Differing from the true lilies in having the bases of the perigone leaves adherent to the surface of the ovary, so that the latter is apparently below the flower (inferior), and lacking the inner circle of stamens, is the iris family (Iridaceae), represented by the wild blue-flag (Iris versicolor) (Fig. 84, A, E), as well as by numerous cultivated species. In iris the carpels are free above and colored like the petals (B), with the stigma on the under side. Of garden flowers the gladiolus and crocus are the most familiar examples, besides the various species of iris; and of wild flowers the little "blue-eyed grass" (Sisyrinchium).



The blue pickerel-weed (Pontederia) is the type of a family of which there are few common representatives (Fig. 84, I, K).

The last family of the order is the Bromeliaceae, all inhabitants of the warmer parts of the globe, but represented in the southern states by several forms, the commonest of which is the so-called "gray moss" (Tillandsia) (Fig. 84, F, H). Of cultivated plants the pineapple, whose fruit consists of a fleshy mass made up of the crowded fruits and the fleshy flower stalks, is the best known.

ORDER II.—Enantioblastae.

The second order of the monocotyledons, Enantioblastae, includes very few common plants. The most familiar examples are the various species of Tradescantia (Fig. 88), some of which are native, others exotic. Of the cultivated forms the commonest is one sometimes called "wandering-jew," a trailing plant with zigzag stems, and oval, pointed leaves forming a sheath about each joint. Another common one is the spiderwort already referred to. In this the leaves are long and pointed, but also sheathing at the base. When the flowers are showy, as in these, the sepals and petals are different, the former being green. The flowers usually open but once, and the petals shrivel up as the flower fades. There are four families of the order, the spiderwort belonging to the highest one, Commelyneae.

ORDER III.—Spadiciflorae.

The third order of the monocotyledons, Spadiciflorae, is a very large one, and includes the largest and the smallest plants of the whole sub-class. In all of them the flowers are small and often very inconspicuous; usually, though not always, the male and female flowers are separate, and often on different plants. The smallest members of the group are little aquatics, scarcely visible to the naked eye, and of extremely simple structure, but nevertheless these little plants produce true flowers. In marked contrast to these are the palms, some of which reach a height of thirty metres or more.

The flowers in most of the order are small and inconspicuous, but aggregated on a spike (spadix) which may be of very large size. Good types of the order are the various aroids (Aroideae), of which the calla (Richardia) is a very familiar cultivated example. Of wild forms the sweet-flag (Acorus), Jack-in-the-pulpit (Arisaema) (Fig. 86, A, D), skunk-cabbage (Symplocarpus), and wild calla may be noted. In Arisaema (Fig. 86, A) the flowers are borne only on the base of the spadix, and the plant is dioecious. The flowers are of the simplest structure, the female consisting of a single carpel, and the male of four stamens (C, D). While the individual flowers are destitute of a perigone, the whole inflorescence (cluster of flowers) is surrounded by a large leaf (spathe), which sometimes is brilliantly colored, this serving to attract insects. The leaves of the aroids are generally large and sometimes compound, the only instance of true compound leaves among the monocotyledons (Fig. 86, B).

[Illustration: FIG. 86.—Types of Spadiciflorae. A, inflorescence of Jack-in-the-pulpit (Arisaema, Aroideae). The flowers (fl.) are at the base of a spike (spadix), surrounded by a sheath (spathe), which has been cut away on one side in order to show the flowers, x 1/2. B, leaf of the same plant, x 1/4. C, vertical section of a female flower, x 2. D, three male flowers, each consisting of four stamens, x 2. E, two plants of a duck-weed (Lemna), the one at the left is in flower, x 4. F, another common species. L, Trisulea, x 1. G, male flower of E, x 25. H, optical section of the female flower, showing the single ovule (ov.), x 25. I, part of the inflorescence of the bur-reed (Sparganium), with female flowers, x 1/2 (Typhaceae). J, a single, female flower, x 2. K, a ripe fruit, x 1. L, longitudinal section of the same. M, two male flowers, x 1. N, a pond-weed (Potomogeton), x 1 (Naiadaceae). O, a single flower, x 2. P, the same, with the perianth removed, x 2. Q, fruit of the same, x 2.]

Probably to be regarded as reduced aroids are the duck-weeds (Lemnaceae) (Fig. 86, F, H), minute floating plants without any differentiation of the plant body into stem and leaves. They are globular or discoid masses of cells, most of them having roots; but one genus (Wolffia) has no roots nor any trace of fibro-vascular bundles. The flowers are reduced to a single stamen or carpel (Figs. E, G, H).

The cat-tail (Typha) and bur-reed (Sparganium) (Fig. 86, I, L) are common representatives of the family Typhaceae, and the pond-weeds (Naias and Potomogeton) are common examples of the family Naiadeae. These are aquatic plants, completely submerged (Naias), or sometimes partially floating (Potomogeton). The latter genus includes a number of species with leaves varying from linear (very narrow and pointed) to broadly oval, and are everywhere common in slow streams.

The largest members of the group are the screw-pines (Pandaneae) and the palms (Palmae). These are represented in the United States by only a few species of the latter family, confined to the southern and southwestern portions. The palmettoes (Sabal and Chamaerops) are the best known.

Both the palms and screw-pines are often cultivated for ornament, and as is well known, in the warmer parts of the world the palms are among the most valuable of all plants. The date palm (Phoenix dactylifera) and the cocoanut (Cocos nucifera) are the best known. The apparently compound ("pinnate" or feather-shaped) leaves of many palms are not strictly compound; that is, they do not arise from the branching of an originally single leaf, but are really broad, undivided leaves, which are closely folded like a fan in the bud, and tear apart along the folds as the leaf opens.

Although these plants reach such a great size, an examination of the stem shows that it is built on much the same plan as that of the other monocotyledons; that is, the stem is composed of a mass of soft, ground tissue through which run many small isolated, fibro-vascular bundles. A good idea of this structure may be had by cutting across a corn-stalk, which is built on precisely the same pattern.

ORDER IV.—Glumaceae.

The plants of this order resemble each other closely in their habit, all having long, narrow leaves with sheathing bases that surround the slender, distinctly jointed stem which frequently has a hard, polished surface. The flowers are inconspicuous, borne usually in close spikes, and destitute of a perigone or having this reduced to small scales or hairs. The flowers are usually surrounded by more or less dry leaves (glumes, paleae) which are closely set, so as to nearly conceal the flowers. The flowers are either hermaphrodite or unisexual.

, the male; [Female], the female flowers, x 1/2. B, a single male flower, x 2. C, a female flower, x 2. D, fruiting spike of another Carex, x 1/2. E, a single fruit, x 1. F, the same, with the outer envelope removed, and slightly enlarged. G, section of F, x 3. em. the embryo. H, a bulrush, Scirpus (Cyperaceae), x 1/2. I, a single spikelet, x 2. J, a single flower, x 3. K, a spikelet of flowers of the common orchard grass, Dactylis (Gramineae), x 2. L, a single flower, x 2. M, the base of a leaf, showing the split sheath encircling the stem, x 1. N, section of a kernel of corn, showing the embryo (em.), x 2.]

There are two well-marked families, the sedges (Cyperaceae) and the grasses (Gramineae). The former have solid, often triangular stems, and the sheath at the base of the leaves is not split. The commonest genera are Carex (Fig. 87, A, G) and Cyperus, of which there are many common species, differing very little and hard to distinguish. There are several common species of Carex which blossom early in the spring, the male flowers being quite conspicuous on account of the large, yellow anthers. The female flowers are in similar spikes lower down, where the pollen readily falls upon them, and is caught by the long stigmas. In some other genera, e.g. the bulrushes (Scirpus) (Fig. 87, H), the flowers are hermaphrodite, i.e. contain both stamens and pistils. The fruit (Fig. 87, F) is seed-like, but really includes the wall of the ovary as well, which is grown closely to the enclosed seed. The embryo is small, surrounded by abundant endosperm (Fig. 87, G). Very few of the sedges are of any economic importance, though one, the papyrus of Egypt, was formerly much valued for its pith, which was manufactured into paper.

The second family, the grasses, on the contrary, includes the most important of all food plants, all of the grains belonging here. They differ mainly from the sedges in having, generally, hollow, cylindrical stems, and the sheath of the leaves split down one side; the leaves are in two rows, while those of the sedges are in three. The flowers (Fig. 87, L) are usually perfect; the stigmas, two in number and like plumes, so that they readily catch the pollen which is blown upon them. A few, like the Indian corn, have the flowers unisexual; the male flowers are at the top of the stem forming the "tassel," and the female flowers lower down forming the ear. The "silk" is composed of the enormously lengthened stigmas. The fruits resemble those of the sedges, but the embryo is usually larger and placed at one side of the endosperm (N, em.).

While most of the grasses are comparatively small plants, a few of them are almost tree-like in their proportions, the species of bamboo (Bambusa) sometimes reaching a height of twenty to thirty metres, with stems thirty to forty centimetres in diameter.

ORDER V.—Scitamineae.



The plants of this order are all inhabitants of the warmer parts of the earth, and only a very few occur within the limits of the United States, and these confined to the extreme south. They are extremely showy plants, owing to their large leaves and brilliant flowers, and for this reason are cultivated extensively. Various species of Canna (Fig. 88) are common in gardens, where they are prized for their large, richly-colored leaves, and clusters of scarlet, orange, or yellow flowers. The leafy stems arise from thick tubers or root stocks, and grow rapidly to a height of two metres or more in the larger species. The leaves, as in all the order, are very large, and have a thick midrib with lateral veins running to the margin. The young leaves are folded up like a trumpet. The flowers are irregular in form, and in Canna only a single stamen is found; or if more are present, they are reduced to petal-like rudiments. The single, perfect stamen (Fig. 88, C, an.) has the filament broad and colored like the petals, and the anther attached to one side. The pistil (gy.) is also petal-like. There are three circles of leaves forming the perigone, the two outer being more or less membranaceous, and only the three inner petal-like in texture. The ovary (o) is inferior, and covered on the outside with little papillae that afterward form short spines on the outside of the fruit (F).

The seeds are large, but the embryo is very small. A section of a nearly ripe seed shows the embryo (em.) occupying the upper part of the embryo sac which does not nearly fill the seed and contains no endosperm. The bulk of the seed is derived from the tissue of the body of the ovule, which in most seeds becomes entirely obliterated by the growth of the embryo sac. The cells of this tissue become filled with starch, and serve the same purpose as the endosperm of other seeds. This tissue is called "perisperm."

Of food plants belonging to this order, the banana (Musa) is much the most important. Others of more or less value are species of arrowroot (Maranta) and ginger (Zingiber).

There are three families: I. Musaceae (banana family); II. Zingiberaceae (ginger family); and III. Cannaceae (Canna, Maranta).

ORDER VI.—Gynandrae.

By far the greater number of the plants of this order belong to the orchis family (Orchideae), the second family of the order (Apostasieae), being a small one and unrepresented in the United States. The orchids are in some respects the most highly specialized of all flowers, and exhibit wonderful variety in the shape and color of the flowers, which are often of extraordinary beauty, and show special contrivances for cross-fertilization that are without parallel among flowering plants.

[Illustration: FIG. 89.—Gynandrae. A, inflorescence of the showy orchis (Orchis spectabilis), x 1 (Orchideae). B, a single flower, with the upper leaves of the perianth turned back to show the column (x). sp. the spur attached to the lower petal or lip. o, the ovary, x 1. C, the column seen from in front. an. the stamen. gy. the stigmatic surface, x 1. D, the two pollen masses attached to a straw, which was inserted into the flower, by means of the viscid disc (d): i, the masses immediately after their withdrawal; ii, iii, the same a few minutes later, showing the change in position. E, diagram of the flower; the position of the missing stamens indicated by small circles.]

The flowers are always more or less bilaterally symmetrical (zygomorphic). The ovary is inferior, and usually twisted so as to turn the flower completely around. There are two sets of perigone leaves, three in each, and these are usually much alike except the lower (through the twisting of the ovary) of the inner set. This petal, known as the "lip" or "labellum," is usually larger than the others, and different in color, as well as being frequently of peculiar shape. In many of them it is also prolonged backward in a hollow spur (see Fig. 89, B). In all of the orchids except the lady's-slippers (Cypripedium) (Fig. 90, B), only one perfect stamen is developed, and this is united with the three styles to form a special structure known, as the "column" or "gynostemium" (Fig. 89, B, C). The pollen spores are usually aggregated into two or four waxy masses ("pollinia," sing. pollinium), which usually can only be removed by the agency of insects upon which all but a very few orchids are absolutely dependent for the pollination of the flowers.



In the lady-slippers there are two fertile stamens, and a third sterile one has the form of a large triangular shield terminating the column (Fig. 90, C, st.).

The ovules of the orchids are extremely small, and are only partly developed at the time the flower opens, the pollen tube growing very slowly and the ovules maturing as it grows down through the tissues of the column. The ripe seeds are excessively numerous, but so fine as to look like dust.

The orchids are mostly small or moderate-sized plants, few of them being more than a metre or so in height. All of our native species, with the exception of a few from the extreme south, grow from fibrous roots or tubers, but many tropical orchids, as is well known, are "epiphytes"; that is, they grow upon the trunks and branches of trees. One genus, Vanilla, is a twining epiphyte; the fruit of this plant furnishes the vanilla of commerce. Aside from this plant, the economical value of the orchids is small, although a few of them are used medicinally, but are not specially valuable.

Of the five thousand species known, the great majority are inhabitants of the tropics, but nevertheless there are within the United States a number of very beautiful forms. The largest and showiest are the lady's-slippers, of which we have six species at the north. The most beautiful is the showy lady's-slipper (Cypripedium spectabile), whose large, pink and white flowers rival in beauty many of the choicest tropical orchids. Many of the Habenarias, including the yellow and purple fringed orchids, are strikingly beautiful as are the Arethuseae (Arethusa, Pogonia, Calopogon). The last of these (Fig. 90, H) differs from all our other native orchids in having the ovary untwisted so that the labellum lies on the upper side of the flower.

A number of the orchids are saprophytic, growing in soil rich in decaying vegetable matter, and these forms are often nearly or quite destitute of chlorophyll, being brownish or yellowish in color, and with rudimentary leaves. The coral roots (Corallorhiza), of which there are several species, are examples of these, and another closely related form, the putty-root (Aplectrum) (Fig. 90, A), has the flowering stems like those of Corallorhiza, but there is a single, large, plaited leaf sent up later.

ORDER VII.—Helobiae.

The last order of the monocotyledons is composed of marsh or water plants, some of which recall certain of the dicotyledons. Of the three families, the first, Juncagineae, includes a few inconspicuous plants with grass-like or rush-like leaves, and small, greenish or yellowish flowers (e.g. arrow-grass, Triglochin).

The second family (Alismaceae) contains several large and showy species, inhabitants of marshes. Of these the water-plantain (Alisma), a plant with long-stalked, oval, ribbed leaves, and a much-branched panicle of small, white flowers, is very common in marshes and ditches, and the various species of arrowhead (Sagittaria) are among the most characteristic of our marsh plants. The flowers are unisexual; the female flowers are usually borne at the base of the inflorescence, and the male flowers above. The gynoecium (Fig. 91, B) consists of numerous, separate carpels attached to a globular receptacle. The sepals are green and much smaller than the white petals. The leaves (F) are broad, and, besides the thickened, parallel veins, have numerous smaller ones connecting these.

[Illustration: FIG. 91.—Types of Helobiae. A, inflorescence of arrowhead (Sagittaria), with a single female flower, x 1/2 (Alismaceae). B, section through the gynoecium, showing the numerous single carpels, x 3. C, a ripe fruit, x 3. D, a male flower, x 1. E, a single stamen, x 3. F, a leaf of Sagittaria variabilis, x 1/6. G, ditch-moss (Elodea), with a female flower (fl.), x 1/2. (Hydrocharideae). H, the flower, x 2. an. the rudimentary stamens. st. the stigma. I, cross-section of the ovary, x 4. J, male inflorescence of eel-grass (Vallisneria), x 1. K, a single expanded male flower, x 12. st. the stamen. L, a female flower, x 1. gy. the stigma.]

The last family is the Hydrocharideae. They are submersed aquatics, or a few of them with long-stalked, floating leaves. Two forms, the ditch-moss (Elodea) (Fig. 91, G, I) and eel-grass (Vallisneria) are very common in stagnant or slow-running water. In both of these the plants are completely submersed, but there is a special arrangement for bringing the flowers to the surface of the water. Like the arrowhead, the flowers are unisexual, but borne on different plants. The female flowers (H, L) are comparatively large, especially in Vallisneria, and are borne on long stalks, by means of which they reach the surface of the water, where they expand and are ready for pollination. The male flowers (Fig. 91, J, K) are extremely small and borne, many together, surrounded by a membranous envelope, the whole inflorescence attached by a short stalk. When the flowers are ready to open, they break away from their attachment, and the envelope opens, allowing them to escape, and they immediately rise to the surface where they expand and collect in great numbers about the open female flowers. Sometimes these are so abundant during the flowering period (late in summer) that the surface of the water looks as if flour had been scattered over it. After pollination is effected, the stem of the female flower coils up like a spring, drawing the flower beneath the water where the fruit ripens.

The cells of these plants show very beautifully the circulation of the protoplasm, the movement being very marked and continuing for a long time under the microscope. To see this the whole leaf of Elodea, or a section of that of Vallisneria, may be used.



CHAPTER XVII.

DICOTYLEDONS.

The second sub-class of the angiosperms, the dicotyledons, receive their name from the two opposite seed leaves or cotyledons with which the young plant is furnished. These leaves are usually quite different in shape from the other leaves, and not infrequently are very thick and fleshy, filling nearly the whole seed, as may be seen in a bean or pea. The number of the dicotyledons is very large, and very much the greater number of living spermaphytes belong to this group. They exhibit much greater variety in the structure of the flowers than the monocotyledons, and the leaves, which in the latter are with few exceptions quite uniform in structure, show here almost infinite variety. Thus the leaves may be simple (undivided); e.g. oak, apple; or compound, as in clover, locust, rose, columbine, etc. The leaves may be stalked or sessile (attached directly to the stem), or even grown around the stem, as in some honeysuckles. The edges of the leaves may be perfectly smooth ("entire"), or they may be variously lobed, notched, or wavy in many ways. As many of the dicotyledons are trees or shrubs that lose their leaves annually, special leaves are developed for the protection of the young leaves during the winter. These have the form of thick scales, and often are provided with glands secreting a gummy substance which helps render them water-proof. These scales are best studied in trees with large, winter buds, such as the horsechestnut (Fig. 92), hickory, lilac, etc. On removing the hard, scale leaves, the delicate, young leaves, and often the flowers, may be found within the bud. If we examine a young shoot of lilac or buckeye, just as the leaves are expanding in the spring, a complete series of forms may be seen from the simple, external scales, through immediate forms, to the complete foliage leaf. The veins of the leaves are almost always much-branched, the veins either being given off from one main vein or midrib (feather-veined or pinnate-veined), as in an apple leaf, or there may be a number of large veins radiating from the base of the leaf, as in the scarlet geranium or mallow. Such leaves are said to be palmately veined.



Some of them are small herbaceous plants, either upright or prostrate upon the ground, over which they may creep extensively, becoming rooted at intervals, as in the white clover, or sending out special runners, as is seen in the strawberry. Others are woody stemmed plants, persisting from year to year, and often becoming great trees that live for hundreds of years. Still others are climbing plants, either twining their stems about the support, like the morning-glory, hop, honeysuckle, and many others, or having special organs (tendrils) by which they fasten themselves to the support. These tendrils originate in different ways. Sometimes, as in the grape and Virginia creeper, they are reduced branches, either coiling about the support, or producing little suckers at their tips by which they cling to walls or the trunks of trees. Other tendrils, as in the poison ivy and the true ivy, are short roots that fasten themselves firmly in the crevices of bark or stones. Still other tendrils, as those of the sweet-pea and clematis, are parts of the leaf.

The stems may be modified into thorns for protection, as we see in many trees and shrubs, and parts of leaves may be similarly changed, as in the thistle. The underground stems often become much changed, forming bulbs, tubers, root stocks, etc. much as in the monocotyledons. These structures are especially found in plants which die down to the ground each year, and contain supplies of nourishment for the rapid growth of the annual shoots.

[Illustration: FIG. 93.—A, base of a plant of shepherd's-purse (Capsella bursa-pastoris), x 1/2. r, the main root. B, upper part of the inflorescence, x 1. C, two leaves: i, from the upper part; ii, from the base of the plant, x 1. D, a flower, x 3. E, the same, with sepals and petals removed, x 3. F, petal. G, sepal. H, stamen, x 10. f, filament. an. anther. I, a fruit with one of the valves removed to show the seeds, x 4. J, longitudinal section of a seed, x 8. K, the embryo removed from the seed, x 8. l, the first leaves (cotyledons). st. the stem ending in the root. L, cross-section of the stem, x 20. fb. fibro-vascular bundle. M, a similar section of the main root, x 15. N, diagram of the flower.]

The structure of the tissues, and the peculiarities of the flower and fruit, will be better understood by a somewhat careful examination of a typical dicotyledon, and a comparison with this of examples of the principal orders and families.

One of the commonest of weeds, and at the same time one of the most convenient plants for studying the characteristics of the dicotyledons, is the common shepherd's-purse (Capsella bursa-pastoris) (Figs. 93-95).

The plant grows abundantly in waste places, and is in flower nearly the year round, sometimes being found in flower in midwinter, after a week or two of warm weather. It is, however, in best condition for study in the spring and early summer. The plant may at once be recognized by the heart-shaped pods and small, white, four-petaled flowers. The plant begins to flower when very small, but continues to grow until it forms a much-branching plant, half a metre or more in height. On pulling up the plant, a large tap-root (Fig. 93, A, r) is seen, continuous with the main stem above ground. The first root of the seedling plant continues here as the main root of the plant, as was the case with the gymnosperms, but not with the monocotyledons. From this tap-root other small ones branch off, and these divide repeatedly, forming a complex root system. The main root is very tough and hard, owing to the formation of woody tissue in it. A cross-section slightly magnified (Fig. 93, M), shows a round, opaque, white, central area (x), the wood, surrounded by a more transparent, irregular ring (ph.), the phloem or bast; and outside of this is the ground tissue and epidermis.

The lower leaves are crowded into a rosette, and are larger than those higher up, from which they differ also in having a stalk (petiole), while the upper leaves are sessile. The outline of the leaves varies much in different plants and in different parts of the same plant, being sometimes almost entire, sometimes divided into lobes almost to the midrib, and between these extremes all gradations are found. The larger leaves are traversed by a strong midrib projecting strongly on the lower side of the leaf, and from this the smaller veins branch. The upper leaves have frequently two smaller veins starting from the base of the leaf, and nearly parallel with the midrib (C i). The surface of the leaves is somewhat roughened with hairs, some of which, if slightly magnified, look like little white stars.

Magnifying slightly a thin cross-section of the stem, it shows a central, ground tissue (pith), whose cells are large enough to be seen even when very slightly enlarged. Surrounding this is a ring of fibro-vascular bundles (L, fb.), appearing white and opaque, and connected by a more transparent tissue. Outside of the ring of fibro-vascular bundles is the green ground tissue and epidermis. Comparing this with the section of the seedling pine stem, a resemblance is at once evident, and this arrangement was also noticed in the stem of the horse-tail.

Branches are given off from the main stem, arising at the point where the leaves join the stem (axils of the leaves), and these may in turn branch. All the branches terminate finally in an elongated inflorescence, and the separate flowers are attached to the main axis of the inflorescence by short stalks. This form of inflorescence is known technically as a "raceme." Each flower is really a short branch from which the floral leaves arise in precisely the same way as the foliage leaves do from the ordinary branches. There are five sets of floral leaves: I. four outer perigone leaves (sepals) (F), small, green, pointed leaves traversed by three simple veins, and together forming the calyx; II. four larger, white, inner perigone leaves (petals) (G), broad and slightly notched at the end, and tapering to the point of attachment. The petals collectively are known as the "corolla." The veins of the petals fork once; III. and IV. two sets of stamens (E), the outer containing two short, and the inner, four longer ones arranged in pairs. Each stamen has a slender filament (H, f) and a two-lobed anther (an.). The innermost set consists of two carpels united into a compound pistil. The ovary is oblong, slightly flattened so as to be oval in section, and divided into two chambers. The style is very short and tipped by a round, flattened stigma.

The raceme continues to grow for a long time, forming new flowers at the end, so that all stages of flowers and fruit may often be found in the same inflorescence.

The flowers are probably quite independent of insect aid in pollination, as the stamens are so placed as to almost infallibly shed their pollen upon the stigma. This fact, probably, accounts for the inconspicuous character of the flowers.

After fertilization is effected, and the outer floral leaves fall off, the ovary rapidly enlarges, and becomes heart-shaped and much flattened at right angles to the partition. When ripe, each half falls away, leaving the seeds attached by delicate stalks (funiculi, sing. funiculus) to the edges of the membranous partition. The seeds are small, oval bodies with a shining, yellow-brown shell, and with a little dent at the end where the stalk is attached. Carefully dividing the seed lengthwise, or crushing it in water so as to remove the embryo, we find it occupies the whole cavity of the seed, the young stalk (st.) being bent down against the back of one of the cotyledons (f).



A microscopic examination of a cross-section of the older root shows that the central portion is made up of radiating lines of thick-walled cells (fibres) interspersed with lines of larger, round openings (vessels). There is a ring of small cambium cells around this merging into the phloem, which is composed of irregular cells, with pretty thick, but soft walls. The ground tissue is composed of large, loose cells, which in the older roots are often ruptured and partly dried up. The epidermis is usually indistinguishable in the older roots. To understand the early structure of the roots, the smallest rootlets obtainable should be selected. The smallest are so transparent that the tips may be mounted whole in water, and will show very satisfactorily the arrangement of the young tissues. The tissues do not here arise from a single, apical cell, as we found in the pteridophytes, but from a group of cells (the shaded cells in Fig. 94, B). The end of the root, as in the fern, is covered with a root cap (r) composed of successive layers of cells cut off from the growing point. The rest of the root shows the same division of the tissues into the primary epidermis (dermatogen) (d), young fibro-vascular cylinder (plerome) (pl.), and young ground tissue (periblem) (pb.). The structure of the older portions of such a root is not very easy to study, owing to difficulty in making good cross-sections of so small an object. By using a very sharp razor, and holding perfectly straight between pieces of pith, however, satisfactory sections can be made. The cells contain so much starch as to make them almost opaque, and potash should be used to clear them. The fibro-vascular bundle is of the radial type, there being two masses of xylem (xy.) joined in the middle, and separating the two phloem masses (ph.), some of whose cells are rather thicker walled than the others. The bundle sheath is not so plain here as in the fern. The ground tissue is composed of comparatively large cells with thickish, soft walls, that contain much starch. The epidermis usually dies while the root is still young. In the larger roots the early formation of the cambium ring, and the irregular arrangement of the tissues derived from its growth, soon obliterate all traces of the primitive arrangement of the tissues. Making a thin cross-section of the stem, and magnifying strongly, we find bounding the section a single row of epidermal cells (Fig. 94, A, ep.) whose walls, especially the outer ones, are strongly thickened. Within these are several rows of thin-walled ground-tissue cells containing numerous small, round chloroplasts. The innermost row of these cells (sh.) are larger and have but little chlorophyll. This row of cells forms a sheath around the ring of fibro-vascular bundles very much as is the case in the horse-tail. The separate bundles are nearly triangular in outline, the point turned inward, and are connected with each other by masses of fibrous tissue (f), whose thickened walls have a peculiar, silvery lustre. Just inside of the bundle sheath there is a row of similar fibres marking the outer limit of the phloem (ph.). The rest of the phloem is composed of very small cells. The xylem is composed of fibrous cells with yellowish walls and numerous large vessels (tr.). The central ground tissue (pith) has large, thin-walled cells with numerous intercellular spaces, as in the stem of Erythronium. Some of these cells contain a few scattered chloroplasts in the very thin, protoplasmic layer lining their walls, but the cells are almost completely filled with colorless cell sap.

A longitudinal section shows that the epidermal cells are much elongated, the cells of the ground tissue less so, and in both the partition walls are straight. In the fibrous cells, both of the fibro-vascular bundle and those lying between, the end walls are strongly oblique. The tracheary tissue of the xylem is made up of small, spirally-marked vessels, and larger ones with thickened rings or with pits in the walls. The small, spirally-marked vessels are nearest the centre, and are the first to be formed in the young bundle.

The epidermis of the leaves is composed of irregular cells with wavy outlines like those of the ferns. Breathing pores, of the same type as those in the ferns and monocotyledons, are found on both surfaces, but more abundant and more perfectly developed on the lower surface of the leaf. Owing to their small size they are not specially favorable for study. The epidermis is sparingly covered with unicellular hairs, some of which are curiously branched, being irregularly star-shaped. The walls of these cells are very thick, and have little protuberances upon the outer surface (Fig. 93, E).

Cross-sections of the leaf may be made between pith as already directed; or, by folding the leaf carefully several times, the whole can be easily sectioned. The structure is essentially as in the adder-tongue, but the epidermal cells appear more irregular, and the fibro-vascular bundles are better developed. They are like those of the stem, but somewhat simpler. The xylem lies on the upper side.

The ground tissue is composed, as in the leaves we have studied, of chlorophyll-bearing, loose cells, rather more compact upon the upper side. (In the majority of dicotyledons the upper surface of the leaves is nearly or quite destitute of breathing pores, and the cells of the ground tissue below the upper epidermis are closely packed, forming what is called the "palisade-parenchyma" of the leaf.)

[Illustration: FIG. 95.—A-D, successive stages in the development of the flower of Capsella, x 50. A, surface view. B-D, optical sections. s, sepals, p, petals. an. stamens. gy. pistil. E, cross-section of the young anther, x 180. sp. spore mother cells. F, cross-section of full-grown anther. sp. pollen spores, x 50. F', four young pollen spores, x 300. F", pollen spores germinating upon the stigma, x 300. pt. pollen tube. G, young pistil in optical section, x 25. H, cross-section of a somewhat older one. ov. ovules. I-L, development of the ovule. sp. embryo sac (macrospore). I-K, x 150. L, x 50. M, embryo sac of a full-grown ovule, x 150. Sy. Synergidae. o, egg cell. n, endosperm nucleus. ant. antipodal cells. N-Q, development of the embryo, x 150. sus. suspensor.]

The shepherd's-purse is an admirable plant for the study of the development of the flower which is much the same in other angiosperms. To study this, it is only necessary to teaze out, in a drop of water, the tip of a raceme, and putting on a cover glass, examine with a power of from fifty to a hundred diameters. In the older stages it is best to treat with potash, which will render the young flowers quite transparent. The young flower (Fig. 95, A) is at first a little protuberance composed of perfectly similar small cells filled with dense protoplasm. The first of the floral leaves to appear are the sepals which very early arise as four little buds surrounding the young flower axis (Fig. 95, A, B). The stamens (C, an.) next appear, being at first entirely similar to the young sepals. The petals do not appear until the other parts of the flower have reached some size, and the first tracheary tissue appears in the fibro-vascular bundle of the flower stalk (D). The carpels are more or less united from the first, and form at first a sort of shallow cup with the edges turned in (D, gy.). This cup rapidly elongates, and the cavity enlarges, becoming completely closed at the top where the short style and stigma develop. The ovules arise in two lines on the inner face of each carpel, and the tissue which bears them (placenta) grows out into the cavity of the ovary until the two placentae meet in the middle and form a partition completely across the ovary (Fig. 95, H).

The stamens soon show the differentiation into filament and anther, but the former remains very short until immediately before the flowers are ready to open. The anther develops four sporangia (pollen sacs), the process being very similar to that in such pteridophytes as the club mosses. Each sporangium (Fig. E, F) contains a central mass of spore mother cells, and a wall of three layers of cells. The spore mother cells finally separate, and the inner layer of the wall cells becomes absorbed much as we saw in the fern, and the mass of mother cells thus floats free in the cavity of the sporangium. Each one now divides in precisely the same way as in the ferns and gymnosperms, into four pollen spores. The anther opens as described for Erythronium.

By carefully picking to pieces the young ovaries, ovules in all stages of development may be found, and on account of their small size and transparency, show beautifully their structure. Being perfectly transparent, it is only necessary to mount them in water and cover.

The young ovule (I, J) consists of a central, elongated body (nucellus), having a single layer of cells enclosing a large central cell (the macrospore or embryo sac) (sp.). The base of the nucellus is surrounded by two circular ridges (i, ii) of which the inner is at first higher than the outer one, but later (K, L), the latter grows up above it and completely conceals it as well as the nucellus. One side of the ovule grows much faster than the other, so that it is completely bent upon itself, and the opening between the integuments is brought close to the base of the ovule (Fig. 95, L). This opening is called the "micropyle," and allows the pollen tube to enter.

The full-grown embryo sac shows the same structure as that already described in Monotropa (page 276), but as the walls of the full-grown ovule are thicker here, its structure is rather difficult to make out. The ripe stigma is covered with little papillae (Fig. 95, F) that hold the pollen spores which may be found here sending out the pollen tube. By carefully opening the ovary and slightly crushing it in a drop of water, the pollen tube may sometimes be seen growing along the stalk of the ovule until it reaches and enters the micropyle.

To study the embryo a series of young fruits should be selected, and the ovules carefully dissected out and mounted in water, to which a little caustic potash has been added. The ovule will be thus rendered transparent, and by pressing gently on the cover glass with a needle so as to flatten the ovule slightly, there is usually no trouble in seeing the embryo lying in the upper part of the embryo sac, and by pressing more firmly it can often be forced out upon the slide. The potash should now be removed as completely as possible with blotting paper, and pure water run under the cover glass.

The fertilized egg cell first secretes a membrane, and then divides into a row of cells (N) of which the one nearest the micropyle is often much enlarged. The cell at the other end next enlarges and becomes divided by walls at right angles to each other into eight cells. This globular mass of cells, together with the cell next to it, is the embryo plant, the row of cells to which it is attached taking no further part in the process, and being known as the "suspensor." Later the embryo becomes indented above and forms two lobes (Q), which are the beginnings of the cotyledons. The first root and the stem arise from the cells next the suspensor.



CHAPTER XVIII.

CLASSIFICATION OF DICOTYLEDONS.

DIVISION I.—Choripetalae.

Nearly all of the dicotyledons may be placed in one of two great divisions distinguished by the character of the petals. In the first group, called Choripetalae, the petals are separate, or in some degenerate forms entirely absent. As familiar examples of this group, we may select the buttercup, rose, pink, and many others.

The second group (Sympetalae or Gamopetalae) comprises those dicotyledons whose flowers have the petals more or less completely united into a tube. The honeysuckles, mints, huckleberry, lilac, etc., are familiar representatives of the Sympetalae, which includes the highest of all plants.



The Choripetalae may be divided into six groups, including twenty-two orders. The first group is called Iuliflorae, and contains numerous, familiar plants, mostly trees. In these plants, the flowers are small and inconspicuous, and usually crowded into dense catkins, as in willows (Fig. 96) and poplars, or in spikes or heads, as in the lizard-tail (Fig. 97, G), or hop (Fig. 97, I). The individual flowers are very small and simple in structure, being often reduced to the gynoecium or andraecium, carpels and stamens being almost always in separate flowers. The outer leaves of the flower (sepals and petals) are either entirely wanting or much reduced, and never differentiated into calyx and corolla.

, male; [Female], female inflorescence. B, a single male flower, x 3. C, section of the ovary of a female flower, x 25. D, acorn of red oak, Quercus (Cupuliferae), x 1/2. E, seed of white birch, Betula (Betulaceae), x 3. F, fruit of horn-bean, Carpinus (Cupuliferae), x 1. G, lizard-tail, Saururus (Saurureae), x 1/4. H, a single flower, x 2. I, female inflorescence of the hop, Humulus (Cannabineae), x 1. J, a single scale with two flowers, x 1. K, a male flower of a nettle, Urtica (Urticaceae), x 5.]

In the willows (Fig. 96) the stamens are bright-colored, so that the flowers are quite showy, and attract numerous insects which visit them for pollen and nectar, and serve to carry the pollen to the pistillate flowers, thus insuring their fertilization. In the majority of the group, however, the flowers are wind-fertilized. An excellent example of this is seen in the common hazel (Fig. 97, A). The male flowers are produced in great numbers in drooping catkins at the ends of the branches, shedding the pollen in early spring before the leaves unfold. The female flowers are produced on the same branches, but lower down, and in much smaller numbers. The stigmas are long, and covered with minute hairs that catch the pollen which is shaken out in clouds every time the plant is shaken by the wind, and falls in a shower over the stigmas. A similar arrangement is seen in the oaks, hickories, and walnuts.

There are three orders of the Iuliflorae: Amentaceae, Piperineae, and Urticinae. The first contains the birches (Betulaceae); oaks, beeches, hazels, etc. (Cupuliferae); walnuts and hickories (Juglandeae); willows and poplars (Salicaceae). They are all trees or shrubs; the fruit is often a nut, and the embryo is very large, completely filling it.

The Piperineae are mostly tropical plants, and include the pepper plant (Piper), as well as other plants with similar properties. Of our native forms, the only common one is the lizard-tail (Saururus), not uncommon in swampy ground. In these plants, the calyx and corolla are entirely absent, but the flowers have both carpels and stamens (Fig. 97, H).

The Urticinae include, among our common plants, the nettle family (Urticaceae); plane family (Plataneae), represented by the sycamore or buttonwood (Platanus); the hemp family (Cannabineae); and the elm family (Ulmaceae). The flowers usually have a calyx, and may have only stamens or carpels, or both. Sometimes the part of the stem bearing the flowers may become enlarged and juicy, forming a fruit-like structure. Well-known examples of this are the fig and mulberry.

The second group of the Choripetalae is called Centrospermae, and includes but a single order comprising seven families, all of which, except one (Nyctagineae), are represented by numerous native species. The latter comprises mostly tropical plants, and is represented in our gardens by the showy "four-o'clock" (Mirabilis). In this plant, as in most of the order, the corolla is absent, but here the calyx is large and brightly colored, resembling closely the corolla of a morning-glory or petunia. The stamens are usually more numerous than the sepals, and the pistil, though composed of several carpels, has, as a rule, but a single cavity with the ovules arising from the base, though sometimes the ovary is several celled.

[Illustration: FIG. 98.—Types of Centrospermae. A, plant of spring-beauty, Claytonia (Portulacaceae), x 1/2. B, a single flower, x 1. C, fruit, with the sepals removed, x 2. D, section of the seed, showing the curved embryo (em.), x 5. E, single flower of smart-weed, Polygonum (Polygonaceae), x 2. F, the pistil, x 2. G, section of the ovary, showing the single ovule, x 4. H, section of the seed, x 2. I, base of the leaf, showing the sheath, x 1. J, flower of pig-weed, Chenopodium (Chenopodiaceae), x 3: i, from without; ii, in section. K, flower of the poke-weed, Phytolacca (Phytolaccaceae), x 2. L, fire-pink, Silene (Caryophyllaceae), x 1/2. M, a flower with half of the calyx and corolla removed, x 1. N, ripe fruit of mouse-ear chick-weed, Cerastium (Caryophyllaceae), opening by ten teeth at the summit, x 2. O, diagram of the flower of Silene.]

The first family (Polygoneae) is represented by the various species of Polygonum (knotgrass, smart-weed, etc.), and among cultivated plants by the buckwheat (Fagopyrum). The goose-foot or pig-weed (Chenopodium) among native plants, and the beet and spinach of the gardens are examples of the family Chenopodiaceae. Nearly resembling the last is the amaranth family (Amarantaceae), of which the showy amaranths and coxcombs of the gardens, and the coarse, green amaranth or pig-weed are representatives.

The poke-weed (Phytolacca) (Fig. 98, K), so conspicuous in autumn on account of its dark-purple clusters of berries and crimson stalks, is our only representative of the family Phytolaccaceae. The two highest families are the purslane family (Portulacaceae) and pink family (Caryophylleae). These are mostly plants with showy flowers in which the petals are large and conspicuous, though some of the pink family, e.g. some chick-weeds, have no petals. Of the purslane family the portulacas of the gardens, and the common purslane or "pusley," and the spring-beauty (Claytonia) (Fig. 98, A) are the commonest examples. The pink family is represented by many common and often showy plants. The carnation, Japanese pinks, and sweet-william, all belonging to the genus Dianthus, of which there are also two or three native species, are among the showiest of the family. The genera Lychnis and Silene (Fig. 98, L) also contain very showy species. Of the less conspicuous genera, the chick-weeds (Cerastium and Stellaria) are the most familiar.

The third group of the Choripetalae (the Aphanocyclae) is a very large one and includes many common plants distributed among five orders. The lower ones have all the parts of the flower entirely separate, and often indefinite in number; the higher have the gynoecium composed of two or more carpels united to form a compound pistil.

The first order (Polycarpae) includes ten families, of which the buttercup family (Ranunculaceae) is the most familiar. The plants of this family show much variation in the details of the flowers, which are usually showy, but the general plan is much the same. In some of them, like the anemones (Fig. 99, A), clematis, and others, the corolla is absent, but the sepals are large and brightly colored so as to appear like petals. In the columbine (Aquilegia) (Fig. 99, F) the petals are tubular, forming nectaries, and in the larkspur (Fig. 99, T) one of the sepals is similarly changed.

Representing the custard-apple family (Anonaceae) is the curious papaw (Asimina), common in many parts of the United States (Fig. 100, A). The family is mainly a tropical one, but this species extends as far north as southern Michigan.



The magnolia family (Magnoliaceae) has several common members, the most widely distributed being, perhaps, the tulip-tree (Liriodendron) (Fig. 100, C), much valued for its timber. Besides this there are several species of magnolia, the most northerly species being the sweet-bay (Magnolia glauca) of the Atlantic States, and the cucumber-tree (M. acuminata); the great magnolia (M. grandiflora) is not hardy in the northern states.

The sweet-scented shrub (Calycanthus) (Fig. 100, G) is the only member of the family Calycanthaceae found within our limits. It grows wild in the southern states, and is cultivated for its sweet-scented, dull, reddish flowers.



The barberry (Berberis) (Fig. 101, A) is the type of the family Berberideae, which also includes the curious mandrake or may-apple (Podophyllum) (Fig. 101, D), and the twin-leaf or rheumatism-root (Jeffersonia), whose curious seed vessel is shown in Figure 101, G. The fruit of the barberry and may-apple are edible, but the root of the latter is poisonous.

The curious woody twiner, moon-seed (Menispermum) (Fig. 101, I), is the sole example in the northern states of the family Menispermeae to which it belongs. The flowers are dioecious, and the pistillate flowers are succeeded by black fruits looking like grapes. The flattened, bony seed is curiously sculptured, and has the embryo curled up within it.



The last two families of the order, the laurel family (Laurineae) and the nutmeg family (Myristicineae) are mostly tropical plants, characterized by the fragrance of the bark, leaves, and fruit. The former is represented by the sassafras and spice-bush, common throughout the eastern United States. The latter has no members within our borders, but is familiar to all through the common nutmeg, which is the seed of Myristica fragrans of the East Indies. "Mace" is the "aril" or covering of the seed of the same plant.

The second order of the Aphanocyclae comprises a number of aquatic plants, mostly of large size, and is known as the Hydropeltidinae. The flowers and leaves are usually very large, the latter usually nearly round in outline, and frequently with the stalk inserted near the middle. The leaves of the perigone are numerous, and sometimes merge gradually into the stamens, as we find in the common white water-lily (Castalia).



There are three families, all represented within the United States. The first (Nelumbieae) has but a single species, the yellow lotus or nelumbo (Nelumbo lutea), common in the waters of the west and southwest, but rare eastward (Fig. 101, F). In this flower, the end of the flower axis is much enlarged, looking like the rose of a watering-pot, and has the large, separate carpels embedded in its upper surface. When ripe, each forms a nut-like fruit which is edible. There are but two species of Nelumbo known, the second one (N. speciosa) being a native of southeastern Asia, and probably found in ancient times in Egypt, as it is represented frequently in the pictures and carvings of the ancient Egyptians. It differs mainly from our species in the color of its flowers which are red instead of yellow. It has recently been introduced into New Jersey where it has become well established in several localities.

The second family (Cabombeae) is also represented at the north by but one species, the water shield (Brasenia), not uncommon in marshes. Its flowers are quite small, of a dull-purple color, and the leaves oval in outline and centrally peltate, i.e. the leaf stalk inserted in the centre. The whole plant is covered with a transparent gelatinous coat.

The third family (Nymphaeaceae) includes the common white water-lilies (Castalia) and the yellow water-lilies (Nymphaea) (Fig. 102, A). In the latter the petals are small and inconspicuous (Fig. 102, C, p), but the sepals are large and showy. In this family the carpels, instead of being separate, are united into a large compound pistil. The water-lilies reach their greatest perfection in the tropics, where they attain an enormous size, the white, blue, or red flowers of some species being thirty centimetres or more in diameter, and the leaves of the great Victoria regia of the Amazon reaching two metres or more in width.

The third order of the Aphanocyclae (Rhoeadinae or Cruciflorae) comprises a number of common plants, principally characterized by having the parts of the flowers in twos or fours, so that they are more or less distinctly cross-shaped, whence the name Cruciflorae.

There are four families, of which the first is the poppy family (Papaveraceae), including the poppies, eschscholtzias, Mexican or prickly poppy (Argemone), etc., of the gardens, and the blood-root (Sanguinaria), celandine poppy (Stylophorum), and a few other wild plants (see Fig. 103, A-I). Most of the family have a colored juice (latex), which is white in the poppy, yellow in celandine and Argemone, and orange-red in the blood-root. From the latex of the opium poppy the opium of commerce is extracted.



The second family, the fumitories (Fumariaceae) are delicate, smooth plants, with curious flowers and compound leaves. The garden bleeding-heart (Dicentra spectabilis) and the pretty, wild Dicentras (Fig. 103, F) are familiar to nearly every one.

Other examples are the mountain fringe (Adlumia), a climbing species, and several species of Corydalis, differing mainly from Dicentra in having the corolla one-sided.

The mustard family (Cruciferae) comprises by far the greater part of the order. The shepherd's-purse, already studied, belongs here, and may be taken as a type of the family. There is great uniformity in all as regards the flowers, so that the classification is based mainly on differences in the fruit and seeds. Many of the most valuable garden vegetables, as well as a few more or less valuable wild plants, are members of the family, which, however, includes some troublesome weeds. Cabbages, turnips, radishes, with all their varieties, belong here, as well as numerous species of wild cresses. A few like the wall-flower (Cheiranthus) and stock (Matthiola) are cultivated for ornament.

The last family is the caper family (Capparideae), represented by only a few not common plants. The type of the order is Capparis, whose pickled flower-buds constitute capers.

The fourth order (Cistiflorae) of the Aphanocyclae is a very large one, but the majority of the sixteen families included in it are not represented within our limits. The flowers have the sepals and petals in fives, the stamens either the same or more numerous.

[Illustration: FIG. 104.—Types of Aphanocyclae (Cistiflorae). A, flower of wild blue violet, Viola (Violaceae), x 1. B, the lower petal prolonged behind into a sac or spur, x 1. C, the stamens, x 2. D, pistil, x 2. E, a leaf, x 1/2. F, section of the ovary, x 2. G, the fruit, x 1. H, the same after it has opened, x 1. I, diagram of the flower. J, flower of mignonette, Reseda (Resedaceae), x 2. K, a petal, x 3. L, cross-section of the ovary, x 3. M, fruit, x 1. N, plant of sundew, Drosera (Droseraceae), x 1/2. O, a leaf that has captured a mosquito, x 2. P, flower of another species (D. filiformis), x 2. Q, cross-section of the ovary, x 4.]

Among the commoner members of the order are the mignonettes (Resedaceae) and the violets (Violaceae), of which the various wild and cultivated species are familiar plants (Fig. 104, A, M). The sundews (Droseraceae) are most extraordinary plants, growing in boggy land over pretty much the whole world. They are represented in the United States by several species of sundew (Drosera), and the still more curious Venus's-flytrap (Dionaea) of North Carolina. The leaves of the latter are sensitive, and composed of two parts which snap together like a steel trap. If an insect lights upon the leaf, and touches certain hairs upon its upper surface, the two parts snap together, holding the insect tightly. A digestive fluid is secreted by glands upon the inner surface of the leaf, and in a short time the captured insect is actually digested and absorbed by the leaves. The same process takes place in the sundew (Fig. 104, N) where, however, the mechanism is somewhat different. Here the tentacles, with which the leaf is studded, secrete a sticky fluid which holds any small insect that may light upon it. The tentacles now slowly bend inward and finally the edges of the leaf as well, until the captured insect is firmly held, when a digestive process, similar to that in Dionoea, takes place. This curious habit is probably to be explained from the position where the plant grows, the roots being in water where there does not seem to be a sufficient supply of nitrogenous matter for the wants of the plant, which supplements the supply from the bodies of the captured insects.



Similar in their habits, but differing much in appearance from the sundews, are the pitcher-plants (Sarraceniaceae), of which one species (Sarracenia purpurea) is very common in peat bogs throughout the northern United States. In this species (Fig. 105, A, B), the leaves form a rosette, from the centre of which arises in early summer a tall stalk bearing a single, large, nodding, dark-reddish flower with a curious umbrella-shaped pistil. The leaf stalk is hollow and swollen, with a broad wing on one side, and the blade of the leaf forms a sort of hood at the top. The interior of the pitcher is covered above with stiff, downward-pointing hairs, while below it is very smooth. Insects readily enter the pitcher, but on attempting to get out, the smooth, slippery wall at the bottom, and the stiff, downward-directed hairs above, prevent their escape, and they fall into the fluid which fills the bottom of the cup and are drowned, the leaf absorbing the nitrogenous compounds given off during the process of decomposition. There are other species common in the southern states, and a California pitcher-plant (Darlingtonia) has a colored appendage at the mouth of the pitcher which serves to lure insects into the trap.

Another family of pitcher-plants (Nepentheae) is found in the warmer parts of the old world, and some of them are occasionally cultivated in greenhouses. In these the pitchers are borne at the tips of the leaves attached to a long tendril.

Two other families of the order contain familiar native plants, the rock-rose family (Cistaceae), and the St. John's-worts (Hypericaceae). The latter particularly are common plants, with numerous showy yellow flowers, the petals usually marked with black specks, and the leaves having clear dots scattered through them. The stamens are numerous, and often in several distinct groups (Fig. 105, C, D).

The last order of the Aphanocyclae (the Columniferae) has three families, of which two, the mallows (Malvaceae), and the lindens (Tiliaceae), include well-known species. Of the former, the various species of mallows (Fig. 106, A) belonging to the genus Malva are common, as well as some species of Hibiscus, including the showy swamp Hibiscus or rose-mallow (H. moscheutos), common in salt marshes and in the fresh-water marshes of the great lake region. The hollyhock and shrubby Althaea are familiar cultivated plants of this order, and the cotton-plant (Gossypium) also belongs here. In all of these the stamens are much branched, and united into a tube enclosing the style. Most of them are characterized also by the development of great quantities of a mucilaginous matter within their tissues.

The common basswood (Tilia) is the commonest representative of the family Tiliaceae (Fig. 106, G). The nearly related European linden, or lime-tree, is sometimes planted. Its leaves are ordinarily somewhat smaller than our native species, which it, however, closely resembles.



The fourth group of the Choripetalae is the Eucyclae. The flowers most commonly have the parts in fives, and the stamens are never more than twice as many as the sepals. The carpels are usually more or less completely united into a compound pistil. There are four orders, comprising twenty-five families.

[Illustration: FIG. 107.—Types of Eucyclae (Gruinales). A, wild crane's-bill Geranium (Geraniaceae), x 1/2. B, a petal, x 1. C, the young fruit, the styles united in a column, x 1/2. D, the ripe fruit, the styles separating to discharge the seeds, x 1/2. E, section of a seed, x 2. F, wild flax. Linum (Linaceae), x 1/2. G, a single flower, x 2. H, cross-section of the young fruit, x 3. I, flower. J, leaf of wood-sorrel, Oxalis (Oxalideae), x 1. K, the stamens and pistil, x 2. L, flower of jewel-weed, Impatiens (Balsamineae), x 1. M, the same, with the parts separated. p, petals. s, sepals. an. stamens. gy. pistil. N, fruit, x 1. O, the same, opening. P, a seed, x 2.]

The first order (Gruinales) includes six families, consisting for the most part of plants with conspicuous flowers. Here belong the geraniums (Fig. 107, A), represented by the wild geraniums and crane's-bill, and the very showy geraniums (Pelargonium) of the gardens. The nasturtiums (Tropaeolum) represent another family, mostly tropical, and the wood-sorrels (Oxalis) (Fig. 107, I) are common, both wild and cultivated. The most useful member of the order is unquestionably the common flax (Linum), of which there are also several native species (Fig. 107, F). These are types of the flax family (Linaceae). Linen is the product of the tough, fibrous inner bark of L. usitatissimum, which has been cultivated for its fibre from time immemorial. The last family is the balsam family (Balsamineae). The jewel-weed or touch-me-not (Impatiens), so called from the sensitive pods which spring open on being touched, is very common in moist ground everywhere (Fig. 107, L-P). The garden balsam, or lady's slipper, is a related species (I. balsamina).



The second order (Terebinthinae) contains but few common plants. There are six families, mostly inhabitants of the warmer parts of the world. The best-known members of the order are the orange, lemon, citron, and their allies. Of our native plants the prickly ash (Zanthoxylum), and the various species of sumach (Rhus), are the best known. In the latter genus belong the poison ivy (R. toxicodendron) and the poison dogwood (R. venenata). The Venetian sumach or smoke-tree (R. Cotinus) is commonly planted for ornament.

The third order of the Eucyclae, the AEsculinae, embraces six families, of which three, the horsechestnuts, etc. (Sapindaceae), the maples (Aceraceae), and the milkworts (Polygalaceae), have several representatives in the northern United States. Of the first the buckeye (AEsculus) (Fig. 108, J) and the bladder-nut (Staphylea) (Fig. 108, G) are the commonest native genera, while the horsechestnut (AEsculus hippocastanum) is everywhere planted.

The various species of maple (Acer) are familiar examples of the Aceraceae (see Fig. 106, A, F).

The fourth and last order of the Eucyclae, the Frangulinae, is composed mainly of plants with inconspicuous flowers, the stamens as many as the petals. Not infrequently they are dioecious, or in some, like the grape, some of the flowers may be unisexual while others are hermaphrodite (i.e. have both stamens and pistil). Among the commoner plants of the order may be mentioned the spindle-tree, or burning-bush, as it is sometimes called (Euonymus) (Fig. 109, A), and the climbing bitter-sweet (Celastrus) (Fig. 109, D), belonging to the family Celastraceae; the holly and black alder, species of Ilex, are examples of the family Aquifoliaceae; the various species of grape (Vitis), the Virginia creeper (Ampelopsis quinquefolia), and one or two other cultivated species of the latter, represent the vine family (Vitaceae or Ampelidae), and the buckthorn (Rhamnus) is the type of the Rhamnaceae.

[Illustration: FIG. 109.—Eucylae (Frangulinae), Tricoccae. A, flowers of spindle-tree, Euonymus, (Celastraceae), x 1. B, cross-section of the ovary, x 2. C, diagram of the flower. D, leaf and fruit of bitter-sweet (Celastrus), x 1/2. E, fruit opening and disclosing the seeds. F, section of a nearly ripe fruit, showing the seeds surrounded by the scarlet integument (aril). em. the embryo, x 1. G, flower of grape-vine, Vitis (Vitaceae), x 2. The corolla has fallen off. H, vertical section of the pistil, x 2. I, nearly ripe fruits of the frost-grape, x 1. J, cross-section of young fruit, x 2. K, a spurge, Euphorbia (Euphorbiaceae), x 1/2. L, single group of flowers, surrounded by the corolla-like involucre, x 3. M, section of the same, [Male], male flowers; [Female], female flowers. N, a single male flower, x 5. O, cross-section of ovary, x 6. P, a seed, x 2. Q, longitudinal section of the seed, x 3. em. embryo.]

The fifth group of the Choripetalae is a small one, comprising but a single order (Tricoccae). The flowers are small and inconspicuous, though sometimes, as in some Euphorbias and the showy Poinsettia of the greenhouses, the leaves or bracts surrounding the inflorescence are conspicuously colored, giving the whole the appearance of a large, showy, single flower. In northern countries the plants are mostly small weeds, of which the various spurges or Euphorbias are the most familiar. These plants (Fig. 109, K) have the small flowers surrounded by a cup-shaped involucre (L, M) so that the whole inflorescence looks like a single flower. In the spurges, as in the other members of the order, the flowers are very simple, being often reduced to a single stamen or pistil (Fig. 109, M, N). The plants generally abound in a milky juice which is often poisonous. This juice in a number of tropical genera is the source of India-rubber. Some genera like the castor-bean (Ricinus) and Croton are cultivated for their large, showy leaves.

The water starworts (Callitriche), not uncommon in stagnant water, represent the family Callitrichaceae, and the box (Buxus) is the type of the Buxaceae.

[Illustration: FIG. 110.—Types of Calyciflorae (Umbelliflorae). A, inflorescence of wild parsnip, Pastinaca (Umbelliferae), x 1/2. B, single flower of the same, x 3. C, a leaf, showing the sheathing base, x 1/4. D, a fruit, x 2. E, cross-section of D. F, part of the inflorescence of spikenard, Aralia (Araliaceae), x 1. G, a single flower of the same, x 3. H, the fruit, x 2. I, cross-section of the H. J, inflorescence of dogwood, Cornus (Corneae). The cluster of flowers is surrounded by four white bracts (b), x 1/3. K, a single flower of the same, x 2. L, diagram of the flower. M, young fruit of another species (Cornus stolonifera) (red osier), x 2. N, cross-section of M.]

The last and highest group of the Choripetalae, the Calyciflorae, embraces a very large assemblage of familiar plants, divided into eight orders and thirty-two families. With few exceptions, the floral axis grows up around the ovary, carrying the outer floral leaves above it, and the ovary appears at the bottom of a cup around whose edge the other parts of the flower are arranged. Sometimes, as in the fuchsia, the ovary is grown to the base of the cup or tube, and thus looks as if it were outside the flower. Such an ovary is said to be "inferior" in distinction from one that is entirely free from the tube, and thus is evidently within the flower. The latter is the so-called "superior" ovary. The carpels are usually united into a compound pistil, but may be separate, as in the stonecrop (Fig. 111, E), or strawberry (Fig. 114, C).

The first order of the Calyciflorae (Umbelliflorae) has the flowers small, and usually arranged in umbels, i.e. several stalked flowers growing from a common point. The ovary is inferior, and there is a nectar-secreting disc between the styles and the stamens. Of the three families, the umbel-worts or Umbelliferae is the commonest. The flowers are much alike in all (Fig. 110, A, B), and nearly all have large, compound leaves with broad, sheathing bases. The stems are generally hollow. So great is the uniformity of the flowers and plant, that the fruit (Fig. 110, D) is generally necessary before the plant can be certainly recognized. This is two-seeded in all, but differs very much in shape and in the development of oil channels, which secrete the peculiar oil that gives the characteristic taste to the fruits of such forms as caraway, coriander, etc. Some of them, like the wild parsnip, poison hemlock, etc., are violent poisons, while others like the carrot are perfectly wholesome.

The wild spikenard (Aralia) (Fig. 110, F), ginseng, and the true ivy (Hedera) are examples of the Araliaceae, and the various species of dogwood (Cornus) (Fig. 110, J-N) represent the dogwood family (Corneae).

The second order (Saxifraginae) contains eight families, including a number of common wild and cultivated plants. The true saxifrages are represented by several wild and cultivated species of Saxifraga, the little bishop's cap or mitre-wort (Mitella) (Fig. 111, D), and others. The wild hydrangea (Fig. 111, F) and the showy garden species represent the family Hydrangeae. In these some of the flowers are large and showy, but with neither stamens nor pistils (neutral), while the small, inconspicuous flowers of the central part of the inflorescence are perfect. In the garden varieties, all of the flowers are changed, by selection, into the showy, neutral ones. The syringa or mock orange (Philadelphus) (Fig. 111, I), the gooseberry, and currants (Ribes) (Fig. 111, A), and the stonecrop (Sedum) (Fig. 111, E) are types of the families Philadelpheae, Ribesieae, and Crassulaceae.



The third order (Opuntieae) has but a single family, the cacti (Cactaceae). These are strictly American in their distribution, and inhabit especially the dry plains of the southwest, where they reach an extraordinary development. They are nearly or quite leafless, and the fleshy, cylindrical, or flattened stems are usually beset with stout spines. The flowers (Fig. 112, A) are often very showy, so that many species are cultivated for ornament and are familiar to every one. The beautiful night-blooming cereus, of which there are several species, is one of these. A few species of prickly-pear (Opuntia) occur as far north as New York, but most are confined to the hot, dry plains of the south and southwest.



The fourth order (Passiflorinae) are almost without exception tropical plants, only a very few extending into the southern United States. The type of the order is the passion-flower (Passiflora) (Fig. 112, B), whose numerous species are mostly inhabitants of tropical America, but a few reach into the United States. The only other members of the order likely to be met with by the student are the begonias, of which a great many are commonly cultivated as house plants on account of their fine foliage and flowers. The leaves are always one-sided, and the flowers monoecious.[13] Whether the begonias properly belong with the Passiflorinae has been questioned.

[13] Monoecious: having stamens and carpels in different flowers, but on the same plant.



The fifth order (Myrtiflorae) have regular four-parted flowers with usually eight stamens, but sometimes, through branching of the stamens, these appear very numerous. The myrtle family, the members of which are all tropical or sub-tropical, gives name to the order. The true myrtle (Myrtus) is sometimes cultivated for its pretty glossy green leaves and white flowers, as is also the pomegranate whose brilliant, scarlet flowers are extremely ornamental. Cloves are the dried flower-buds of an East-Indian myrtaceous tree (Caryophyllus). In Australia the order includes the giant gum-trees (Eucalyptus), the largest of all known trees, exceeding in size even the giant trees of California.

Among the commoner Myrtiflorae, the majority belong to the two families Onagraceae and Lythraceae. The former includes the evening primroses (OEnothera), willow-herb (Epilobium) (Fig. 113, D), and fuchsia; the latter, the purple loosestrife (Lythrum) and swamp loosestrife (Nesaea). The water-milfoil (Myriophyllum) (Fig. 113, J) is an example of the family Haloragidaceae, and the Rhexias of the eastern United States represent with us the family Melastomaceae.

The sixth order of the Calyciflorae is a small one (Thymelinae), represented in the United States by very few species. The flowers are four-parted, the calyx resembling a corolla, which is usually absent. The commonest member of the order is the moosewood (Dirca) (Fig. 113, A), belonging to the first of the three families (Thymelaeaceae). Of the second family (Elaeagnaceae), the commonest example is Shepherdia, a low shrub having the leaves covered with curious, scurfy hairs that give them a silvery appearance. The third family (Proteaceae) has no familiar representatives.

The seventh order (Rosiflorae) includes many well-known plants, all of which may be united in one family (Rosaceae), with several sub-families. The flowers are usually five-parted with from five to thirty stamens, and usually numerous, distinct carpels. In the apple and pear (Fig. 114, I), however, the carpels are more or less grown together; and in the cherry, peach, etc., there is but a single carpel giving rise to a single-seeded stone-fruit (drupe) (Fig. 114, E, H). In the strawberry (Fig. 114, A), rose (G), cinquefoil (Potentilla), etc., there are numerous distinct, one-seeded carpels, and in Spiraea (Fig. 114, F) there are five several-seeded carpels, forming as many dry pods when ripe. The so-called "berry" of the strawberry is really the much enlarged flower axis, or "receptacle," in which the little one-seeded fruits are embedded, the latter being what are ordinarily called the seeds.



From the examples given, it will be seen that the order includes not only some of the most ornamental, cultivated plants, but the majority of our best fruits. In addition to those already given, may be mentioned the raspberry, blackberry, quince, plum, and apricot.



The last order of the Calyciflorae and the highest of the Choripetalae is the order Leguminosae, of which the bean, pea, clover, and many other common plants are examples. In most of our common forms the flowers are peculiar in shape, one of the petals being larger than the others, and covering them in the bud. This petal is known as the standard. The two lateral petals are known as the wings, and the two lower and inner are generally grown together forming what is called the "keel" (Fig. 115, A, B). The stamens, ten in number, are sometimes all grown together into a tube, but generally the upper one is free from the others (Fig. 115, C). There is but one carpel which forms a pod with two valves when ripe (Fig. 115, D). The seeds are large, and the embryo fills the seed completely. From the peculiar form of the flower, they are known as Papilionaceae (papilio, a butterfly). Many of the Papilionaceae are climbers, either having twining stems, as in the common beans, or else with part of the leaf changed into a tendril as in the pea (Fig. 115, A), vetch, etc. The leaves are usually compound.

Of the second family (Caesalpineae), mainly tropical, the honey locust (Gleditschia) and red-bud (Cercis) (Fig. 115, G) are the commonest examples. The flowers differ mainly from the Papilionaceae in being less perfectly papilionaceous, and the stamens are almost entirely distinct (Fig. 115, H). The last family (Mimosaceae) is also mainly tropical. The acacias, sensitive-plant (Mimosa), and the sensitive-brier of the southern United States (Schrankia) (Fig. 115, I) represent this family. The flowers are quite different from the others of the order, being tubular and the petals united, thus resembling the flowers of the Sympetalae. The leaves of Mimosa and Schrankia are extraordinarily sensitive, folding up if irritated.



CHAPTER XIX.

CLASSIFICATION OF DICOTYLEDONS (Continued).

DIVISION II.—Sympetalae.

The Sympetalae or Gamopetalae are at once distinguished from the Choripetalae by having the petals more or less united, so that the corolla is to some extent tubular. In the last order of the Choripetalae we found a few examples (Mimosaceae) where the same thing is true, and these form a transition from the Choripetalae to the Sympetalae.

There are two great divisions, Isocarpae and Anisocarpae. In the first the carpels are of the same number as the petals and sepals; in the second fewer. In both cases the carpels are completely united, forming a single, compound pistil. In the Isocarpae there are usually twice as many stamens as petals, occasionally the same number.

There are three orders of the Isocarpae, viz., Bicornes, Primulinae, and Diospyrinae. The first is a large order with six families, including many very beautiful plants, and a few of some economic value. Of the six families, all but one (Epacrideae) are represented in the United States. Of these the Pyrolaceae includes the pretty little pyrolas and prince's-pine (Chimaphila) (Fig. 116, J); the Monotropeae has as its commonest examples, the curious Indian-pipe (Monotropa uniflora), and pine-sap (M. hypopitys) (Fig. 116, L). These grow on decaying vegetable matter, and are quite devoid of chlorophyll, the former species being pure white throughout (hence a popular name, "ghost flower"); the latter is yellowish. The magnificent rhododendrons and azaleas (Fig. 116, F), and the mountain laurel (Kalmia) (Fig. 116, I), belong to the Rhodoraceae. The heath family (Ericaceae), besides the true heaths (Erica, Calluna), includes the pretty trailing-arbutus or may-flower (Epigaea), Andromeda, Oxydendrum (Fig. 116, E), wintergreen (Gaultheria), etc. The last family is represented by the cranberry (Vaccinium) and huckleberry (Gaylussacia).

[Illustration: FIG. 116.—Types of Isocarpous sympetalae (Bicornes). A, flowers, fruit, and leaves of huckleberry, Gaylussacia (Vaccinieae), x 1. B, vertical section of the flower, x 3. C, a stamen: i, from in front; ii, from the side, x 4. D, cross-section of the young fruit, x 2. E, flower of sorrel-tree, Oxydendrum (Ericaceae), x 2. F, flower of azalea (Rhododendron), x 1/2. G, cross-section of the ovary, x 3. H, diagram of the flower. I, flower of mountain laurel (Kalmia), x 1. J, prince's-pine, Chimaphila (Pyrolaceae), x 1/2. K, a single flower, x 1. L, plant of pine-sap, Monotropa, (Monotropeae), x 1/2. M, section of a flower, x 1.]

The second order, the primroses (Primulinae), is principally represented in the cooler parts of the world by the true primrose family (Primulaceae), of which several familiar plants may be mentioned. The genus Primula includes the European primrose and cowslip, as well as two or three small American species, and the commonly cultivated Chinese primrose. Other genera are Dodecatheon, of which the beautiful shooting-star (D. Meadia) (Fig. 117, A) is the best known. Something like this is Cyclamen, sometimes cultivated as a house plant. The moneywort (Lysimachia nummularia) (Fig. 117, D), as well as other species, also belongs here.



The sea-rosemary (Statice) and one or two cultivated species of plumbago are the only members of the plumbago family (Plumbagineae) likely to be met with. The remaining families of the Primulinae are not represented by any common plants.

The third and last order of the Isocarpous sympetalae has but a single common representative in the United States; viz., the persimmon (Diospyros) (Fig. 117, E). This belongs to the family Ebenaceae, to which also belongs the ebony a member of the same genus as the persimmon, and found in Africa and Asia.

The second division of the Sympetalae (the Anisocarpae) has usually but two or three carpels, never as many as the petals. The stamens are also never more than five, and very often one or more are abortive.

[Illustration: FIG. 118.—Types of Anisocarpous sympetalae (Tubiflorae). A, flower and leaves of wild phlox (Polemoniaceae), x 1/2. B, section of a flower, x 1. C, fruit, x 1. D, flower of blue valerian (Polemonium), x 1. E, flowers and leaf of water-leaf, Hydrophyllum (Hydrophyllaceae), x 1/2. F, section of a flower, x 1. G, flower of wild morning-glory, Convolvulus (Convolvulaceae), x 1/2. One of the bracts surrounding the calyx and part of the corolla are cut away. H, diagram of the flower. I, the fruit of a garden morning-glory, from which the outer wall has fallen, leaving only the inner membranous partitions, x 1. J, a seed, x 1. K, cross-section of a nearly ripe seed, showing the crumpled embryo, x 2. L, an embryo removed from a nearly ripe seed, and spread out; one of the cotyledons has been partially removed, x 1.]

The first order (Tubiflorae) has, as the name indicates, tubular flowers which show usually perfect, radial symmetry (Actinomorphism). There are five families, all represented by familiar plants. The first (Convolvulaceae) has as its type the morning-glory (Convolvulus) (Fig. 118, G), and the nearly related Ipomoeas of the gardens. The curious dodder (Cuscuta), whose leafless, yellow stems are sometimes very conspicuous, twining over various plants, is a member of this family which has lost its chlorophyll through parasitic habits. The sweet potato (Batatas) is also a member of the morning-glory family. The numerous species, wild and cultivated, of phlox (Fig. 118, A), and the blue valerian (Polemonium) (Fig. 118, D), are examples of the family Polemoniaceae.



The third family (Hydrophyllaceae) includes several species of water-leaf (Hydrophyllum) (Fig. 118, E) and Phacelia, among our wild flowers, and species of Nemophila, Whitlavia and others from the western states, but now common in gardens.

The Borage family (Borragineae) includes the forget-me-not (Myosotis) and a few pretty wild flowers, e.g. the orange-flowered puccoons (Lithospermum); but it also embraces a number of the most troublesome weeds, among which are the hound's-tongue (Cynoglossum) (Fig. 119, A), and the "beggar's-ticks" (Echinospermum), whose prickly fruits (Fig. 119, C) become detached on the slightest provocation, and adhere to whatever they touch with great tenacity. The flowers in this family are arranged in one-sided inflorescences which are coiled up at first and straighten as the flowers expand.

The last family (Solaneae) includes the nightshades (Solanum) (Fig. 119, D), to which genus the potato (S. tuberosum) and the egg-plant (S. Melongena) also belong. Many of the family contain a poisonous principle, e.g. the deadly nightshade (Atropa), tobacco (Nicotiana), stramonium (Datura), and others. Of the cultivated plants, besides those already mentioned, the tomato (Lycopersicum), and various species of Petunia (Fig. 119, H), Solanum, and Datura are the commonest.

The second order of the Anisocarpae consists of plants whose flowers usually exhibit very marked, bilateral symmetry (Zygomorphism). From the flower often being two-lipped (see Fig. 120), the name of the order (Labiatiflorae) is derived.

Of the nine families constituting the order, all but one are represented within our limits, but the great majority belong to two families, the mints (Labiatae) and the figworts (Scrophularineae). The mints are very common and easily recognizable on account of their square stems, opposite leaves, strongly bilabiate flowers, and the ovary splitting into four seed-like fruits (Fig. 120, D, F).

The great majority of them, too, have the surface covered with glandular hairs secreting a strong-scented volatile oil, giving the peculiar odor to these plants. The dead nettle (Lamium) (Fig. 120, A) is a thoroughly typical example. The sage, mints, catnip, thyme, lavender, etc., will recall the peculiarities of the family.

The stamens are usually four in number through the abortion of one of them, but sometimes only two perfect stamens are present.

[Illustration: FIG. 120.—Anisocarpous sympetalae (Labiatiflorae). A, dead nettle, Lamium, (Labiatae), x 1/2. B, a single flower, x 1. C, the stamens and pistil, x 1. D, cross-section of the ovary, x 2. E, diagram of the flower; the position of the absent stamen is indicated by the small circle. F, fruit of the common sage, Salvia (Labiatae), x 1. Part of the persistent calyx has been removed to show the four seed-like fruits, or nutlets. G, section of a nutlet, x 3. The embryo fills the seed completely. H, part of an inflorescence of figwort, Scrophularia (Scrophularineae), x 1. I, cross-section of the young fruit, x 2. J, flower of speedwell, Veronica (Scrophularineae), x 2. K, fruit of Veronica, x 2. L, cross-section of K. M, flower of moth-mullein, Verbascum (Scrophularineae), x 1/2. N, flower of toad-flax, Linaria (Scrophularineae), x 1. O, leaf of bladder-weed, Utricularia (Lentibulariaceae), x 1. x, one of the "traps." P, a single trap, x 5.]

The Scrophularineae differ mainly from the Labiatae in having round stems, and the ovary not splitting into separate one-seeded fruits. The leaves are also sometimes alternate. There are generally four stamens, two long and two short, as in the labiates, but in the mullein (Verbascum) (Fig. 120, M), where the flower is only slightly zygomorphic, there is a fifth rudimentary stamen, while in others (e.g. Veronica) (Fig. 120, J) there are but two stamens. Many have large, showy flowers, as in the cultivated foxglove (Digitalis), and the native species of Gerardia, mullein, Mimulus, etc., while a few like the figwort, Scrophularia (Fig. 120, H), and speedwells (Veronica) have duller-colored or smaller flowers.

[Illustration: FIG. 121.—Anisocarpous sympetalae (Labiatiflorae). A, flowering branch of trumpet-creeper, Tecoma (Bignoniaceae), x 1/4. B, a single flower, divided lengthwise, x 1/2. C, cross-section of the ovary, x 2. D, diagram of the flower. E, flower of vervain, Verbena (Verbenae), x 2: i, from the side; ii, from in front; iii, the corolla laid open. F, nearly ripe fruit of the same, x 2. G, part of a spike of flowers of the common plantain, Plantago (Plantagineae), x 1; The upper flowers have the pistils mature, but the stamens are not yet ripe. H, a flower from the upper (younger) part of the spike. I, an older expanded flower, with ripe stamens, x 3.]

The curious bladder-weed (Utricularia) is the type of the family Lentibulariaceae, aquatic or semi-aquatic plants which possess special contrivances for capturing insects or small water animals. These in the bladder-weed are little sacs (Fig. 120, P) which act as traps from which the animals cannot escape after being captured. There does not appear to be here any actual digestion, but simply an absorption of the products of decomposition, as in the pitcher-plant. In the nearly related land form, Pinguicula, however, there is much the same arrangement as in the sundew.

The family Gesneraceae is mainly a tropical one, represented in the greenhouses by the magnificent Gloxinia and Achimenes, but of native plants there are only a few parasitic forms destitute of chlorophyll and with small, inconspicuous flowers. The commonest of these is Epiphegus, a much-branched, brownish plant, common in autumn about the roots of beech-trees upon which it is parasitic, and whence it derives its common name, "beech-drops."

The bignonia family (Bignoniaceae) is mainly tropical, but in our southern states is represented by the showy trumpet-creeper (Tecoma) (Fig. 121, A), the catalpa, and Martynia.

The other plants likely to be met with by the student belong either to the Verbenaceae, represented by the showy verbenas of the gardens, and our much less showy wild vervains, also belonging to the genus Verbena (Fig. 121, E); or to the plantain family (Plantagineae), of which the various species of plantain (Plantago) are familiar to every one (Fig. 121, G, I). The latter seem to be forms in which the flowers have become inconspicuous, and are wind fertilized, while probably all of its showy-flowered relatives are dependent on insects for fertilization.

The third order (Contortae) of the Anisocarpae includes five families, all represented by familiar forms. The first, the olive family (Oleaceae), besides the olive, contains the lilac and jasmine among cultivated plants, and the various species of ash (Fraxinus), and the pretty fringe-tree (Chionanthus) (Fig. 122, A), often cultivated for its abundant white flowers. The other families are the Gentianaceae including the true gentians (Gentiana) (Fig. 122, F), the buck-bean (Menyanthes), the centauries (Erythraea and Sabbatia), and several other less familiar genera; Loganiaceae, with the pink-root (Spigelia) (Fig. 122, D), as the best-known example; Apocynaceae including the dog-bane (Apocynum) (Fig. 122, H), and in the gardens the oleander and periwinkle (Vinca).

[Illustration: FIG. 122.—Anisocarpous sympetalae (Contortae). A, flower of fringe-tree, Chionanthus (Oleaceae), x 1. B, base of the flower, with part of the calyx and corolla removed, x 2. C, fruit of white ash, Fraxinus (Oleaceae), x 1. D, flower of pink-root, Spigelia (Loganiaceae), x 1/2. E, cross-section of the ovary, x 3. F, flower of fringed gentian, Gentiana (Gentianaceae), x 1/2. G, diagram of the flower. H, flowering branch of dog-bane, Apocynum (Apocynaceae), x 1/2. I, vertical section of a flower, x 2. J, bud. K, flower of milk-weed, Asclepias (Asclepiadaceae), x 1. L, vertical section through the upper part of the flower, x 2. gy. pistil. p, pollen masses. an. stamen. M, a pair of pollen masses, x 6. N, a nearly ripe seed, x 1.]

The last family is the milk-weeds (Asclepiadaceae), which have extremely complicated flowers. Our numerous milk-weeds (Fig. 122, K) are familiar representatives, and exhibit perfectly the peculiarities of the family. Like the dog-banes, the plants contain a milky juice which is often poisonous. Besides the true milk-weeds (Asclepias), there are several other genera within the United States, but mostly southern in their distribution. Many of them are twining plants and occasionally cultivated for their showy flowers. Of the cultivated forms, the wax-plant (Hoya), and Physianthus are the commonest.

[Illustration: FIG. 123.—Anisocarpous sympetalae (Campanulinae). A, vertical section of the bud of American bell-flower, Campanula (Campanulaceae), x 2. B, an expanded flower, x 1. The stamens have discharged their pollen, and the stigma has opened. C, cross-section of the ovary, x 3. D, flower of the Carpathian bell-flower (Campanula Carpatica), x 1. E, flower of cardinal-flower, Lobelia (Lobeliaceae), x 1. F, the same, with the corolla and sepals removed. an. the united anthers. gy. the tip of the pistil. G, the tip of the pistil, x 2, showing the circle of hairs surrounding the stigma. H, cross-section of the ovary, x 3. I, tip of a branch of cucumber, Cucurbita (Cucurbitaceae), with an expanded female flower ([Female]). J, androecium of a male flower, showing the peculiar convoluted anthers (an.), x 2. K, cross-section of the ovary, x 2.]

The fourth order (Campanulinae) also embraces five families, but of these only three are represented among our wild plants. The bell-flowers (Campanula) (Fig. 123, A, D) are examples of the family Campanulaceae, and numerous species are common, both wild and cultivated.

[Illustration: FIG. 124.—Anisocarpous sympetalae (Aggregatae). A, flowering branch of Houstonia purpurea, x 1 (Rubiaceae). B, vertical section of a flower, x 2. C, fruit of bluets (Houstonia coerulea), x 1. D, cross-section of the same. E, bedstraw, Galium (Rubiaceae), x 1/2. F, a single flower, x 2. G, flower of arrow-wood, Viburnum (Caprifoliaceae), x 2. H, the same, divided vertically. I, flowering branch of trumpet honeysuckle, Lonicera (Caprifoliaceae), x 1/2. J, a single flower, the upper part laid open, x 1. K, diagram of the flower. L, part of the inflorescence of valerian, Valeriana, (Valerianeae), x 1. M, young; N, older flower, x 2. O, cross-section of the young fruit; one division of the three contains a perfect seed, the others are crowded to one side by its growth. P, inflorescence of teasel, Dipsacus (Dipsaceae), x 1/4. fl. flowers. Q, a single flower, x 1. R, the same, with the corolla laid open.]

The various species of Lobelia, of which the splendid cardinal-flower (L. Cardinalis) (Fig. 123, E) is one of the most beautiful, represent the very characteristic family Lobeliaceae. Their milky juice contains more or less marked poisonous properties. The last family of the order is the gourd family (Cucurbitaceae), represented by a few wild species, but best known by the many cultivated varieties of melons, cucumbers, squashes, etc. They are climbing or running plants, and provided with tendrils. The flowers are usually unisexual, sometimes dioecious, but oftener monoecious (Fig. 123, I).

[Illustration: FIG. 125.—Anisocarpous sympetalae (Aggregatae). Types of Compositae. A, inflorescence of Canada thistle (Cirsium), x 1. B, vertical section of A. r, the receptacle or enlarged end of the stem, to which the separate flowers are attached. C, a single flower, x 2. o, the ovary. p, the "pappus" (calyx lobes). an. the united anthers. D, the upper part of the stamens and pistil, x 3: i, from a young flower; ii, from an older one. an. anthers. gy. pistil. E, ripe fruit, x 1. F, inflorescence of may-weed (Maruta). The central part (disc) is occupied by perfect tubular flowers (G), the flowers about the edge (rays) are sterile, with the corolla much enlarged and white, x 2. G, a single flower from the disc, x 3. H, inflorescence of dandelion (Taraxacum), the flowers all alike, with strap-shaped corollas, x 1. I, a single flower, x 2. c, the split, strap-shaped corolla. J, two ripe fruits, still attached to the receptacle (r). The pappus is raised on a long stalk, x 1. K, a single fruit, x 2.]