, etc.) which are insoluble in water. Certain acids excreted by the roots aid in making these substances soluble (see Chapter III). In a num- ber of plants the roots have become associated with fungus or bacterial organisms which assist in the manufacture of nitro- genous food substances, or even in the absorption of ordinary food solution from the soil, or in making use of the decaying humus of the forest (see Chapter IX). 792. (8) The maintenance of the required balance between the environment and the increasing or changing requirements of the plant.—In this matter the entire plant participates. Men- tion is made here only of the general relation which the root ‘sustains to its own environment and the increased burden placed upon it by the shoot. The increase in the root system keeps pace with the increasing size of the stem system. The roots become stronger, their ramifications wider, and the number of absorbing rootlets more numerous. The observation is some- times offered that the correlation between the root system of a plant, and the form of the stem system and position of the leaves, is of such a nature that plants with a tap-root system have their leaves so arranged as to shed the water to the center of the sys- tem, while plants with a fibrous root system have their leaves so arranged as to shed the water outward. In support of this attention is called to the radiate type of the leaf system of the dandelion, beet, etc. In the second place the imbricate type as manifested in broad-leaved trees, and in the overlapping branch systems of many pines, etc. One should note, however, that in the former class the leaves are often arranged to shed as much water outward as inward. As to the latter class, there is need of experiment to determine whether these empirical observations are correct, for the following reasons: rst, Root and leaf distri- bution are governed by other and more important laws, the root being influenced by the location of food in the soil which usually forms a very thin stratum while the shoot and leaf is mainly in- fluenced by light, and root distribution is much wider in a lateral direction than that of the branches. 2d, In light rains the leaf ROOTS. 415 surface holds back practically all the rain which is then evap- orated into the air and lost to the root systems. 3d, In heavy and long-continued rains the water breaks through the leat system to such an extent that roots under the tree would be as well supplied as those outside, and the ground outside being saturated anyway, the roots do not need the small additional water which may have been shed outward. 4th, It is the habit of plants where left undisturbed (except in rare cases), to grow in more or less dense formations or societies. Here there is no opportunity for any appreciable centrifugal distribution of rain- fall and yet the root distribution is practically the same, except that the root systems of adjacent plants are interlaced. Il. Kinds of Roots. 793. The root system.—From the foregoing, it will be under- stood that the roots of a plant taken together form the root sys- tem of that plant. In soil roots in general we usually recognize two kinds of root systems. 794. The fibrous-root system.—Roots which are composed of numerous slender branching roots resembling “fibers,’”’ are termed jibrous, or the plant is said to have a fibrous-root system. The bean, corn, most grasses, and many other plants have fibrous- root systems. 795. The tap-root system.—Plants with a recognizable cen- tral shaft-like root, more or less thickened and considerably stouter than the lateral roots, are said to have tap roots, or they have a tap-root system. ‘The dandelion, beet, carrot (see crown tuber) are examples. The hickory, walnut, and some other trees have very prominent tap-roots when young. The tap-root is maintained in old age, but the lateral roots often become finally as large as the tap-root. Besides tap-roots and fibrous- roots, which include the larger number, several other kinds of roots are to be enumerated. 796. Aerial roots—Aerial roots are most abundantly devel- oped in certain tropical plants, especially in the orchids and aroids. Many examples of these plants are grown in conserva- 416 RELATION TO ENVIRONMENT. tories. The amount of moisture is so great in these tropical regions that the roots are abundantly supplied without the soil relation. Certain of the roots hang free in the air and are pro- vided with a special sheath of spongy tissue called the velamen, through which moisture is absorbed from the air. Other roots attach themselves to the trunk or branches of the tree on which the orchid is growing, and furnish the support to the epiphyte, as such plants are often called. Among the tangle of these clinging roots falling leaves are caught. Here they decay and nourishing roots grow from the clinging roots into this mass of decaying leaves and supply some of the plant food. Aerial roots sometimes possess chlorophyll. There are a number of plants, however, in temperate regions which have aerial roots. ‘These are chiefly used to give the stem support as it climbs on trees or on walls. ‘They are sometimes called clinging roots. A common example is the climbing poison ivy (Rhus radicans), the trumpet creeper, etc. Such aerial roots are called adventitious roots. 797. Bracing roots, or prop roots.—These are developed in a great variety of plants and serve to brace or prop the plant where the fibrous-root system is in- sufficient to support the heavy shoot system, or the shoot sys- tem branches so widely props are needed to holdup jue branches. In the common In- dian corn several whorls of bracing roots arise from the nodes near the ground and ex- ... tend outward and downward to ~ the ground, though the upper whorls do not always succeed in ae oe reaching the ground.) ine Bracing roots of Indian corn. 3 ; screw-pine sO common in greenhouses affords an excellent example of prop roots. The roots are quite large, and long before the root reaches the soil the ROOTS. AI7 large root-cap is evident. The banyan tree of India is a classic example of prop roots for supporting the wide-reaching branches. The mangrove in our own subtropical forests of Florida is a nearer example. 798. Buttresses are formed at the junction of the root and trunk, and therefore are part root and part stem. Splendid Fig. 4409. Buttresses of silk-cotton tree, Nassau. examples of buttresses are formed on the silk-cotton tree. They are sometimes formed on the elm and other trees in low swampy ground. 799. Fleshy roots, or root tubers.—These are enlargements of the root in the form of tubers, as in the sweet potato, the dahlia, etc. They are storage reservoirs for food. Portions of the roots become thick and fleshy and contain large quantities of sugar, as in the sweet potato, or of zmulin (a carbohydrate) in the root- tubers of the dahlia and other composites. 800. Water roots and roots of water plants.—These are roots which are developed in the water, or in the soil. Water-rocts are sometimes formed on land plants where the root comes in 418 RELATION TO ENVIRONMENT. contact with a body of water, or a stream. Water-roots usually possess no root-hairs, or but a few, as can be seen by comparing water-roots with soil-roots, or by comparing roots of plants grown in water cultures. The greater body of water in contact with the root and the more delicate epidermis of the root render less necessary the root-hairs. The duck-meats (Lemna) are good examples of plants having only water-roots. Other aquatic plants like the potamogetons, etc., have true roots which grow into the soil and serve to anchor the plant, but they are not devel- oped as special organs of absorption, since the stem and leaves largely perform this function. 801. Holdfasts——These are organs for anchorage which are not true roots. ‘These are especially well developed in some of the alge (Fucus, Laminaria, etc.). They are usually called holdjasts. The holdfasts of the larger alge are mainly for anchoring the plant. They do not function as absorbing organs, and the structure is different from that of true roots. 802. Haustoria or suckers is a name applied to another kind of holdfast employed by parasitic plants. In the dodder the haustorium penetrates the tissue of the fost (the plant on which the parasite grows), and besides furnishing a means of attach- ment, it serves as an absorbing organ by means of which the parasite absorbs food from its host. ‘The parasitic fungi like the powdery mildews which grow on the surface of their hosts have simple haustoria which serve both as organs of attachment and absorption, while in the rusts which grow in the interior of their hosts the haustoria are merely absorbing organs. 803. Rootlets, or rhizoids——Many of the alge, liverworts and mosses have slender, hair-like organs of attachment and absorp- tion. These plants do not have true roots. Because of the slender form and small size of these organs, they are called rhizoids, or rootlets. In form many of them resemble the root- hairs of higher plants. tae CHAPTER XLIt. tit hlCORAE-SHOOn, I. The Parts of the Flower. THE portion of the stem on which the flowers are borne is the flower shoot or axis, or taken together with the flowers, it is knowr as the Flower Cluster. 804, The flower.—The flower is best understood by an exam- ination, first of one of the types known as a “complete” flower, as in the buttercup, the spring beauty, the bloodroot, the apple, the rose, etc. There are two sets of organs or members in the complete flower—(1) the floral envelope; (2) the essential or necessary members or organs. The floral envelope when complete consists of—rst, an outer envelope, the calyx, made up of several leaflike structures (sepals), very often possessing chlorophyll, which envelop all the other parts of the flower when in bud; 2d, an inner envelope, the corolla, also made up of several leaflike parts (petals), usu- ally bright colored and larger than the sepals. The outer and inner floral envelopes are usually in whorls (though in close spirals in many of the buttercup family, etc.), and for reasons discussed elsewhere (Chapter XXXIV) represent leaves. The essential or necessary members of the flower are also usually in whorls and likewise represent leaves, but only in rare cases is there any suggestion, either in their form or color, of a leaf relationship. These members are in two sets: (1) The outer, or andrecium, consisting of a few or many parts (stamens); (2) the inner set, the gynecium, consisting of a few or many parts (carpels). 419 420 RELATION TO ENVIRONMENT. 805. Purpose of the flower.—While the ultimate purpose of all plants is the production of seed or its equivalent through which the plant gains distribution and perpetuation, the flower is the specialized part of the seed plant which utilizes the food and energies contributed by other members of the plant organization for the production of seed. In addition to this there are definite functions performed by the members of the flower, which come under the general head of plant work, or flower work. 806. The calyx, or the sepals.—These are chiefly protective, affording protection to the young stamens and carpels in the flower bud. Where the corolla is absent, sepals are usually present and then assume the function of the petals. In a few instances the calyx may possibly ultimately join in the formation of the fruit (examples: the butternut, walnut, hickory). 807. The corolla, or petals.—The petals are partly protective in the bud, but their chief function where well developed seems to be that of attracting insects, which through their visits to the flower aid in “ pollination,” especially “cross pollination.” 808. The stamens.—The stamens (=microsporophylls) are flower organs for the production of pollen, or pollen-spores (=microspores). The sta/k (not always present) is the filament, the anther is borne on the filament when the latter is present, The anther consists of the anther sacs or pollen sacs (microspo- rangium) containing the pollen-spores, and the connective, the sterile tissue lying between and supporting the anther sac. The stamens are usually separate, but sometimes they are united by their filaments, or by their anthers. When the pollen is ripe they open by slits or pores and the pollen is scattered; or in rarer cases the pollen mass (pollinium) is removed through the agency of insects (see Insect pollination, Chap. XLITI). 809. The pistil—The pistil consists of the “ovary,” the style (not always present), and the stigma. ‘These are well shown in a simple pistil, common examples of which are found in the buttercup, marsh marigold, the pea, bean, etc. The simple pistil is equivalent to a carpel (=macrosporophyll), while the compound pistil consists of two or several carpels joined, as in Po ae THE FLORAL SHOOT. 421 the toothwort, trillium, lily, etc. The ovary is the enlarged part which below is attached to the receptacle of the flower, and con- tains within the ovules. The style, when present, is a slender elongation of the upper end of the ovary. The stigma is sup- ported on the end of the style when the latter is present. It is often on a capitate enlargement of the style or extends down one side, or when the style is absent it is usually seated directly on the upper end of the ovary. The stigmatic surface is glutinous or “sticky,’”? and serves to hold the pollen-spores when they come in contact with it. The ovules are within the ovary and are arranged in differct ways in different plants. The pollen-grain (or better pollen- spore=microspore), after it has been transferred to the stigma, ““germinates,” and the pollen tube grows down through the tissue of the stigma and style, or courses down the stylar canal until it reaches the ovule. Here it usually enters the ovule (macrosporangium) at the micropyle (in some of the ament- bearing plants it enters at the chalaza), and the sperm-cells are emptied into the embryo sac in the interior of the ovule. 810. Fertilization —One of the sperms unites with the egg in the embryo sac. This is fertilization, and from the fertilized egg the young embryo is formed still within the ovule. Double jertilization,—the other sperm-cell sometimes unites with one or both of the “polar” nuclei which have united to form the “definitive” or “endosperm” nucleus. As a result of fertiliza- tion, the embryo plant is formed within the ovule, the coats of which enlarge by growth forming the seed coats, and altogether forming the seed. (See Chapters XXXIV, XXXV, XXXVI.) II. Kinds of Flowers. 811. Absence of certain flower parts.—The complete flower contains all the four series of parts. When any one of the series of parts is lacking, the flower is said to be incomplete. Where only one series of the floral envelopes is present the flowers are said to be apelalous (the petals are absent), examples: elm, buckwheat, 422 RELATION TO ENVIRONMENT, etc. Flowers which lack both floral envelopes are naked. When pistils are absent but stamens are present the flowers are stami- nate, whether floral envelopes are present or not; and so when stamens are absent and pistils present the flower is pistillate. It both stamens and pistils are absent the flower is said to be sterile or neutral (snowball, marginal or showy flowers in hydrangea). Flowers with both stamens and pistils, whether or not they have floral envelopes, are perject (or hermaphrodite), so if only one of these sets of essential organs of the flower is present the flower is imperject, or diclinous. Sometimes the imperfect, or diclinous, flowers are on the same plant, and the plant is said to be mone- cious (of one household). When staminate flowers are on cer- tain individual plants, and the pistillate flowers of the same species are on other individuals, the plant is diwcious (or of two households). When some of the flowers of a plant are diclinous and others are perfect, they are said to be polygamous. Many of these variations relating to the presence or absence of flower parts in one way or another contribute to the well-being of the plant. Some indicate a division of labor; thus in the neutral flowers of certain species of hydrangea or viburnum, the showy petals serve to attract insects which aid in the pollination of the fertile flowers. It must not be understood, however, that all variations in plants which results in new or different forms of flowers is for the good of the species. For example, under cultivation the flowers of viburnum and hydrangea sometimes are all neu- tral and showy. While such variations sometimes contribute to the happiness of man, the plant has lost the power of developing seed. In diclinous flowers cross pollination is necessitated. 812. Form of the flower.—The flower as a whole has form. This is so characteristic that in general all flowers of the different individuals of a species are of the same shape, though they may vary in size. In general, flowers of closely related plants of dif- ferent species are of the same type as to form, so that often in the shape of the flower alone we can see the relationship of kind, though the form of the flower is not the most important nor always the sure index of kinship. Since many flowers resemble oe Se if us! =, THE FLORAL SHOOT. 423 certain familiar objects, names are often used which relate to these objects. Flowers are said to be regular, or wregular. In a regular flower all of the parts of a set or series are of the same shape and size, while in irregular flowers the parts are of a different shape or size in some of the sets. The flowers of the pea family (Papi- lionacee), of the mint family (Labiate), of the morning glory, larkspur, monkshood, etc., are irregular (fig. 450). The corolla usually gives the characteristic form to the flower, and the name is usually applied to the form of the corolla. Some of the different forms are wheel-shaped or rotate corolla when the petals spread out at once like the spokes of a wheel, as in the potato, tomato, or bittersweet; salver-shaped when the 5 pee La Fig. 450. Several forms of flowers. Regular flowers. wh, wheel-shaped corolla; sa, salver-shaped; tub, tubular-shaped. Irregular flowers. pa, butterfly or papilio- Maceous; per, personate or masked flower; Jab, gaping or ringent corolla. The two latter are called bilabiate flowers. petals spread out at right angles from the end of a corolla tube, as in the phlox; bell-shaped, or campanulate, as in the harebell or campanula; /unnel-shaped, as in the morning glory; tubular, when the ends of the petals spread but little or none from the end of the corolla tube, as in the turnip flower or in the disk florets of the composites. The butterfly, or papilionaceous cor- olla is peculiar as in the pea or bean. The upper petal is the “banner,” the two lateral ones the “wings,’’? and the two lower imey.: keel,”? The /abiate corolla is charcteristic of the mint family where the gamosepalous corolla is unequally divided, so that the two 424 REEATION TO-ENVIRONMENT, upper lobes are sharply separated from the three lower forming two “lips.” The labiate corolla of the toadflax, or snapdragon is personate, or masked, because the lower lip arches upward like a palate and closes the entrance to the corolla tube; that of the dead nettle (Lamium) is ringent or gaping, because the lips are spread wide apart. In some plants the labiate corolla is not very marked and differs but shghtly from a regular form. The ligulate or strap-shaped corolla is characteristic of the flowers of the dandelion or chicory, or of the ray flowers of other composites (fig. 451). The lower part of the gamosepalous corolla is tubular, and the upper part is strap-shaped, as if that part of the tube were split on one side and spread out flat. These forms of the flower should be studied in appropriate examples. 813. Union of flower parts.—In the buttercup flower all the parts of each series are separate from one another and from other series of parts. Each one is attached to the receptacle of the flower, which is a very much shortened portion of the flower axis. ‘Ihe calyx being composed of separate and distinct parts is said to be polysepalous, and the corolla is likewise polypetal- ous. The stamens are distinct, and the pistils are simple. In many flowers, however, there is a greater or lesser union of parts. 814. Union of parts of the same series or cycle-—The parts coalesce, either slightly or to a great extent. Usually they are not so completely coalesced but what the number of parts of the series can be determined. Where the sepals are united the calyx is gamosepalous, when the petals are united the corolla is gamo petalous. Union of the sepals or of the corolla is quite common, but union of the stamens is rare except in a few families where it is quite characteristic. When the stamens are united by their anthers, they are syngenesious. ‘This is the case in most flowers of the composite family. When all the stamens are united into one group by their filaments, they are moxa- delphous (one brotherhood), as in holyhock, hibiscus, cotton, LAE FLORAL SIPOO7. 425 marsh-mallow, etc. When they are united by their filaments in two groups, they are diadelphous (two brotherhoods), as in the pea and most members of the pea family. In most species of St. John’s wort (Hypericum), the stamens are united in threes (triadel phous). 815. The carpels are often united.—The pistil is then said to be compound. Where the pistils are consolidated, usually the adjacent walls coalesce and thus separate the cavity of each ovary. Each cavity in the compound pistil is a Jocule. In some cases the adjacent walls disappear so that there is one com- mon cavity for the compound pistil (examples: purslane, chick- weeds, pinks, etc.). In a few cases there is a false partition (example, in the toothwort and other crucifers). The compound pistil is very often lobed slightly, so that the different pistils can be discerned. More often the styles or stigmas are distinct, and thus indicate the number of pistils united. 816. Union of the parts of different series——While in the buttercup and many other flowers, all the different parts are inserted on the torus or receptacle, in other flowers one series of parts may be joined to another. This is adnation of parts, or the two or more series are adnate. In the morning glory the stamens are inserted on the inner face of the corolla tube; the same is true in the mint family, and there are many other ex- amples. ‘The insertion of parts, whether free or adnate, is usually spoken of in reference to their relation to the pistil. Thus, in the buttercup the floral envelopes and stamens are all free and hypogynous they are below the pistil. The pistil in thi: case is superior. In the cherry, pear, etc., the petals and stamen- are borne on the edge of the more or less elevated tube of the calyx, and are said to be perigynous, 1.e., around the pisti! In the cranberry, huckleberry, etc., the calyx is for the most part united with the wall of the ovary with the short calyx limbs projecting from the upper surface. The petals and stamens are inserted on the edge of the calyx above the ovary; they are, therefore, epzgynous, and the ovary being under the calyx, as it were, 1s zmjerior. | 426 RELATION TO ENVIRONMENT. Ill. Arrangement of Flowers, or Mode of Inflores- cence. 817. Flowers are solitary or clustered.—Solitary flowers are more simple in their arrangement, i.e., it is easier for us to deter- mine and name their relation to each other and to other parts of the plant. They are either axillary, i.e., on short lateral shoots in the axils of ordinary foliage leaves, or they are terminal, i.e., they are borne on the end of the main axis of an ordinary foliage shoot. In either case they are so far separated, and the foliage leaves are so prominent, they do not form recognizable groups or clusters. The manner of arrangement of flowers on the shoot is called inflorescence, while the group of flowers so arranged is the flower cluster. Two different modes of inflorescence are usually recognized in the arrangement of flowers on the stem. (1) The corymbose, or indeterminate inflorescence (also indefinite inflorescence), in which the flowers arise from axillary buds, and the terminal bud may continue to grow. (2) The cymose or determinate inflor- escence (also definite inflorescence) in which the flowers arise from terminal buds. This arrests the growth of the shoot in length. There are several advantages to the plant in the different modes of inflorescence, chief among which is the massing of the flowers, thus increasing the chances for effective pollination. A. FLOWER CLUSTERS WITH INDETERMINATE INFLORESCENCE. 818. The simplest mode of indeterminate inflorescence is where the flowers arise in the axils of normal foliage leaves, while the terminal bud, as in the florist’s smilax, the bellwort, moneywort, apricot, etc., continues to grow. The flowers are solitary and axillary. In other cases which are far more numer- ous, the flowers are associated into more or less definite clusters in which are a number of recognizable types. The word type used in this sense, it should be understood, does not refer to an THE FLORAL SHOOT. 427 original structure which is the source of others. It merely refers to a mode of inflorescence which we attempt to recognize, and about which we group those forms which have a resemblance to one another. There are many forms of flower clusters which do not conform to any one of our recognized types, and are very puzzling. ‘The evolution of the flower clusters has been natural, and we cannot make them all conform to an artificial classifica- tion. These types are named merely as a matter of convenience in the expression of our ideas. The types usually recognized are as follows: 819. The raceme.—The flower-shoot is more or less elongated, and the leaves are reduced to a minute size termed bracts, while the flowers on lateral axes are solitary in the axils of the bracts. The reduction in the size of the leaves and the somewhat limited growth of the shoot in length, makes the flowers more prominent, and brings them into closer relation than if they were formed in the axils of the leaves on the ordinary foliage shoot. The choke cherry, currant, pokeweed, sourwood, etc., are examples of a raceme (fig. 569). In most plants with the raceme type, while the inflorescence is indeterminate, and the uppermost flowers (those toward the end of the main shoot) are younger, still the period of flowering is somewhat restricted and the raceme stops growing. In a few plants, however, as in the common “shep- herd’s purse,’ the raceme continues to grow throughout the summer, so that the lower flowers may have ripened their seed while the terminal portion of the raceme is still growing and producing new flowers. Compound racemes are formed when by branching of the flower-shoot there are several racemes in a cluster, as in the false Solomon’s seal (Smilacina racemosa). 820. The panicle —The panicle is developed from the raceme type by the branching of the lateral flower-axes forming a loose open flower cluster, as in the oat. 821. The thyrsus is a compact panicle of pyramidal form, as in the lilac, horsechestnut, etc. 822. The corymb.—The corymb shows likewise an easy tran- sition from the raceme type, by the shortening of the main axis 428 RELATION TO ENVIRONMENT. of inflorescence, and the lengthening of the lower, lateral flower peduncles so that the flower cluster is more or less flattened on top. This represents the szmple corymb. A compound corymo 1s one in which some of the flower peduncles branch again form- ing secondary corymbs, as in the mountain ash. It is like a panicle with the lower flower stalks elongated. 823. The umbel.—The umbel is developed from the raceme, or corymb. ‘The main flower-shoot remains very short or unde- veloped with several flowers on long peduncles arising close to- gether around this shortened axis, in the form of a whorl or clus- ter. Examples are found in the milkweed, water pennywort (Hydrocotyle), the oxheart cherry, etc. A compound umbel is one in which the peduncles are branched, forming secondary umbels, as in the caraway, parsnip, carrot, etc. 824. The spike.—In the spike the main axis is long, and the solitary flowers in the axils of the bracts are usually sessile, and often very much crowded. The plaintain, mullein (fig. 422), etc., are examples. The spike is a raceme, only the flowers are sessile and crowded. In the grasses the flower cluster is branched, and the branchlets bearing a few flowers are spikeicts. 825. The head.—When the flower axis is very much short- ened and the flowers crowded and sessile or nearly so, forming a globose or compressed cluster, it is a head or capi.ulum. ‘The transition is from a spike by the shortening of the main axis, as in the clover, button bush (Cephalanthus), etc., or in the short- ening of the peduncles in an umbel, as in the daisy, dandelion, and other composite flowers. In these the head is surrounded by an involucre, which in the young head often envelopes the mass of flowers, thus affording them protection. In some other composites (Lactuca, for example) the involucre affords pro- tection for a longer period, even while the seeds are ripening. 826. The spadix.—When the main axis of the flower cluster is fleshy, the spike or head forms a spadix, as in the Indian tur- nip, the skunk cabbage, the calla, etc. The spadix is usually more or less enclosed in a spaihe, a somewhat strap-shaped leaf. 527, The catkin—A spike which is usually caducous, Le, THE FLORAL SHOOT. 420 falls away after the maturity of the flower or fruit, is called a catkin, or an ament. The flower clusters of the alder, willow, (fig. 555), poplar, and the staminate flower clusters of the oak, hickory, hazel, birch, etc., are aments. So characteristic is this Bice AS le Head of sunflower showing centripetal inflorescence of tubular flowers. (Photo by the Author.) mode of inflorescence that the plants are called amentiferous, or amentaceous. 828. Anthesis of flowers with indeterminate inflorescence.— In the anthesis of the raceme as well as in other corymbose forms the lower (or outer) flowers being older, open first. The open- ing of the flowers then takes place from below, upward; or from the outside, inward toward the center of inflorescence. The anthesis, i.e., the opening of the flowers of corymbose forms is said to be centripetal, i.e., it progresses from outside, inward. The anthesis of the fuller’s teazel is peculiar, since it shows both types. ‘There are several distinct advantages to the plant where 430 RELATION TO ENVIRONMENT. anthesis extends over a period of time, as it favors cross pollina- tion, favors the formation of seed in case conditions should be Pigs 452. Heads of fuller’s teazel in different stages of flowering. unfavorable at one period of anthesis, distributes the drain on the plant for food, etc. B. FLOWER CLUSTERS WITH DETERMINATE INFLORESCENCE. 829. The simplest mode of determinate inflorescence is a plant with a solitary terminal flower, as in the hepatica, the tulip, etc. The leaves in these two plants are clustered in the form of a rosette, and the aerial shoot is naked and bears the single flower at its summit. Such a flower-shoot is a scape. As in the case of the indeterminate inflorescence, so here the larger number of flower-shoots are more complex and specialized, resulting in the evolution of flower clusters or masses. Accompanying the association of flowers into clusters there has been a reduction in leaf surface on the flower-shoot so that the flowers predominate in mass and are more conspicuous. Among the recognized modes of determinate inflorescence, the following are the chief ones: 830. The cyme.—In the cyme the terminal flower on the main axis opens first and the remaining flowers are borne on lateral shoots, which arise from the axils of leaves or bracts, below. THE FLORAL SHOOT. A431 These lateral shoots usually branch and elongate so that the terminal flowers on all the branches reach nearly the same height as the terminal flower on the main shoot, forming a somewhat flattened or convex top of the flower cluster. This is illustrated A B 0 Fig. 453. Diagrams of cymose inflorescence. A, dichasium; B, scorpioid cyme; C, heli- coid cyme. (After Strasburger.) in the basswood flower. The anthesis of the cyme is centrijugal, i.e., from the inside outward to the margin. But it is often more or less mixed, since the lateral shoots if they bear more than one flower are dimunitive cymes and the terminal flower opens before the lateral ones. Where the flower cluster is quite large and the branching quite extensive, compound cymes are formed, as in the dogwood, hydrangea, etc. 831. The helicoid cyme.—Where successive lateral branch- ing takes place, and always continues on the same side a curved flower cluster is formed, as in the forget-me-not and most mem- bers of the borage family. This is known as a helicoid cyme (fig. 453, C). Each new branch becomes in turn the “false” axis bearing a new branch on the same side. 832. The scorpioid cyme.—A scorpioid cyme (fig. 453, B) is formed where each new branch arises on alternate sides of the “Talse” “axis. 833. The forking cyme is where each “false” axis produces two branches opposite, so that it represents a false dichotomy (example, the flower cluster of chickweed). 834. Some of these flower clusters are peculiar and it is diffi- 432 RELATION TO ENVIRONMENT. cult to see how the helicoid, or scorpioid, cymes are of any advantage to the plant over a true cyme. ‘The inflorescence of the plant being determinate, if the flowering is to be extended over a considerable period a peculiar form would necessarily result. In the helicoid cyme continued branching takes place on one side, and the result in the forget-me-not is a continued inflorescence in its effect like that of a continued raceme (com- pare shepherd’s-purse). But we should not expect that all of the complex and specialized structures from simple and gen- eralized ones are beneficial to the plant. In many plants we recognize evolution in the direction of advantageous structures. But since the plant cannot consciously evolve these structures, we must also recognize that there may be phases of retrogression in which the structures evolved are not so beneficial to the plant as the more simple and generalized ones of its ancestors. Varia- tion and change do not result in advancing the plant or plant structures merely along the lines which will be beneficial. The tendency is in all directions. ‘The result in general may be dia- gramed by a tree with divergent and wide-reaching branches. Some die out; others remain subordinate or dormant; while still others droop downward, showing a retrogression. But in this backward evolution they do not return to the condition of their ancestors, nor is the same course retraced. A new down- ward course is followed just as the downward-growing branch follows a course of its own, and does not return in the trunk. CHAPTER XLII. PrOLULNA TION: Origin of heterospory, and the necessity for pollination. 835. Both kind» of sexual organs on the same prothallium.—TIn the ferns, as we have seen, the sexual organs are borne on the prothallium, a small, leaf-like, heart-shaped body growing in moist situations. In a great many cases both kinds of sexual organs are borne on the same prothallium. While it is per- haps not uncommon, in some species, that the egg cell in an archegonium may be fertilized by a spermatozoid from an antheridium on the same pro- thallium, it happens many times that it is fertilized by a spermatozoid from another prothallium. This may be accomplished in several ways. In the first place antheridia are usually found much earlier on the prothallium than are the archegonia. When these antheridia are ripe, the spermatozoids es- cape before the archegonia on the same prothallium are mature. 836, Cross fertilization in monecious prothallia.—By swimming about in the water or drops of moisture which are at times present in these moist situa- tions, these spermatozoids may reach and fertilize an egg which is ripe in an archegonium borne on another and older prothallium. In this way what is termed cross fertilization is brought about nearly as effectually as if the prothallia were dicecious, i.e. if the antheridia and archegonia were all borne on separate prothallia. 837, Tendency toward diecious prothallia.—In other cases some fern pro- thallia bear chiefly archegonia, while others bear only antheridia. In these cases cross fertilization is enforced because of this separation of the sexual organs on different prothallia. These different prothallia, the male and female, are largely due to a difference in food supply, as has been clearly proven by experiment. 838. The two kinds of sexual organs on different prothallia.—In the horse- tails (equisetum) the separation of the sexual organs on different prothallia has become quite constant. Although all the spores are alike, so far as we can determine, some produce small male plants exclusively, while others produce 433 434 RELATION TO ENVIRONMENT. large female plants, though in some cases the latter bear also antheridia. It has been found that when the spores are given but little nutriment they form male prothallia, and the spores supplied with abundant nutriment form female prothallia. 839, Permanent separation of sexes by different amounts of nutriment sup- plied the spores.—This separation of the sexual organs of different prothallia, which in most of the ferns, and in equisetum, is dependent on the chance supply of nutriment to the germinating spores, is made certain when we come to such plants as isoetes and selaginella. Here certain of the spores receive more nutriment while they are forming than others. In the large sporangia (macrosporangia) only a few of the cells of the spore-producing tissue form spores, the remaining cells being dissolved to nourish the growing macro- spores, which are few in number. In the small sporangia (microsporangia) __all the cells of the spore-producing tissue form spores. Consequently each one has a less amount of nutriment, and it is very much smaller, a micro- spore. The sexual nature of the prothallium in selaginella and isoetes, then, is predetermined in the spores while they are forming on the sporophyte. The microspores are to produce male prothallia, while the macrospores are to produce female prothallia. 840. Heterospory.—This production of two kinds of spores by isoetes, selaginella, and some of the other fern plants is eferospory, or such plants are said to be heterosporous. Heterospory, then, so far as we know from liv- ing forms, has originated in the fern group. In all the higher plants, in the gymnosperms and angiosperms, it has been perpetuated, the microspores being represented by the pollen, while the macrospores are represented by the em- bryo sac; the male organ of the gymnosperms and angiosperms being the antherid cell in the pollen or pollen tube, or in some cases perhaps the pollen grain itself, and the female organ in the angiosperms perhaps reduced to the egg cell of the embryo sac. 841, In the pteridophytes water serves as the medium for conveying the sperm cell to the female organ.—In the ferns and their allies, as well as in the liverworts and mosses, surface water is a necessary medium through which the generative or sperm cell of the male organ, the spermatozoid, may reach the germ cell of the female organ. The sperm cell is here motile. This is true in a large number of cases in the algze, which are mostly aquatic plants, while in other cases currents of water float the sperm cell to the female organ. 842, In the higher plants a modification of the prothallium is necessary. —As we pass to the gymnosperms and angiosperms, however, where the primitive phase (the gametophyte) of the plants has become dependent solely on the modern phase (the sporophyte) of the plant, surface water no longer serves as the medium through which a motile sperm cell reaches the egg cell to fertilize it, The female prothallium, or macrospore, is, in nearly al] en ee POLLINATION. 435 cases, permanently enclosed within the sporangium, so that if there were motile sperm cells on the outside of the ovary, they could never reach the egg to fertilize it. 843. But a modification of the microspore, the pollen tube, enables the sperm cell to reach the egg cell. The tube grows through the nucellus, or first through the tissues of the ovary, deriving nutriment therefrom. 844, But here an important consideration should not escape us. The pol- len grains (microspores) must in nearly all cases first reach the pistil, in order that in the growth of this tube a channel may be formed through which the generative cell can make its way to theegg cell. The pollen passes from the anther locule, then, to the stigma of the ovary. This process is termed pollination. Pollination. 845. Self pollination, or close pollination.—Perhaps very few of the ad- mirers of the pretty blue violet have ever noticed that there are other flowers than those which appeal to us through the beautiful colors of the petals. How many have observed that the brightly colored flowers of the blue violet rarely ‘‘set fruit’’? Underneath the soil or débris at the foot of the plant are smaller flowers on shorter, curved stalks, which do not open. When the anthers dehisce, they are lying close upon the stigma of the ovary, and the pollen is deposited directly upon the stigma of the same flower. This method of pollination is se/f pollination, or close pollination. These small, closed flowers of the violet have been termed ‘“ c/ezstogamous,” because they are pollinated while the flower is closed, and fertilization takes place as a result. ‘ But self pollination takes place in the case of some open flowers. In some cases it takes place by chance, and in other cases by such movements of the stamens, or of the flower at the time of the dehiscence of the pollen, that it is quite certainly deposited upon the stigma of the same flower. 846, Wind pollination.—The pine is an example of wind-pollinated flowers. Since the pollen floats in the air or is carried by the ‘‘ wind,’’ such flowers are anemophilous, Other anemophilous flowers are found in other conifers, in grasses, sedges, many of the ament-bearing trees, and other dicotyledons, Such plants produce an abundance of pollen and always in the form of ‘*dust,’’ so that the particles readily separate and are borne on the wind, 847, Pollination by insects.—A large number of the plants which we have noted as being anemophilous are moncecious or dicecious, i.e. the stamens and pistils are borne in separate flowers. The two kinds of flowers thus formed, the male and the female, are borne either on the same individual (monce- cious) or on different individuals (dicecious). In such cases cross pollination, 436 RELATION TO ENVIRONMENT. i.e. the pollination of the pistil of one flower by pollen from another, is sure to take place, if it is pollinated at all. Even in moncecious plants cross pollination often takes place between ftowers of different individuals, so that ye y \) : i KM \ ie \ in Whe SENS Vu SS . ae Fig. 454. Vicla cucullata; blue flowers above, cleistogamous flowers smaller and curved below. Section of pistil at_right. more widely different stocks are united in the fertilized egg, and the stra-in is kept more vigorous than if very close or identical strains were united. 848, But there are many flowers in which both stamens and pistils are pres- ent, and yet in which cross pollination is accomplished through the agency o! insects, 859, Pollination of the bluet.—In the pretty bluet the stamens and styles of the flowers are of different length as shown in figures 455, 476. The stamens of the long-styled flower are at about the same level as the stigma of the short-styled flower, while the stamens of the latter are on POLLINATION. 437 about the same level as the stigma of the former. What does this interesting relation of the stamens and pistils in the two different flowers mean? As the butterfly thrusts its ‘‘tongue’’ down into the tube of the long-styled flower Fig. 45 5- Dichogamous flower of the bluet (Houstonia ccerulea), the long-styled form. for the nectar, some of the pollen will be rubbed off and adhere toit. When now the butterfly visits a short-styled flower this pollen will be in the right position to be rubbed off onto the stigma of the short style. The positions of Fig. 456. Dichogamous flower of bluet (Houstonia ccerulca), the short-styled form. the long stamens and long style are such that a similar cross pollination will be effected. 850. Pollination of the primrose.—In the primroses, of which we have examples growing in conservatories, that blossom during the winter, we have almost identical examples of the beautiful adaptations for cross polli- nation by insects found in the bluet. The general shape of the corolla is ——— ee . 438 RELATION TO ENVIRONMENT. the same, but the parts of the flower are in fives, instead of in fours as in the bluet. While the pollen of the short-styled primulas sometimes must fall on the stigma of the same flower, Darwin has found that such pollen is Fig. 457. Dichogamous flowers of primula. not so potent on the stigma of its own flower as on that of another, an ad- ditional provision which tends to necessitate cross pollination. In the case of some varieties of pear trees, as the bartlett, it has been found that the flowers remain largely sterile not only to their own pollen, or pollen of the flowers on the same tree, but to all flowers of that variety. However, they become fertile if cross pollinated from a different variety of pear. 851. Pollination of the skunk’s cabbage.—In many other flowers cross pollination is brought about through the agency of insects, where there is a difference in time of the maturing of the stamens and pistils of the same flower. The skunk’s cabbage (Spathyema foetida), though repulsive on account of its fetid odor, is nevertheless a very interesting plant to study for several reasons. Early in the spring, before the leaves appear, and in many cases as soon as the frost is out of the hard ground, the hooked beak of the large fleshy spathe of this plant pushes its way through the soil. If we cut away one side of the spathe as shown in fig. 459 we shall have the flowering spadix brought closely to view. In this spadix the pistil of each crowded flower has pushed its style through between the plates of armor formed by the converging ends of the sepals, and stands out alone with the brush-like stigma ready for pollination, while the stamens of all the flowers of this spadix are yet hidden beneath. The insects which pass from the spadix of one plant to another will, in crawling over the projecting stigmas, rub off some of the pollen which has been caught while visiting a plant where the stamens are scattering their pollen. In this way cross pollin- ation is brought about. Such flowers, in which the stigma is prepared POLLINATION. ‘ig. 458. Skunk’s cabbage. 439 Fig. 459. 440 Proterogyny in skunk’s cabbage. (Photograph by the author.) ee POLLINATION. 441 / Fig. 460, >| Skunk’s cabbage; upper flowers proterandrous, lower ones proterogynous 442 RELATION TO ENVIRONMENT. for pollination before the anthers of the same flower are ripe, are proter- ogynous. 852. Now if we observe the spadix of another plant we may see a condi- tion of things similar to that shown in fig. 460. In the flowers in the upper part of the spadix here the anthers are wedging their way through between the armor-like plates formed by the sepals, while the styles of the same flowers are still beneath, and the stigmas are not ready for pollination. Such flowers are proterandrous, that is, the anthers are ripe before the stigmas of the same flowers are ready for pollination. In this spadix the upper flowers are proterandrous, while the lower ones are proterogynous, so that it might happen here that the lower flowers would be pollinated by the pollen falling on them from the stamens of the upper flowers. This would be cross pol- lination so far as the flowers are concerned, but not so far as the plants are concerned. In some individuals, however, we find all the flowers proter- androus. 853 Spiders have discovered this curious relation of the flowers and in- sects.—On several different occasions, while studying the adaptations of the flowers of the skunk’s cabbage for cross pollination, I was interested to find that the spiders long ago had discovered something of the kind, for they spread their nets here to catch the unwary but useful insects. I have not seen the net spread over the opening in the spathe, but it is spread over the spadix within, reaching from tip to tip of either the stigmas, or stamens, or both. Behind the spadix crouches the spider-trapper. The insect crawls over the edge of the spadix, and plunges unsuspectingly into the dimly lighted chamber below, where it becomes entangled in the meshes of the net. Flowers in which the ripening of the anthers and maturing of the stigmas occur at different times are also said to be dichogamous. 854 Pollination of jack-in-the-pulpit.—The jack-in-the-pulpit (Ariszema triphyllum) has made greater advance in the art of enforcing cross pollina- tion. The larger number of plants here are, as we have found, dicecious, the staminate flowers being on the spadix of one plant, while the pistillate flowers are on the spadix of another. In a few plants, however, we find both female and male flowers on the same spadix. 855, The pretty bellflower (Campanula rotundifolia) is dichogamous and proterandrous (fig. 462). Many of the composites are also dichoga- mous. 856. Pollination of ox:chids.— But some of the most marvellous adaptations for cross pollination by insects are found in the orchids, or members of the orchis family. The larger number of the members of this family grow in the tropics. Many of these in the forests are supported in lofty trees where they are brought near the sunlight, and such are called ‘‘epiphytes.’? A number of species of orchids are distributed in temperate regions, BROLEINA LION. 443 857. Cypripedium, or lady-slipper.—One species of the lady-slipper is shown in fig. 468. ‘The labellum in this genus is shaped like a shoe, as one Fig. 461. A group of jacks. can see by the section of the flower in fig. 468. The stigma is situated at si, while the anther is situated at a, upon the style. The insect enters about the middle of the boat-shaped labellum. In going out it passes up and out 444 RELATION TO ENVIRONMENT. at the end near the flower stalk. In doing this it passes the stigma first and the anther last, rubbing against both. The pollen caught on the head of Fig. 462. Proterandry in the bell-flower (campanula). Left figure shows the syngencecious stamens surrounding the immature style and stigma. Middle figure shows the immature stigma being pushed through the tube and brushing out the pollen; while in the right-hand figure, after ie pollen has disappeared, the lobes of the stigma open out to receive pollen from another ower. the insect, will not touch the stigma of the same flower, but will be in posi- tion to come in contact with the stigma of the next flower visited. 858 Epipactis.—In epipactis, shown in fig. 469, the action is similar to that of the blue iris. Fig. 463. Kalmia latifolia, showing position of anthers before insect visits, and at the right the scattering of the pollen when disturbed by insects. Middle figure section of flower. 849, In some of the tropical orchids the pollinia are set free when the insect touches a certain part of the flower, and are thrown in such a way that the disk of the pollinium strikes the insect’s head and stands upright. By the time the insect reaches another flower the pollinium has bent downward sufh- POLLINATION. 445 ciently to strike against the stigma when the insect alights on the labellum. In the mountains of North Carolina I have seen a beautiful little orchid, in which, if one touches a certain part ef the flower with a lead-pencil or other suitable object, the pollinium is set free suddenly, turns a complete somer- sault in the air, and lands with the disk sticking to the pencil. Many of the Spray of leaves and flowers of cytisus. orchids grown in conservatories can be used to demonstrate some of these peculiar mechanisms. 860. Pollination of the canna.—In the study of some of the marvellous adaptations of flowers for cross pollination one is led to inquire if, after all, plants are not intelligent beings, instead of mere automatons which respond Fig. 465 Flower of cytisus grown in conservatory. Same flower scattering poller. to various sorts of stimuli. No plant has puzzled me so much in this respect as the canna, and any one will be well repaid for a study of recently opened flowers, even though it may be necessary to rise early in the morning to unravel the mystery, before bees or the wind have irritated the labellum. The canna flower is a bewildering maze of petals and petal-like members, eee 446 RELATION TO ENVIRONMENT. The calyx is green, adherent to the ovary, and the limb divides into three, lanceolate lobes. The petals are obovate and spreading, while the stamens have all changed to petal-like members, called staminodia. Only one still shows its stamen origin, since the anther is seen at one side, while the fila- ment is expanded laterally and upwards to form the staminodium. Fig. 466. Spartium, showing the dusting of the pollen through the opening keels on the under side of aninsect. (Irom Kerner and Oliver.) 861, The ovary has three locules, and the three styles are usually united into a long, thin, strap-shaped style, as seen in the figure, though in some cases three, nearly distinct, filamentous styles are present. The end of this strap-shaped style has a peculiar curve on one side, the outline being some- d POLLINATION. 447 times like a long narrow letter S. It is on the end of this style, and along the crest of this curve, that the stigmatic surface lies, so that the pollen Section of flower of cypripedium. s¢, stigma; @, at theleft stamen. The insect enters the labellum at the center, passes under and against the stigma, and out through the opening 4, where it rubs against the pollen. In passing through another flower this pollen is rubbed off on the stigma. must be deposited on the stigmatic end or margin in order that fertilization may take place. Fig. 467. 862, If we open carefully canna-flower buds Cypripedium. which are nearly ready to open naturally, by unwrapping the folded petals and staminodia, we shall see the anther-bearing Fig. 460. Epipactis with portion of perianth removed to show details. 2, labellum; s#, stigma; + rostellum ; /, pollinium. When the insect approaches the flower its head strikes the disk of the pollinium and pulls the pollinium out. At this time the pollinium stands up out of the way of the stigma. By the time the insect moves to another flower the pollinia have moved downward so that they are in position to strike the stigma and leave the pollen. At the right is the head of a bee, with two pollinia (a) attached. 448 RELATION TO ENVIRONMENT. staminodium is so wrapped around the flattened style that the anther lies closely pressed against the face of the style, near the margin oposite that on which the stigma hes. 863, The walls of the anther locules which lie against the style become changed to a sticky substance for their entire length, so that they cling firmly to the surface of the style and also to the mass of pollen within the locules. The result is that when the flower opens, and this staminodium unwraps itself from the embrace of the style, the mass of pollen is left there de- posited, while the empty anther is turned around to one side. 668. Why does the flower de- posit its own pollen on the style? Some have regarded this as the act of pollination, and have concluded, therefore, that cannas are neces- sarily self pollinated, and that cross pollination does not take place. But why is there such evi- dent care to deposit the pollen on ES ee the side of the style away from the Canna flowers with the perianth removed to .. : - 5 ak show the depositing of the pollen on the style by Stigmatic margin : If we visit the 2S SENSE cannas some morning, when a number of the flowers have just opened, and the bumblebees are humming around seeking for nectar, we may be able to unlock the secret. 864, We see that in a recently opened canna flower, the petal which directly faces the style in front stands upward quite close to it, so that the flower now is somewhat funnelshaped. This front petal is the Zade//um, and is the landing place for the bumblebee as he alights on the flower. Here he comes humming along and alights on the labellum with his head so close to the style that it touches it. But just the instant that the bee attempts to crowd down in the flower the labellum suddenly bends downward, as shown in fig. 468. In so doing the head of the bumblebee scrapes against the pollen, bearing some of it off. Now while the bee is sipping the nectar it is too far below the stigma to deposit any pollen on the latter. When the bum- blebee flies to another newly opened flower, as it alights, some of the pollen of the former flower is brushed on the stigma. 865. One can easily demonstrate the sensitiveness of the labellum of recently opened canna flowers, if the labellum has not already moved down in response to some stimulus. Take a lead-pencil, or a knife blade, or even POLLINATION. 449 the finger, and touch the upper surface of the labellum by thrusting it between the latter and the style. The labellum curves quickly downward. 866, Sometimes the bumblebees, after sipping the nectar, will crawl up over the style in a blundering manner. In this way the flower may be pol- oe SOE OCs x a oe. @\° ae ‘° even 0 P) ‘9 2 ey. wo? t ee Fig. 471. Pollination of the canna flower by bumblebee. Canna flower. Pollen on style, sta- men at left. linated with its own pollen, which is equivalent to self pollination, Un- doubtedly self pollination does take place often in flowers which are adapted, to a greater or less degree, for cross pollination by insects. CHAPTER XLIV. THE SF RUG I, Parts of the Fruit. 867. After the flower comes the fruit.—With the perfection of the fruit the seed is usually formed. ‘This is the end towards which the energies of the plant have been directed. While the seed consists only of the ripened ovule and the contained em- bryo, the fruit consists of the ripened ovary in addition, and in many cases with other accessory parts, as calyx, receptacle, etc., combined with it. The wall of the mpened ovary is called a pericarp, and the walls of the ovary form the walls of the fruit. 868. Pericarp, endocarp, exocarp, etc.—This is the part of the fruit which envelops the seed and may consist of the carpels alone, or of the carpels and the adherent part of the receptacle, or calyx. In many fruits the pericarp shows a differentiaticn into layers, or zones of tissue, as in the cherry, peach, plum, etc. The outer, which is here soft and fleshy, is exocarp, while the inner, which is hard, is the endocarp. An intermediate layer is sometimes recognized and is called mesocarp. In such cases the skin of the fruit is recognized as the epicarp. Epicarp and mesocarp are more often taken together as exocarp. In general fruits are dry or fleshy. Dry fruits may be grouped under two heads. Those which open at maturity and scatter the seed are dehiscent. ‘Those which do not open are indehiscent. 450 THE FRUIT. | 451 II. Indehiscent Fruits. 869. The akene——The thin dry wall of the ovary encloses the single seed. It usually does not open and free the seed within. Such a fruit is an akene. An akene is a dry, indehiscent fruit. All of the crowded but separate pistils in the buttercup flower when ripe make a head of akenes, which form the fruit of the buttercup. Other examples of akenes are Fig. 472. found in other members of the buttercup family, “Sf$.2t2csn also in the composites, etc. The sunflower seed is a good example of an akene. 870. The samara.—The winged fruits of the maple (fig. 574), elm, etc., are indehiscent fruits. They are sometimes called . key fruits. 871. The caryopsis is a dry fruit in which the seed is con- solidated with the wall of the ovary, as in the wheat, corn, and other grasses. 872. The schizocarp is a = dry fruit consisting of several Fiz. 473. locules (from a _ syncarpous ee acorn: gynecium). At maturity the carpels separate from each other, but do not themselves dehisce and free the seed, as in the carrot family, mallow family. 873. The acorn.—The acorn fruit consists of the acorn and the “cup” at the base in which the acorn sits. The cup is a curious structure, and is supposed to be composed of an involucre of numerous small leaves at the base of the pistillate flower, which become consolidated into a hard cup-shaped body. When the acorn is ripe it easily separates from the cup, but the hard pericarp forming the “shell” of the acorn remains closed. Frost may cause it to crack, but very often the pericarp is split open at the smaller end by wedge-like pressure exerted by the emerging radicle during germination. EFS wy, ZZ 1 Z Z Ea ~~ LG in 452 RELATION TO ENVIRONMENT. 874. The hazelnut, chestnut, and beechnut.—In these fruits a crown of leaves (involucre) at the base of the flower grows around aa arn Fig. 474. Germinating acorn of white oak. the nut and completely envelops it, forming the husk or burr. When the fruit is ripe the nut is easily shelled out from the husk. In the beechnut and chestnut the burr dehisces as it dries and allows the nut to drop out. But the fruit is not dehiscent, since the pericarp is still intact and encloses the seed. 875. The hickory-nut, walnut, and butternut.—In these fruits the “shuck” of the hickory-nut and the “hull” of the walnut and butternut are different from the involucre of the acorn or hazelnut, etc. In the hickory-nut the “shuck” probably con- sists partly of calyx and partly of involucral bracts consolidated, probably the calyx part predominating. This part of the fruit splits open as it dries and frees the “nut,” the pericarp being very hard and indehiscent. In the walnut and butternut the “hull” is probably of like origin as the “shuck”’ of the hickory nut, but it does not split open as it ripens. It remains fleshy. The walnut and butternut are often called drupes or stone fruits, but the fleshy part of the fruit is not of the same origin as the fleshy part of the true drupes, like the cherry, peach, plum, etc. III. Dehiscent Fruits. 876. Of the dehiscent fruits several prominent types are rec- ognized, and in general they are sometimes called pods. There is a single carpel (simple pistil), and the pericarp is dry (gynce- THE FRUIT. | AS3 cium apfocarpous); or where there are several carpels united the pistil is compound (gyncecium syncar pous). 877. The capsule-——When the capsule is syncarpous it may dehisce in three different ways: 1st. When the carpels split along the line of their union with each other longitudi- K >) i ( A ‘Sle nally (septicidal dehiscence), re SA ee ee as in the azalea or rhodo- dendron. 2d. When _ the Fig. 475. - - Diagrams illustrating three types (in cross- carpels split down the mid- section) of the dehiscence of dry fruits. Loc, He. dine (loculici andes loculicidal; Sep, Septicidal, Septifragal. cence), as in the fruit of the iris, lily, etc. 3d. When the carpels open by pores (poricidal dehiscence), as in the poppy. Some syncarpous capsules have but one locule, the partitions between the different locules when young having disappeared. ‘The “bouncing-bet” is an example, and the seeds are attached to a central column in four rows corresponding to the four locules present in the young stage. 878, A follicle is a capsule with a single carpel which splits open along the ventral or upper suture, as in the larkspur, peony. 879. The legume, or true pod, is a capsule with a single carpel which splits along both sutures, as the pea, bean, etc. As the pod ripens and dries, a strong twisting ten- sion is often produced, which splits the pod suddenly, scattering the seeds. 880. The silique.—In the toothwort, shepherd’s-purse, and nearly all of the plants in the mustard family the fruit consists of two united carpels, which separate at maturity, leaving the par- Septifragal tition wall persistent. Such a fruit is a silique; when short it is a silicle, or pouch. 881. A pyxidium, or pyxis, is a cap- sule which opens with a lid, as in the Fig. 476. . Fruit of sweet pea; a pod. plantain. 454 RELATION TO ENVIRONMENT. IV. Fleshy and Juicy Fruits. 882. The drupe, or stone-fruit.—In the plum, cherry, peach, apricot, etc., the outer portion (exocarp) of the pericarp (ovary) becomes fleshy, while the inner portion (endocarp) becomes hard and stony, and encloses the seed, or “pit.’’ Such a fruit is known as a drupe, or as a stone-fruit. In the almond the fleshy part of the fruit is removed. 883. The raspberry and blackberry.—While these fruits are Fig. 477. Drupe, or stone-fruit, of plum. known popularly as “berries,” they are not berries in the tech- nical sense. Each ovary, or pericarp, in the flower forms a single small fruit, the outer portion being fleshy and the inner stony, just as in the cherry or plum. It isa drupelet (little drupe). All of the drupelets together make the “berry,” and as they ripen the separate drupelets cohere more or less. It is a collection, or aggregation, of fruits, and consequently they are sometimes called collective fruits, or aggregate fruits. In the raspberry the fruit separates from the receptacle, leaving the latter on the stem, while the drupelets of the blackberry and dewberry adhere to the receptacle and the latter separates from the stem. THE FRUIT. 455 884. The berry.—In the true berry both exocarp (including mesocarp) and endocarp are fleshy or juicy. Good examples are found in cranberries, huckleberries, gooseberries, currants, snowberries, tomatoes, etc. The calyx and wall of the pistil are adnate, and in fruit become fleshy so that the seeds are im- bedded in the pulpy juice. The seeds themselves are more or less stony. In the case of berries, as well as in strawberries, rasp- berries, and blackberries, the fruits are eagerly sought by birds and other animals for food. The seeds being hard are not digested, but are passed with the other animal excrement and thus gain dispersal. V. Reinforced, or Accessory, Fruits. When the torus (receptacle) is grown to the pericarp in fruit, the fruit is said to be reinforced. The torus may enclose the pericarps, or the latter may be seated upon the torus. 885. In the strawberry the receptacle of the flower becomes Fig. 478. Fruit of raspberry. larger and fleshy, while the “seeds,’’ which are akenes, are sunk in the surface and are hard and stony. The strawberry thus 456 RELATION TO ENVIRONMENT, differs from the raspberry and blackberry, but like them it is not a true berry. 886. The apple, pear, quince, etc.—In the flower the calyx, corolla, and stamens are perigynous, 1.e., they-are seated on the margin of the receptacle, or torus, which is elevated around the pistils. In fruit the receptacle becomes consolidated with the wall of the ovary (with the pericarp). The torus thus rein- jorces the pericarp. ‘The torus and outer portion of the pericarp become fleshy, while the inner portion of the pericarp becomes papery and forms the “core.’’ The calyx persists on the free end of the fruit. Such a fruit is called a pome. ‘The receptacle, or torus, of the rose-flower, closely related to the apple, is in- _ structive when used in comparison. The rose-fruit is called a 74 hip.” 887. The pepo.—The fruit of the squash, pumpkin, cucum- ber, etc., is called a pepo. ‘The outer part of the fruit is the recep- tacle (or torus), which is consolidated with the outer part of the three-loculed ovary. The calyx, which, with the corolla and stamens, was epigynous, falls off from the young fruit. VI. Fruits of Gymnosperms. The fruits of the gymnosperms differ from nearly all of the angiosperms in that the seed formed from the ripened ovule is naked from the first, i.e., the ovary, or carpel, does not enclose the seed. 888. The cone-fruit is the most prominent fruit of the gymno- sperms, as can be seen in the cones of various species of pine, spruce, balsam, etc. 889. Fleshy fruits of the gymnosperms.—Some of the fleshy fruits resemble the stone-fruits and berries of the angiosperms. The cedar “‘berries,’’ for example, are fleshy and contain several seeds. But the fleshy part of the fruit is formed, not from peri- carp, since there is no pericarp, but from the outer portion of the ovules, while the inner walls of the ovules form the hard stone surrounding the endosperm and embryo. An examination THE FRUIT. 457 of the pistillate flower of the cedar (juniper) shows usually three flask-shaped ovules on the end of a fertile shoot subtended by as many bracts (carpels?). The young ovules are free, but as they grow they coalesce, and the outer walls become fleshy, forming a berry-like fruit with a three-rayed crevice at the apex marking the number of ovules. The red fleshy fruit of the yew (taxus) resembles a drupe which is open at the apex. The stony seed is formed from the single ovule on the fertile shoot, while the red cup-shaped fleshy part is formed from the outer integument of the ovule. The so-called “aril” of the young ovule is a rudi- mentary outer integument. The fruit of the maidenhair tree (ginkgo) is about the size of a plum and resembles very closely a stone-fruit. But it is merely a ripened ovule, the outer layer becoming fleshy while the inner layer becomes stony and forms the pit which encloses the em- bryo and endosperm. The so-called “aril,” or “collar,” at the base of the fruit is the rudimentary carpel, which sometimes is more or less completely expanded into a true leaf. The fruit of cycas is similar to that of ginkgo, but there is no collar at the base. In zamia the fruit is more like a cone, the seeds being formed, however, on the under sides of the scales. VII. The “ Fruit” of Ferns, Mosses, etc. 890. The term “fruit” is often applied in a general or popu- lar sense to the groups of spore-producing bodies of ferns (/ruit- dots, or sori), the spore-capsules of mosses and liverworts, and also to the fruit-bodies, or spore-bearing parts, of the fungi and alge. CHAPTER XLV. SEED ~DISPERSAL 891, Means for dissemination of seeds.—During late summer or autumn a walk in the woods or afield often convinces us of the perfection and variety of means with which plants are provided for the dissemination of their seeds, especially when we discover that several hundred seeds or fruits of different plants are stealing a ride at our expense and annoyance. The hooks and barbs on various seed-pods catch into the hairs of passing animals and the seeds may thus be transported ~ considerable distances. Among the plants familiar to us, which have such contrivances for unlawfully gaining transportation, are the beggar-ticks or stick tights, or sometimes called a\ \) q y i Y WSS SAU) \ \ \\ Fig. 470- Fig. 480, _ Bur of bidens or bur-marigold, show- Seed pod of tick-treefoil (desmodium); at the ing barbed seeds. right some of the hooks greatly magnified. bur-marigold (bidens), the tick-treefoil (desmodium), or cockle-bur (xanthi- um), and burdock (arctium). 892, Other plants like some of the sedges, etc., living on the margins of streams and of lakes, have seeds which are provided with floats. The wind or the flowing of the water transports them often to distant points. 458 = SEED DISPERSAL. 459 893. Many plants poszess attractive devices, and offer a substantial reward, as a price for the distribution of their seeds. Fruits and berries are devoured by birds and other animals ; the seeds within, often passing un- harmed, may be carried long distances. Starchy and albuminous seeds and ; WANN WS ‘Ss ey) ' Fig. 481. Seeds of geum showing the hooklets where the end of the style is kneed. grains are also devoured, and while many such seeds are destroyed, others are not injured, and finally are lodged in suitable places for growth, often remote from the original locality. Thus animals willingly or unwillingly become agents in the dissemination of plants over the earth. Man in the development of commerce is often responsible for the wide distribution of harmful as well as beneficial species. 894, Other plants are more independent, and mechanisms are employed for violently ejecting seeds from the pod or fruit. The unequal tension of the pods of the common vetch (Vicia sativa) when drying causes the valves to contract unequally, and on a dry summer day the valves twist and pull in opposite directions until they suddenly snap apart, and the seeds are thrown forcibly for some distance. In the impatiens, or touch-me-not as it is better known, when the pods are ripe, often the least touch, or a pinch, or jar, sets the five valves free, they coil up suddenly, and the small seeds are thrown for several yards in all directions. During autumn, on dry days, the pods of the witch hazel contract unequally, and the valves are suddenly spread apart, and the seeds are hurled away. Other plants have seeds provided with tufts of pappus, or hair-like masses, or wing-like outgrowths which serve to buoy them up as they 460 RELATION TO ENVIRONMENT. are whirled along, often miles away. In late spring or early summer the pods of the willow burst open, exposing the seeds, each with a tuft of white hairs making a mass of soft down. As the delicate hairs dry, Fig. 482. Touch-me-not (Impatiens fulva); side and front view of flower below; above unvpened pod, and opening to scatter the seed. they straighten out in a loose spreading tuft, which frees the individual seeds from the compact mass. Here they are caught by currents of air and float off singly or in small clouds. 895. The prickly lettuce.—In late summer or early autumn the seeds of the prickly lettuce (Lactuca scariola) are caught up from the roadsides by the winds, and carried to fields where they are unbidden as well as unwel- come guests. This plant is shown in fig. 483. 896. The wild lettuce.—A related species, the wild lettuce (Lactuca cana- densis) occurs on roadsides and in the borders of fields, and is about one meter in height. The heads of small yellow or purple flowers are arranged in a loose or branching panicle. The flowers are rather inconspicuous, the rays projecting but little above the apex of the enveloping involucral bracts, which closely press together, forming a flower-head more or less flask- shaped. At the time of flowering the involucral bracts spread somewhat at the apex, and the tips of the flowers are a little more prominent. As the flowers then wither, the bracts press closely together again and the head is closed. As the seeds ripen the bracts die, and in drying bend outward and down- ward, around the flower stem below, or they fall away. The seeds are SEED DISPERSAL. — 461 thus exposed. The dark brown achenes stand over the surface of the recep- tacle, each one tipped with the long slender beak of the ovary. The ‘‘pap- pus,”’ which is so abundant in many of the plants belonging to the composite family, forms here a pencil-like tuft at the tip of this long beak. As the involucral bracts dry and curve down- ward, the pappus also p dries, and in doing so Py bends downward and | stands outward, brist- 3 ee \ VA 1 | ling like the spokes of : asmallwheel. Itisan Nie 64 interesting coincidence NY that this takes place simultaneously with the pappus of all the seeds of a head, so that the ends of the pappus bristles of ad- joining seeds meet, forming a many-sided dome of a delicate and beautiful texture. This causes the beaks of the achenes to be crowded apart, and with the leverage thus broughtto bear upon the achenes they are pried off the receptacle. They are thus in a position to be wafted away by the gentlest zephyr, and they go sailing away on the wind like a miniature parachute. . SE 5 ES SS) _ As they come slowly & Fig. 483. to the ground the seed is thus carefully low- ered first, so that it touches the ground in a position for the end which contains the root of the embryo to come in contact with the soil. Lactuca scariola. 462 RELATION TO ENVIRONMENT. 897. The milkweed, or silkweed.—The common milkweed, or silkweed (Asclepias cornuti), so abundant in rich grounds, is attractive not only Fig. 484. Milkweed (Asclepias cornuti); dissemination of seed. because of the peculiar pendent flower clusters, but also for the beautiful floats with which it sends its seeds skyward, during a puff of wind, to finally lodge on the earth. 898. The large boat-shaped, tapering pods, in late autumn, are packed with oval, flattened, brownish seeds, which overlap each other in rows like shingles on a roof. These make a pretty picture as the pod in drying splits along the suture on the convex side, and exposes them to view. The silky tufts of numerous long, delicate white hairs on the inner end of each seed, in drying, bristle out, and thus lift the seeds out of their enclosure, where they are caught by the breeze and borne away often to a great distance, where they will germinate if conditions become favorable, and take their places as contestants in the battle for existence. 899. The virgin’s bower.—The virgin’s bower (Clematis virginiana), too, clambering over fence and shrub, makes a show of having transformed its SEED DISPERSAL. 463 exquisite white flower clusters into grayish-white tufts, which scatter in the autumn gusts into hundreds of arrow-headed, spiral plumes. The achenes Fig. 485. Seed distribution of virgin’s bower (clematis). have plumose styles, and the spiral form of the plume gives a curious twist to the falling seed (fig. 485). CHAPTER XLVIE VEGETATION IN RELATION TO ENVIRONMENT.* I. Factors Influencing Vegetation Types. 900. All plants are subject to the influence of environment from the time the seed begins to germinate until the seed is formed again, or until the plant ceases to live. A suitable amount of warmth and moisture is necessary that the seed may germi nate. Moisture may be present, but if it is too cold, germination will not take place. So in all the processes of life there are several conditions of the environment, or the ‘‘outside” of plants, which must be favorable for successful growth and reproduction. Not only is this true, but the surroundings of plants to a large extent determine the kind of plants which can grow in particular localities. It is also evident that the reaction of environment on plants has in a large measure caused them to take on certain forms and structures which fit them better to exist under local conditions. In other cases where plants have varied by muta- tion (p. 338) some of the new forms may be more suited to the conditions of environment than others and they are more apt to survive. These conditions of environment acting on the plant are jactors which have an important determining influence * on the existence, habitat, habit, and form of the plant. These factors are sometimes spoken of as ecological factors, and the study of plants in this relation is sometimes spoken of as ecology, * For a fuller discussion of this subject by the author see Chapters XLVI-— LVII of his “College Text-book of Botany’? (Henry Holt & Co.). t otkos=house, and Aoyvos =discourse. 464 WACTORS INFLOBNCING VEGETATION TYPES. 465 which means a study of plants in their home or a study of the household relations of plants. ‘These factors are of three sorts: ist, physical factors; 2d, climatic factors; 3d, biotic factors. 901. Physical factors.—Some of these factors are water, light, heat, wind, chemical or physical condition of the soil, etc. Water is a very important factor for all plants. Even those growing on land contain a large percentage of water, which we have seen is rapidly lost by transpiration, and unless water is available for root absorption the plant soon suffers, and aquatic plants are injured very quickly by drying when taken from the water. Excess of soil water is injurious to some plants. Lzght is impor- tant in photosynthesis, in determining direction of growth as well as in determining the formation of suitable leaves in most plants, and has an influence in the structure of the leaf according as the light may be strong, weak, etc. Heat has great influence on plant growth and on the distribution of plants. The growth period for most vegetation begins at 6° C. (=43°F.), or in the tropics at 10°-12° C., but a much higher temperature is usually necessary for reproduction. Some arctic alge, however, fruit at 1.8°C. The upper limit favorable for plants in general is 45°-50° C., while the optimum temperature is below this. Very high temperatures are injurious, and fatal to most plants, but some alge grow in hot springs where the temperature reaches 80°-90° C. Some desert plants are able to endure a temperature of 70° C., while some flowering plants of other regions are killed at 45°C. Some plants are specifically susceptible to cold, but most plants which are injured by freezing suffer because the freezing is a drying process of the protoplasm (see p. 374). Wand may serve useful purposes in pollination and in aeration, but severe winds injure plants by causing too rapid transpiration, by felling trees, by breaking plant parts, by deforming trees and shrubs, and by mechanical injuries from “‘sand-blast.”’ Ground covers protect plants in several ways. Snow during the winter checks radiation of heat from the ground so that it does not freeze to so great a depth, and this is very important for many trees and shrubs. It also prevents alternate freezing and thaw- 466 RELATION TO ENVIRONMENT. ing of the ground, which ‘‘heaves’”? some plants from the soil. Leaves and other plant remains mulch the soil and check evapora- tion of water. The influence of the chemical condition of the soil is very marked in alkaline areas where the concentration of salt in the soil permits a very limited range of species. So the physical and mechanical conditions of the soil influence plants because the moisture content of the ground is so closely dependent on its physical condition. Rocky and gravelly soil, other things being equal, is dry. Clay is more retentive of moisture than sand, and moisture also varies according to the per cent of humus mixed with it, the humus increasing the per- centage of moisture retained. 902. Climatic factors.—These factors are operative over very wide areas. ‘There are two climatic factors: rainfall or atmos- pheric moisture, and temperature. A very low annual rainfall in warm or tropical countries causes a desert; an abundance of rain permits the growth of forests; extreme cold prevents the growth of forests and gives us the low vegetation of arctic and alpine regions. 903. Biotic factors.—These are animals which act favorably in pollination, seed distribution, or unfavorably in destroying or injuring plants, and man himself is one of the great agencies in checking the growth of some plants while favoring the growth of others. Plants also react on themselves in a multitude of ways for good or evil. Some are parasites on others; some in symbiosis (see p. 85) aid in providing food; shade plants are protected by those which overtop them; mushrooms and other fungi disintegrate dead plants to make humus and finally plant food; certain bacteria by nitrification prepare nitrates for the higher plants (see p. 83). Il. Vegetation Types and Structures. 904. Responsive type of vegetation.—In studying vegetation in relation to environment we are more concerned with the form of the plants which fits them to exist under the local con- VEGETATION TYPES AND STRUCTURES. 467 ditions than we are with the classification of plants according to natural relationships. Plants may have the same vegetation type, grow side by side, and still belong to very different floristic types. For example, the cactus, yucca, three-leaved sumac, the sage-brush, etc., have all the same general vegetation type and thrive in desert regions. The red oaks, the elms, many goldenrods, trillium, etc., have the same general vegetation type, but represent very different floristic types. The latter plants grow in regions with abundant rainfall throughout the year, where the growing season is not very short and temperature conditions are moderate. Some goldenrods grow in very sandy soil which dries out quickly. These have fleshy or succulent leaves for storing water, and while they are of the same floristic type as goldenrods growing in other places, the vegetation type is very different. The types of vegetation which fit plants for growing in special regions or under special conditions, they have taken on in response to the influence of the conditions of their envi- ronment. While we find all gradations between the different types of vegetation, looking at the vegetation in a broad way, several types are recognized which were proposed by Warming as follows: 905. Mesophytes.—These are represented by land plants under temperate or moderate climatic and soil conditions. The normal land vegetation of our temperate region is composed of mesophytes, that is, the plants have mesophytic structures during the growing season. The deciduous forests or thickets of trees and shrubs with their undergrowth, the meadows, pas- tures, prairies, weeds, etc., are examples. In those portions of the tropics where rainfall is great the vegetation is mesophytic the year around. 906. Xerophytes.—These are plants which are provided with structures which enable them to live under severe conditions of dryness, where the air and soil are very dry, as in deserts or semideserts, or where the soil is very dry or not retentive of moisture, as in very sandy soil which is above ground water, or in rocky areas. Since the plants cannot obtain much water from the soil they must be provided with structures which will SSS 468 RELATION TO ENVIRONMENT. enable them to retain the small amount they can absorb from the soil and give it off slowly. Otherwise they would dry out by evaporation and die. Some of the structures which enable xerophytic plants to withstand the conditions of dry climate and soil are lessened leaf surface, increase in thickness of leaf, increase in thickness of cuticle, deeply sunken stomates, compact growth, also succulent leaves and stems, and in some cases loss of the leaf. Evergreens of the north temperate and the arctic regions are xerophytes. 907. Hydrophytes,—These are plants which grow in fresh water or in very damp situations. The leaves of aerial hydrophytes are very thin, have a thin cuticle, and lose water easily, so that if the air becomes quite dry they are in danger of drying up even though the roots may be supplied with an abun- dance of water. ‘The aquatic plants which are entirely submerged have often thin leaves, or very finely divided or slender leaves, since these are less liable to be torn by currents of water. The stems are slender and especially lack strengthening tissue, since the water buoys them up. Removed from the water they droop of their own weight, and soon dry up. ‘The stems and leaves have large intercellular spaces filled with air which aids in aera- tion and in the diffusion of gases. Some use the term hygrophytes. 908. Halophytes.—These are salt-loving plants. They grow in salt water, or in salt marshes where the water is brackish, or in soil which contains a high per cent of certain salts, for example the alkaline soils of the West, especially in the so-called ‘‘Bad Lands”? of Dakota and Nebraska, and in alkaline soils of the Southwest and California. These plants are able to withstand a stronger concentration of salts in the water than other plants. They are also found in soil about salt springs. 909. Tropophytes.*—Tropophytes are plants which can live as mesophytes during the growing season, and then turn to a xerophytic habit in the resting season. Deciduous trees and shrubs, and perennial herbs of our temperate regions, are in this sense tropophytes, while many are at the same time mesophytes * Term used by Schimper. PLANT FORMATIONS. 469 if they exist in the portions of the temperate region where rain- fall is abundant. In the spring and summer they have broad and comparatively thin leaves, transpiration goes on rapidly, but there is an abundance of moisture in the soil, so that root absorption quickly replaces the loss and the plant does not suffer. In the autumn the trees shed their leaves, and in this condition with the bare twigs they are able to stand the drying effect of the cold and winds of the winter because transpiration is now at a minimum, while root absorption is also at a minimum because of the cold condition of the soil. Perennial herbs like trilium, dentaria, the goldenrods, etc., turn to xerophytic habit by the death of their aerial shoots, while the thick underground shoot which is also protected by its subterranean habit carries the plant through the winter. 910. While these different vegetation types are generally dominant in certain climatic regions or under certain soil con- ditions, they are not the exclusive vegetation types of the regions. For example, in desert or semidesert regions the dominant vegetation type is made up of xerophytes. But there is a mesophytic flora even in deserts, which appears during the rainy season where temperature conditions are favorable for growth. ‘This is sometimes spoken of as the rainy-season flora. The plants are annuals and by formation of seed can tide over the dry season. So in the region where mesophytes grow there are xerophytes, examples being the evergreens like the pines, spruces, rhododendrons; or succulent plants like the stonecrop, the purslane, etc. Then among hydrophytes the semiaquatics are really xerophytes. The roots are in water, and absorption is slow because there are no root hairs, or but few, and the aerial parts of the plant are xerophytic. III. Plant Formations. 911. The term plant formation is applied to associations of plants of the same kind, though there is a great difference in the use of the word by different writers which leads to some con- 470 RELATION TO ENVIRONMENT. fusion.* It is sometimes applied to an association of individuals of a species, or of several species occupying a rather definite area of ground where the soil conditions are not greatly different (individual formation); by others it is applied to the plants of a definite physiographic area, as a swamp, moor, strand, or beach, bank, rock hill, clay hill, ravine, bluff, etc. (principal for- mation); and ina broad sense it is applied to the plants of climatic regions, of those in bodies of water, etc. (general formations). Space here is too limited to discuss all these kinds of formations, | but the nature of the general formations will be pointed out. | The general formations may be grouped into four divisions: 1st. Climatic formations. 2d. Edaphic formations. 3d. Aquatic formations. 4th. Culture formations. 912. Climatic formations.—Climatic influences extend over I wide regions, so that climate controls the general type of vegeta- tion of a region. In the sense of control there are two climatic factors, temperature and moisture, especially soil moisture. | Temperature exerts a controlling influence over the vegetation type only where the total heat during the period of growth and | reproduction is very low. ‘This occurs in polar lands and at | high elevations where the climate is alpine. In the temperate and tropical regions of the globe moisture, not heat, controls | the general vegetation type. ‘These vegetation types in general | are coincident with rainfall distribution, and Schimper recognizes | here three types, which with the arctic-alpine type would make four climatic formations as follows: 1st. The woodland formation.—This formation is characterized by trees and shrubs, and it is what is called a close formation. By this it is meant that so far as the climate is concerned the conditions are favorable for the development of trees and shrubs | in such abundance that they become the dominant vegetation type of the region and grow close together. Other plants, as * Sec the author’s ‘‘College Text-book of Botany.’”’ Chapter XLIX. PEAN DM VEO KR MATION ,S. 471 herbs, grasses, etc., occur, but they grow as subordinate elements of the general vegetation type, and as undergrowth. The land portion of the globe, therefore, outside of arctic and alpine regions, where the annual precipitation is 40 to 60 or more inches, is the area for woodland formation. In some places, the eastern part of England, for example, the annual precipitation is 25 to 30 inches, but the cool temperature permits a forest growth. It is true there are places where forests do not grow,— where man cuts them down, for example. But if cultivated lands in this region were allowed to go to waste, they would in time grow up to forest again. * So there are swamps where the soil is too wet for trees, or sandy or rocky areas where there is not a suf- ficient amount of soil or water to support forest trees. But here it is the soil conditions, not climatic conditions, which pre- vent the development of the forest. But we know that swamps are being filled in and the ground gradually becoming higher and drier, and that soil is slowly accumulating in rocky areas, so that in time if left to natural forces these places would become forested. So this area of heavy annual rainfall is a potential forest area. ‘These areas are determined by warm currents of moisture-laden air from the ocean moving over cooler land areas where the moisture is precipitated. In general these areas are along the coasts of great continents and on mountains. There- fore the interior of a continent is apt to be dry because most of the moisture has been precipitated before it reaches the interior. Deserts or steppes are therefore usually near the interior of continents. Some exceptions to this general rule are found: central South America, which is a region of exceptional rainfall because the moisture-laden winds here come from the warmest part of the ocean; the desert region west of the Andes mountains, where the winds are not favorable; southern California, where the winds come chiefly from a cooler portion of the Pacific ocean and move over an area of high temperature, etc. 2d. Grassland jormation.—Grasses form the dominant vege- tation type where the annual rainfall is approximately 15 to 25 inches. In true grasslands the formation is a close one since 472 - RELATION TO ENVIRONMENT. there is still a sufficient amount of moisture to provide for all the plants which can stand on the ground. Yet there is not enough moisture to permit the growth of forest as the dominant type without aid and protection by man. The so-called prairie regions are examples. Trees and shrubs do occur, but they cannot compete successfully with the grasses because the climatic Fig. 486. Typical prairie scene, a few miles west of Lincoln, Nebraska. (Bot. Dept., Univ. Nebraska. ) conditions are favorable for the latter and unfavorable for the former. On the border line between forest and prairie the line of division is not a clear-cut one because conditions grade from one to the other. The two formations are somewhat mixed, like the outposts of contending armies, arms of the forest or prairie extending out here and there. In the United States the prairies extend from Illinois to about the rooth meridian, and beyond this to the foothills of the Rockies and southwest to the Sonora Nevada desert the region is drier, the rainfall varying from 10 to 20 inches. This is the area of the Great Plains, and while grasses of the bunch type are dominant, they make PLANT FORMATIONS. 473 a more or less open formation because the moisture is not suf- ficient to supply all the plants which could be crowded on the ground, each individual tuft needing an area of ground surround- ing it on which it can draw for moisture. Such a formatior is an open one, and in this respect is similar to desert formations. 3d. Desert formations.—These occur where the annual rain- fall is still lower, 10 to 4 inches or even less, 2 to 3 inches, while in one place in Chili it is as low as $ inch. In the great Sahara desert it is about 8 inches, while in the Sonora Nevada desert Fig. 487. Winter range in northwestern Nevada, showing open formation; white sage (Eurotia lanata) in foreground, salt-bush (Atriplex confertifolia) and bud-sage (Artemisia spinescens) at base of hill, red sage (Kochia ae on the higher slope. (After Griffiths, Bull. 38, Bureau Plant Ind., U. S. Dept. Agr.) in the southwestern United States it is 4 to 8 inches. Here the formation is an open one. Im the forest and prairie forma- tions the plants compete with each other for occupancy of the ground, since climatic conditions are favorable, so that the struggle against climate isnot severe. Butin the desert plants do not com- pete with each other; since the climate is so austere, the struggle is against the climate. Hence plants stand at some distance from each other because the roots need the moisture from the ground for some distance around them. There is not enough moisture for all the plants that begin, and those which get the start take 474 RELATION TO ENVIRONMENT. the moisture away from the intervening ones, which then die. Since the struggle is against the adverse conditions of climate i and not a competition between plants to occupy the ground, i no one floristic type dominates as in the case of the grasses and I forests of the grassland and woodland formations, but grass- land and woodland types grow together. So we find grasses, | trees, and shrubs growing without competition in the desert. The dominant vegetation type is xerophytic. 4th. Arctic-alpine formation. This formation extends from i the limit of tree growth to the region of perpetual ice and snow. | Fig. 488. Northern limit of tree growth, Alaska. (Copyright, 1899, by E. H. Harriman.) The forest here comes in competition with climate, with the - severe cold of the long winter night, so that tree growth is limited, and on the border line with the woodland formation the trees are stunted, bent to one side by the heavy snows, or the tops are killed by the cold wind. The arctic zone of plant growth is: sometimes spoken of as the ‘‘cold waste,”’ since conditions here are somewhat similar to those in the desert, the extreme cold PLANT SOCIETIES. 475 exercising a drying effect on vegetation, and the vegetation type then is largely xerophytic. 913. Edaphic * formations.—Edaphic formations may occur in any of the climatic-formation areas. ‘They are controlled by the condition of soil or ground. The condition of the soil is unfavorable for the growth of the general vegetation type of that region, or is more favorable for another vegetation type, so that soil conditions overcome the climatic conditions. These areas include swamps, moors, the strand or beach, rocky areas, etc., as well as oases in the desert, warm oases in the arctic zone, river bottoms in the prairie and plains region, alkaline areas, etc. The edaphic formations may be close or open according to the nature of the soil. The edaphic formations then are infiltrated in the climatic formations, the different vegetation types fitting together like pieces of mosaic, which can be seen in some places from a mountain top, or if one could take a bird’s-eye view of the landscape or from a balloon. 914. Aquatic formations.—These are made up of water plants and are of two general kinds: fresh-water plant forma- tions in ponds, lakes, streams; and salt-water plant formations in the ocean and inland salt seas. 915. Culture formations.— Culture formations are largely controlled by man, who destroys the climatic or edaphic forma- tion and by cultivation protects cultivated types, or by allowing land to go to ‘‘waste” permits the growth of weeds, though weeds are often abundant in the culture areas. In general the culture formations may be grouped into two subdivisions: rst, the vegetation of cultivated places; and 2d, the vegetation of waste places, as abandoned fields, roadsides, etc. IV. Plant Societies. 916. Plant societies are somewhat definite associations of the vegetation of an area marked by physiographic conditions. A single plant society is nearly if not altogether identical with a * Edagos =ground. 476 RELATION TO ENVIRONMENT. ‘‘principal formation,’ but is a more popular expression, and besides includes all the plants growing on the area, while in the use of the term ‘‘principal formation” we have reference mainly to the dominant plants and the most conspicuous subordinate species. 917. Complex character of plant societies.—In their broadest analysis all plant societies are complex. Every plant society has one or several dominant species, the individuals of which, because of their number and size, give it its peculiar character. The society may be so nearly pure that it appears to consist of the individuals of a single species. But even in those cases there are small and conspicuous plants of other species which occupy spaces between the dominant ones. Usually there are several or more kinds in the same society. The larger individuals come into competition for first place in regard to ground and light, the smaller ones come into competition for the intervening spaces for shade, and so on down in the scale of size and shade _ tolerance. Then climbing plants (lianas) and epiphytes (lichens, alga, mosses, ferns, tree orchids, etc.) gain access to light and sup- port by growing on other larger and stouter members of the society. Parasites (dodder, mistletoes, rusts, smuts, mildews, bacteria, etc.) are present, either actually or potentially, in all societies, and in their methods of obtaining food sap the life and health of their hosts. Then come the scavenger members, whose work it is to clean house, as it were, the great army of saprophytic fungi (molds, mushrooms, etc.), and bacteria ready to lay hold on dead and dying leaves, branches, trunks, roots, etc., disin- tegrate them, and reduce them to humus, where other fungi change them into a form in which the larger members of the plant society can utilize them as plant food and thus continue the cycle of matter through life, death, decay, and into life again. Mycorhiza (see Chapter IX) or other forms of mutualistic symbiosis occur which make atmospheric nitrogen available for food, or shorten the path from humus to available food, or the humus plants feed on the humus directly. Nor should we leave out of account the myriads of nitrate and nitrite bacteria PLANT SOCIETIES. 477 (see Chapter IX) which make certain substances in the soil avail- able to the higher members of the society. Most plant societies are also benefited or profoundly influenced in other ways by animals, as the flower-visiting insects, birds which feed on injurious insects, the worms which mellow up the soil and cover dead organic matter so that it may more thoroughly decay. In short, every plant society is a great cosmos like the universe itself of which it is a part, where multitudinous forms, processes, influences, evolutions, degenerations, and regenerations are at work. 918. Forest Societies.*—Each different climatic belt or region has its characteristic forest. For example, the forests of the Hudsonian zone in North America are different from those of the Canadian zone, and these in turn different from those in the transition zone (mainly in northern United States). The forests of the Rocky mountains and of the Pacific coast differ from those of the Alleghanian, Carolinian (mainly middle United States) or Austroriparian (southern United States) areas. Finally, tropical forests are strikingly different from those of other regions. Similar variations occur in the forests of other regions of the globe. The character of these forests depends largely on climatic factors. The character of the forest varies, however, even in the same climatic area, dependent on soil conditions, or success in seeding and ground-gaining of the different species in competition, etc. 919. General structure of the forest.—Structurally the forest possesses three subdivisions: the floor, the canopy, and the interior. The floor is the surface soil, which holds the rootage of the trees, with its covering of leaf-mold and carpet of leaves, mosses, or other low, more or less compact vegetation. The canopy is formed by the spreading foliage of the tree crowns, which, in a forest of an even and regular stand, meet and form a continuous mass of foliage through which some light filters down into the interior. Where the stand is irregular, i.e., the * For a full discussion of forest societies see Chapter L in the author’s “College Text-book of Botany.” We es | i ie ti) t i 478 RELATION 70 ENVIRONMENT. trees of different heights, the canopy is said to be ‘‘compound” or ‘‘storied.”? Where it is uneven, there are open places in the canopy which admit more light, in which case the under- growth may be different. The interior of the forest lies between the canopy and the floor. It provides for aeration of the floor and interior occupants, and also room for the boles or tree trunks Fig. 480. Mature forest of redwood (Sequoia sempervirens). (Bureau of Forestry, U.S. Dept. Agr., Bull. 38.) (called by foresters the wood mass of the forest) which support the canopy and provide the channels for communication and food exchange between the floor and canopy. The canopy manufactures the carbohydrate food and assimilates the mineral and proteid substances absorbed by the roots in the soil; and also gets rid of the surplus water needed for conveying food materials from the floor to the place where they are elaborated. It is the seat where energy is created for work, and also the place for seed production. PLANT SOCIETIES. 479 920. Longevity of the forest.—The forest is capable of self- perpetuation, and, except in case of unusual disaster or the action of man, it should live indefinitely. As the old trees die they are gradually replaced by younger ones. So while trees may come and trees may go, the forest goes on forever. 921. Autumn colors.—One of the striking effects produced by the deciduous forests is that of the autumn coloring of the leaves. It is more pronounced in the forests of the United States than in corresponding life zones in the eastern hemisphere because of the greater number of species. With the disintegration of the chlorophyll bodies, other colors, which in some cases were masked by the green, appear. In other cases decomposition products result in the formation of other colors, as red, scarlet, yellow, brown, purple, maroon, etc., in different species. These coloring substances to some extent are believed to protect the nitrogenous substances in the leaf from injury. The colors absorb the sun’s rays, which otherwise might destroy these nitrogenous substances before they have passed back through -the petiole of the leaf into the stem, where they may be stored for food. The gorgeous display of color, then, which the leaves of many trees and shrubs put on is one of the many useful adapta- tions of the plants. 922. Importance of the forest in the disposal of rainfall. The importance of the forest in-disposing of the rainfall is very great. The great accumulation of humus on the forest floor holds back the water both by absorption and by checking its flow, so that it does not immediately flow quickly off the slopes into the drain- age system of the valley. It percolates into the soil. Much of itis held in the humus and soil. What is not retained thus filters slowly through the soil and is doled out more gradually into the valley streams and mountain ttributaries, so that the flood period is extended, and its injury lessened or entirely pre- vented, because the body of water moving at any one time is not dangerously high. The winter snow is shaded and in the spring melts slowly, and the spring freshets are thus lessened. The action of the leaves and humus in retarding the flow of the 480 RELATION TO ENVIRONMENT. water prevents the washing away of the soil; the roots of trees bind the soil also and assist in holding it. 923. Absence of forest encourages serious floods.—The great floods of the Mississippi and its tributaries are due to the rapidity — with which heavy rainfall flows from the rolling prairies of the west, and from the deforested areas west of the Alleghany system. The serious floods in recent years in some of the South Atlantic States are in part due to the increasing area of deforestation in the Blue Ridge and southern Alleghany system. 924. The prairie and plains societies.—These are to be found in the grassland formation. In the prairies “‘meadows” are formed in the lower ground near river courses where there is greater moisture in soil. ‘The grasses here are principally “sod- formers’? which have creeping underground stems which mat together, forming a dense sod. On the higher and drier ground the ‘‘bunch”’ grasses, like buffalo-grass, beard-grass, or broom- sedge, etc., are dominant, and in the drier regions as one approaches desert conditions the vegetation gradually takes on more the character of the desert, so that in the plains sage- brush, the prickly-pear cactus, etc., occur. Besides the dominant vegetation of the society there are subordinate species, and the societies are especially marked by a spring and autumn flora of conspicuous flowering plants which are mixed with the grasses. 925. Desert societies.—These are composed of plants which possess a form or structure which enables them to exist in a very dry climate where the air is very dry and the soil contains but little moisture. The true desert plants are perennial. The growth and flowering period occurs during the rainy season, or those portions of the rainy season when the temperature is favor- able, and they rest during the very dry season and cold. Charac- teristic desert plants are the cacti with thick succulent green stems or massive trunks, the leaves being absent or reduced to mere spines which no longer function in photosynthesis; yuccas with thick, narrow and long leaves with a firm and thick cuticle; small shrubs or herbs with compact rounded habit and small thick gray leaves. All of these structures conserve moisture. PLANT SOCIETIES. 481 The mesquite tree is one of the common trees in portions of the Sonora Nevada desert. Besides the true desert plants, desert societies have a rainy-season flora consisting of annuals, which Fig. 490. Desert vegetation, Arizona, showing large succulent trunks of cactus with shrubs and stunted trees. Open formation. (Photograph by Tuomey.) can germinate, vegetate, flower, and seed during the period of rain and before the ground moisture has largely disappeared, and these pass the resting period in seed. 926. Arctic-alpine Societies.—The most striking of the arctic plant societies are the ‘“‘polar tundra,” tion largely made up of mosses, lichens, etc., only partially decayed because of the great cold of the subsoil, and perhaps also because of humus acid in the partially decayed vegetation. These tundras are brightened by numerous flowering plants which are characterized by short stems, a rosette of leaves near the ground, and by large bright-colored flowers. Heaths, saxi- frages, and dwarf willow abound. Alpine-plant societies are similar to the arctic, although some of the conditions are more extensive mats of vegeta- SO a 482 RELATION TO ENVIRONMENT. severe than in the arctic region. This is principally due to the Fig. 401. Polar tundra with scattered flowers, Alaska. (Copyright by E. H. Harriman.) fact that during the summer while the plants are growing they Fig. 402. Perennial rosette plant from alpine flora of the Andes, showing short stem. rosette of leaves, and large flower. (After Schimper.) are subject to a high temperature during the day and a very low PLANT SOCIETIES. 483 temperature at night, whereas during the summer in arctic regions while the plants are growing there is continuous warmth for growth and continuous light for photosynthesis. Five types of alpine plants are recognized by some. 1st. Elfin tree. This type has short, gnarled, often horizontal stems, as seen in pines, birches, and other trees growing in alpine heights. 2d. The alpine shrubs. In the highest alpine belts they are dwarfed and creeping, richly branched and spreading close to the ground, while at lower belts they are more like lowland shrubs. 3d. The cushion type. The branching is very profuse and the branches are short and touch each other on all sides, forming compact masses (examples saxifrages, androsace, mosses, etc.). 4th. Rosette plants. These are perennial, short stems and very strong roots, and play an important part in the alpine meadows. sth. Alpine grasses. These usually have much shorter leaves than grasses of the low- lands and consequently form a low sward. 927. Edaphic plant societies.—These are equivalent to edaphic plant formations, and the vegetation is of course controlled by the peculiar conditions of the soil. There are a number of different kinds of edaphic plant societies determined by the character of the physiographic areas. ist. Sphagnum moors. These are formed in shallow basins originally with more or less water. The growth of the sphagnum moss along with other vegetation and its partial decay in the water builds up ground rapidly so that in course of time the pond may be completely filled in. This filling in proceeds from the shore toward the center, and in the early stages of course there would be a pond in the center. ‘The partial decay of vegetation creates an excess of humus acid which retards absorption by the roots. The conditions are such, then, as require aerial structures for retarding the loss of water, and plants growing in such moors are usually xerophytes. Some of the plants are identical with those growing in the arctic tundra. 2d. Sand * strand oj beach. ‘The quantity of sand with very little or no admixture of humus or plant food makes it difficult for plants to obtain a sufficient amount of * See Chapter LIV of the author’s “College Text-book of Botany.” ee ae SS eee 484 RELATION TO ENVIRONMENT. water even where rainfall is abundant. The same may be said of the sand dunes farther back from the shore. The plants of these areas are then usually xerophytes. Some of the plants accustomed to growing in such localities are American sea-rocket, seaside spurge, bugseed, sea-blite, sea-purslane, the sand- cherry, dwarf willow, marram-grass, certain species of beard- grass, etc. 3d. Rocky shores or areas. Here lichens and mosses first grow, later to be followed by herbs, grasses, shrubs, and trees, as decayed plant remains accumulate in the rock crevices. ath. Shores of ponds, or swamp moors. Here the vegetation often takes on a zonal arrangement if the ground gradually slopes to the shore and out into the pond. In Fig. 493 is shown Fig. 493. Macrophytes in the upper zone of the photic region. Ascophyllum and Fucus at low tide, Hunter’s Island, New York City. (Photograph by M. A. Howe.) zonal distribution of plants. The different kinds of plants are drawn into these zones by the varying amount of ground water in the soil, or the varying depth of the water on the margin of the pond as one proceeds from the land towards the deeper water. On the border lines or tension lines between the different zones the plants are struggling to occupy here ground which is suitable for each adjacent individual formation. Other edaphic societies are those of marl ponds, alkaline areas, oases in deserts, 485 PLANT SOCIETIES, ‘aye'T BsnAey ‘a10yS yyNoG ‘s}ue]d jo i AO) ro) | WOTJNGLI}SIp [BUOT 486 RELATION TO ENVIRONMENT. warm oases in arctic lands, the forested areas along river bottoms in prairie or plains regions, etc. 928. Aquatic plant societies—In general we might distinguish three kinds. ist. Fresh-water plant societies, with floating alge like spirogyra, cedogonium, etc., the floating duck-meats, riccias; the plants of the lily type with roots and stems attached to the bottom and leaves floating on the surface, like the water-lily and certain pondweeds, and finally the completely submerged ones like certain pondweeds, the bassweed (Chara), etc. 2d. Marine plant societies, which are made up mostly of the red and brown alge or ‘“‘seaweeds,” though some green alge _and flowering plants also occur. 3d. The salt marshes where the water is brackish and there is usually a luxuriant growth of marsh-grasses. CHAPTER XLVIL. CLASSIFICATION OF THE ANGIOSPERMS. Relation of Species, Genus, Family, Order, -etc. 929. Species.—It is not necessary for one to be a botanist in order to recognize, during a stroll in the woods where the tril- lium is flowering, that there are many individual plants very like each other. They may vary in size, and the parts may differ a little in form. When the flowers first open they are usually white, and in age they generally become pinkish. In some individuals they are pinkish when they first open. Even with these variations, which are trifling in comparison with the points of close agreement, we recognize the individuals to be of the same kind, just as we recognize the corn plants, grown from the seed of an ear of corn, as of the same kind. Individuals of the same kind, in this sense, form a species. The white wake- robin, then, is a species. But there are other trilliums which differ greatly from this one. The purple trillium (T. erectum) shown in fig. 495 is very different from it. So are a number of others. But the purple trillium is a species. It is made up of individuals variable, yet very like one another, more so than any one of them is like the white wake-robin. 930. Genus.—Yet if we study all parts of the plant, the perennial root-stock, the annual shoot, and the parts of the flower, we find a great resemblance. In this respect we find that there are several species which possess the same general characters, In other words, there is a relationship between 487 488 CLASSIFICATION OF ANGIOSPERMS. these different species, a relationship which includes more than the individuals of one kind. It includes several kinds. Obviously, then, this is a relationship , with broader limits, and of a higher grade, than that of the individuals of aspecies. The grade next higher than species we call genus. Trillium, then, is a genus. Briefly _ the characters of the genus trillium are as follows: 931. Genus trillium—Perianth of | six parts: sepals 3, herbaceous, per- \ | \ sistent; petals colored. Stamens 6 (in i | two whorls), anthers opening inward. Ovary 3-loculed, 3-6-angled; stig- mas 3, slender, spreading. ...& ° iz Pt = : Herbs with a stout per- ae yy Fig. 495. ennial rootstock, with Lo ee tan ae fleshy, scale-like leaves, 7 tae Yan Oe from which the low annual ; TOOLsT eek. shoot arises, bearing a terminal flower and 3 large netted-veined leaves in a whorl. Note.—In speaking of the genus the present usage is to say trillium, but two words are usually employed in speaking of the species, as Trillium grandiflorum, T. erectum, etc. 932. Genus erythronium.—The yellow adder-tongue, or dogtooth violet (Erythronium americanum), shown in fig. 496, | is quite different from any species of trillium. It differs more | from any of the species of trillium than they do from each other. The perianth is of six parts, light yellow, often spotted | near the base. Stamens are 6. The ovary is obovate, tapering at the base, 3-valved, seeds rather numerous, and the style is elongated. The flower stem, or scape, arises from a scaly bulb deep in the soil, and is sheathed by two elliptical-lanceolate, GEMS) HAMIL, ILC, 489 mottled leaves. The smaller plants have no flower and but one leaf, while the bulb is nearer the surface. Each year new bulbs are formed at the end x of runners from a parent bulb. These runners penetrate each year deeper into the soil. The deeper bulbs bear the flower stems. 933. Genus lil- ium.— While the lily differs from either the trillium or erythronium, yet we recognize a re- lationship when we compare the peri- anth of six col- ored parts, the 6 Fig. 406. Adder-tongue (erythronium). At left below pistil, and stamens, and the three stamens opposite three parts of the perianth. Bulb Beidedand long * ‘° "eh 3-loculed ovary. 934. Family Liliaceze.—The relationship between genera, as between trillium, erythronium, and lilium, brings us to a still higher order of relationship, where the limits are broader than in the genus. Genera which are thus related make up the family. In the case of these genera the family has been named after the lily, and is the lily family, or Liliaceae. 935. Order, class, group.—JIn like manner the lily family, the iris family, the amaryllis family, and others which show characters of close relationship are united into an order which has broader limits than the family. This order is the lily order, wll bj Ny st, HY * LZ ee SER D C2 490 CLASSIFICA TION OF ANGIOSPERMS, or order Liliales. ‘The various orders unite to make up the class, and the classes unite to form a group. 936. Variations in usage of the terms class, order, etce.— Thus, according to the system of classification adopted by some, the angiosperms form a group. The group angiosperms is then divided into two classes, the monocotyledones and dicotyledones. (It should be remembered that all systematists do not agree in assigning the same grade and limits to the classes, subclasses, etc. For example, some treat of the angiosperms as a class, and the monocotyledons and dicotyledons as subclasses; while others would divide the monocotyledons and dicotyledons into classes, instead of treating each one as a class or as a subclass. Systematists differ also in usage as to the termination of the ordinal name; for example, some use the word Liliales for Lilu- jflore, in writing of the order.) 937. Monocotyledones.—In the monocotyledons there is a single cotyledon on the embryo; the leaves are parallel veined; the parts of the flower are usually in threes; endosperm is usu- ally present in the seed; the vascular bundles are usually closed, and are scattered irregularly through the stem as shown by a ERS hag fh ay Sr A Fig. 407. B A. Cross-section of the stem of an oak tree thirty-seven years old, showing the annual rings. rm, the medullary rays; m, the pith (medulla). £&. Cross-section of the stem of a palm tree, showing the scattered bundles. cross-section of the stem of a palm (fig. 497), or by the arrange- ment of the bundles in the corn stem (fig. 57). Thus a single character is not sufficient to show relationship in the class (nor ORDER. CLASS, GROUP: AQ! is it in orders, nor in many of the lower grades), but one must use the sum of several important characters. 938. Dicotyledones.—In the dicotyledons there are two cotyledons on the embryo; the venation of the leaves is reticu- late; the endosperm is usually absent in the seed; the parts of the flower are frequently in fives; the vascular bundles of the stem are generally open and arranged in rings around the stem, as shown in the cross-section of the oak (fig. 497). There are exceptions to all the above characters, and the sum of the characters must be considered, just as in the case of the monocotyledons. 939. Taxonomy.— This grouping of plants into species, genera, families, etc., according to characters and relationships is classification, or taxonomy. To take Trillium grandiflorum for example, its position in the system, if all the principal subdivisions should be included in the outline, would be indicated as follows: Group, Angiosperms. Class, Monocotyledones. Order, Liliales. Family, Lilacee. Genus, Trillium. Species, grandiflorum. In the same way the position of the toothwort would be indi- cated as follows: Group, Angiosperms. Class, Dicotyledones. Order, Papaverales. Family, Crucifere. Genus, Dentaria. Species, diphylla. But in giving the technical name of the plant only two of these names are used, the genus and species, so that for the toothwort we say Dentaria diphylla, and for the white wake- robin we say Trillium grandiflorum. 940. Kingdom and Subkingdom.—Organic beings form alto- gether two kingdoms, the Animal Kingdom and the Plant King- 492 CLASSIFICA TION. dom. The Plant Kingdom is then divided into a number of subkingdoms as follows: ist, Subkingdom ‘Thallophyta, the thallus plants, including the Alge and Fungi; 2d, Subkingdom Bryophyta, the moss-like plants, including the Liverworts and Mosses; 3d, Subkingdom Pteridophyta, the fern-like plants, including Ferns, Lycopods, Equisetum, Isoetes, etc.; 4th, Sub- kingdom Spermatophyta, the seed-plants, including Gymno- sperms and Angiosperms. Subkingdoms are divided into groups of lower order down to the classes. So there are subclasses, subfamilies or tribes, subgenera, and even subspecies. But taking the principal taxonomic divisions from the greater to the lesser rank, the order would be as follows: Plant Kingdom. Subkingdom, Spermatophyta. Group (not used in a definite sense). Class, Gymnosperme. Order, Pinales. Family, Pinacee. Genus, Pinus. Species, strobus, or, in full, Pinus strobus, the white pine. Group Angiosperme. I, CLASS MONOCOTYLEDONES, 941. Order Pandanales.—Aquatic or marsh plants. The cattail flags (Typha) and the bur-reeds (Sparganium), each rep- resenting a family. The name of the order is taken from the tropical genus Pandanus (the screw-pine often grown in green-houses). 942. Order Naiadales——Aquatic or marsh herbs. Three families are mentioned here. The pondweed family (Naiadacez), named after one genus, Naias. ‘The largest genus is Potamogeton, the species of which are known as pondweeds. Ruppia occidentalis occurs in | ORDERS OF ANGIOSPERMS. 493 saline ponds in Nebraska, and R. maritima along the seacoast and in saline districts in the interior. The water-plantain family (Alismacez) includes the water- plantain (Alisma) and the arrow-leaves (Sagittaria). The tape-grass family (Vallisneriacez) includes the tape-grass, or eel-grass (the curious Vallisneria spiralis). 943. Order Graminales.—Two families. The grass family (Graminez), the grasses and grains. The sedge family (Cyperacee), the sedges. 944. Order Palmales, with one family, Palmacez, includes the palms, abundant in the tropics and extending into Florida. Cultivated in greenhouses. 945. Order Arales. The arum family (Aracee). Flowers in a fleshy spadix. Ex- amples: Indian turnip (Ariseema), sweet-flag (Acorus), skunk- cabbage (Spathyema). The duckweed family (Lemnacez). (Examples: Lemna, Spirodela, Wolffia. See paragraphs 51-53.) 946. Order Xyridales, from the genus Xyris, the yellow- eyed grass family (Xyridacee). Species mostly tropical, but a few in North America. Other examples are the pipewort family (Eriocaulacee, example, Eriocaulon septangulare), the pineapple family (Bromeliacee, example, the pineapple culti- vated in Florida); the Florida moss or hanging moss (Tillandsia © usneoides); the spiderwort family (Commelinacez), including the spiderwort (Tradescantia, several species in North America) ; the pickerel-weed family (Pontederiacez), including the genus Pontederia in borders of ponds and streams. 947. Order Liliales.—Some of the families are as fol- lows: The rush family (Juncacee, example, Juncus), with many species, plants of usually swamp habit. The lily family (Liliacee, examples: Lilium, Allium=Onion, Erythronium, Yucca). The iris family (Iridacee, examples: Iris, the blue-flag, fleur-de-lis, etc.). AQ4 CLASSIFICA TION. The lily-of-the-valley family (Convallariacee, examples: lily- of-the-valley, Trillium, etc.) . The amaryllis family (Amaryllidacez, examples: Narcissus, the daffodil; Cooperia, in southwestern United States). 948. Order Scitaminales.— This order includes the large showy cultivated Canna of the canna family. 949. Order Orchidales. Example, the orchid family (Orchi- dace) with Cypripedium, Orchis, etc. II, CLASS DICOTYLEDONES, SERIES 1. CHORIPETAL. Petals wanting (Apetale, or Archichlamydz of some authors), or present and distinct from one another (Polypetale, or Metachlamyde). 950. Order Casuarinales, confined to tropical seacoasts (example, Casuarina). 951. Order Piperales includes the lizard’s-tail family (Sau- ruracee), Saururus cernuus, lizard’s-tail, in the eastern United States. 952. Order Salicales.— Shrubs or trees, flowers in aments. Includes the willows and poplars (Salix and Populus of the willow family, Salicacee. , 953. Order Myricales.—Shrubs or small trees. Includes the sweet-gale (Myrica gale) in wet places in northern United States and British North America, Myrica cerifera forming thickets on sand-dunes along the Atlantic coast, and the sweet-fern (Comptonia peregrina=C. asplenifolia) in the eastern United States in dry soil of hillsides. 954. Order Leitneriales—Shrubs or trees. Includes the cork- wood, Leitneria floridana (Leitneriacez). 955. Order Juglandales.—Trees, staminate flowers in aments. The walnut family (Juglandacez, examples: walnut, butternut, etc. Juglans; hickory, Hicoria=Carya. 956. Order Fagales.—Trees and shrubs. Flowers in aments, or the pistillate ones with an involucre which forms a cup in fruit, as in the acorn of the oak. ORDERS OF ANGIOSPERMS. 495 The birch family (Betulacee, examples: Betula, birch; Cory- lus, hazelnut; Alnus, alder, etc.). The beech family (Fagacee—=Cupulifere, examples: Fagus, beech; Castanea, chestnut; Quercus, oak. 957. Order Urticales.—Trees, shrubs, or herbs. Examples: the elm family (Ulmacez), the mulberry family (Moracez), and the nettle family (Urticacez). 958. Order Santalales, herbs or shrubs, mostly parasitic. The mistletoe family (Loranthacez), with the American mistletoe (Phoradendron flavescens), parasitic on deciduous trees in the South Atlantic, Central, and Gulf States (N. J. toning: Ter.). The sandalwood family (Santalaceze, example, the bastard toad-flax, Comandra umbellata), widely distributed in North America. 959. Order Aristolochiales.— Herbs or vines with heart- shaped or kidney-shaped leaves. The birthwort family (Aris- tolochiacee, example, Aristolochia serpentaria, the Virginia snake-root, eastern United States; wild ginger, or heart-leaf, Asarum canadense, eastern North America.) 960. Order Polygonales—Examples: the buckwheat family (Polygonacez), including buckwheat (Fagopyrum), and numer- ous species of Polygonum, known as smartweed, water-pepper, tear-thumb, bindweed, knotweed, prince’s-feather, etc. 961. Order Chenopodiales—Herbs. There are several fam- ilies; one of the largest is the goosefoot family (Chenopodiacez). The genus Chenopodium includes many species, known as goose- foot, lamb’s-quarters, etc. Here belong aiso the Russian thistle (Salsola tragus) and the saltwort (S. kali). The former is some- times a troublesome weed in the central and western United States, naturalized from Europe. The latter occurs along the Atlantic coast on seabeaches. Atriplex occurs in salty or alkaline soil, also the glasswort (Salicornia herbacea), the bugseed (Cori- spermum). The pokeweed family (Phytolaccacez), the Amaranth family (Amaranthacee), the purslane family (Portulacacee, including the purslane or “‘pursley,’? Portulaca oleracea, and 490 CLASSIFICA TION. the spring-beauty, Claytonia virginica), and the pink family (Caryophyllacez), belong here. 962. Order Ranales.—Herbs, shrubs, or trees. Examples are: The water-lily family (Nympheacez), with the yellow water-lily (Nymphea advena=Nuphar advena) and the white water-lily (Castalia odorata=Nymphea odorata). The magnolia family (Magnoliacee), including the mag- nolias (Magnolia) and the tulip-tree (Liriodendron). The crow- foot family (Ranunculacez), with is buttercups, hepatica, clem- ais, etc: 963. Order Papaverales. Ba ce herbs. Examples are: The poppy family (Papaveracez), including the opium or garden poppy (Papaver somniferum), the blood-root (Sangui- naria canadensis), the Dutchman’s-breeches (Bicuculla cucul- laria=Dicentra cucullaria), squirrel’s-corn (Bicuculla canaden- sis=D. canadensis). The mustard family (Cruciferee), including the toothwort (Dentaria), shepherd’s-purse (Bursa bursa-pastoris=Capsella bursa-pastoris, the cabbage, turnip, etc. 964. Order Sarraceniales.—Insectivorous plants. The pitcher-plant family (Sarraceniaceze). Examples: Sarra- cenia purpurea, the pitcher-plant, in peat-bogs, northern and eastern North America. The sundew family (Droseracee). Examples: Drosera rotun- difolia, and other sundews. 965. Order Rosales—Herbs, shrubs or trees. Seventeen families are given in the eastern United States. Examples: The riverweed family (Podostemacez), containing the river- weed (Podostemon). The saxifrage family (Saxifragacee), containing a number of species. Example, Saxifraga virginiensis. The gooseberry family (Grossulariacee), including the wild and the cultivated gooseberry. } The witch-hazel family (Hamamelidacee), including the witch-hazel (Hamamelis), in eastern North America, and the sweet-gum (Liquidambar styraciflua). ORDERS OF ANGIOSPERMS. 497 The plane-tree family (Platanacez), with the plane-tree, or buttonwood (Platanus occidentalis), eastern North America. (Other species occur in western United States.) The rose family (Rosacez), including roses, spireas, rasp- berries, strawberries, the shrubby cinquefoil (Dasiphora fruti- cosa), etc. The apple family (Pomacez), including the apple, mountain- ash, pear, June-berry (or shadbush, also service-berry), the haw- thorns (Crategus). The plum family (Drupacez), including the cherries, plums, peaches, etc. The pea family (Papilionacee), including the pea, bean, clover, vetch, lupine, etc., a very large family. 966. Order Geraniales.— Herbs, shrubs, or trees. Nine families in the eastern United States. Examples: The geranium family (Geraniacez), with the cranesbill (Gera- nium maculatum) and others. The wood-sorrel family (Oxalidacez), with the wood-sorrel (Oxalis acetosella) and others. The flax family (Linacee). Example, flax (Linum vul- - garis). The spurge family (Euphorbiacee). Plants with a milky juice, and curious, degenerate flowers. Examples: the castor- oil plant (Ricinus), the spurges (many species of Euphorbia). 967. Order Sapindales.-— Mostly trees or shrubs. Twelve families in the eastern United States. Example : The sumac family (Anacardiacee), containing the sumacs in the genus Rhus. (Examples: the poison-ivy (R. radicans), a climbing vine, in thickets and along fences, in eastern United States. Sometimes trained over porches. The poison - oak (R. toxicodendron), a low shrub. Poison-sumac or poison-alder (R. vernix=R. venenata), sometimes called ‘‘thunderwood,”’ or dogwood, is a large shrub or small tree, very poisonous. The smoke-tree (Cotinus cotinoides) belongs to the same family, and is often planted as an ornamental tree. The maple family (Ace- racee), including the maples (Acer). / 498 “CLASSIFICA TIONG The buckeye family (Hippocastanacez), including the horse- chestnut (4Zsculus hippocastanum), much planted as a shade tree along streets. Also there are several species of buckeye in the same genus. The jewelweed family (Balsaminacez), including the touch- me-not (Impatiens biflora and aurea) in moist places. The garden balsam (Imp. balsamea) also belongs here. 968. Order Rhamnales.—Shrubs, vines, or small trees. There are two families, the buckthorn (Rhamnacez), the grape family (Vitaceze), including the grapes (Vitis), the American ivy (Par- thenocissus quinquefolia=Ampelopsis quinquefolia), in woods and thickets, eastern North America, and much planted as a trailer over porches. The Japanese ivy (P. tricuspidata=A, veitchii) used as a trailer on the sides of buildings belongs here: 969. Order Malvales.—Herbs, shrubs, or trees. The linden family (Tiliacee). Example, the basswood or American linden (Tilia americana.) The mallow family (Malvacez), including the hollyhock, the mallows, rose of Sharon (Hibiscus), etc. 970. Order Parietales, with seven families in the eastern United States. The St.-John’s-wort (Hypericum) and the vio- lets each represent a family. The violets (Violacez) are well- known flowers. 971. Order Opuntiales—These include the cacti (Cactacez), chiefly growing in the dry or desert regions of America. 972. Order Thymeleales, with two families and few species. 973. Order Myrtales.— Land, marsh, or aquatic plants. The most conspicuous are in the evening primrose family (Onagracee), including the fireweeds, or willow herbs (Epilobium), and the evening primrose (Onagra biennis=(Enothera _bien- nis). 974, Order Umbellales.—Herbs, shrubs, or trees, flowers in umbels. The ginseng family (Araliaceze). This includes the spikenards — ORDERS OF ANGIOSPERMS. 499 and sarsaparillas in the genus Aralia, and the ginseng (or “sang’’), Panax quinquefolium. The carrot family (Umbellifere). This family includes the wild carrot (Daucus carota), the poison-hemlock (Cicuta), the cultivated carrot and parsnip, and a large number of other genera and species. The dogwood family (Cornacee). The flowering dogwood (Cornus florida), abundant in eastern North America, is an example. SERIES 2. GAMOPETALA (=Sympetale or Metachla- mydez). Petals partly or wholly united, rarely separate or wanting. 975. Order Ericales.— There are six families in eastern United States. Examples: The wintergreen family (Pyrolacez), including the shin-leaf (Pyrola elliptica). The Indian-pipe family (Monotropacee), with the Indian- pipe (Monotropa uniflora) and other humus saprophytes. (See paragraphs 182-191.) The heath family (Ericacee). Examples: Labrador tea (Ledum), in bogs and swamps in northern North America. The azaleas, with several species widely distributed, are beauti- ful flowering shrubs, and many varieties are cultivated. The rhododendrons are larger with larger flower-clusters, also beau- tiful flowering shrubs. R. maximum in the Alleghany Moun- tains and vicinity, from Nova Scotia to Ohio and Georgia. R. catawbiense, usually at somewhat higher elevations, Virginia to Georgia. The mountain laurel (Kalmia latifolia) and other species rival the rhododendrons and azaleas in beauty. The trailing arbutus (Epigzea repens) in sandy or rocky woods is a well-known small trailing shrub in eastern North America. The sourwood (Oxydendrum arboreum) is a tree with white racemes of flowers in August, and scarlet leaves in autumn. The spring or creeping wintergreen (Gaultheria procumbens) is a small shrub with aromatic leaves, and bright red spicy berries. The huckleberry family (Vaccinacez) includes the huckle- berries (example, Gaylussacia resinosa, the black or _high- 500 CLASSIFICA TION. bush huckleberry, eastern United States), the mountain cran- berry (Vitis-Idza vitisidea=Vaccinium vitisidea) in the north- ern hemisphere; the bilberries and blueberries (of genus Vacci- nium); the cranberries (examples: the large American cranberry, Oxycoccus macrocarpus and the European cranberry, Oxycoce- cus oxycoccus, in cold bogs of northern North America, the latter also in Europe and Asia). 976. Order Primulales——Two families here. The primrose family (Primulacez) contains the loosestrifes (Steironema), star- flower (Trientalis), etc. 977. Order Ebenales.—Of the four families, the ebony fam- ily (Ebenacez) contains the well-known persimmon (Diospyros virginiana) and the storax family (Styracacez) with the silver- bell, or snowdrop tree (Mohrodendron carolinum). 978. Order Gentianales.—Herbs, shrubs, vines, or trees. Six families in the United States. The olive family (Oleacez) includes the common lilac (Syrin- ga), the ash trees (Fraxinus), the privet (Ligustrum). The gentian family (Gentianacee) among other genera in- cludes the gentians (Gentiana). The milkweed family (Asclepiadacez) contains plants mostly with a milky juice. Asclepias with many species is one of the most prominent genera. 979. Order Polemoniales.—Mostly herbs, rarely shrubs and trees. Fifteen families in the eastern United States. The morning-glory family (Convolvulacez) includes the bindweeds (Convolvulus), the morning-glory (Ipomea), etc. The dodder family (Cuscutacez) includes the dodders, or ‘“‘love-vines.”” There are nearly thirty species in the United States. The stems are slender and twine around other plants upon which they are parasitic (see paragraph 179). The phlox family (Polemoniacee). The most prominent genus is Phlox. Over forty species occur in North America. The borage family (Boraginacez) includes the heliotrope (Heliotropium), the hound’s-tongue (Cynoglossum), the forget- rae-not (Myosotis), and others. ORDERS OF ANGIOSPERMS. 501 The vervain family (verbenacez) contains the verbenas. The mint family (Labiate) contains the mints (Mentha), skull- cap (Scutellaria), dead-nettles (Lamium). The potato family (Solanacez) includes the ground-cherry (Physalis), the nightshades (Solanum), the tomato (Lycoper- sicon), tobacco (Nicotiana). The figwort family (Scrophulariacez) includes the common mullein (Verbascum), the monkey-flower (Mimulus), the toad- flax (Linaria), turtle’s-head (Chelone), and many other genera and species. The bladderwort family (Lentibulariaceze) includes the curi- ous bog or aquatic plants with finely dissected leaves, and with bladders in which insects are caught (Utricularia). The trumpet-creeper family (Bignoniacez) includes the trum- pet-creeper (Bignonia), the catalpa tree, and others. 980. Order Plantaginales with one family (Plantaginacee) includes the plantains (Plantago). 981. Order Rubiales with three families is represented by The madder family (Rubiacez) with the bluets (Houstonia), the button-bush (Cephalanthus), the partridge-berry (Mitchella), the bedstraws (Galium), etc. The honeysuckle family (Caprifoliaceze) with the elder (Sam- bucus), the arrowwoods and cranberry trees (Viburnum), the honeysuckles (Lonicera), etc. 982. Order Valerianales with two families includes The teasel family (Dipsacacee). Example, Fuller’s teasel (Dipsacus). 983. Order Campanulales with five families, the corolla usually gamopetalous. The gourd family (Cucurbitacee) includes the pumpkin, squash, melon, and a few feral species. Example, the star- cucumber (Sicyos angulatus), in moist places in eastern and middle United States. The bell-flower family (Campanulacez) includes the hare- bells or bell-flowers (Campanula), the lobelias (example, Lobelia cardinalis, the cardinal-flower), etc. 502 CLASSIFICA TION. The chicory family (Cichoriacez) includes the chicory or succory (Cichorium intybus, known also as blue-sailors), the oyster-plant or salsify (Tragopogon porrifolius), the dandelion (Taraxacum taraxacum=T. densleonis), the lettuce (Lactuca), the hawkweed (Hieraceum), and others. The ragweed family (Ambrosiacez) includes the ragieeee (Ambrosia), the cockle-bur (Xanthium), and others. The thistle family (Composite) includes the thistle (Carduus), asters (Aster), goldenrods (Solidago), sunflowers (Helianthus), eupatoriums or joepye-weeds, thoroughworts (Eupatorium), cone-flowers or black-eyed Susans (Rudbeckia), tickseed (Core- opsis), bur-marigold or beggar-ticks or devil’s-bootjack (Bidens), chrysanthemums, etc. INDEX. Absorption, 13, 22-28 Aceracee, 497 Acorn, 451 Acorus, 493 ZEcidiomycetes, 218 AEcidiospore, 189 #Esculus hippocastanum, 498 Agaricacee, 199, 219 Agaricus arvensis, 206 Agaricus campestris, 200-207 Akene, 451 Albumen, 98 Albuminous, 98, 108 Alder, 495 Alge, 136-176 Alge, absorption by, 22 Alismacez, 493 Alpine formation, 474 AJpine plant societies, 483 Amanita phalloides, 207, 208 Amaranth, 495 Amaryllidacee, 494 Aments, 429 American mistletoe, 495 Ampelopsis, 498 Ancylistales, 215 Andreales, 249 Androecium, 319, 419 Anemophilous, 435 Angiosperms, morphology of, 318- 348; classification, 487 Antheridiophore, 227 Antheridium, 144, 149, 155, 176, 223, 228, 240, 245, 246, 266, 287, 433 Anthesis, 429 Anthoceros, 240, 241 Anthocerotales, 242 Anthocerotes, 242. Apogamy, 346 Apogeotropic 126 (ap’’o-ge’’o-trop’ic), Apogeotropism (ap’’o-ge-ot’ropism), 126 Apple, 456, 497 Apple family, 497 Aquatic formations, 475 Aquatic plant societies, 486 Arace®, 493 Archegonia (ar-che-go/ni-a), 223, 229, 233, 241, 244-246, 267, 288, 291, 307, 308 Archegoniophore, 229 Archegonium, 433 Archesporium (ar’’che-spo/ri-um), 239 Archidiales, 249 Arctic formation, 481 Aril, 457 Ariseema, 493 Arisema triphyllum, 442, 443 Aristolochiales, 705 Arrow leaf, 492 Arum family, 493 Asclepias, 500 Asclepias cornuti, 462 Ascomycetes (as-co-my-ce’tes), 195— 198, 216-218 ASCUS, 190, 213 Ash of plants, 79, 80 Ash tree, 500 Aspidium acrostichoides, 253, 257 Assimilation, 67, tog Aster, 502 Atriplex, 495 Auriculariales, 218 Autotrophic plants, 85 Azalea, 499 Azolla, 296 Bacteria, 164, 165 Bacteria, nitrite and nitrate, 83 Bacteriales, 164, 165 523 504 INDEX. Bacteroid, 93 Bangiales, 175 Basidiomycetes (ba-sid’’i-o-my-ce’- tes), 199-208, 218 Basidium, 201, 213 Bast, 50-52 Batrachospermum, 171-173, 175 Bazzania, 25 Beard-grasses, 480 Bedstraws, 501 Beechnut, 452 Beet, osmose in, 15, 16, 17, 18 Begonia, 407 Bellflower, 501 Berry, 454, 455, 456 Betulacee, 495 Bicuculla, 496 Bidens, 458 ~ Bignonia, 501 Bilberries, 500 Biotic factors, 466 Birch, 495 Bird’s-nest fungi, 220 Blackberry, 454 Black fungi, 198 Bladderwort, 501 Blasia, 164, 236 Bloodroot, 496 Bluets, 436, 437, 501 Boletus, 209 Boletus edulis, 209 Boraginacee, 500 Botrychium, 295 Botrydiacez, 162 Botrydium granulatum, 146, 162 Broom sedge, 480 Brown alge, 167-170 Bryales, 349 Buds, winter condition of, 374- Sf Buckeye family, 498 Buckthorn, 498 Buckwheat, 495 Buffalo-grass, 480 Bug seed, 495 Bulb, 372 Bunch-grasses, 480 Butternut, 452, 494 Buttonbush, 501 Buttonwood, 497 Cacti, 395, 498 Callithamnion, 173 Calyptrogen, 361 Cambium, 50, 52, 358, 363 Campanula rotundifolia, 442, 444, 510 Campanulales, 501 Canna, 445-449, 494 Capsella bursa-pastoris, 496 Capsule, 453 Carbohydrate, 71, 75, 80, go Carbon dioxide, 62-67, 110-113 Cardinal flower, 501 Carpogonium, 172, 176 Carrot family, 799 Caryophyllacee, 496 »Caryopsis, 451 Cassia marilandica, 402 Cassiope, 395 Castalia odorata, 496 Castor-oil plant, 497 Catalpa, 501 Catkin, 428 Cattail-flag, 492 Caulidium, 371 Cedar apples, 194 Cell, 3; artificial 20 Cell sap, 3, 40 Ceratopteris thalictroides, 296 Chetophora, 151, 162 Cheetophoracee, 162 Chara, 176 Charales, 176 Chemical condition of soil, 466 Chemosynthetic assimilation, 109 Chenopodiales, 495 Chenopods, 495 Chestnut, 452, 494 Chicory family, 502 Chlamydomonas, 159, 160 Chlamydospores, 180 Chloral hydrate, 65, 87 Chlorophycez, 158 Chlorophyll, 2, 67, 72 Chloroplast, 68, 69, 71 Christmas fern, 251-253 Chromoplast, 71 Chromosomes, 342-345 Chroococcacee, 163 Chrysanthemum, 502 Chytridiales, 215 Cichoriacez, 502 Cichorium intybus, 502 Clavaria botrytes, 212 Clavariacez, 210, 219 Claytonia virginica, 496 Cleistogamous, 435 INDEX. Clematis virginiana, 462, 463, 706 Climatic factors, 466 Climatic formations, 470 Clostridium pasteurianum, 93 Clover, 497 Club mosses, 284, 289 Coccogonales, 163 Cocklebur, 502 Cold wastes, 474 Coleochetaceex, 162 Coleochete, 153-156, 226 Collenchyma, 356, 363 Comandra, 495 Compass plants, 409 Composite, 502 Comptonia asplenifolia, 494 Cone fruit, 456 Confervoidez, 162 Conifer, 316 Conjugation, 179 Convallariacez, 494 Cooperia, 494 Cordyceps, 218 Coreopsis, 502 Cork, 357, 363 Corm, 373 Cortex, 50 Corymb, 427 Cotyledon, 99-101 Cranberry, 500 Crategus, 497 Crowfoot family, 496 Cruciferze, 496 Cryptonemiales, 175 Cucurbitacez, 501 Culture formations, 470, 475 Cultures, water, 28, 29 Cup fungi, 199 Cupuliferz, 495 Cuscuta, 83, 500 Cushion type of vegetation, 483 Cuticle, 43 Cyanophycee, 163 Cyatheacez, 295 Cycadales, 316 Cycas, 311, 312, 457 Cyclosis, 9, 10 Cyclosporales, 171 Cyme, 430, 432 Cyperacee, 493 Cypripedium, 443, 447, 494 Cystocarp, 174 Cystopteris bulbifera, 260 KOO, /562, WAV Awahite 505 Cystopus, 215 Cytase, 92, 108 Cytisus, 445 Cytoplasm (cy’to-plasm), 5 Dacryomycetales, 219 Dahlia, 108 Dandelion, 502 Dasiphora fruticosa, 497 Daucus carota, 499 Dehiscence, 453 Dentaria, 322-324 Dentaria diphylla, 496 Dermatogen, 359 Desert formation, 473 Desert societies, 480 Desmodium, 458 Desmodium gyrans, 399 Diadelphous (di’’a~-del’ phous), 425 Diageotropism (di’’a-ge-ot/ro-pism), 126 Diaheliotropic (di’’a-he’’li-o-trop’- 1G) et" Diaheliotropism (di’’a-he’’li-ot’ro- pism), 127 Diastase, 77, 78, 108, 116 Diatoms, 166 Dichogamous (di-chog’a-mous), 437, 442 Dicentra, 496 Dicotyledons, 494 Dictyophora, 219 Diffusion, 13-20 Digestion, 107, 108, 109 Dimorphism of ferns, 273-280 Dicecious, 435' Dionza muscipula, 133 Dipodascus, 216 Dipsacus, 501 Discomycetes, 217 Dodder, 83, 84, 500 Dogwood, 499 Dothidiales, 218 Downy mildews, 185 Drosera rotundifolia, 133, 496 Drupacez, 497 Drupe, 454 Duckweeds, 26, 28 Dudresnaya, 175 Dunes, 484 Ebenales, 500 Ecological factors, 464 506 Ecology (sometimes written cecol- ogy), 464 Ectocarpus, 167 Edaphic formations, 475 Elaphomyces, 217, 218 Elder, 501 Elm family, 495 Elodea, 61-63 Embryo of ferns, 269-272 Embryo sac, 326-328 Empusa, 215 Endocarp, 450 Endomyces, 216 Endosperm, 103, 105, 107, 300, 309; nucleus, 327, 329-334 Entomophthorales, 215 Enzyme, 92, 98, 116, 117 Epidermal system, 358 Epidermis, 358, 359, 363 Epigeea repens, 499 Epigynous, 425 Epilobium, 498 Epinastic (ep-i-nas’tic), 129 Epinasty (ep/i-nas-ty), 129 Epipactis, 444, 447 Epiphegus, 84 Epiphytes, 416 Equisetales, 296 Equisetinez, 296 Equisetum, 280-283 Ericacee, 499 Ericales, 499 Erythronium, 493 Etiolated plants (e’ti-o-la’’ted), 68 Euascomycetes, 217 Eubasidiomycetes, 219 Eupatorium, 403, 502 Euphorbiacez, 497 Eurotium oryze, 78 Evening primrose family, 498 Exalbuminous, 108 Exoascus, 217 Exobasidiales, 219 Exocarp, 450 Fagales, 494 Fehling’s solution, 75, 76 Ferment, 98, 108, 116 Ferns, 251-279, 292, 457; classifica- tion of, 295 Fertilization, 307, 308, 328, 329, 140, 145, 169, 172, 174, 197, 421 Fibrovascular bundles, 49-54 Figwort family, sor INDEX. Filicales, 295 Filicinee, 295 Fittonia, 404 Flagellates, 83, 165 Flax, 497 Flower cluster, 419 Flower, form of, 422; parts of, 419; union of parts, 424 Flowers,- arrangements of, 426; kinds of, 421 -Follicle, 453 Forest, formations 471; societies, 477 Forests, relation to rainfall, 479 Fresh-water societies, 486 Frond, 352 Fruit, 450-457; parts of, 450 Frullania, 25, 236 Fucus, 168-170 Fungi, absorption by, 22; classifica- tion of, 213-222; nutrition of, 86- 90; respiration in, 115 Gametangium (gam/’et-an’gi-um), 140 ; Gamete (gam/ete), 138, 139 Gametophore (gam/et-o-phore), 230, 248 Gametophyte (gam/et-o-phyte), 225, 226, 244, 245, 250, 202, 270, 2am 292, 294, 305, 314, 317, 336-339, 340-348, 434 Gamopetalous (gam/’’o-pet’a-lous), 424 Gamosepalous (gam-o-sep’a-lous), 424 Gas in plants, 60-64 Gasteromycetes, 219 Gemme, 179, 235 General formations, 470 Gentian, 500 Geotropism 127, ALO Geraniacez, 497 Geraniales, 497 Geranium family, 497 Germ, 459 Gigartinales, 175 Gingko, 313-315, 457 Gingkoales, 316 Ginseng, 499 Glasswort, 495 Gleicheniacez, 295 Glucose, 108. See sugar. (ge-ot’ro-pism), 125- INDEX. Gnetales, 316 ComGdidnmts, 143, 172, 174, £73— 184 Gonidiangium 178 Gonidium, 213 Gooseberry, 496 Goosefoot family, 495 Cracilaria, 172,\174, 175 Graminales, 492 Graminee, 492 Grape, 498 Grass family, 492 Grassland formation, 471 Green alge, 158 Growth, 118-124, 380 Gulfweed, 170 Gymnosperms, 311, 456 Gymnosporangium, 194 Gyncecium, 320, 419, 451, 452 Gyrocephalus, 219 (go/’nid-an’gi-um), Halophytes, 468 Harpochytrium, 214, 215 Haustorium, 87, 88 Hawkweed, 502 Hawthorn, 497 Hazelnut, 452, 495 Head, 428 Heart leaf, 495 Heath family, 499 Heliotrope, 500 Hehotropism (he-li-ot’ro-pism), 127-131, 133, 397 Helvellales, 217 Hemiascomycetes, 216 Hemibasidiomycetes, 218 Hepatice, 242 Heterospory (het’’er-os’po-ry), 434 Heterothallic, 180 Heterotrophic plants, 85 Hickory, 494 Hickory nut, 452 Hilum, ror, 102 Hippocastanacee, 498 Holdfasts, 418 Hollyhock, 498 Homothallic, 180 Honeysuckle, 501 Hormogonales, 163 Horse-chestnut, 498 Horsetails, 280-283 Houstonia coerulea, 437 Huckleberry, 499 507 Humus saprophytes, 85, 91 Hybridization, 338 Hydnacee, 210, 219 Hydnum coralloides, 210 Hydnum repandum, 211 Hydrocarbon, 75 Hydrodictyacez, 161 Hydrophytes, 468 Hydropterales, 295 Hydrotropism (hy-drot’ro’pism), 133, 134, 412 Hygrophytes, 468 Hymeniales, 219 Hymenogastrales, 219 Hymenomycetes, 219 Hymenomycetinee, 219 Hymenophyllacee, 295 Hypericum, 498 Hypocotyl (hy’po-co’’tyl), rox Hypocreales, 217 Hypogenous, 425 Hyponastic (hy-po-nas’tic), 129 Hyponasty (hy’po-nas-ty), 129 Hysteriales, 217 Impatiens, 498 Impatiens fulva, 460 Indian-pipe, 499: Indian-turnip, 493 Indusium, 252 Inflorescence, 426 Insectivorous plants, 133, 496 Integument, 304 Intramolecular respiration, 113, 114 Inulase, 108 Inulin, 108, 417 Iodine, 65 Ipomeea, 500 Iridacee, 493 Iris, 493 Irritability, 125-135 Isoetales, 296 Isoetes, 289-291, 292 Isoetineze, 296 Ivy, 498 Jack-in-the-pulpit, 373 Jewelweed, 498 Juglandales, 494 June-berry, 497 Jungermanniales, 242 Kalmia latifolia, 444 Karyokinesis, 341-344 508 Kelps, 168 Kingdom, 492 Labiatz, 423, 501 Laboulbeniales, 218 Labrador tea, 499 Lactuca canadensis, 460 Lactuca scariola, 409, 460, 461 Lagenidium, 214, 215 Laminaria, 168, 169 Lamium, 424, 501 Larch, 367 Laurel, 499 Leaf patterns, 404 Leathesia difformis, 168 Leaves, form and arrangement, 383- 391; function of, 387; protective modifications of, 392; protective positions, 395; reduction of sur- face, 394; relation to light, 397; structure of, 40-43, 131, 391, 393 Legumes, 92, 93, 453 Leguminose (=Papilionacez), 396, 399 Leitneria floridana, 494 Leitneriales, 494 Lemanea, 171, 173, 175, 492 Lemna, 418 Lemna trisulca, 26, 27 Lenticel, 357, 358 Lepiota naucina, 208 Lettuce, 502 Leucoplast, 71 Lichens, 86, 93-95, 220, 221 Light, 465 Liliacee, 490, 493 Liliales, 490, 493 Lilium, 489-493 Linaria vulgaris, 501 Linden, 498 Linum vulgaris, 497 Lipase, 108 Liquidambar, 496 Liriodendron, 496 Live-forever, 394 Liverworts, 222-239; absorption by, 23-25; classification of, 242 Lobelia, 501 Lupinus perennis, 353 Lycoperdales, 220 Lycopodiacez, 296 Lycopodiales, 296 Lycopodiinee, 296 Lycopodium, 284-286 INDEX. Macrosporangium, 94, 302, 304, 311. Cia aii Macrospore, 287, 290, 326-328, 434 Magnolia, 496 Mallow family, 498 Malvales, 498 Maple family, 497 Marchantia, 24, 226-236 Marchantiales, 242 Marine plant societies, 486 Marratiales, 295 Marsilia, 370 Marsiliacee, 296 Matoniacez, 295 Medicago denticulata, 92 Mediulla, 50 Members of the flower, 335 Members of the plant, 349-353 Meristem, 359 Mesocarp, 450 Mesophytes, 467 Microsporangia, 294, 299 Microspore, 287, 209; 435 Microsporophylls, 299, 320, 420 Milkweed family, 500 Mimosa, 132, 396 Mimulus, 501 Mint family, sor Mistletoe, 84, 495 Mitchella, 5o1 Mixotrophic plants, 85 Mnium, 243-246 Molds, nutrition of, 86-90 Molds, water, 181 Monadelphous, 424 Monoblepharidales, 215 Monoblepharis, 215 Monocotyledons, 490, 492 Moneecious, 435 Monotropa uniflora, 499 Morchella, 198, 199 Morel, 198, 199 Morning-glories, 500 Mosaics, 405 Mosses, 243-248, 457; absorption by, 25; classification of, 248 Mucor, 6, 7, 15, 118, 110; 177—-Eoo 215 Mucorales, 215 Mulberry, 704 Mullein, 366, 394, 501 Mushrooms, 199-208 Mustard family, 496 2909, 312, : See eee es SS ee— INDEX. Mutation, 338 Mutualism, 95 Mycelium, 6, 86-90 Mycetozoa, 213, 214 Mycorhiza, 86, 91, 92, 217 Myosotis, 500 Myrica cerifera, 494 Myrica gale, 494 Myricales, 494 Myriophyllum, 403 Myrtales, 498 Myxobacteriales, 165 Myxomycetes, 83, 213, 214 Naiadacez, 492 Naiadales, 492 Naias, 492 Nemalion, 171, 172, 175 Nemalionales, 175 Nettle, 495 Nicotiana, 501 Nidulariales, 220 Nitella, 8, 9, 176 Nitrobacter, 83 Nitrogen, 92, 93 Nitromonas, 83 Nostocacee, 164 Nucellus, 304 Nucleus, 3, 4; morphology of, 340- 345 Nuphar advena, 496 Nutation, 123, 124 Nymprea odorata, 496 Oak, 495 Oak family, 495 (Edogoniacee, 162 (Edogonium, 147-151, 350 (Enothera biennis, 498 (Enothera gigas, 338 (Enothera lamarkiana, 338 Olpidium, 214, 215 Onagar biennis, 498 Onagracee, 498 Onoclea sensibilis, 254, 273-278 Oogonium, 144, 150, 155 Oomycetes, 214, 215 Ophiogiossales, 295 Ophioglossum, 295 Opuntiales, 498 Orchidacee, 494 Orchidales, 494 Orchids, 442 Oscillatoriaceze, 163 509 Osmosis, 13-20 Osmundacee, 295 Ostrich fern, 279 Ovules5302)-321, 334, 42x Oxalis, 497 Oxycoccus, 500 Oxydendrum arboreum, 5o1 Oxygen, 63, I10-113 Palisade cells, 41, 43 Palmacee, 493 Palmales, 493 Palms, 408 Pandanales, 492 Pandanus, 492 Pandorina, 160, 350 Panicle, 427 Papaverales, 496 Papilionacee, 423, 497 Parasites, 83, 84, 86 Parasitic fungi, nutrition of, 86-go Parenchyma, 50, 356, 363 Parietales, 498 Parkeriacee, 296 Parmelia, 96 Parthenogenesis, 184 Partridge berry, 501 Pea, 497 Pea family, 497 Pear, 456 Pediastrum, 161 Pellia, 164 Pellonia, 405 Peltigera, 94, 95 Pepo, 456 Pericycle, 360 Peridinez, 166 Perigynous, 425 Penisperm, 331, 1332 Perisporiales, 217 Peronospora, 183, 215 Peronosporales, 215 Persimmon, 500 Pezizales, 217 Phacidiales, 217 Pheophycee, 167 Pheosporales, 171 Phallales, 219 Phloem, 50-52, 360, 361, 363 Phlox family, 500 Phoradendron flavescens, 495 Photosynthesis, 67, 68, 70, 117 Phycomycetes (Phy’’co-my-ce’tcs), 214, 215 510 Phyllidium, 371 Phylloclades, 373, 395 Phyllotaxy, 375, 384 Physical condition of soil, 465 Physical factors, 465 Phytolaccacez, 495 Phytomyxa leguminosarum, 92 Phytophthora, 182, 184, 215 Pickerel weed, 493 Pilularia, 296 Pinales, 216 Pine, white, 297-310 Piperales, 494 Pitcher-plant, 496 Pith, 50 Plant-food, sources of, 81 Plant-formations, 496 Plant-substance, analysis 80 Plantaginales, 501 Plantago, 501 Plasmolysis (plas-mol’y-sis), 19 Plasmopara, 183, 215 Plectascales, 217 Plectobasidiales, 220 Pleurococcacez, 161 Pleurococcus, 161 Plum family, 497 Plumule, 99 Podostemon, 496 Poison-hemlock, 499 Poison-ivy, 497 Poison-oak, 497 Poisonous mushrooms, 207, 208 Poison-sumac, 497 Pokeweed, 495 Polemoneales, 500 Pollen-grain, 299, 305 Pollination, 303, 304, 420, 430, 433-— 449 Pollinium, 420 Polygonales, 495 Polygonum, 495 Polypodiacez, 296 Polyporacee, 209, 219 Polyporus, 209, 210 Polyporus mollis, 92 Polyporus sulphureus, 209 Pomacee, 497 Pondweeds, 492 Poppy, 496 Porella, 237 Portulaca, 495 Potamogeton, 492 Obey 79; SS INDEX. Potato, 501 Powdery mildews, 195-198, 217 Primrose, 498, 500 Primula, 438 Primulales, 500 Procatgp; 172.) 17440675 Progeotropism (pro’’ge-ot/ro-pism), 126 Promycelium (pro’/my-ce’li-um), 192 Proterandrous, 441, 442 Proterandry, 444 Proterogenous, 441, 442 Proterogeny, 440 Prothallium, 265, 287, 288, 291, 292, 304, 305, 311, 325, 328, 335, 433, 434 Protoascales, 216 Protoascomycetes, 216 Protobasidiomycetes, 218 Protococcoidee, 158, 621 Protodiscales, 217 Protomyces, 216 Protonema (pro’’to-ne’ma), 248, 264 Protoplasm, 1-12, 42-43, 342; move- ment of, 7-11 Psilotacee, 296 Pteridophytes, 295, 434 Pteris cretica, 346 Puccinia, 187 Puff-balls, 220 Pumpkin, 501 Purslane, 495 Pyrenoid, 2, 3 Pyrenomycetes, 217 Pyrola, 499 Pyxidium, 453 Quercus, 495 Quillworts, 289-291 Quince, 456 Raceme, 427 Radicle, 99 Ragweed, 502 Rainy-season flora, 481 Ranales, 496 Ranunculacee, 496 Raspberry, 454, 455 Red algz, 171, 628; uses of, 175 Reproduction, 137, 143, 149, 154, 155, 179, 185, 186 Respiration, 110-116, 117 Rhamnales, 498 Rhizoids, 24-26 INDEX. Rhizome, 354 Rhizomorph (rhi’zo-morph), 89 Rhizophidium, 214, 215 Rhizopus, 177-180, 215 Rhododendron, 499 Rhodomeniales, 175 Rhodophycee, 171. Rhus radicans, 416, 497 Riccia, 23, 164, 222-226 Ricinus, 497 Riverweed, 496 Root, function of, 410-418 Root-hairs, absorption by, 19, 30, 32 Root-hairs, action on soil, 82 Root pressure, 33, 34, 45 Root, structure of, 30, 361 362 Root tubercles, 92 Roots, kinds of, 415 Rosacez, 497 Rosales, 496 Rose family, 497 Rosette, 405 Rosette plants, 483 Rubiales, 501 Rudbeckia, 502 Rusts, 187-194 Salicacez, 494 Salix, 494 Salsify, 502 Salviniacez, 296 Samara, 451 Sandalwood, 495 Sanguinaria, 496 Santalales, 495 Sap, rise of, 53, 54 Sapindales, 497 Saprolegnia, 181-184 Saprolegniales, 215 Saprophytes, 83-85 Sargassum, 170 Sarraceniales, 496 Sarsaparilla, 499 Saxifrage, 496 Schizeacez, 295 Schizocarp, 451 Schizomycetes, 164 Schizophycee, 163 Sclerenchyma, 356-357, 361, 363 Scouring-rush, 282 Screw-pine, 409, 492 Scrophulariacee, 501 Sedge family, 492 511 Seed, dispersal of, 458-463 Seed plants, 338 Seed, structure of, 98, 102 Seedlings, 97-107 Secds, 330-334 Selaginella, 286-288, 292 Selaginellacez, 296 Sensitive fern, 273 Sensitive plants, 132, 396, 399 Sexual organs, 144, 147 Shadbush, 497 Shepherd’s-purse, 496 Shoot, floral, 419, 432 Shoots, 353-355; types of, 36;— 373; Winter condition of, 374- 3tT Sieve tissue, 358, 363 Sieve tubes, 52, 53 Silique, 453 Silk-cotton tree, 417 Silver bell, 500 Siphonee, 146, 1€2 Skunk’s cabbage, 439-442 Slime molds, 83 Smoke- ree, 497 Societies, 475 Solanum, 501 Solidago, 502 Sourwood, 499 Spadix, 428 Spartium, 446 Spathyema foetida, 438, 493 Spermagonia, 190 Spermatophytes, 338 Sphacelaria, 168 Spherella lacustris, 158, 159 Spherella nivalis, 158, 350 Spheriales, 218 Sphagnales, 248 Sphagnum, 164 Spiderwort, II, 493 Spike, 428 Spirodela polyrhiza, 27 Spirogyra, 1-5, 13, 14, 60, 72, 136- 140, 350 Sporangia, 178-182 Sporangium, 253-258, 281, 290 Spores, , 225, 256-258, 263, 264, 281 Sporocarp, 173 Sporogonium (spo’’ro-go’ni-um), 224, 231, 233, 234, 237) 238, 239; 241, 240, 247; 248 Sporophyll, 274, 281, 292 512 INDEX. | Sporophyte (spo’ro-phyte), 225, 226, 232, 234, 237-239, 241, 242, 250, 261, 208, 270, 283, 292, 294, 314, 315, 317, 336-339, 340-348 434 Spurge family, 497 Squash, s5o1 Staminodium, 446 Starch, formation of, 68, 70-74; changed to sugar, 77, 78; translo- cation of, 73; digestion of, 75 Stems, types of, 365-373 Stems, woody, structure of, 381-382 Stoma (pi. stomata) (sto’ma-ta), 42- 44, 46 Strawberry, 455, 497 Sugar, test for, 75, 76 Sumac, 497 Sundew, 133, 496 Sunflower, 399-401, 502 Sweet gum, 496 Symbiosis, 85, 86, 92-95 Synergids (syn’/er-gids), 327, 330 Syngencesious, 424 Synthetic assimilation, 67 Tape-grass, 493 Taraxacum densleonis, 502 Teasel, 501 Telegraph-plant, 399 Teleutospore, 188 Temperature, 134, 135, 465 Tetrasporacee, 161 Tetraspores, 173, 174 Thallophytes, 352 Thallus, 352 Thelephoracez, 219 Thistle family, 502 Thunderwood, 497 Thyrsus, 427 Tilia, 498 Tillandsia, 493 Tissue, tensions of, 57-59 Tissues, classification of, 363, 364; kinds of, 356-359; organization of, 356-362 Toad-flax, 501 Tomato, 501 Tradescantia, 493 Tragopogon, 502 Trailing arbutus, 499 Trametes pini, 90 Transpiration, 35-46 Tremellales, 218, 219 Triadelphous, 425 Trillium, 318-322, 494 Trumpet-creeper, 501 Tuberales, 217 Tubers, 373 Tundra, 481 Turgescence, 14, 15 Turgor, 20; restoration of, 56, 57 Typha, 493 Ulmacez, 495 Ulmus americana, 495 Ulothrix, 162 Ulotrichacee, 162 Ulvacee, 162 Umbel, 428 Umbellales, 498 Uredinales, 218 Uredinee, 187-194, 218 Uredospore, 189 Uromyces caryophyllinus, 87 Urticales, 495 Ustilaginales, 218 Ustilaginez, 218 Utricularia, 501 Vaccinium, 499 Vacuoles, 7, 8 Valerianales, 501 Vallisneria spiralis, 493 Variation, 338 Vascular tissue, 358, 363 Vaucheria, 142-146 Vaucheriacez, 162 Vegetation types, 464 Venus’ flytrap, 133 Verbascum, 5o0r Verbena, 501 Vessels, 52, 53 Vetch, 92, 497 Viburnum, 501 Vicia sativa, 459 Viola cucullata, 436 Violacee, 498 Virgin’s-bower, 462, 463 Viscum album, 84 Vitacee, 498 Volvocacee, 158 Walnut, 452, 494 Water, 465; flow of, in plants, 53, 54 Water-lilies, 496 Water-plantain, 493 White pine, 396 Wild carrot, 499 INDEX. 513 Willow family, 494 Yeast, 216; fermentation of, 115, Wind, 471 116 Wintergreen, 499; leaf of, 43 Yucca, 480, 493 Witch-hazel, 496 Wolffia, 28 ; Zamia, 313, 316, 457 Woodland formation, 470 Zoogonidia, 143, 149, 178-184 Zoospore, 149, 154 Xerophytes, 467 Zygomycetes, 215 Xylem, 50, 52, 360, 361, 363 Zygospore, 2, 138-140, 157, 160, 179, Xylogen, 92 180 Xyridales, 493 Zygote (zy’gote), 138, 179 co s me - ; & a : - ; 2 t t | fare’ «peat 4 awOr NOTABLE NATURE BOOKS. FERNS A Manual for the Northeastern States. By C. E, WATERS, Ph.D. (Johns Hopkins), With Analytical Keys Based on the Stalks. With over 200 illustrations from original drawings and photographs. 362 pp. Square 8vo. Boxed. $3.00 net, (By mail, $3.34.) A popular, but thoroughly scientific book, including all the ferns in the region covered by Britton’s Manual. Much infor- mation is also given concerning reproduction and classification, fern photography, etc. PROF. L. M. UNDERWOOD, OF COLUMBIA: “Tt is really more scientific than cone would expect from a work of a somewhat popular nature. The photographs are very fine, very carefully selected and will add much to the text. I do not see how they could be much finer.” THE PLANT WORLD: ; “This book is likely to prove the leading popular work on ferns. 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Geological Survey :—I am im- pressed with the admirable plan of the work and with the thorough manner in which geological principles and processes and their results have been presented. The text is written in an entertaining style and is supplemented by admirable illustrations, so that the student cannot fail to obtain a clear idea of the nature and work of geological agencies, of the present status of the science, and of the spirit which actuates the working geologist. Henry S. Williams, Professor in Vale University:—I believe it is the best treatise on this part of the subject which we have seen in America. R. S. Woodward, Professor in Columbia University :—It is admir- able tor its science, admirable for its literary perfection, and admirable for its unequalled illustrations. T. C. Hopkins, Professor in Syracuse University :—It gives us the most advanced thought on all the great questions of dynamical and structural geology to be found in geological literature. H. Foster Bain, U.S. Geological Survey :—The book is pre-eminently a teaching book and I have no doubt that it will at once become the standard American text-book on geology. William N. Rice, Professor in Wesleyan University:—The book is full of new ideas. It is one of the indispensable books for the library of every working geologist and every one who wishes to be an up-to-date teacher of geology. T. A. Jaggar, Jr., Assistant Professor in Harvard University:— The book appears to be an excellent statement of modern American geol- ogy, with abundant new illustrative material, based upon the most recent work of government and other surveys. It is especially satisfactory to have in hand a geological volume which does not attempt to cover the whole field. Modern geology is much too large a subject to be condensed into a single volume. HENRY HOLT & CO, 29 West 284 street New York VIL 05 THE METRIC SYSTEM. NAVE NAL) AL UIH TVET HINA ILI} HTH ITI{EEE HTH HI I{ITH = The upper edge is in millimeters, the lower in centimeters and half 1o-centimeter rule. : centimeters. UNITS. THE MOST COMMONLY USED DIVISIONS AND MULTIPLES. Centimeter (cm), 1/100 meter; Millimeter (mm), 1/1000 meter: Micron (u), 1/1000 millimeter. The Tue METER, for e ae a ae (ut) / LENGTH micron 1S the unit in micrometry. a Kilometer, 1000 meters; used in measuring roads and other | long distances. Millizram (mg), 1/1000 gram. Tue GRAM, for ) ;- & (mg) / sm . Kilogram, 1000 grams, used for ordinary masses, like WEIGHT ..... te groceries, etc. Tue Liter, for ( Cubic Centimeter (cc), 1/1ooo liter. This is more CAPACITY... common than the correct form, Milliliter. Divisions of the units are indicated by Latin prefixes: dec?, 1/10; centt, 1/100; mz/i, 1/1000. Multiples are designated by Greek prefixes: deka, 10 times; ecto, 100 times; #220, 1000 times; 7zy77a, 10,000 times. TABLE OF METRIC AND ENGLISH MEASURES. METER — 100 centimeters, 1000 millimeters, 1,000,000 microns, 39.3704 inches. Millimeter (mm) = 1000 microns, 1/10 millimeter, 1/1000 meter, 1/25 inch, approximately. MIcRON (jz) (unit of measure in micrometry)=1/1000 mm, I/ 1000000 me- ter (0.000039 inch), 1/25000 inch, approximately. Inch (in.) = 25.399772 mm (25.4 mm, approx.). LITER — 1000 milliliters or 1000 cubic centimeters, I quart (approx. ). Cubic centimeter (cc or cctm) = 1/1000 liter. Fluid ounce (8 fluidrachms) = 29.578 cc (30 CC, approx. ). GRAM <= 15.432 grains. Kilogram (kilo) = 2.204 avoirdupois pounds (2} pounds, approx. ). Ounce Avoirdupois (4374 grains) = 28.349 grams ) (30 grams, Ounce Troy or Apothecaries’ (480 grains) = 31.103 grams) approx. ). TEMPERATURE. To change Centigrade to Fahrenheit: (C. x 2) +32 =F. For example, to find the equivalent of 10° Centigrade, C. = 107, (202) 32 — Ope To change Fahrenheit to Centigrade: (F.— 32°) X $= C. For example, to reduce 50° Fahrenheit to Centigrade, F. = 50°, and (50°— 32°) X $= TO: C5 or — 40° Fahrenheit to Centigrade, f= = fo. (= 40°— 32°) = "72", whence — 72° X 3 = — 40°C. From ‘The Microscope” (by S. H. Gage) by permission. : ES , : A, ce ir 1 A ' . f x y ‘ ry a! . | « nets ere w