Elementary Botany - free ebook by George Francis Atkinson

ELEMENTARY BOTANY

BY GEORGE FRANCIS ATKINSON, Ph.B. Professor of Botany in Cornell University THIRD EDITION, REVISED NEW YORK HENRY HOLT AND COMPANY 1905 Copyright, 1898, 1905 BY HENRY HOLT AND COMPANY ROBERT DRUMMOND, PRINTER, NEW YORK...

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PREFACE.

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 physiological 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 gre

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CHAPTER I. PROTOPLASM. [1]

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 protoplasm . 2. In most cases protoplasm cannot be seen without the help of a microscope, and it will be necessary for us here to employ one if we wish to see protoplasm, and t

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CHAPTER II. ABSORPTION, DIFFUSION, OSMOSE.

29. We may next endeavor to learn how plants absorb water or nutrient substances in solution. There are several very instructive experiments, which can be easily performed, and here again some of the lower plants will be found useful. 30. Osmose in spirogyra. —Let us mount a few threads of this plant in water for microscopic examination, and then draw under the cover glass a five per cent solution of ordinary table salt (NaCl) with the aid of filter paper. We shall soon see that the result is si

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CHAPTER III. HOW PLANTS OBTAIN WATER.

In connection with the study of the means of absorption from the soil or water by plants, it will be found convenient to observe carefully the various forms of the plant. Without going into detail here, the suggestion is made that simple thread forms like spirogyra, œdogonium, and vaucheria; expanded masses of cells as are found in the thalloid liverworts, the duckweed, etc., be compared with those liverworts, and with the mosses, where leaf-like expansions of a central axis have been differenti

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CHAPTER IV. TRANSPIRATION, OR THE LOSS OF WATER BY PLANTS.

68. We should now inquire if all the water which is taken up in excess of that which actually suffices for turgidity is used in the elaboration of new materials of construction. We notice when a leaf or shoot is cut away from a plant, unless it is kept in quite a moist condition, or in a damp, cool place, that it becomes flaccid, and droops. It wilts, as we say. The leaves and shoot lose their turgidity. This fact suggests that there has been a loss of water from the shoot or leaf. It can be rea

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CHAPTER V. PATH OF MOVEMENT OF WATER IN PLANTS.

93. In our study of root pressure and transpiration we have seen that large quantities of water or solutions move upward through the stems of plants. We are now led to inquire through what part of the stems the liquid passes in this upward movement, or in other words, what is the path of the “sap” as it rises in the stem. This we can readily see by the following trial. 94. Place the cut ends of leafy shoots in a solution of some of the red dyes. —We may cut off leafy shoots of various plants and

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CHAPTER VI. MECHANICAL USES OF WATER.

111. Turgidity of plant parts. —As we have seen by the experiments on the leaves, turgescence of the cells is one of the conditions which enables the leaves to stand out from the stem, and the lamina of the leaves to remain in an expanded position, so that they are better exposed to the light, and to the currents of air. Were it not for this turgidity the leaves would hang down close against the stem. Fig. 61. Restoration of turgidity (Sachs). 112. Restoration of turgidity in shoots. —If we cut

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CHAPTER VII. STARCH AND SUGAR FORMATION.

121. Gas given off by green plants in the sunlight. —Let us take some green alga, like spirogyra, which is in a fresh condition, and place one lot in a beaker or tall glass vessel of water and set this in the direct sunlight or in a well lighted place. At the same time cover a similar vessel of spirogyra with black cloth so that it will be in the dark, or at least in very weak light. Fig. 63. Oxygen gas given off by spirogyra. Fig. 64. Bubbles of oxygen gas given off from elodea in presence of s

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CHAPTER VIII. STARCH AND SUGAR CONCLUDED. ANALYSIS OF PLANT SUBSTANCE.

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. Fig. 72. Leaf of tropæolum with portion covered with corks to pre

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CHAPTER IX. HOW PLANTS OBTAIN THEIR FOOD. I.

170. The necessary constituents of plant food. —As indicated in Chapter 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

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CHAPTER X. HOW PLANTS OBTAIN THEIR FOOD, II.

202. It is evident from some of the studies which we have made in connection 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 supplied 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 connection with the study of the nutrition of the plant, therefore, it

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CHAPTER XI. RESPIRATION.

220. One of the life processes in plants which is extremely interesting, and which is exactly the same as one of the life processes of animals, is easily demonstrated in several ways. 221. Simple experiment to demonstrate the evolution of CO₂ during germination. —Where there are a number of students 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 vase

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CHAPTER XII. GROWTH.

By growth is usually meant an increase in the bulk of the plant accompanied generally by an increase in plant substance. 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. If the 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. —It will be instructive

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CHAPTER XIII. IRRITABILITY.

259. We should now examine the movements of plant parts in response to the influence of certain stimuli. By this time we have probably observed that the direction which the root and stem take upon germination of the seed is not due to the position in which the seed happens to lie. Under normal conditions we have seen that the root grows downward and the stem upward. 260. Influence of the earth on the direction of growth. —When the stem and root have been growing in these directions for a short t

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CHAPTER XIV. SPIROGYRA.

283. In our study of protoplasm and some of the processes of plant life we became acquainted with the general appearance of the plant spirogyra. It is now a familiar object to us. And in taking up the study of representative plants of the different groups, we shall find that in knowing some of these lower plants the difficulties of understanding methods of reproduction and relationship are not so great as they would be if we were entirely ignorant of any members of the lower groups. Fig. 128. Th

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CHAPTER XV. VAUCHERIA.

299. The plant vaucheria we remember from our study in an earlier chapter. It usually occurs in dense mats floating on the water or lying on damp soil. The texture and feeling of these mats remind one of “felt,” and the species are sometimes called the “green felts.” The branched threads are continuous, that is there are no cross walls in the vegetative threads. This plant multiplies itself in several ways which would be too tedious to detail here. But when fresh bright green mats can be obtaine

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CHAPTER XVI. ŒDOGONIUM.

309. Œdogonium is also an alga. The plant is sometimes associated with spirogyra, and occurs in similar situations. Our attention was called to it in the study of chlorophyll bodies. These we recollect are, in this plant, small oval disks, and thus differ from those in spirogyra. 310. Form of œdogonium. —Like spirogyra, œdogonium forms simple threads which are made up of cylindrical cells placed end to end. But the plant is very different from any member of the group to which spirogyra belongs.

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CHAPTER XVII. COLEOCHÆTE.

322. Among the green algæ coleochæte is one of the most interesting. Several species are known in this country. One of these at least should be examined if it is possible to obtain it. It occurs in the water of fresh lakes and ponds, attached to aquatic plants. Fig. 155. Stem of aquatic plant showing coleochæte, natural size. Fig. 156. Thallus of Coleochæte scutata. 323. The shield-shaped coleochæte. —This plant (C. scutata) is in the form of a flattened, circular, green plate, as shown in fig

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CHAPTER XVIII. CLASSIFICATION AND ADDITIONAL STUDIES OF THE ALGÆ.

In order to show the general relationship of the algæ studied, the principal classes are here enumerated as well as some of the families. In some of the groups not represented by the examples studied above, a few species are described which may serve as the basis of additional studies if desired. The principal classes [17] of algæ are as follows: Class Chlorophyceæ. 331. These are the green algæ, so called because the chlorophyll green is usually not masked by other pigments, though in some form

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CHAPTER XIX. FUNGI: MUCOR AND SAPROLEGNIA.

Mucor. 387. In the chapter on growth, and in our study of protoplasm, we have become familiar with the vegetative condition of mucor. We now wish to learn how the plant multiplies and reproduces itself. For this study we may take one of the mucors. Any one of several species will answer. This plant may be grown by placing partially decayed fruits, lemons, or oranges, from which the greater part of the juice has been removed, in a moist chamber; or often it occurs on animal excrement when placed

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CHAPTER XX. FUNGI CONTINUED.

“Rusts” (Uredineæ). 400. The fungi known as “rusts” are very important ones to study, since all the species are parasitic, and many produce serious injuries to crops. Fig. 206. Wheat leaf with red-rust, natural size. Fig. 207. Portion of leaf enlarged to show sori. Fig. 208. Natural size. Fig. 209. Enlarged. Fig. 210. Single sorus. Figs. 206, 207.—Puccinia graminis, red-rust stage (uredo stage). Figs. 208-210.—Black rust of wheat, showing sori of teleutospores. Fig. 210. Single sorus. Figs. 20

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CHAPTER XXI. THE HIGHER FUNGI.

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 mildews”; examples, uncinula, microsphæra, podosphæra, 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 gr

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CHAPTER XXII. CLASSIFICATION OF THE FUNGI.

429. Classification of the fungi. —Those who believe that the fungi represent a natural group of plants arrange them in three large series related to each other somewhat as follows: The Gonidium Type or Series. The number of gonidia in the sporangium 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. The Basidium Type or Series. The number of gonidia on a basidium

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CHAPTER XXIII. LIVERWORTS (HEPATICÆ).

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 liverworts. Two of these liverworts belonging to the genus riccia are illustrated in figs. 30 , 252 . 474. Form of the floating riccia (R. fluitans). —The general form of floating riccia is that of a narrow, irregular, flattened, ribbon-like object, which forks repeatedly, in a dichotomous manner, so that ther

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CHAPTER XXIV. LIVERWORTS CONTINUED.

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. 488. Sporogonium of marchantia. —If we examine the plant shown in fig. 181 we shall see oval bodies which stand out between the rays of the female receptacle, supported on short stalks. These are the sporogonia, or sp

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CHAPTER XXV. MOSSES (MUSCI).

513. We are now ready to take up the more careful study of the moss plant. There are a great many kinds of mosses, and they differ greatly from each other in the finer details of structure. Yet there are certain general resemblances which make it convenient to take for study almost any one of the common species in a neighborhood, which forms abundant fruit. Some, however, are more suited to a first study than others. (Polytrichum and funaria are good mosses to study.) 514. Mnium. —We will select

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CHAPTER XXVI. FERNS.

529. In taking up the study of the ferns we find plants which are very beautiful objects of nature and thus have always attracted the interest of those who love the beauties of nature. But they are also very interesting to the student, because of certain remarkable 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 o

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CHAPTER XXVII. FERNS CONTINUED.

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 that the form of the plant which bears the sexual organs is developed from the spores. This is true, and if we should examine old decaying logs, or decaying wood in damp places in the near vicinity of ferns, we should probably find tiny, green, thin, heart-shaped growths, lying close to the substratum. These are als

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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 sim

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CHAPTER XXIX. HORSETAILS.

571. Among the relatives of the ferns are the horsetails, so called because of the supposed resemblance 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 resemblance to the ferns which we have been studying. But then relationship in plants does not depend on mere resemblance of outward form, or of the prominent part of the plant. Fig. 321. Portion of fertile plant of Equisetum arvense showing whorls of

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CHAPTER XXX. CLUB MOSSES.

Fig. 326. Lycopodium clavatum, branch bearing two fruiting spikes; at right sporophyll with open sporangium; single spore near it. 578. What are called the “club mosses” make up another group of interesting plants which rank as allies of the ferns. They are not of course true mosses, but the general habit of some of the smaller species, and especially the form and size of the leaves, suggest a resemblance to the larger of the moss plants. 579. The clavate lycopodium. —Here is one of the club mos

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CHAPTER XXXI. QUILLWORTS (ISOETES).

Fig. 336. Isoetes, mature plant, sporophyte stage. 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, except t

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CHAPTER XXXII. COMPARISON OF FERNS AND THEIR RELATIVES.

596. Comparison of selaginella and isoetes with the ferns. —On comparing 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 selaginella and isoetes upon what exists in the ferns. There is a division of labor between the sporophylls, in which some of them be

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CHAPTER XXXIII. GYMNOSPERMS.

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 to the tree. In old and dense forest

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CHAPTER XXXIV. FURTHER STUDIES ON GYMNOSPERMS.

Fig. 366. Macrosporophyll of Cycas revoluta. 627. In such gymnosperms as cycas, illustrated in the frontispiece, there is a close resemblance to the members of the fern group, especially the ferns themselves. This is at once suggested by the form of the leaves. The stem is short and thick. The leaves have a stout midrib and numerous narrow pinnæ. 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 fru

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CHAPTER XXXV. MORPHOLOGY OF THE ANGIOSPERMS: TRILLIUM; DENTARIA.

639. General appearance. —As one of the plants to illustrate this group we may take the wake-robin, as it is sometimes called, or trillium. 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 ridge

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CHAPTER XXXVI. GAMETOPHYTE AND SPOROPHYTE OF ANGIOSPERMS.

650. Male prothallium of angiosperms. —The first division which takes place in the nucleus of the pollen grain occurs, in the case of trillium and many others of the angiosperms, 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 division of the nucleus into two nuclei took place soon after the formation of the four cells from the mother cell. The nucleus divided in the y

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CHAPTER XXXVII. MORPHOLOGY OF THE NUCLEUS AND SIGNIFICANCE OF GAMETOPHYTE AND SPOROPHYTE.

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 mother cells are formed as a last division of the fertile tissue (archesporium) of the sporangium. In ordinary cell division the nucleus always divides prior to the division of the cell. In many cases it is directly connected with the laying down

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CHAPTER XXXVIII. THE ORGANIZATION OF THE PLANT.

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 essentially different from early animal life. The simplest ones which are clearly recognized as plants are found among the lower algæ 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 a

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CHAPTER XXXIX. THE DIFFERENT TYPES OF STEMS. WINTER SHOOTS AND BUDS.

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 oth

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CHAPTER XL. FOLIAGE LEAVES.

746. Influence of foliage leaves on the form of the stem. —The marked effect which foliage has upon the aspect of the plant or upon the landscape is evident to all observers. Perhaps it is usual to look upon the stem as having been developed for the display of the foliage without taking into account the possibility that the foliage may have a great influence upon the form or habit of the stem. It is very evident, however, that the foliage exercises a great influence on the form of the stem. For

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CHAPTER XLI. THE ROOT.

784. The most obvious function of the roots of ordinary plants are two: 1st, To furnish anchorage and partial support, and 2d, absorption of liquid nutriment from the soil. The environmental 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: 785. (1) Permeation of t

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CHAPTER XLII. THE FLORAL SHOOT.

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 known as the Flower Cluster . 804. The flower. —The flower is best understood by an examination, first of one of the types known as a “complete” flower, as in the buttercup, the spring-beauty, the blood-root, 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. T

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CHAPTER XLIII. POLLINATION.

Origin of heterospory, and the necessity for pollination. 835. Both kinds of sexual organs on the same prothallium. —In 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 perhaps not uncommon, in some species, that the egg-cell in an archegonium may be fertilized by a spermatozoid from an antheridium on the sa

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CHAPTER XLIV. 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 embryo, 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 ripened ovary is called a pericarp , and the walls of the ovary form the walls of the

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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 distanc

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CHAPTER XLVI. VEGETATION IN RELATION TO ENVIRONMENT.[47]

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 germinate. 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 fa

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CHAPTER XLVII. 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 trillium 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,

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