Fig. 81.Fig. 81.—A, plant of the yellow adder-tongue (Erythronium americanum), × ⅓.B, the bulb of the same, × ½.r, roots.C, section ofB.st.the base of the stem bearing the bulb for next year (b) at its base.D, a single petal and stamen, × ½.f, the filament.an.anther.E, the gynœcium (pistil), × 1.o, ovary.st.style.z, stigma.F, a full-grown fruit, × ½.G, section of a full-grown macrosporangium (ovule), × 25:i,ii, the two integuments.sp.macrospore (embryo sac).H, cross-section of the ripe anther, × 12.I, a single pollen spore, × 150, showing the two nuclei (n,nʹ).J, a ripe seed, × 2.K, the same, in longitudinal section.em.the embryo.L, cross-section of the stem, × 12.fb.fibro-vascular bundle.M, diagram of the flower.
Fig. 81.—A, plant of the yellow adder-tongue (Erythronium americanum), × ⅓.B, the bulb of the same, × ½.r, roots.C, section ofB.st.the base of the stem bearing the bulb for next year (b) at its base.D, a single petal and stamen, × ½.f, the filament.an.anther.E, the gynœcium (pistil), × 1.o, ovary.st.style.z, stigma.F, a full-grown fruit, × ½.G, section of a full-grown macrosporangium (ovule), × 25:i,ii, the two integuments.sp.macrospore (embryo sac).H, cross-section of the ripe anther, × 12.I, a single pollen spore, × 150, showing the two nuclei (n,nʹ).J, a ripe seed, × 2.K, the same, in longitudinal section.em.the embryo.L, cross-section of the stem, × 12.fb.fibro-vascular bundle.M, diagram of the flower.
A cross-section of the stem shows numerous whitish areas scattered through it. These are the fibro-vascular bundles which in the monocotyledons are of a simple type. The bulb is composed of thick scales, which are modified leaves, and on cutting it lengthwise, we shall probably find the young bulb of next year (Fig.C,b) already forming inside it, the youngbulb arising as a bud at the base of the stem of the present year.
The flower is made up of five circles of very much modified leaves, three leaves in each set. The two outer circles are much alike, but the three outermost leaves are slightly narrower and strongly tinged with red on the back, completely concealing the three inner ones before the flower expands. The latter are pure yellow, except for a ridge along the back, and a few red specks near the base inside. These six leaves constitute the perigone of the flower; the three outer are called sepals, the inner ones petals.
The next two circles are composed of the sporophylls bearing the pollen spores.[12]These are the stamens, and taken collectively are known as the “Andrœcium.” Each leaf or stamen consists of two distinct portions, a delicate stalk or “filament” (D,f), and the upper spore-bearing part, the “anther” (an.). The anther in the freshly opened flower has a smooth, red surface; but shortly after, the flower opens, splits along each side, and discharges the pollen spores. A section across the anther shows it to be composed of four sporangia or pollen sacs attached to a common central axis (“connective”) (Fig.H).
The central circle of leaves, the carpels (collectively the “gynœcium”) are completely united to form a compound pistil (Fig. 81,E). This shows three distinct portions, the ovule-bearing portion below (o), the “ovary,” a stalk above (st.), the “style,” and the receptive portion (z) at the top, the “stigma.” Both stigma and ovary show plainly their compound nature, the former being divided into three lobes, the latter completely divided into three chambers, as well as being flattened at the sides with a more or less decided seam at the three angles. The ovules, which are quite large, are arranged in two rows in each chamber of the ovary, attached to the central column (“placenta”).
The flowers open for several days in succession, but only when the sun is shining. They are visited by numerous insects which carry the pollen from one flower to another and deposit it upon the stigma, where it germinates, and the tube, growing down through the long style, finally reaches the ovules and fertilizes them. Usually only a comparatively small number of the seeds mature, there being almost always a number of imperfect ones in each pod. The pod or fruit (F) is full-grown about a month after the flower opens, and finally separates into three parts, and discharges the seeds. These are quite large (Fig. 81,J) and covered with a yellowish brownouter coat, and provided with a peculiar, whitish, spongy appendage attaching it to the placenta. A longitudinal section of a ripe seed (K) shows the very small, nearly triangular embryo (em.), while the rest of the cavity of the seed is filled with a white, starch-bearing tissue, the endosperm.
Fig. 82.Fig. 82.—Erythronium.A, a portion of the wall of the anther, × 150.B, a single epidermal cell from the petal, × 150.C, cross-section of a fibro-vascular bundle of the stem, × 150.tr.vessels.D,E, longitudinal section of the same, showing the markings of the vessels, × 150.F, a bit of the epidermis from the lower surface of a leaf, showing the breathing pores, × 50.G, a single breathing pore, × 200.H, cross-section of a leaf, × 50.st.a breathing pore.m, the mesophyll.fb.a vein.I, cross-section of a breathing pore, × 200.J, young embryo, × 150.
Fig. 82.—Erythronium.A, a portion of the wall of the anther, × 150.B, a single epidermal cell from the petal, × 150.C, cross-section of a fibro-vascular bundle of the stem, × 150.tr.vessels.D,E, longitudinal section of the same, showing the markings of the vessels, × 150.F, a bit of the epidermis from the lower surface of a leaf, showing the breathing pores, × 50.G, a single breathing pore, × 200.H, cross-section of a leaf, × 50.st.a breathing pore.m, the mesophyll.fb.a vein.I, cross-section of a breathing pore, × 200.J, young embryo, × 150.
A microscopical examination of the tissues of the plant shows them to be comparatively simple, this being especially the case with the fibro-vascular system.The epidermis of the leaf is readily removed, and examination shows it to be made up of oblong cells with large breathing pores in rows. The breathing pores are much larger than any we have yet seen, and are of the type common to most angiosperms. The ordinary epidermal cells are quite destitute of chlorophyll, but the two cells (guard cells) enclosing the breathing pore contain numerous chloroplasts, and the oblong nuclei of these cells are usually conspicuous (Fig. 82,G). By placing a piece of the leaf between pieces of pith, and making a number of thin cross-sections at right angles to the longer axis of the leaf, some of the breathing pores will probably be cut across, and their structure may be then better understood. Such a section is shown inFigure 82,I.The body of the leaf is made up of chlorophyll-bearing cells of irregular shape and with large air spaces between (H,m). The veins traversing this tissue are fibro-vascular bundles of a type structure similar to that of the stem, which will be described presently.The stem is made up principally of large cells with thin walls, which in cross-section show numerous small, triangular, intercellular spaces (i) at the angles. These cells contain, usually, more or less starch. The fibro-vascular bundles (C) are nearly triangular in section, and resemble considerably those of the field horse-tail, but they are not penetrated by the air channel, found in the latter. The xylem, as in the pine, is toward the outside of the stem, but the boundary between xylem and phloem is not well defined, there being no cambium present. In the xylem are a number of vessels (C,tr.) at once distinguishable from the other cells by their definite form, firm walls, and empty cavity. The vessels in longitudinal sections show spiral and ringed thickenings. The rest of the xylem cells, as well as those of the phloem, are not noticeably different from the cells of the ground tissue, except for their much smaller size, and absence of intercellular spaces.The structure of the leaves of the perigone is much like that of the green leaves, but the tissues are somewhat reduced. The epidermis ofthe outer side of the sepals has breathing pores, but these are absent from their inner surface, and from both sides of the petals. The walls of the epidermal cells of the petals are peculiarly thickened by apparent infoldings of the wall (B), and these cells, as well as those below them, contain small, yellow bodies (chromoplasts) to which the bright color of the flower is due. The red specks on the base of the perigone leaves, as well as the red color of the back of the sepals, the stalk, and leaves are due to a purplish red cell sap filling the cells at these points.The filaments or stalks of the stamens are made up of very delicate colorless cells, and the centre is traversed by a single fibro-vascular bundle, which is continued up through the centre of the anther. To study the latter, thin cross-sections should be made and mounted in water. Each of the four sporangia, or pollen sacs, is surrounded on the outside by a wall, consisting of two layers of cells, becoming thicker in the middle of the section where the single fibro-vascular bundle is seen (Fig. 81,H). On opening, the cavities of the adjacent sporangia are thrown together. The inner cells of the wall are marked by thickened bars, much as we saw in the pine (Fig. 82,A), and which, like these, are formed shortly before the pollen sacs open. The pollen spores (Fig. 81,I) are large, oval cells, having a double wall, the outer one somewhat heavier than the inner one, but sufficiently transparent to allow a clear view of the interior, which is filled with very dense, granular protoplasm in which may be dimly seen two nuclei (n,ni.), showing that here also there is a division of the spore contents, although no wall is present. The spores do not germinate very readily, and are less favorable for this purpose than those of some other monocotyledons. Among the best for this purpose are the spiderwort (Tradescantia) andScilla.Owing to the large size and consequent opacity of the ovules, as well as to the difficulty of getting the early stages, the development and finer structure of the ovule will not be discussed here. The full-grown ovule may be readily sectioned, and a general idea of its structure obtained. A little potash may be used to advantage in this study, carefully washing it away when the section is sufficiently cleared. We find now that the ovule is attached to a stalk (funiculus) (Fig. 81,G,f), the body of the ovule being bent up so as to lie against the stalk. Such an inverted ovule is called technically, “anatropous.” The ovule is much enlarged where the stalk bends. The upper part of the ovule is on the whole like that of the pine, but there are two integuments (i,ii) instead of the single one found in the pine.As the seed develops, the embryo sac (G,sp.) enlarges so as to occupy pretty much the whole space of the seed. At first it is nearly filled witha fluid, but a layer of cells is formed, lining the walls, and this thickens until the whole space, except what is occupied by the small embryo, is filled with them. These are called the “endosperm cells,” but differ from the endosperm cells of the gymnosperms, in the fact that they are not developed until after fertilization, and can hardly, therefore, be regarded as representing the prothallium of the gymnosperms and pteridophytes. These cells finally form a firm tissue, whose cells are filled with starch that forms a reserve supply of food for the embryo plant when the seed germinates. The embryo (Fig. 81,K,em.,Fig. 82,J), even when the seed is ripe, remains very small, and shows scarcely any differentiation. It is a small, pear-shaped mass of cells, the smaller end directed toward the upper end of the embryo sac.
A microscopical examination of the tissues of the plant shows them to be comparatively simple, this being especially the case with the fibro-vascular system.
The epidermis of the leaf is readily removed, and examination shows it to be made up of oblong cells with large breathing pores in rows. The breathing pores are much larger than any we have yet seen, and are of the type common to most angiosperms. The ordinary epidermal cells are quite destitute of chlorophyll, but the two cells (guard cells) enclosing the breathing pore contain numerous chloroplasts, and the oblong nuclei of these cells are usually conspicuous (Fig. 82,G). By placing a piece of the leaf between pieces of pith, and making a number of thin cross-sections at right angles to the longer axis of the leaf, some of the breathing pores will probably be cut across, and their structure may be then better understood. Such a section is shown inFigure 82,I.
The body of the leaf is made up of chlorophyll-bearing cells of irregular shape and with large air spaces between (H,m). The veins traversing this tissue are fibro-vascular bundles of a type structure similar to that of the stem, which will be described presently.
The stem is made up principally of large cells with thin walls, which in cross-section show numerous small, triangular, intercellular spaces (i) at the angles. These cells contain, usually, more or less starch. The fibro-vascular bundles (C) are nearly triangular in section, and resemble considerably those of the field horse-tail, but they are not penetrated by the air channel, found in the latter. The xylem, as in the pine, is toward the outside of the stem, but the boundary between xylem and phloem is not well defined, there being no cambium present. In the xylem are a number of vessels (C,tr.) at once distinguishable from the other cells by their definite form, firm walls, and empty cavity. The vessels in longitudinal sections show spiral and ringed thickenings. The rest of the xylem cells, as well as those of the phloem, are not noticeably different from the cells of the ground tissue, except for their much smaller size, and absence of intercellular spaces.
The structure of the leaves of the perigone is much like that of the green leaves, but the tissues are somewhat reduced. The epidermis ofthe outer side of the sepals has breathing pores, but these are absent from their inner surface, and from both sides of the petals. The walls of the epidermal cells of the petals are peculiarly thickened by apparent infoldings of the wall (B), and these cells, as well as those below them, contain small, yellow bodies (chromoplasts) to which the bright color of the flower is due. The red specks on the base of the perigone leaves, as well as the red color of the back of the sepals, the stalk, and leaves are due to a purplish red cell sap filling the cells at these points.
The filaments or stalks of the stamens are made up of very delicate colorless cells, and the centre is traversed by a single fibro-vascular bundle, which is continued up through the centre of the anther. To study the latter, thin cross-sections should be made and mounted in water. Each of the four sporangia, or pollen sacs, is surrounded on the outside by a wall, consisting of two layers of cells, becoming thicker in the middle of the section where the single fibro-vascular bundle is seen (Fig. 81,H). On opening, the cavities of the adjacent sporangia are thrown together. The inner cells of the wall are marked by thickened bars, much as we saw in the pine (Fig. 82,A), and which, like these, are formed shortly before the pollen sacs open. The pollen spores (Fig. 81,I) are large, oval cells, having a double wall, the outer one somewhat heavier than the inner one, but sufficiently transparent to allow a clear view of the interior, which is filled with very dense, granular protoplasm in which may be dimly seen two nuclei (n,ni.), showing that here also there is a division of the spore contents, although no wall is present. The spores do not germinate very readily, and are less favorable for this purpose than those of some other monocotyledons. Among the best for this purpose are the spiderwort (Tradescantia) andScilla.
Owing to the large size and consequent opacity of the ovules, as well as to the difficulty of getting the early stages, the development and finer structure of the ovule will not be discussed here. The full-grown ovule may be readily sectioned, and a general idea of its structure obtained. A little potash may be used to advantage in this study, carefully washing it away when the section is sufficiently cleared. We find now that the ovule is attached to a stalk (funiculus) (Fig. 81,G,f), the body of the ovule being bent up so as to lie against the stalk. Such an inverted ovule is called technically, “anatropous.” The ovule is much enlarged where the stalk bends. The upper part of the ovule is on the whole like that of the pine, but there are two integuments (i,ii) instead of the single one found in the pine.
As the seed develops, the embryo sac (G,sp.) enlarges so as to occupy pretty much the whole space of the seed. At first it is nearly filled witha fluid, but a layer of cells is formed, lining the walls, and this thickens until the whole space, except what is occupied by the small embryo, is filled with them. These are called the “endosperm cells,” but differ from the endosperm cells of the gymnosperms, in the fact that they are not developed until after fertilization, and can hardly, therefore, be regarded as representing the prothallium of the gymnosperms and pteridophytes. These cells finally form a firm tissue, whose cells are filled with starch that forms a reserve supply of food for the embryo plant when the seed germinates. The embryo (Fig. 81,K,em.,Fig. 82,J), even when the seed is ripe, remains very small, and shows scarcely any differentiation. It is a small, pear-shaped mass of cells, the smaller end directed toward the upper end of the embryo sac.
The integuments grow with the embryo sac, and become brown and hard, forming the shell of the seed. The stalk of the ovule also enlarges, and finally forms the peculiar, spongy appendage of the seeds already noticed (Fig. 81,J,K).
Inthe following chapter no attempt will be made to give an exhaustive account of the characteristics of each division of the monocotyledons, but only such of the most important ones as may serve to supplement our study of the special one already examined. The classification here, and this is the case throughout the spermaphytes, is based mainly upon the characters of the flowers and fruits.
The classification adopted here is that of the German botanist Eichler, and seems to the author to accord better with our present knowledge of the relationships of the groups than do the systems that are more general in this country. According to Eichler’s classification, the monocotyledons may be divided into seven groups; viz., I.Liliifloræ; II.Enantioblastæ; III.Spadicifloræ; IV.Glumaceæ; V.Scitamineæ; VI.Gynandræ; VII.Helobiæ.
The plants of this group agree in their general structure with the adder’s-tongue, which is a thoroughly typical representative of the group; but nevertheless, there is much variation among them in the details of structure. While most of them are herbaceous forms (dying down to the ground each year), a few, among which may be mentioned the yuccas (“bear grass,” “Spanish bayonet”) of our southern states, develop a creeping or upright woody stem, increasing in size from year to year. The herbaceous forms send up their stemsyearly from underground bulbs, tubers,e.g.Trillium(Fig. 83,A), or thickened, creeping stems, or root stocks (rhizomes). Good examples of the last are the Solomon’s-seal (Fig. 83,B),Medeola(C,D), and iris (Fig. 84A). One family, the yams (Dioscoreæ), of which we have one common native species, the wild yam (Dioscorea villosa), have broad, netted-veined leaves and are twining plants, while another somewhat similar family (Smilaceæ) climb by means of tendrils at the bases of the leaves. Of the latter the “cat-brier” or “green-brier” is a familiar representative.
Fig. 83.Fig. 83.—Types ofLiliifloræ.A,Trillium, × ¼.B, single flower of Solomon’s-seal (Polygonatum), × 1.C, upper part of a plant.D, underground stem (rhizome) of Indian cucumber root (Medeola), × ½.E, a rush (Juncus), × 1.F, a single flower, × 2.A–D,Liliaceæ;E,Juncaceæ.
Fig. 83.—Types ofLiliifloræ.A,Trillium, × ¼.B, single flower of Solomon’s-seal (Polygonatum), × 1.C, upper part of a plant.D, underground stem (rhizome) of Indian cucumber root (Medeola), × ½.E, a rush (Juncus), × 1.F, a single flower, × 2.A–D,Liliaceæ;E,Juncaceæ.
The flowers are for the most part conspicuous, and in plan like that of the adder’s-tongue; but some, like the rushes (Fig. 83,E), have small, inconspicuous flowers; and others, like the yams and smilaxes, have flowers of two kinds, male and female.
Fig. 84.Fig. 84.—Types ofLiliifloræ.A, flower of the common blue-flag (Iris), × ½ (Iridaceæ).B, the petal-like upper part of the pistil, seen from below, and showing a stamen (an.).st.the stigma, × ½.C, the young fruit, × ½.D, section of the same, × 1.E, diagram of the flower.F, part of a plant of the so-called “gray moss” (Tillandsia), × ½ (Bromeliaceæ).G, a single flower, × 2.H, a seed, showing the fine hairs attached to it, × 1.I, plant of pickerel-weed (Pontederia), × ¼ (Pontederiaceæ).J, a single flower, × 1.K, section of the ovary, × 4.
Fig. 84.—Types ofLiliifloræ.A, flower of the common blue-flag (Iris), × ½ (Iridaceæ).B, the petal-like upper part of the pistil, seen from below, and showing a stamen (an.).st.the stigma, × ½.C, the young fruit, × ½.D, section of the same, × 1.E, diagram of the flower.F, part of a plant of the so-called “gray moss” (Tillandsia), × ½ (Bromeliaceæ).G, a single flower, × 2.H, a seed, showing the fine hairs attached to it, × 1.I, plant of pickerel-weed (Pontederia), × ¼ (Pontederiaceæ).J, a single flower, × 1.K, section of the ovary, × 4.
The principal family of theLiliifloræis theLiliaceæ, including some of the most beautiful of all flowers. All of the true lilies (Lilium), as well as the day lilies (Funkia,Hemerocallis) of the gardens, tulips, hyacinths, lily-of-the-valley, etc., belong here, as well as a number of showy wild flowers including several species of tiger-lilies (Lilium), various species ofTrillium(Fig. 83,A), Solomon’s-seal (Polygonatum) (Fig. 83,B), bellwort (Uvularia), and others. In all of these, exceptTrillium, the perigone leaves are colored alike, and the leaves parallel-veined; but in the latter the sepals are green and the leaves broad and netted-veined. The fruit of theLiliaceæmay beeither a pod, like that of the adder’s-tongue, or a berry, like that of asparagus or Solomon’s-seal.
Fig. 85.Fig. 85.—Enantioblastæ.A, inflorescence of the common spiderwort (Tradescantia), × ½ (Commelyneæ).B, a single stamen, showing the hairs attached to the filament, × 2.C, the pistil, × 2.
Fig. 85.—Enantioblastæ.A, inflorescence of the common spiderwort (Tradescantia), × ½ (Commelyneæ).B, a single stamen, showing the hairs attached to the filament, × 2.C, the pistil, × 2.
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 (Iridaceæ), 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 theBromeliaceæ, 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.
The second order of the monocotyledons,Enantioblastæ, includes very few common plants. The most familiar examplesare the various species ofTradescantia(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,Commelyneæ.
The third order of the monocotyledons,Spadicifloræ, 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 (Aroideæ), of which the calla (Richardia) is a very familiar cultivated example. Of wild forms the sweet-flag (Acorus), Jack-in-the-pulpit (Arisæma) (Fig. 86,A,D), skunk-cabbage (Symplocarpus), and wild calla may be noted. InArisæma(Fig. 86,A) the flowers are borne only on the base of the spadix, and the plant is diœcious. The flowers are of the simplest structure, the female consisting of a single carpel, and the male of fourstamens (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).
Fig. 86.Fig. 86.—Types ofSpadicifloræ.A, inflorescence of Jack-in-the-pulpit (Arisæma,Aroideæ). 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, × ½.B, leaf of the same plant, × ¼.C, vertical section of a female flower, × 2.D, three male flowers, each consisting of four stamens, × 2.E, two plants of a duck-weed (Lemna), the one at the left is in flower, × 4.F, another common species.L,Trisulea, × 1.G, male flower ofE, × 25.H, optical section of the female flower, showing the single ovule (ov.), × 25.I, part of the inflorescence of the bur-reed (Sparganium), with female flowers, × ½ (Typhaceæ).J, a single, female flower, × 2.K, a ripe fruit, × 1.L, longitudinal section of the same.M, two male flowers, × 1.N, a pond-weed (Potomogeton), × 1 (Naiadaceæ).O, a single flower, × 2.P, the same, with the perianth removed, × 2.Q, fruit of the same, × 2.
Fig. 86.—Types ofSpadicifloræ.A, inflorescence of Jack-in-the-pulpit (Arisæma,Aroideæ). 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, × ½.B, leaf of the same plant, × ¼.C, vertical section of a female flower, × 2.D, three male flowers, each consisting of four stamens, × 2.E, two plants of a duck-weed (Lemna), the one at the left is in flower, × 4.F, another common species.L,Trisulea, × 1.G, male flower ofE, × 25.H, optical section of the female flower, showing the single ovule (ov.), × 25.I, part of the inflorescence of the bur-reed (Sparganium), with female flowers, × ½ (Typhaceæ).J, a single, female flower, × 2.K, a ripe fruit, × 1.L, longitudinal section of the same.M, two male flowers, × 1.N, a pond-weed (Potomogeton), × 1 (Naiadaceæ).O, a single flower, × 2.P, the same, with the perianth removed, × 2.Q, fruit of the same, × 2.
Probably to be regarded as reduced aroids are the duck-weeds (Lemnaceæ) (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 familyTyphaceæ, and the pond-weeds (NaiasandPotomogeton) are common examples of the familyNaiadeæ. 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 (Pandaneæ) and the palms (Palmæ). 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 (SabalandChamærops) 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 (Phœnix 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 thisstructure may be had by cutting across a corn-stalk, which is built on precisely the same pattern.
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, paleæ)which are closely set, so as to nearly conceal the flowers. The flowers are either hermaphrodite or unisexual.
Fig. 87.Fig. 87.—Types ofGlumaceæ.A, a sedge,Carex(Cyperaceæ). ♂, the male; ♀, the female flowers, × ½.B, a single male flower, × 2.C, a female flower, × 2.D, fruiting spike of anotherCarex, × ½.E, a single fruit, × 1.F, the same, with the outer envelope removed, and slightly enlarged.G, section ofF, × 3.em.the embryo.H, a bulrush,Scirpus(Cyperaceæ), × ½.I, a single spikelet, × 2.J, a single flower, × 3.K, a spikelet of flowers of the common orchard grass,Dactylis(Gramineæ), × 2.L, a single flower, × 2.M, the base of a leaf, showing the split sheath encircling the stem, × 1.N, section of a kernel of corn, showing the embryo (em.), × 2.
Fig. 87.—Types ofGlumaceæ.A, a sedge,Carex(Cyperaceæ). ♂, the male; ♀, the female flowers, × ½.B, a single male flower, × 2.C, a female flower, × 2.D, fruiting spike of anotherCarex, × ½.E, a single fruit, × 1.F, the same, with the outer envelope removed, and slightly enlarged.G, section ofF, × 3.em.the embryo.H, a bulrush,Scirpus(Cyperaceæ), × ½.I, a single spikelet, × 2.J, a single flower, × 3.K, a spikelet of flowers of the common orchard grass,Dactylis(Gramineæ), × 2.L, a single flower, × 2.M, the base of a leaf, showing the split sheath encircling the stem, × 1.N, section of a kernel of corn, showing the embryo (em.), × 2.
There are two well-marked families, the sedges (Cyperaceæ) and the grasses (Gramineæ). The former have solid, often triangular stems, and the sheath at the base of the leaves is not split. The commonest genera areCarex(Fig. 87,A,G) andCyperus, of which there are many common species, differing very little and hard to distinguish. There are several common species ofCarexwhich 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.
Fig. 88.Fig. 88.—Scitamineæ.A, upper part of a flowering plant of Indian shot (Canna), much reduced in size (Cannaceæ).B, a single flower, × ½.C, the single stamen (an.), and petal-like pistil (gy.), × 1.D, section of the ovary, × 2.E, diagram of the flower. The place of the missing stamens is indicated by small circles.F, fruit, × ½.G, section of an unripe seed.em.embryo.p, perisperm, × 2.
Fig. 88.—Scitamineæ.A, upper part of a flowering plant of Indian shot (Canna), much reduced in size (Cannaceæ).B, a single flower, × ½.C, the single stamen (an.), and petal-like pistil (gy.), × 1.D, section of the ovary, × 2.E, diagram of the flower. The place of the missing stamens is indicated by small circles.F, fruit, × ½.G, section of an unripe seed.em.embryo.p, perisperm, × 2.
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 ofCanna(Fig. 88) are common in gardens, where they are prized for their large, richly-coloredleaves, 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 inCannaonly 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 papillæ 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.Musaceæ(banana family); II.Zingiberaceæ(ginger family); and III.Cannaceæ(Canna,Maranta).
By far the greater number of the plants of this order belong to the orchis family (Orchideæ), the second family of the order(Apostasieæ), 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.
Fig. 89.Fig. 89.—Gynandræ.A, inflorescence of the showy orchis (Orchis spectabilis), × 1 (Orchideæ).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, × 1.C, the column seen from in front.an.the stamen.gy.the stigmatic surface, × 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.
Fig. 89.—Gynandræ.A, inflorescence of the showy orchis (Orchis spectabilis), × 1 (Orchideæ).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, × 1.C, the column seen from in front.an.the stamen.gy.the stigmatic surface, × 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 theovary) 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 (seeFig. 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.
Fig. 90.Fig. 90.—Forms ofOrchideæ.A, putty-root (Aplectrum), × 1.B, yellow lady’s-slipper (Cypripedium), × ½.C, the column of the same, × 1.an.one of the two perfect stamens.st.sterile, petal-like stamen.gy.. stigma.D,Arethusa, × ½.E, section of the column, × 1:an.stamen.gy.stigma.F, the same, seen from in front.G,Habenaria, × 1.H,Calopogon, × 1. In the last the ovary is not twisted, so that the lip (L) lies on the upper side of the flower.
Fig. 90.—Forms ofOrchideæ.A, putty-root (Aplectrum), × 1.B, yellow lady’s-slipper (Cypripedium), × ½.C, the column of the same, × 1.an.one of the two perfect stamens.st.sterile, petal-like stamen.gy.. stigma.D,Arethusa, × ½.E, section of the column, × 1:an.stamen.gy.stigma.F, the same, seen from in front.G,Habenaria, × 1.H,Calopogon, × 1. In the last the ovary is not twisted, so that the lip (L) lies on the upper side of the flower.
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 theHabenarias, including the yellow and purple fringed orchids, are strikingly beautiful as are theArethuseæ(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 coralroots (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 ofCorallorhiza, but there is a single, large, plaited leaf sent up later.
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,Juncagineæ, 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 (Alismaceæ) 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 gynœcium (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.
Fig. 91.Fig. 91.—Types ofHelobiæ.A, inflorescence of arrowhead (Sagittaria), with a single female flower, × ½ (Alismaceæ).B, section through the gynœcium, showing the numerous single carpels, × 3.C, a ripe fruit, × 3.D, a male flower, × 1.E, a single stamen, × 3.F, a leaf ofSagittaria variabilis, × ⅙.G, ditch-moss (Elodea), with a female flower (fl.), × ½. (Hydrocharideæ).H, the flower, × 2.an.the rudimentary stamens.st.the stigma.I, cross-section of the ovary, × 4.J, male inflorescence of eel-grass (Vallisneria), × 1.K, a single expanded male flower, × 12.st.the stamen.L, a female flower, × 1.gy.the stigma.
Fig. 91.—Types ofHelobiæ.A, inflorescence of arrowhead (Sagittaria), with a single female flower, × ½ (Alismaceæ).B, section through the gynœcium, showing the numerous single carpels, × 3.C, a ripe fruit, × 3.D, a male flower, × 1.E, a single stamen, × 3.F, a leaf ofSagittaria variabilis, × ⅙.G, ditch-moss (Elodea), with a female flower (fl.), × ½. (Hydrocharideæ).H, the flower, × 2.an.the rudimentary stamens.st.the stigma.I, cross-section of the ovary, × 4.J, male inflorescence of eel-grass (Vallisneria), × 1.K, a single expanded male flower, × 12.st.the stamen.L, a female flower, × 1.gy.the stigma.
The last family is theHydrocharideæ. 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, especiallyinVallisneria, 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 abundantduring 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 ofElodea, or a section of that ofVallisneria, may be used.