FIG. 10.—COMMON PRICKLY PEAR CACTUS (Opuntia Opuntia) Native along the Atlantic Coast. The green joints of the stem function as leaves and store water.FIG. 10.—COMMON PRICKLY PEAR CACTUS(Opuntia Opuntia)Native along the Atlantic Coast. The green joints of the stem function as leaves and store water.
to secure the plant’s survival. Other stems, looking and acting like leaves, reveal their true nature by producing buds, and the curious feature of the common butcher’s-broom (Figure 11), often colored scarlet for Christmas decorations, bearing flowers from the middle of what is apparently a leaf, but is actually a modified stem, is explained by this ability of stems to modify their habits to suit conditions. The butcher’s-broom is an inhabitant of dry regions along the Mediterranean, where a reduction or
FIG. 11.—BUTCHER’S-BROOM (Ruscus aculeatus) Note leaflike stems with flowers arising from the center.FIG. 11.—BUTCHER’S-BROOM(Ruscus aculeatus)Note leaflike stems with flowers arising from the center.
absence of leaf surface is a decided advantage. In many partly desert or dry regions this production of leaflike stems or branches is common, an excellent garden example being asparagus, which came originally from Europe and the feathery growth of which is all stem. In Tasmania a kind of yew tree produces no leaves, all the foliage being modified stem, which is true of many kinds of spurge in the West Indies, where an almost impenetrable scrub islargely made up of a shrub which is apparently covered with leaves, all actually part of the branches and stems.
FIG. 12.—DUCKWEED The smallest known flowering plant, with no leaves and tiny leaflike stems floating on the surface. Flowers are borne from the margin of the stem. (Eight times natural size).FIG. 12.—DUCKWEEDThe smallest known flowering plant, with no leaves and tiny leaflike stems floating on the surface. Flowers are borne from the margin of the stem. (Eight times natural size).
While stems, such as the Big Trees or the giant cactus, may be among the largest of nature’s creations they may be also the smallest, as the duckweed that floats on ponds is the tiniest of all flowering plants and its flat expanded surface is wholly stem. Figure 12 on this page better illustrates this strange modification of a stem than words could do.
From what has been read it will be seen that stems are not “just stems”—they are among nature’s most ingenious devices to secure the survival of the plant.Whether buried in the ground, and producing, almost by stealth, buds that develop into mature plants, or thrusting leaves to the utmost limits of their reach, or climbing by an intricately varied mechanism, or changing their character to suit desert conditions, or floating on the water—it matters not. Each modification of form or use secures to the individual plant its chances to survive; and in most cases its only chance, as anyone may see by the sudden death which follows a series of changes which prevents a stem from performing its proper tasks.
As the palm reader is supposed to be able to tell your history and future from veins in your hand, and as the veins in the wing of a butterfly tell their story to an entomologist, so the veins of a leaf are more significant than almost any other characteristic of a plant. Most leaves have their veins, or skeleton, with a single midrib and many branches off it on each side, which themselves break up into a fine network of veins. Such leaves arenetveined(Figures 13-24). Others, such as corn and grass, have the veins running side by side from one end of the leaf to the other, sometimes with small branches off them, but instead of the veins forming a network they are parallel, and such are calledparallel-veinedleaves (Figure 38). In the chapter on Plant Families and Their Relationship more will be said as to the amazing regularity with which netveined leaves are associated with certain kinds of flowers and parallel-veined with other kinds, how these distinctions have been recognized since hundreds of years before Christ, long before their true import was understood. There are variations from both these
Banyan Tree (Ficus bengalensis). A fig tree of India, whose adventitious roots make frequent connection between the tree top and the ground. Starting as thin, whiplike streamers these roots ultimately form new trunks. (Courtesy Brooklyn Botanic Garden.)Banyan Tree (Ficus bengalensis). A fig tree of India, whose adventitious roots make frequent connection between the tree top and the ground. Starting as thin, whiplike streamers these roots ultimately form new trunks. (Courtesy Brooklyn Botanic Garden.)
Banyan Tree (Ficus bengalensis). A fig tree of India, whose adventitious roots make frequent connection between the tree top and the ground. Starting as thin, whiplike streamers these roots ultimately form new trunks. (Courtesy Brooklyn Botanic Garden.)
Laceleaf (Aponogeton fenestralis). A submerged aquatic plant, with permanently skeletonized leaves, and an inhabitant of forest pools in Madagascar. (After Engler & Prantl. Courtesy of Brooklyn Botanic Garden.)Laceleaf (Aponogeton fenestralis). A submerged aquatic plant, with permanently skeletonized leaves, and an inhabitant of forest pools in Madagascar. (After Engler & Prantl. Courtesy of Brooklyn Botanic Garden.)
Laceleaf (Aponogeton fenestralis). A submerged aquatic plant, with permanently skeletonized leaves, and an inhabitant of forest pools in Madagascar. (After Engler & Prantl. Courtesy of Brooklyn Botanic Garden.)
Root Hairs with Fine Soil Particles Attached. Note soil, water, and air spaces. Much magnified. (After U. S. Department of Agriculture. Courtesy of Brooklyn Botanic Garden.)Root Hairs with Fine Soil Particles Attached. Note soil, water, and air spaces. Much magnified. (After U. S. Department of Agriculture. Courtesy of Brooklyn Botanic Garden.)
Root Hairs with Fine Soil Particles Attached. Note soil, water, and air spaces. Much magnified. (After U. S. Department of Agriculture. Courtesy of Brooklyn Botanic Garden.)
FIG. 13-24.—FORMS AND TIPS OF LEAVES Fig. 13. A linear leaf with an acute tip. Fig. 14. Lanceolate leaf with an acuminate tip. Fig. 15. Oblanceolate leaf broadest above the middle. Fig. 16. Ovate, broadest below the middle. Fig. 17. Spatulate, broadest above the middle and with an elongated base. Fig. 18. Elliptical. Fig. 19. Obovate in which the general shape is ovate, but broadest toward the tip. Fig. 20. Oblong. Fig. 21. Orbicular or nearly round. Fig. 22. Deltoid or somewhat triangular, an ovate leaf with a broad base. Fig. 23. Kidney-shaped or reniform with heart-shaped base. Fig. 24. Peltate leaf of common garden nasturtium; note circular blade with leafstalk attached to the center.FIG. 13-24.—FORMS AND TIPS OF LEAVESFig. 13. A linear leaf with an acute tip. Fig. 14. Lanceolate leaf with an acuminate tip. Fig. 15. Oblanceolate leaf broadest above the middle. Fig. 16. Ovate, broadest below the middle. Fig. 17. Spatulate, broadest above the middle and with an elongated base. Fig. 18. Elliptical. Fig. 19. Obovate in which the general shape is ovate, but broadest toward the tip. Fig. 20. Oblong. Fig. 21. Orbicular or nearly round. Fig. 22. Deltoid or somewhat triangular, an ovate leaf with a broad base. Fig. 23. Kidney-shaped or reniform with heart-shaped base. Fig. 24. Peltate leaf of common garden nasturtium; note circular blade with leafstalk attached to the center.
Fig. 13. A linear leaf with an acute tip. Fig. 14. Lanceolate leaf with an acuminate tip. Fig. 15. Oblanceolate leaf broadest above the middle. Fig. 16. Ovate, broadest below the middle. Fig. 17. Spatulate, broadest above the middle and with an elongated base. Fig. 18. Elliptical. Fig. 19. Obovate in which the general shape is ovate, but broadest toward the tip. Fig. 20. Oblong. Fig. 21. Orbicular or nearly round. Fig. 22. Deltoid or somewhat triangular, an ovate leaf with a broad base. Fig. 23. Kidney-shaped or reniform with heart-shaped base. Fig. 24. Peltate leaf of common garden nasturtium; note circular blade with leafstalk attached to the center.
types, but in nearly every case, once the difference is noted—and scarcely any other character of a plant is so much worth notice—they cannot be mistaken.
During the winter nearly all leaves are folded in various ways in a bud for protection from the elements. Nature shows herself in some of her wisest moods in the selection of methods to accomplish this. In some buds, notably those of the horse-chestnut, the bud is coated with a sticky substance to protect the tender young leaves inside. In others there is a hard outer coat, as in the hickory, impregnable to the most driving sleet, others again have the leaf rolled so tightly and pointed so sharply at the end, as in the beech, that water cannot cling to the bud nor soak in, until the warmth of spring gives the signal for the annual miracle of the bursting out of foliage. Leaf buds are sometimes hard to find on certain plants, as they are formed at the base of a leafstalk and covered by it during the growing season. It is only as the leaf falls in the autumn that the hollow base of its stalk is seen to have hidden during the summer the young bud for the following season. The plane tree or sycamore is a good example of a plant where no leaf buds can be found until the falling of the leaves in autumn.
The forms of leaves are infinite in their variety, and the reasons for some of their peculiarities in this respect are not yet understood. The average netveined leaf is obviously composed of ablade(Figure 25), and at the base a stalk known as apetiole. Sometimes at the base of the petiole—which is lacking in many leaves—there are two tiny leaflike appendages, calledstipules, which are of no apparent use to the plant, and, as if in recognition of this fact, they often fall off long before autumn. In some plants, however, stipules are permanent, while in certain others they are never found, as, for instance, in the horse-chestnut tree.
FIG. 25-35.—FORMS AND BASES OF LEAVES Fig. 25. Simple leaf with blade, leafstalk (petiole), and two stipules at the base. Margins of the leafblade serrate or saw-toothed. Fig. 26. Leaf with a sagittate base, or shaped like an arrowhead, the lobes pointing downward, and with entire margins. Fig. 27. Retuse or emarginate tip, somewhat indented. Fig. 28. With the base auriculate or with rounded basal lobes. Fig. 29. Hastate, like an arrowhead but the lobes pointing outward. Fig. 30. With cuneate base (wedge-shaped). Fig. 31. Cuspidate tip with a usually hard and stiff point. Fig. 32. Perfoliate, the leaf bases joined and the stem passing through them. Fig. 33. Truncate, the top flattened. Fig. 34. Pinnately lobed, with deep indentations cut toward the midrib. Fig. 35. Palmately lobed, out toward the top of the leafstalk.FIG. 25-35.—FORMS AND BASES OF LEAVESFig. 25. Simple leaf with blade, leafstalk (petiole), and two stipules at the base. Margins of the leafblade serrate or saw-toothed. Fig. 26. Leaf with a sagittate base, or shaped like an arrowhead, the lobes pointing downward, and with entire margins. Fig. 27. Retuse or emarginate tip, somewhat indented. Fig. 28. With the base auriculate or with rounded basal lobes. Fig. 29. Hastate, like an arrowhead but the lobes pointing outward. Fig. 30. With cuneate base (wedge-shaped). Fig. 31. Cuspidate tip with a usually hard and stiff point. Fig. 32. Perfoliate, the leaf bases joined and the stem passing through them. Fig. 33. Truncate, the top flattened. Fig. 34. Pinnately lobed, with deep indentations cut toward the midrib. Fig. 35. Palmately lobed, out toward the top of the leafstalk.
Fig. 25. Simple leaf with blade, leafstalk (petiole), and two stipules at the base. Margins of the leafblade serrate or saw-toothed. Fig. 26. Leaf with a sagittate base, or shaped like an arrowhead, the lobes pointing downward, and with entire margins. Fig. 27. Retuse or emarginate tip, somewhat indented. Fig. 28. With the base auriculate or with rounded basal lobes. Fig. 29. Hastate, like an arrowhead but the lobes pointing outward. Fig. 30. With cuneate base (wedge-shaped). Fig. 31. Cuspidate tip with a usually hard and stiff point. Fig. 32. Perfoliate, the leaf bases joined and the stem passing through them. Fig. 33. Truncate, the top flattened. Fig. 34. Pinnately lobed, with deep indentations cut toward the midrib. Fig. 35. Palmately lobed, out toward the top of the leafstalk.
The outline of leaves is as varied as nature itself. Some of the common kinds are shown in drawings (Figures 13-24), which tell more of the story than pages of description could do. Their margins, too, their tips, their bases (Figures 25-35), all parts of them, in fact, are so variable and yet in each kind of plant so uniform, that in the description of the plants of any region the botanist has used these characteristics of leaves as one method of identifying the particular plant in hand.
The terms used to designate these different kinds of leaf margins or forms of blade are precise, nearly universally used, but need to be studied only by those who, because of special fondness for the subject, are likely to need them in using books which are beyond the scope of the present one. If, for instance, the reader is interested in finding out what his native roadside plants are, he would need a book describing them, and there are many for different parts of the country. In such books he would find these terms, which say so much in a single word (there are other sets of terms for flowers, fruits, and seeds) totally unfamiliar and quite likely to disgust him at the start. A little study may open up to him that most interesting and easily accessible of recreations, a first-hand familiarity with the wild flowers of one’s own neighborhood.
All leaves are not as simple as the figures show them to be. In many the midrib or principal vein is much elongated and there are smallleaflets, sometimes even scores of them, all fastened to a common stalk. Such are calledcompoundleaves (Figures 36-37), which may be found in ash, hickory,rosebushes, blackberries, peas, beans, and thousands of other plants.
FIG. 36-38.—COMPOUND AND PARALLEL-VEINED LEAVES Fig. 36. Palmately compound leaf, the five leaflets all arising from the tip of the common leafstalk. Fig. 37. Pinnately compound leaf, the leaflets arising from the sides of the common leafstalk. Fig 38. A parallel-veined leaf. All the other leaves figured are netted-veined.FIG. 36-38.—COMPOUND AND PARALLEL-VEINED LEAVESFig. 36. Palmately compound leaf, the five leaflets all arising from the tip of the common leafstalk. Fig. 37. Pinnately compound leaf, the leaflets arising from the sides of the common leafstalk. Fig 38. A parallel-veined leaf. All the other leaves figured are netted-veined.
Fig. 36. Palmately compound leaf, the five leaflets all arising from the tip of the common leafstalk. Fig. 37. Pinnately compound leaf, the leaflets arising from the sides of the common leafstalk. Fig 38. A parallel-veined leaf. All the other leaves figured are netted-veined.
While leaves are literally factories in which one of the most wonderful things in the world is produced,it is so much a part of what plants do or their behavior that the story of it will be given in the chapter on Plant Behavior. Sunlight is absolutely necessary for the process, and to reach this sunlight leaves are attached to their stems in a variety of ways. Some are always opposite each other, as in the common privet, lilac, or honeysuckle; others always alternate, as in the mustard or the rose. There are many variations of these simple arrangements, but in every case the process results in giving each leaf the utmost exposure to the light without which the plant must wither and die. So vital is this exposure to light that in some plants parts of the leaves producetendrils, as in the case of peas, in order that some near-by support may be used. In one African relative of our lily, this change of leaf form has been so great that its long slender leaf tip is wonderfully adapted to reaching up and catching by its curved tip some support to lift it from the gloom of the tropical forest floor.
Looking down from above on any small plant or bush, or from the sky on a forest, about all that can be seen are the thousands of leaves, all so arranged that it is as though some celestial photographer asked every one of them to so place themselves that they would all be “in the picture.” The competition between leaves on the same plant and between leaves on rival plants is infinitely keener than the friendly pushing of a crowd to get in a picture,and it lasts forever. Furthermore, failure to get in means certain death. So intricate is the method of leaf arrangement, so marvelous the adjustments that all plants must make to insure ample light, that it is not inaptly calledleaf mosaic. As we shall see in the chapter on Plant Distribution, particularly inforests, certain variations or partial failures of the process have far-reaching results.
If leaves did not perform this most important function to perfection, all animals, including man as well, would perish, and it would almost seem that their obligation to us and the plant world might stop there as long as their success in reaching the light is so overwhelming. But there are no union hours of labor, no regulation as to the kind of work leaves may perform, and some actually reach out for new tasks to do, and do them. In one, our common pitcher plant, the leaf, as is implied by the name, is formed into a slender hollow pitcher, wide at the mouth, but narrow at the base. Inside the pitcher are slender downward-pointing hairs so arranged that an insect may crawl in, but never out. The lower down the luckless insect gets the more certain is its death, and, to clinch matters, there is a tiny pool at the bottom where it is not only drowned, but, due to the composition of the mixture in the pool, digested. Only a very few plants can do this; only a minute fraction of the world’s vegetation can digest animal matter. Some experiments on the pitcher plant, which grows in bogs, show that it will digest bits of beefsteak dropped into the liquid at the base of the pitcher.
In the East Indies and in Africa there is a pitcher plant—in fact, scores of varieties of them—which grows up on the branches of trees. In this case the pitcher may be as long as some of our American kinds, often twelve to eighteen inches, and many of them are attached to a slender leafstalk two to three feet long, by which they hang suspended. Insects, literally by the thousands, are caught in these gaudy traps, for many of the pitchers are beautifully colored,and near the opening they secrete a sweetish liquid that lures their prey. They are, in fact, such curious and handsome plants that they are commonly grown in greenhouse collections.
Nature sometimes finds still other ways of using strange and curious-shaped leaves, and in our American bogs is a group of plants, also insect digesters, still more unusual than the pitcher plants. In bright sunny places in open bogs one may often find small reddish, glistening plants, called sundews, usually only a few inches tall, covered with sticky hairs. In fact, the glistening is due to the secretion of the sticky substance, a tiny drop of which may be found at the end of each hair. Flying insects are caught in these leaves, and, as a fly on fly paper, the greater the struggle the more involved does the insect become among the sticky threads. Once caught by such a plant, escape is practically impossible.
Lying in ambush for chance insects, as these sundews and pitcher plants do, may seem nearly the limit of what is to be expected of leaves. Merely to be always on the job, with a plentiful supply of insect digester, might seem to be all that could well be expected from what, after all, are only modified leaves. But nature’s devices are infinite, and there are still other ways to accomplish the apparently impossible. In a small section of the southeastern States there grows a plant that not only lies passively in wait for insects, but actually captures them. This flycatcher, known as Venus’s flytrap, has two valves to the leaf blade, supported on a stout broad stalk so arranged that their fringed surfaces face each other. If an insect—and many do—alights between these valves, they close together rapidly and the prisoner is hopelessly caught by the interlockingmarginal bristles that fringe each valve. In this case there are glands on the face of the valves, against which the live insect is tightly pressed, and which secrete a digestive fluid. When nothing remains the valves slowly open and are ready for the next victim. They may be made to close by slight irritation with a lead pencil, and it is the impact of the insect that releases one of the most curious examples of movement in leaves known to us. There are a few other plants in different parts of the world that by still other modifications of their leaves catch and digest insects, but none of them are to be considered as “insect eaters,” or other names implying that they have definite designs on the life of passing insects. The process is sufficiently remarkable, the success of the operation so sure, that there is nothing gained by attributing to such plants, as many have done in the past, malignant characters that are possibly confined only to man. The whole wonderful process is more reasonably explained by realizing that all these insectivorous plants are so by virtue of necessity, that many of them are bog plants, which are often hard put to it to get suitable food, and that the extraordinary change of shape and function is but one more contribution of leaves to the economy of nature.
In dry or desert regions, where the conservation of moisture is essential to plant growth, water storage by leaves is nearly as great an aid to the plant as we have seen it to be in the stems of cactus, South African spurges, etc. Our common century plant, whose leaves are, in some kinds, a hundred times thicker than in ordinary foliage leaves, is a good example of leaves adapted to water storage. In our southwestern deserts hundreds of species of plantscan exist only by virtue of the fact that their leaves are so changed in their form or structure that they serve as reservoirs for water storage. This may be accomplished by thickening, or it is more often contrived by a thick coating of hairs. The surfaces of thousands of different kinds of leaves are clothed with hairs either on the upper or lower side, or sometimes on both sides. In many cases they are quite obviously protection from too rapid drying out of the leaf. In others, as in the nettle, the hairs secrete a stinging substance which seems to insure the plant against grazing animals.
Leaves, then, are for something more than to provide the beautiful foliage which is their most spectacular accomplishment. So varied is this in its beauty, from plain green leaves to the wonderful coloring found in begonias, coleus, and many other garden plants, that the sheer beauty of the panorama of foliage is likely to blind us to the more important uses of leaves. First of all must we consider them the factories, in which night and day are produced the food of all plants and most animals. Then in certain cases we have seen that, by every ingenious device known to nature, they perform other special work, such as helping the plant to climb where that is necessary, catching or even capturing insects and digesting them when that peculiar service is demanded of them, and, finally, serving as storage reservoirs in regions where water is scarce. Probably no part of the plant works so unceasingly each season at its varied tasks. In the autumn, dropping to the forest floor, its decomposition furnishes still other food for the plant, and, to crown all, this busy life and by no means unprofitable death leaves behind it, as a promise for the continuance of the work,a snugly protected leaf bud which will repeat the process the next season.
While the plant’s and, consequently, our debt to the leaf is seen to be tremendous, it cannot be ignored that, if plants produced nothing but leaves, the end of all plant life would come with the death from old age or disease of the present generation of plants. Except for those kinds that reproduce themselves by division or extension of their rootstocks, which bear buds, there would be no provision for increase. As only a comparatively small number of plants can reproduce by this method, it is obvious that something more must be provided to secure new generations of plants. Flowers, and the fruits and seeds which inevitably follow them, do this. All plants, with some exceptions to be noted later, produce flowers at some time in their life. In the case of the century plant, only once, after which they die. But except for ferns, mushrooms, seaweed, yeast, bacteria, and some other forms of so-called flowerless plants, a flower or blossom is to be found at some stage in the life of all plants.
If we examine the leaves of a goldenrod, we find that they are large below and diminish in size toward the top. Just below and among the flower clusters they are so much reduced in size and often changed in color that they cease to be ordinary foliage leaves, and are known asbracts. The occurrence of bracts is nearly universal in flowering plants, and they form not only an apparently transitional stage between leaves and flowers, but an actual one.
In a complete and perfect flower there are, at the bottom of it, a row of green leaflike sheaths which
FIG. 39-45.—THE FLOWER Fig. 39. A perfect and complete flower. A, petals, all of them forming the corolla; B, sepals, all of them forming the calyx; C, the stamen, composed of (C) the filament, and (C1) the anther, which produces the pollen; D, the pistil, consisting of the swollen base (D) the ovary, a slender shank (D1) the style, and the swollen or branched tip (D2) the stigma. (H. D. House, “Wild Flowers of New York.”) Fig. 40. Typical flower of the pea family. Two petals unite to form the keel (below), two more unite to form the wings (center), the remaining and larger petal forms the standard. In most plants of this family the stamens and pistils are concealed within the keel. Fig. 41. Two-lipped inequilateral flower, common in such plants as Salvia, Snapdragon, etc. Note the united calyx and corolla. Fig. 42. Gamopetalous or united and regular corolla of the Fringed Gentian. Figs. 43, 44, and 45, flowers of the Compositæ or daisy family. Many small flowers grouped in heads and usually surrounded by one or more series of bracts. Fig. 43. Flowers all tubular, the small one at the left being an individual flower. Common examples are Boneset and the common garden Ageratum. Fig. 44. Flowers both tubular and with rays, the tubular in the center and the rays on the margin. Below is an individual tubular flower on the right, and on the left an individual ray flower. Note that its five united divisions correspond to the five petals in other plants. Common examples are the daisy, sunflower, black-eyed Susan, etc. Fig. 45. Flowers all ray flowers, an individual one at the right. The Compositæ with only ray flowers usually have a milky juice and have often been grouped in a separate family, the Cichoriaceæ. Common examples are dandelion, chicory, and lettuce.FIG. 39-45.—THE FLOWERFig. 39. A perfect and complete flower. A, petals, all of them forming the corolla; B, sepals, all of them forming the calyx; C, the stamen, composed of (C) the filament, and (C1) the anther, which produces the pollen; D, the pistil, consisting of the swollen base (D) the ovary, a slender shank (D1) the style, and the swollen or branched tip (D2) the stigma. (H. D. House, “Wild Flowers of New York.”) Fig. 40. Typical flower of the pea family. Two petals unite to form the keel (below), two more unite to form the wings (center), the remaining and larger petal forms the standard. In most plants of this family the stamens and pistils are concealed within the keel. Fig. 41. Two-lipped inequilateral flower, common in such plants as Salvia, Snapdragon, etc. Note the united calyx and corolla. Fig. 42. Gamopetalous or united and regular corolla of the Fringed Gentian. Figs. 43, 44, and 45, flowers of the Compositæ or daisy family. Many small flowers grouped in heads and usually surrounded by one or more series of bracts. Fig. 43. Flowers all tubular, the small one at the left being an individual flower. Common examples are Boneset and the common garden Ageratum. Fig. 44. Flowers both tubular and with rays, the tubular in the center and the rays on the margin. Below is an individual tubular flower on the right, and on the left an individual ray flower. Note that its five united divisions correspond to the five petals in other plants. Common examples are the daisy, sunflower, black-eyed Susan, etc. Fig. 45. Flowers all ray flowers, an individual one at the right. The Compositæ with only ray flowers usually have a milky juice and have often been grouped in a separate family, the Cichoriaceæ. Common examples are dandelion, chicory, and lettuce.
Fig. 39. A perfect and complete flower. A, petals, all of them forming the corolla; B, sepals, all of them forming the calyx; C, the stamen, composed of (C) the filament, and (C1) the anther, which produces the pollen; D, the pistil, consisting of the swollen base (D) the ovary, a slender shank (D1) the style, and the swollen or branched tip (D2) the stigma. (H. D. House, “Wild Flowers of New York.”) Fig. 40. Typical flower of the pea family. Two petals unite to form the keel (below), two more unite to form the wings (center), the remaining and larger petal forms the standard. In most plants of this family the stamens and pistils are concealed within the keel. Fig. 41. Two-lipped inequilateral flower, common in such plants as Salvia, Snapdragon, etc. Note the united calyx and corolla. Fig. 42. Gamopetalous or united and regular corolla of the Fringed Gentian. Figs. 43, 44, and 45, flowers of the Compositæ or daisy family. Many small flowers grouped in heads and usually surrounded by one or more series of bracts. Fig. 43. Flowers all tubular, the small one at the left being an individual flower. Common examples are Boneset and the common garden Ageratum. Fig. 44. Flowers both tubular and with rays, the tubular in the center and the rays on the margin. Below is an individual tubular flower on the right, and on the left an individual ray flower. Note that its five united divisions correspond to the five petals in other plants. Common examples are the daisy, sunflower, black-eyed Susan, etc. Fig. 45. Flowers all ray flowers, an individual one at the right. The Compositæ with only ray flowers usually have a milky juice and have often been grouped in a separate family, the Cichoriaceæ. Common examples are dandelion, chicory, and lettuce.
surround and often half inclose the brightly colored petals within. This outer covering of flowers is calledcalyx(Figure 39B), the individual parts of it,where they are separated,sepals. Their chief use is to protect the interior petals while they are inclosed in the bud. The calyx may or may not have bracts just underneath it, as it does very conspicuously in the case of the flowering dogwood, whose white “flowers” are really only brightly colored bracts. The transition between bracts and calyx is not difficult to see in many plants, and where it is impossible the evidence from their internal structure confirms what our eye might be inclined to doubt.
Just inside the calyx is what most people call the “flower,” which is really composed of more highly colored sepals, but which we callpetals(Figure 39A). Where these are joined together the collection, which forms tubular flowers like the lily of the valley, is called acorolla. It is, of course, the petals or corollas of flowering plants that give our landscapes their greatest beauty, their most gorgeous coloring. While this from one point of view amply justifies a prodigal nature in strewing the earth with beautiful flowers, the true value of the color to the plant is in quite other directions, which will be explained a little later.
Toward the base of the corolla, or sometimes on the petals or sepals, may be found a series of slender appendages, usually threadlike or a little thicker, crowned at the top by a distinctly large knob. The individual appendage is known as astamen(Figure 39C), its threadlike portion afilament(Figure 39C), and the knoblike top ananther(Figure 39C1).
Directly in the middle of the flower there is still another organ, usually swollen at the base, slender in the shank, and either thickened or branched at the tip. This central part of nearly all flowers is called collectively a pistil (Figure 39D), its swollenbase anovary(Figure 39D), the slender shank thestyle(Figure 39D1), and the thickened or branched tip astigma(Figure 39D2). A perfect and complete flower, then, is composed as follows:
The stamen is the male organ of reproduction and the pistil the female. The actual process of fertilization, pregnancy, the forming of the fruit and later the seed, and the latter’s birth of a new plant, comprise one of the most fascinating of those provisions of nature which secure the perpetuation of the plant world. In the life history of even the commonest weed along the roadside there is this constant renewal of life by sexual reproduction, just as in animals and in man. In the chapter on “How Plants Produce Their Young” will be found some account of this supreme function of flowers, after which, as if their usefulness were over, they wither and perish.
Not all flowers are perfect or complete. Some lack petals, as the buckwheat, where the colored calyx replaces petals. Others have neither calyx nor corolla, as in the sycamore or plane tree. Most plants, however, have both calyx and corolla. In some very few plants certain of the flowers have no stamens, when they are said to bepistillateor female flowers, and certain others have no pistils, when they are calledstaminateor male flowers. In other words, the sexes are in different flowers in the same cluster or plant, as is true of the walnut and hickories, when they are said to bemonœcious. In still others the sexes are on entirely different plants, in whichcase they arediœcious, as in practically all willows. In the latter case there arepistillateor female plants andstaminateor male plants.
While it is a commonplace that peas do not look like daisies, nor a carnation like a rose, this simple observation does not begin to tell us of the wonderfully different flower shapes and colors that are to be found along any roadside. The perfect and complete flower that we have been studying is quite regular, composed as often as not of four or five petals, as many sepals, with five or ten stamens and perhaps a single pistil. Yet there is literally no limit to the variations from this scheme, and some of these must be understood here in order that the life-histories and behavior of plants discussed in later chapters may tell their full story.
The figures on page 44 show a regular flower, with five separate petals and sepals (Fig. 39). Such flowers are said to bepolypetalous, i.e., separate petals. Sometimes three of the petals are larger, two smaller, in which case the flower is lopsided or, as it is said,inequilateral. Again all the petals are united to form a regular and equilateral tube, as in lily of the valley, when they aregamopetalous,i.e., united petals (Figure 42). As we shall see in the chapter on Plant Families, this is a distinction between two great groups of plants, as important in their classification as negro and white man are in classifying humans.
In peas, beans, the locust tree, and related plants the petals are much changed to form an irregular flower, with a keellike or prow-shaped part made from the uniting of two petals. Two more unite to form the wings, and the remaining and larger petal forms the standard. Figure 40 and the explanationunder it illustrate this unusual form of flowers.
Our common garden salvia shows still another type of flower, which is tubular and irregular (Figure 41). There is an arching, hoodlike structure at the top overhanging a lower lip. This kind of irregularity is common in thousands of different sorts of plants and, usually, it is a device to insure fertilization of the flower by insect visitors. So necessary are these for pregnancy in many plants, that an orchid, once discovered in Madagascar with a tube eighteen inches deep, puzzled the botanists, who were unable to understand how the plant produced seed in the absence of any known insect with a tongue as long as that. Darwin said at once that such an insect would one day be discovered on that island. Years after, Baron von Humboldt, a German naturalist, found the insect and explained the mystery.
Perhaps there is no feature of plant life that shows such an amazing amount of variation as the forms of flowers, and while only a few of the simplest deviations from the normal have been discussed here, it must not be forgotten that this infinite variety is a reflection of the ingeniousness of nature in securing a plentiful supply of seed. Form, color, the secretion of sweetish nectar, the night or day blooming of different kinds of flowers, every device that will make fertilization certain, by the flower itself, by insects, or even by the wind, is used in such prodigal fashion, that we come to see the importance of it to all plants only by a realization of the complexity of it and the provisions against its failure.
One apparently most lavish method of securing fertilization is the arrangement of flowers inclusters. While many flowers are quite solitary, the great mass of individual plants produce a few or dozens, or even hundreds of flowers—in fact, certain relatives of the common carrot may produce over a thousand flowers in a single cluster. The form and plan of arrangement of these clusters follows a rather definite scheme, and here, as in the case of leaves and parts of individual flowers, the figures tell the story better than words. In the common dandelion and daisy, and their thousands of relatives, the “flower” (Figures 43-45), as commonly understood, is really composed of scores or even hundreds of true flowers in each head. In the case of the daisy the yellow center, if picked apart, is seen to be really made up of scores of tiny tubular flowers, each just as truly a flower as a single rose. The rays, or what are incorrectly called “petals,” which fringe the golden center with white, if carefully separated and examined closely, will be found to be also a complete flower, the true petals of which are all joined to make the strap-shaped ray. If one looks sharply, the united edges of these petals may be seen by the ridges or channels that represent their joined edges. Because plants of this sort produce two sets of flowers in each head, one conspicuous by its brightly colored rays and with another tubular set in the center which makes doubly certain the fertilization and seed supply, they are considered the most highly developed of all plants. It is not a close aristocracy, nor an exclusive one, for over eleven thousand different kinds of plants, scattered all over the world, have their flowers arranged in this fashion or some slight modification of it. They possess, above all others, the certainty that there will be no slip in their fertilization, pregnancy,and subsequent birth of a new generation. Because this is the great object of all flowers, and these daisylike plants have brought it to such perfection, they are most surely to be classed as the highest type upon the earth to-day.
FIG. 46-50.—TYPES OF FLOWER CLUSTERS Fig. 46. A spike, the individual flowers attached directly to the common stalk. Fig. 47. A raceme, a spikelike cluster where individual flowers are stalked. Fig. 48. An umbel, the individual flower stalks all arising from one point. Fig. 49. Individual flower stalks of different lengths but the cluster usually flat-topped (corymb). Fig. 50. A flower cluster in which the end of the stem is terminated by a flower from the base of which side branchlets similarly tipped with flowers arise (cyme).FIG. 46-50.—TYPES OF FLOWER CLUSTERSFig. 46. A spike, the individual flowers attached directly to the common stalk. Fig. 47. A raceme, a spikelike cluster where individual flowers are stalked. Fig. 48. An umbel, the individual flower stalks all arising from one point. Fig. 49. Individual flower stalks of different lengths but the cluster usually flat-topped (corymb). Fig. 50. A flower cluster in which the end of the stem is terminated by a flower from the base of which side branchlets similarly tipped with flowers arise (cyme).
Fig. 46. A spike, the individual flowers attached directly to the common stalk. Fig. 47. A raceme, a spikelike cluster where individual flowers are stalked. Fig. 48. An umbel, the individual flower stalks all arising from one point. Fig. 49. Individual flower stalks of different lengths but the cluster usually flat-topped (corymb). Fig. 50. A flower cluster in which the end of the stem is terminated by a flower from the base of which side branchlets similarly tipped with flowers arise (cyme).
While highly irregular flowers are common in nature, conspicuous examples being the orchids in any florist’s window, or the milkweeds along the roadside, they can nearly always be seen to have various changes in the shape of their petals, or sepals, or stamens, or pistils, which are adaptations to their mode of life, but which always result in fertilization. Some plants, true monstrosities of nature, are not only far from having the usual arrangementof flower parts, but they even produce increased numbers of one part at the expense of others.
Double buttercups, and hundreds of our most beautiful garden blossoms, have been rescued by cultivation or the arts of the gardeners. Some roses seem to be practically all petals, but for every increase of petals there must be a decrease of some other part of the flower, and more often than enough it is the stamens and pistils that lose out in this transformation. Just as there is a decrease almost to the vanishing point in the birthrate when people become too effete and cultivated, so in plants there seems to be a point beyond which they cannot be pushed without suffering partial or often complete inability to produce young. The more highly they have been developed, oftentimes the greater their beauty, the less able are they to see to it that the chief function of flowers is accomplished. Such garden plants are increased by root division, cuttings and other arts of the gardener. Naturally true double flowers are almost unknown in wild plants, and the habit seems to have been brought about by too easy a time of it, too little struggle, too much food, or by any other of those things that produce effete but beautiful things, charming in their way, but of no significance in the sturdy struggle for existence that all wild plants must meet or perish. Another curious modification of a flower bud is cauliflower. Here the bud has been so developed, its calyx, sepals, etc., so transformed that the large, cabbagelike head, produced at the apex of the main stem of the plant, has by so much lost all semblance of a flower that it is actually a vegetable.
FIG. 51.—FLOWER ARRANGEMENT PECULIAR TO THE ARUM FAMILY Fig. 51. The outer leaflike tubular or hooded spathe surrounds in our common Jack-in-the-Pulpit a clublike spadix, upon which are crowded the tiny flowers.FIG. 51.—FLOWER ARRANGEMENT PECULIAR TO THE ARUM FAMILYFig. 51. The outer leaflike tubular or hooded spathe surrounds in our common Jack-in-the-Pulpit a clublike spadix, upon which are crowded the tiny flowers.
Fig. 51. The outer leaflike tubular or hooded spathe surrounds in our common Jack-in-the-Pulpit a clublike spadix, upon which are crowded the tiny flowers.
No feature of a landscape gives us more pleasure than its flowers, over which poets have sung and artists have painted their most charming pictures, even a musician has composed a very beautiful piano piece, “To a Water Lily.” But their true place in the scheme of nature has a deeper significance: the wonderful color and symmetry of their parts, the plan of their arrangement, their transformation into curious forms, like the Madagascar orchid, and hundreds of others—all these point to their supreme function, an act of self-sacrifice comparable only to the fall of a leaf when its task is done. Petals, too,wither and die when the fertilized ovary, already a mother, begins the slow process of maturing its young and the end of the flowering stage is reached. Such a climax is this in certain plants that the whole plant dies, as we have already noted in the case of the century plant. The toddy or wine palm of India, often sixty or seventy years old and more than a hundred feet tall, flowers only once, and, as if in recognition of the fact that it has done that for which it grew, slowly dies as the seed ripens. More humbleannuals, like buckwheat, and hundreds of others, live only one brief growing season, produce flowers and seeds, and then die, leaving behind them the only means of perpetuating their kind. The dormant seed carries over the winter the life they were themselves unable to maintain, as perennials and woody plants do in their buds.
The number of different kinds of fruits that one can buy even in the greatest markets in the world is so small, compared to all fruits that are annually produced by plants, that they might almost be likened to an ear of corn as against a Missouri cornfield. If, as we have seen, all flowering plants must produce fruits, then what we commonly call such can be only a fraction of what actually makes up nature’s annual harvest. It follows that fruits often occur in unfamiliar disguises and, as we shall see presently, some of the things we have been calling fruits may be so only partly, if at all.
Disregarding what we call fruits and looking at it from the plant’s point of view, a fruit is anything in which, or upon which, a seed is developed or ripened quite without regard as to whether it isedible by man or not. As the ovary is the female organ of reproduction and contains the yet undeveloped seed, it follows also that fruits are practically always a development of some part or modification of the ovary or the upper end of the flower stalk upon which it rests and from which it is often scarcely separable.
Familiar enough is the distinction between dry fruits, such as a pea pod and fleshy ones like oranges, and this quality of being fleshy or dry is practically universal. Among fleshy fruits a few well-known types may be mentioned, such as the orange, tomato, grape, gooseberry, and cranberry, all trueberries. There are, of course, thousands of less familiar examples of berries, but, whether with a hard rind as in the orange or not, they are a direct development, or often a mere swelling of the ovary, with sometimes the adhering calyx, and contain the seed. In apples and pears, known aspomes, the fleshy part is a development of part calyx and part the receptacle upon which the ovary is supported while still in the flower. The ovary in these fruits is the parchmentlike interior which contains the seed. Plums and cherries, which have a single stone, instead of numerous seeds buried in the flesh, are known as drupes. These familiar examples are matched by thousands of others of which we hear nothing, alldrupesand all formed directly from the ripened ovary and without much change, except the increase of size, juiciness and large development of the tiny immature seed, now transformed into a stone. In the watermelon, pumpkin, and related plants, is still another kind of fleshy fruit, called apepo. All of this, including the hard rind, is transformed ovary and calyx completely incorporated, and forming inthe pumpkin perhaps the largest fleshy fruit known. In a considerable number of plants there is not a single ovary, but several, or in some cases many. These occasionally all develop into what is called an aggregate fruit, of which examples are the blackberry, mulberry, magnolia, and many others.
While it would be logical to think that these fleshy fruits were designed to make delicious food for man, that, in the light of what we have seen to be the real function of the flower, is an assumption which, while flattering, is far from the truth. It is much more certain that fleshy fruits help plants in the dispersal of their seeds and that this fleshy, juicy character is just one more device of nature to see to it that not only do plants produce seeds, but that the seeds are carried and so spread the plant over considerable areas. Birds and animals eat such fruits in enormous quantities and, in fact, bird migrations are thought to be not so much response to winter cold as to the fact that fruits are scarce then. When it is remembered that some birds make tremendous flights, often over 10,000 miles in a few days, their capacity to spread seeds through their droppings may be imagined. In the chapter on plant distribution some truly remarkable cases of such seed dispersal will be given.
The chance of having seed carried great distances, because it is embedded in a fleshy, often brightly colored fruit, would seem to put plants having dry fruits at a disadvantage. Birds and animals cannot be expected to look after the dispersal of those fruits that are neither tempting to the sight nor to the taste. And it must be confessed that quite other qualities in dry fruits insure their dispersal. Some are so nutritious, like theacorn,that thrifty squirrels store them over the winter, as they do many other seeds which are harvested from dry fruits. Various grains are often so stored by man, and rice, wheat, buckwheat, and other cereals are common cases. In nearly all grains the seed fills so completely the fruit that cereals are very generally, but mistakenly, called seeds. A grain of wheat or corn is just as complete a fruit as a watermelon. Only its outer coat and inner seed are so closely welded together as not to be usually recognized as a fruit, with the seed inside.
One of the commonest types of dry fruit is thecapsule(Figure 53), well named, as it is almost an exact counterpart of the capsule of the druggist, in that it is in many cases composed of a lower part and an upper, usually merely a domed lid. Others again, instead of splitting around the sides, split from top to bottom. Still others, as peas and beans, known aslegumes(Figure 57), are pods that not only split lengthwise, but have no central partition, as do many other fruits of the same general type. When the seed is ripe nearly all pods andlegumesfinally split open, and the seed or seeds tumble out. A few, as in the violet and touch-me-not or jewelweed, apparently realizing that merely to spill out ripe seeds at the proper time will not spread the species very far, open their fruits with a sudden explosion and literally shoot their seeds considerable distances. The artillery plant, commonly grown in greenhouses, a delicate feathery herb from tropical America, opens its flowers with a report like a toy popgun and shoots its small pollen grains for several feet, but not its seeds as stated by some.
But many fruits do not open at all and seem to be at the greatest disadvantage in the effort to insure