DIVISION V.
ANGIOSPERMÆ.
See pages 3 and 224. To this Division belong the majority of the Flowering-plants. They are divided into two parallel classes, the Monocotyledons and the Dicotyledons, which differ from each other not only in the number of cotyledons, which, with a few exceptions, is one in the former, two in the latter, but also in the internal structure of the stem, the venation of the leaves, the number of the parts of the flower, etc. Assuming that these two classes have sprang from a common origin, it is amongst the Helobieæ in the first, and amongst the Polycarpicæ in the second class that we might expect to find closely allied forms, which might reasonably be supposed to have varied less from this original type. As for the rest, they seem to stand quite parallel, without exhibiting any close relationship. It is scarcely proved that the Monocotyledons are the older class.
[Our knowledge of the forms included under the Angiosperms has recently been considerably increased by Treub (Ann. d. Jar. Bot. d. Buitenzorg, 1891), who has shown that the Casuarinas differ in many important points from the typical Angiosperms. Among other characters the pollen-tube is found to enter the ovule near the chalaza and therefore at the opposite end to the micropyle, and Treub therefore suggests that these plants should be placed in a subdivision termed Chalazogams.
According to this view the principal divisions of the Angiosperms would be represented thus:—
Angiospermæ.
| Sub-division. | Sub-division. |
| Chalazogames. | Porogames. |
| Class. | Classes. |
| Chalazogames. | Monocotyledones, Dicotyledones. |
More recently Nawaschin (Bull. Acad. Imp. Sci. St. Petersb., ser. iii., xxxv.) has shown that Betula, and Miss Benson (Trans. Linn. Soc., 1894) that Alnus, Corylus, and Carpinus also belong to the Chalazogams.
Our knowledge, however, is still so incomplete that one would hesitate to accord the full systematic value which Dr. Treub attaches to his discovery until the limits of the Chalazogamic group are better defined; and it would hardly be justifiable to include the Casuarinas and the above-noted genera in one family.]
Class 1. Monocotyledones.
The embryo has only one cotyledon; the leaves are as a rule scattered, with parallel venation; the vascular bundles of the stem are closed, there is no increase of thickness. The flower is typically constructed of five 3-merous whorls, placed alternately.
The embryo is generally small in proportion to the abundant endosperm (exceptions, see Helobieæ), and its single cotyledon is often sheath-like, and very large. On the germination of the seed either the entire cotyledon, or its apex only, most generally remains in the seed and absorbs the nutritive-tissue, while the lower portion elongates and pushes out the plumule and radicle, which then proceed with their further growth. The primary root in most cases soon ceases to grow, but at the same time, however, numerous lateral roots break out from the stem, and become as vigorous as the primary root, or even more so. Increase in thickness does not take place in these roots; they branch very little or not at all, and generally die after a longer or shorter time.
The stem is frequently a corm, bulb, or other variety of underground stem, as the majority of the Monocotyledons are perennial, herbaceous plants; it has scattered, closed vascular bundles (Fig. 276), and no cambium by which a continuous thickening may take place. The stem of the Palms, however, attains a very considerable thickness, which is due to the meristem of its growing-point continually increasing in diameter for a lengthened period (often for many years), until it has reached a certain size. In this condition the growing-point has the form of an inverted cone, and it is only when this cone has attained its requisite size that the formation of a vertical cylindrical stem commences. Certain tree-like Liliaceæ, as Dracæna, Aloe, etc., have a continuous increase in thickness; this is due to a meristematic layer, which arises in the cortex, outside the original vascular bundles, which were formed at the growing-point of the stem. This meristem continues to form thick-walled parenchyma and new, scattered vascular bundles. The primary vascular bundles, in the Palms and others, run in a curved line from their entrance into the stem at the base of the leaf, towards the centre of the stem, and then bend outwards and proceed downwards in a direction more parallel to the sides of the stem (Fig. 277). The bundles formed later, in those stems which increase in thickness, are not continued into the leaves.
The branching as a rule is very slight, the axillary buds of the majority of the leaves never attaining development, e.g. in the Palms, bulbous plants and others. As the cotyledon arises singly, the succeeding leaves also must be scattered, but they are frequently arranged in two rows (Grasses, Iris, etc). The first leaf borne on a branch (the “Fore-leaf,”[24]—the bracteole, if on a floral shoot) has generally, in the Monocotyledons, a characteristic form and position, being situated on the posterior side of its own shoot, and hence turned towards the main axis; it is sometimes provided with two laterally-placed keels (Figs. 279 f, 290 øi), but the midrib is often absent. It arises in some cases from two primordia, which at the beginning are quite distinct, and thus has been regarded as formed by two leaves. It is, however, only one leaf, a fact which is evident from several circumstances, one being that it never supports more than one shoot, and this stands in the median plane (Fig. 279).
Fig. 276.—Transverse section of the stem of a Palm: v v is the wood portion, b b the bast portion of the vascular bundled.
Fig. 277.—Diagrammatic representation of the course of the vascular bundles, from the stem into the leaves in a Monocotyledon.
The leaves are amplexicaul, and have a large sheath but no stipules; the blade is most frequently long, ligulate, or linear, entire, with parallel venation, the veins being straight or curved (Figs. 300, 309). Connecting the large number of veins which run longitudinally, there are as a rule only weak transverse ones. It is very rarely that other forms of leaves are found, such as cordate (Figs. 302, 312), or that the blade is branched, or the venation is, for example, pinnate or palmate (Figs. 225, 298); these deviations are especially found in the Araceæ, the Palms, the Scitamineæ (Fig. 308), the Dioscoreaceæ, and in several aquatic plants. The incisions in the Palm-leaf are derived by the splitting of an originally entire leaf.
The structure of the flower is generally as follows: Pr3 + 3, A3 + 3, G3, rarely S3 + P3 with the other members unchanged.[25] Instead of 3, the numbers 2 and 4 may occur; rarely others. In all these instances there are 5 whorls, which regularly alternate with one another, most frequently in the 3-merous flower, as in the diagram (Fig. 278). This diagram is found in the following orders: Liliaceæ, Convallariaceæ, Juncaceæ, Bromeliaceæ, Amaryllidaceæ, Dioscoreaceæ, Palmæ, some Araceæ, and in some small orders, and may be considered as the typical structure and also the starting point for the exceptional orders. The ovary in many Monocotyledons has many ovules, and the fruit becomes a many-seeded berry or capsule; this form is no doubt the oldest. In others the number of seeds becomes reduced to 1, and the fruit then becomes a cypsela, or a drupe (e.g. Gramineæ, Cyperaceæ, Palmæ, etc).
Fig. 278.—Diagram of the ordinary, regular flower in the Monocotyledons: s is the bract.
Fig. 279.—Diagram of Iris: f the bracteole; in its axil is a shoot with its bracteole.
Fig. 280.—Diagram of Orchis: l the lip; σ σ the two staminodes.
Deviations from this typical floral structure in some instances may be traced to suppression, very rarely to a splitting of certain members, the typical relative positions not being changed. Thus, the Iridaceæ, the Cyperaceæ, most of the Gramineæ and some Juncaceæ deviate in having only 3 stamens (Fig. 279), the inner whorl (indicated by *) not becoming developed. The Musaceæ differ in the posterior stamen not being developed; Zingiberaceæ (Fig. 314), Marantaceæ, and Cannaceæ, in the fact that only 1 of all the stamens bears an anther, and the others are either suppressed or developed into petaloid staminodes, with some perhaps cleft in addition. The Orchideæ deviate in having, generally, only the anterior stamen of all the 6 developed (Fig. 280). In this, as in other instances, the suppression of certain parts of the flower is often connected with zygomorphy (i.e. symmetry in one plane), chiefly in the inner perianth-whorl, but also in the other whorls. In the Orchids, the perianth-leaf (the labellum, Fig. 280 l) which is directly opposite the fertile stamen, is larger and altogether different from the others. The perianth-leaves may also be suppressed; see, for example, the two diagrams of the Cyperaceæ (Fig. 284). In some orders the suppression of these leaves, which form the basis of the diagram, is so complete that it is hard to reduce the actual structure of the flower to the theoretical type, e.g. the Grasses (Fig. 290) and Lemna (Fig. 303). In the first family, which especially comprises water-plants, a somewhat different structure is found; thus Fig. 282 differs somewhat from the ordinary type, and other flowers much more so; but the floral diagrams which occur in this family may perhaps be considered as the most probable representatives of an older type, from which the ordinary pentacyclic forms have taken their origin. In favour of this theory we have the larger number of whorls, the spiral arrangement of some of these in the flower, with a large and indefinite number of stamens and carpels, the perfectly apocarpous gynœceum which sometimes occurs, etc., etc.
The Monocotyledons are divided into 7 Families:—
1. Helobieæ. This family forms a group complete in itself. It commences with hypogynous, perfect flowers, whose gynœcium is apocarpous and terminates in epigynous and more or less reduced forms.
2. Glumifloræ. These have as a starting point the same diagram as the following families, but otherwise develope independently.
3. Spadicifloræ. Also an independent branch, or perhaps two different ones which terminate in much reduced forms.
4. Enantioblastæ. These ought perhaps to be amalgamated with the following family.
5. Liliifloræ. These advance from forms with the typical diagram and hypogynous flower, to epigynous and reduced forms.
6. Scitamineæ and
7. Gynandræ. Two isolated families, which probably have taken their origin from Liliifloræ, and have epigynous, mostly zygomorphic, and much reduced forms.
Family 1. Helobieæ.
To this family belong only water- or marsh-plants; the endosperm is wanting, and they possess an embryo with a very large hypocotyl prolonged downwards and often club-like. The perianth is often differentiated into calyx and corolla; the flower is regular, and in the first orders to be considered, may be reduced to the ordinary Monocotyledonous type; there are, however, usually found two 3-merous whorls of carpels (Fig. 282), and thus in all 6 whorls, or again, the number of carpels may be indefinite; the number of stamens also may be increased, either by the division of the members of a whorl, or by the development of additional whorls. Syncarps,[26] with nut or follicular fruitlets, are very common, for example, in the first orders; in the last (Hydrocharitaceæ) the carpels are not only united, but the ovary is even inferior.
The primitive type appears to be a hypogynous flower, similar to that of the Juncaginaceæ or Alismaceæ, with several 3-merous whorls, and free carpels, each with many ovules; the green perianth in this instance being no doubt older than the coloured ones. If we take a flower with this structure as the starting point, then the family developes partly into epigynous forms, partly into others which are so strongly reduced and exceptional that it is scarcely possible to refer them to the ordinary type. The family, through the peculiar Zostereæ, appears to approach the Araceæ, in which Potamogetonaceæ and Najadaceæ are included by some authorities. However, the inclusion of Potamogeton, and with it Ruppia and Zannichellia, in the Juncaginaceæ appears quite correct. It would scarcely be right to separate Zostereæ from these. Great stress has often been laid upon the similarity with the Ranunculaceæ which is found in the Alismaceæ, but it is scarcely more than an analogous resemblance.
Order 1. Juncaginaceæ. The ☿, regular, hypogynous flowers have the perianth 3 + 3, sepaloid, stamens 3 + 3 (with extrorse anthers), and carpels 3 + 3 (free or united), of which last, however, one whorl may be suppressed (in Triglochin maritima all 6 carpels are developed, in T. palustris the inner whorl is unfertile). Inflorescence long spikes. Embryo straight.—Marsh-plants with radical, rush-like leaves, arranged in two rows, and often sheathing and ligulate (“squamulæ intravaginales”); the inflorescence is a spike or raceme.—Scheuchzeria. Carpels almost free; in each at least two ovules. Follicles.—Triglochin has long, fine racemes without bracts or bracteoles; one ovule in each carpel. The carpels in the two native species are united, but separate when ripe as a schizocarp, loosening from below; they open along the ventral suture or remain closed; a linear central column remains. The most reduced is Lilæa (1–2 sp. Am.)—Protogynous. About 10 species. Temp. Fossils in Tertiary.
Order 2. Potamogetonaceæ. The aquatic plants belonging to this order are perennial, living entirely submerged, or with floating leaves, and preferring still water. The leaves are alternate, in some linear and grass-like, in others there is an elliptical floating blade, supported by a linear submerged petiole. Axillary scales. The fruit is generally a syncarp with nuts or drupes; the embryo is curved, of very various forms.
Potamogeton (Pond-weed). The rhizome is creeping, sympodial (with two internodes in each shoot-generation); the inflorescence is a terminal, many-flowered spike, without floral-leaves; below it are found 2 foliage-leaves placed nearly at the same height, from whose axils the branching is continued cymosely. The flowers are ☿, 4-merous, naked, and consist only of 4 stamens, with the connectives, broadly developed at the back of the anthers, resembling a perianth, and of 4 free, sessile carpels. They are common plants in fresh water. The spike, during the flowering, is raised above the water. Wind-pollinated and protogynous.—Closely allied is Ruppia (Tassel Pond-weed), in salt or brackish water. The spike has only two naked flowers, each consisting of 2 stamens and 4 carpels. The stalks of the individual carpels are considerably prolonged.—Zannichellia (Horned Pond-weed) is monœcious; the ♀-flower consists of 4 (2–9) carpels, with membranous, bell-shaped perianth; long styles; the ♂-flower has 1 (-2) stamens. Althenia.
Zostera (Grass-wrack) is an entirely submerged, marine plant with creeping rhizome (with displacement of buds) and strap-shaped leaves. The flowering shoots are sympodia with displacement of the axes (Fig. 281). The inflorescence is a peculiar, flatly-compressed spike, on one side of which the flowers are borne (Fig. 281). This inflorescence may be considered, no doubt correctly, to be derived from the symmetrical spike of Potamogeton by strongly dorsiventral development, and by a strong suppression of the floral parts taking place simultaneously. Two rows of flowers are developed, but of these one is so pressed into the other that apparently only one is present. Each flower consists of only 1 stamen and 1 carpel situated at the same height (Fig. 281); the unilocular ovary encloses 1 pendulous ovule and bears a bifid style. As regards the perianth (?) one leaf may be present (Z. nana, Fig. 281 D). The pollen-grains are filamentous. Pollination takes place under water. Posidonia and Cymodocea are allied to these. About 70 species.
Fig. 281.—Zostera. A Diagram of the branching of the floral shoots: I, II ... are the successive shoot-generations, every other one being shaded; g1 g2 ... fore-leaves; sp1 sp2 ... spathes for the successive spikes. Each shoot is united for some distance with the parent axis (indicated by the half-shaded internodes). Each shoot commences with a fore-leaf turning towards the parent axis, g; succeeding this is the spathe, sp; and then the inflorescence. The fore-leaf supports a new lateral shoot. B Diagram of a shoot, II, which is borne laterally in the axil of the fore-leaf g1, on the shoot I, g2 its fore-leaf; sp2 its spathe; sti squamulæ intravaginales. II Is the spadix with stamens and carpels; b a perianth-leaf (or connective expansion, similar to those which occur in Potamogeton). C The upper portion of a young spadix with development of flowers. D Part of a spadix with 2 flowers; the parts which theoretically belong to one another are connected by a dotted line.
Order 3. Aponogetonaceæ. Aquatic plants with tuberous stem. They have a single, petaloid perianth (3–2–1–leaved), most frequently 6 stamens and 3(-6) carpels. Straight embryo.—About 15 species (Africa, Madagascar, Tropical Asia and Australia).—Aponogeton distachyos and A. (Ouvirandra) fenestralis are grown in conservatories; the latter has lattice-like, perforated leaves.
Order 4. Najadaceæ. Only one genus Najas (about 10 species); annual fresh water plants with leaves in pairs and solitary, unisexual flowers. The ♂ flower is remarkable in having a terminal stamen, which has either 4 longitudinal loculi or 1 central one; on this account the stamen of Najas is considered by some authorities to be a stem and not a leaf-structure. The unilocular gynœceum and the single, erect, anatropous ovule are also terminal. Pollination takes place under the water.
Order 5. Alismaceæ. The regular, hypogynous flowers are in some species unisexual by the suppression of either andrœcium or gynœceum; they have a 6-merous perianth, generally differentiated into 3 sepals and 3 petals; generally 6 stamens in the outer whorl (by the division of the 3; Fig. 282) and often several 3-merous whorls inside these, and 6–∞ free carpels arranged cyclically or spirally. Fruit a syncarp.—Marsh- or water-plants with radical leaves and long-stalked inflorescences.
A. Butomeæ. Follicles with many seeds, which are borne on nearly the whole of the inner surface of the cyclic carpels (as in Nymphæaceæ). Embryo straight.—Butomus (Flowering Rush, Fig. 282), has an umbel (generally composed of 3 helicoid cymes). S 3, P 3, stamens 9 (6 + 3, i.e. the outer whorl doubled), G 3 + 3. B. umbellatus; creeping rhizome with triangular Iris-like leaves.—Hydrocleis. Limnocharis.
Fig. 282.—Diagram of Butomus: f bracteole.
B. Alismeæ. Fruit achenes. Latex common (in the intercellular spaces). The flowers are arranged most frequently in single or compound whorls. Embryo curved, horse-shoe shaped.—Alisma has S 3, P 3, A 6 (in 1 whorl, grouped in pairs, i.e. doubled in front of the sepals), and 1 whorl of 1-seeded achenes on a flat receptacle. The leaves are most frequently radicle, long-stalked; the lamina have curved longitudinal veins, and a richly branched venation. A. plantago.—Elisma (E. natans) has epitropous (turned inwards) ovules, whilst the ovules of Alisma, Sagittaria and others are apotropous (turned outwards).—Echinodorus (E. ranunculoides) has a convex receptacle, carpels many, united and capitate. Damasonium.—Sagittaria (Arrow-head) has monœcious flowers, several whorls of stamens and spirally-arranged achenes on a very convex receptacle. S. sagittifolia reproduces by tuberous buds formed at the end of long, submerged branches. The leaves, in deep and rapidly running water, are long and strap-shaped, but in the air arrow-shaped.
Honey is secreted in the flower and pollination effected by insects. Alisma plantago has 12 nectaries. The submerged flowers of Elisma natans remain closed and are self-pollinated. Butomus has protandrous flowers. There are about 50 species, which mostly grow outside the Tropics.—Uses insignificant. The rhizome of some is farinaceous.
Order 6. Hydrocharitaceæ. This order differs chiefly from the preceding in its epigynous flowers. These are in general unisexual (diœcious), and surrounded by a 2-leaved or bipartite spathe; they are 3-merous in all whorls, but the number of whorls is generally greater than 5, sometimes even indefinite. The perianth is divided into calyx and corolla. The ovary is unilocular with parietal placentation, or more or less incompletely plurilocular. The fruit is berry-like, but usually ruptures irregularly when ripe. Embryo straight.—Most often submerged water-plants, leaves seldom floating on the surface. Axillary scales (squamulæ intravaginales).
Hydrocharis. Floating water-plants with round cordate leaves; S3, P3 (folded in the bud); ♂-flowers: 3 (-more) flowers inside each spathe; stamens 9–15, the most internal sterile. ♀-flowers solitary; three staminodes; ovary 6-locular, with many ovules attached to the septa; styles 6, short, bifid. [The petals of the ♀-flowers bear nectaries at the base. In this and the following genus the pollination is without doubt effected by insects.] H. morsus ranæ (Frog-bit) has runners; it hibernates by means of special winter-buds.—Stratiotes; floating plants with a rosette of linear, thick, stiff leaves with spiny margin, springing from a short stem, from which numerous roots descend into the mud. Inflorescence, perianth, and ovary nearly the same as in Hydrocharis, but the ♂-flower has 12 stamens in 3 whorls, of which the outer 6 are in 1 whorl (dédoublement), and inside the perianth in both flowers there are numerous (15–30) nectaries (staminodes?). S. aloides (Water-soldier); in N. Eur. only ♀-plants.—Vallisneria spiralis is a tropical or sub-tropical plant, growing gregariously on the mud in fresh water. The leaves are grass-like, and the plants diœcious; the ♂-flowers are detached from the plant, and rise to the surface of the water, where they pollinate the ♀-flowers. These are borne on long, spirally-twisted peduncles which contract after pollination, so that the ♀-flower is again drawn under the water, and the fruits ripen deeply submerged.—Elodea canadensis is also an entirely submerged plant. The leaves are arranged in whorls on a well-developed stem. Only ♀-plants in Europe (introduced about 1836 from N. Am). This plant spreads with great rapidity throughout the country, the reproduction being entirely vegetative. Hydrilla, Halophila, Thalassia, Enhalus.—In many of these genera the number of whorls in the flower is remarkably reduced; for example, in Vallisneria, in the ♂-flowers to 2: Pr 3, A (1-) 3, in the ♀ to 3: Pr 3, Staminodes 3, G 3.—About 40 species; Temp. and Trop.
Family 2. Glumifloræ.
The hypogynous flowers in the Juncaceæ are completely developed on the pentacyclic, trimerous type, with dry, scarious perianth. Even in these the interior whorl of stamens becomes suppressed, and the ovary, which in Juncus is trilocular with many ovules, becomes in Luzula almost unilocular, but still with 3 ovules. The perianth in the Cyperaceæ and Gramineæ is reduced from hairs, in the first of these, to nothing, the flowers at the same time collecting more closely on the inflorescence (spike) supported by dry bracts (chaff); the number of stamens is almost constantly 3; stigmas linear; the ovary has only 1 loculus with 1 ovule, and the fruit, which is a capsule in the Juncaceæ, becomes a nut or caryopsis.—The endosperm is large and floury, the embryo being placed at its lower extremity (Figs. 286 B, 291).—The plants belonging to this order, with the exception of a few tropical species, are annual or perennial herbs. The stems above ground are thin, and for the most part have long internodes, with linear, parallel-veined leaves which have long sheaths, and often a ligule, i.e. a membranous projection, arising transversely from the leaf at the junction of the sheath and blade. The underground stems are short or creeping rhizomes. The flowers are small and insignificant. Wind- or self-pollination.
Order 1. Juncaceæ (Rushes). The regular, hermaphrodite, hypogynous flowers have 3 + 3 brown, dry, free perianth-leaves projecting like a star during the opening of the flower; stamens 3 + 3 (seldom 3 + 0) and 3 carpels united into one gynœceum (Fig. 283); the ovary is 3- or 1-locular; there is as a rule 1 style, which becomes divided at the summit into 3 stigmas, often bearing branches twisted to the right (Fig. 283). Fruit a capsule with loculicidal dehiscence. The embryo is an extremely small, ellipsoidal, cellular mass, without differentiation into the external organs.
Fig. 283.—Flower of Luzula.
Juncus (Rush) has glabrous foliage-leaves, generally cylindrical, rarely flat; the edges of the leaf-sheath are free (“open” leaf-sheaths) and cover one another. The capsule, 1- or 3-locular, with many seeds—Luzula (Wood-Rush) has flat, grass-like leaves with ciliated edges; the edges of the leaf-sheath are united (“closed” leaf-sheath). The capsule unilocular and 3-seeded.—Prionium: S. Africa; resembling a Tacona.
The interior whorl of stamens, in some species, disappears partially or entirely (J. supinus, capitatus, conglomerates, etc.)
Some of the numerous Juncus-species (e.g. J. effusus, glaucus, conglomeratus, etc.), have false, lateral inflorescences, the axis of the inflorescence being pushed to one side by its subtending leaf, which apparently forms a direct continuation of the stem, and resembles it both in external and internal structure. The foliage-leaves of this genus were formerly described as “unfertile stems,” because they are cylindrical, erect, and resemble stems, and consequently the stem was said to be “leafless”: J. effusus, glaucus, conglomeratus. Stellate parenchynatous cells are found in the pith of these stems and in the leaves. Other species have distinct terminal inflorescences and grooved leaves; J. bufonius (Toad-rush), compressus, and others. The inflorescences most often present the peculiarity of having the lateral axes protruding above the main axis. Their composition is as follows:—The flowers have either no bracteoles, and the inflorescences are then capitulate; or they have 1–several bracteoles. Each branch has then, first, a 2-keeled fore-leaf placed posteriorly (“basal-leaf”), and succeeding this are generally several leaves borne alternately and in the same plane as the basal-leaf, the two uppermost (the “spathe-leaves”) being always barren; those which lie between the basal-leaves and the spathe-leaves are termed “intermediate-leaves.” If only branches occur in the axils of the basal-leaves, then the succeeding branches are always borne on the posterior side of the axis, and form a fan[27]; if the basal-leaf is barren, and if there is only one fertile intermediate-leaf, then the lateral axes are always on the upper side, and a sickle[27]-like inflorescence occurs; if there are 2 fertile intermediate-leaves, then a dichasium is formed, and in the case of there being several, then a raceme, or spike.
Juncaceæ are, by several authors, classed among the Liliifloræ, but there are so many morphological and partly anatomical features agreeing with the two following orders, that they may, no doubt, most properly be regarded as the starting point of these, especially of the Cyperaceæ, which they resemble in the type of flowers, the inflorescence, the type of mechanical system, and the stomata.
Pollination by means of the wind. Cross-pollination is often established by protogyny. J. bufonius has partly triandrous and cleistogamic, partly hexandrous, open flowers.—Distribution. The 200 species are spread over the entire globe, but especially in cold and temperate countries; they are seldom found in the Tropics.—Uses. Very slight; plaiting, for instance.
Order 2. Cyperaceæ. The majority are perennial (seldom annual) herbs living in damp situations, with a sympodial rhizome and grass-like appearance. The stems are seldom hollow, or have swollen nodes, but generally triangular, with the upper internode just below the inflorescence generally very long. The leaves are often arranged in 3 rows, the leaf-sheath is closed (very seldom split), and the ligule is absent or insignificant. The flowers are arranged in spikes (spikelets) which may be united into other forms of inflorescences (chiefly spikes or racemes). The flowers are supported by a bract, but have no bracteoles. In some genera the perianth is distinctly represented by six bristles corresponding to six leaves (Figs. 284 A, 286 A); in others it is represented by an indefinite number of hairs (Fig. 284 B), and very frequently it is altogether wanting. The inner whorl of stamens is absent, and the flower has therefore 3 stamens (rarely more or less than 3), the anthers are attached by their bases to the filament (innate) and are not bifid (Figs. 286). Gynœceum simple, formed of 3 or 2 carpels; 1 style, which is divided at the extremity, as in the Juncaceæ, into 3 or 2 arms; the single loculus of the ovary contains one basal, erect, anatropous ovule; the stigmas are not feather-like. Fruit a nut, whose seed is generally not united with the pericarp. The embryo is small, and lies at the base of the seed in the central line, surrounded on the inner side by the endosperm (Fig. 286 B). On germination the cotyledon does not remain in the seed.
Fig. 284.—Diagram of structure of: A Scirpus silvaticus; B Eriophorum angustifolium.
A regular perianth, with 6 scale-like perianth-leaves in 2 whorls, is found in Oreobolus. In Scirpus littoralis the perianth-leaves are spreading at the apex, and divided pinnately.
The branching of the inflorescence is often the same as in the Juncaceæ, and supports the theory that these two orders are related. In Rhynchospora and others, the “spikelets” are really only “spike-like” and to some extent compound.
A. Scirpeæ. Hermaphrodite Flowers.
1. Spikelets cylindrical, the bracts arranged spirally (in many rows). The lower ones are often barren, each of the others supports a flower.—Scirpus (Club-rush). The spikelets are many-flowered; the perianth is bristle-like or absent, and does not continue to grow during the ripening of the fruit (Fig. 286 A). Closely allied to this is Heleocharis, with terminal spikes.—Eriophorum (Cotton-grass) differs chiefly in having the perianth-hairs prolonged, and forming a bunch of white, woolly hairs (Fig. 284 B).
Cladium and Rhynchospora (Beak-rush) differs especially in the few-flowered, compound spikelets which are collected into small bunches; the latter has received its name from the fact that the lowermost portion of the style remains attached to the fruit as a beak.
2. Spikelets compressed, the bracts arranged only in two rows; the other characters as in the first-mentioned. Cyperus (spikelets many-flowered); Schœnus (Bog-rush); spikelets few-flowered; S. nigricans has an open sheath.
Fig. 285.—Carex: A diagram of a male flower; B of a female flower with 3 stigmas; C of a female flower with 2 stigmas; D diagrammatic figure of a female flower; E similar one of the androgynous (false) spikelet of Elyna. The ♂ is here represented placed laterally; it is terminal, according to Pax.
Fig. 286.—A Flower of Scirpus lacustris. B Seed of Carex in longitudinal section.
B. Cariceæ. Unisexual Flowers.
In the ♂-flowers there is no trace of a carpel, and in the ♀ no trace of a stamen. Floral-leaves in many rows. In some (Scleria, certain Carex-species), ♂-and ♀-flowers are borne in the same spikelet, the latter at the base or the reverse; in the majority each spikelet is unisexual.
Carex (Fig. 285) has naked, most frequently monœcious flowers. The ♂-spikes, which are generally placed at the summit of the whole compound inflorescence, are not compound; in the axil of each floral-leaf (bract) a flower is borne, consisting only of a short axis with three stamens (Fig. 285 A). The ♀-spikes are compound; in the axil of each floral-leaf is borne a very small branch (Fig. 285 D, a) which bears only one leaf, namely, a 2-keeled fore-leaf (utriculus, utr. in the figures) which is turned posteriorly (as the fore-leaves of the other Monocotyledons), and being obliquely sheath-like, envelopes the branch (in the same manner as the sheath of the vegetative leaves), and forms a pitcher-like body. In the axil of this leaf the ♀-flower is situated as a branch of the 3rd order, bearing only the 2–3 carpels, which are united into one gynœceum. The style protrudes through the mouth of the utriculus. The axis of the 2nd order (a in Fig. 285 D) may sometimes elongate as a bristle-like projection (normally in Uncinia, in which it ends as a hook, hence the name); this projection is in most cases barren, but it sometimes bears 1–several bracts which support male-flowers; this is normal in Elyna (or Kobresia) and Schœnoxiphium; the axis (a in 285 E) bears at its base a female-flower supported by the utriculus, and above it a male-flower supported by its bract.
Pollination by means of the wind. Protogynous. Sometimes self-pollinated. The order embraces nearly 3,000 species, found all over the world. Carex and Scirpus are most numerous in cold and temperate climates, and become less numerous towards the equator. The reverse is the case with Cyperus and other tropical genera. They generally confine themselves to sour, swampy districts; some, on the other hand, are characteristic of sand-dunes, such as Sand-star (Carex arenaria). There are about 70 native species of Carex.
Uses. In spite of their large number, the Cyperaceæ are of no importance as fodder-grasses, as they are dry and contain a large amount of silica; hence the edges of many of the triangular stems or leaves are exceedingly sharp and cutting. Cyperus esculentus has tuberous rhizomes, which contain a large amount of fatty oil and are edible (earth-almonds); it has its home in the countries of the Mediterranean, where it is cultivated.
Cyperus papyrus (W. Asia, Egypt, Sicily) attains a height of several metres, and has stems of the thickness of an arm which were used by the ancient Egyptians for making paper (papyrus). Some serve for plaiting, mats, etc. (Scirpus lacustris, etc.). Isolepis is an ornamental plant.
Fig. 287.—Triticum: A axis (rachis) of ear showing the notches where the spikelets were inserted; B an entire spikelet; C a flower with the pales; D a flower without the pales, showing the lodicules at the base; E glume; F outer pale; G inner pale; H fruit; I longitudinal section of fruit.
Order 3. Gramineæ (Grasses). The stems are cylindrical, generally hollow with swollen nodes, that is, a swelling is found at the base of each leaf which apparently belongs to the stem, but in reality it is the swollen base of the leaf. The leaves are exactly alternate; the sheath is split (excep. Bromus-species, Poa pratensis, P. trivialis, Melica, Dactylis, etc., in which the sheath is not split), and the edges overlap alternately, the right over the left, and vice versâ; the ligule is nearly always well developed. In general, the flowers are hermaphrodite; they are borne in spikelets with alternate floral-leaves, and the spikelets themselves are borne in either spikes or panicles. The two (seldom more) lowest floral-leaves in each spikelet (Fig. 289 øY, nY) are barren (as the covering-leaves in many umbels and capitula); these are termed the glumes. The succeeding floral-leaves, each of which supports one flower as its bract, are called the outer pales (nI); these sometimes each bear an “awn” (a bristle-like body which projects in the median line either from the apex or the back); sometimes the upper ones are barren. Each flower has a bracteole, which is placed on the inside opposite the main axis; it is thin, binerved or two-keeled, and never has an awn; it is known as the inner pale (øI). Immediately succeeding the bracteole are: (a) some small, delicate scales (lodicules, Figs. 287 D, 288 C, 290 L); (b) three stamens with anthers versatile, so as to be easily moved, and usually notched at each end (Fig. 287 C); and (c) a simple gynœceum formed of one carpel with two styles having generally spirally-branched stigmas (Figs. 287 D, 288 C). The ovary is unilocular, and contains one ascending or pendulous, anatropous ovule. Fruit a nut, whose seed is always firmly united with the thin pericarp (“caryopsis”). The embryo is larger than in the Cyperaceæ and is placed at the base of the seed, but on the outer convex surface of the pericarp (Figs. 287 I, 288 288 D, 291), outside the endosperm; plumule large with several leaf-primordia. On germination the cotyledon remains in the seed.
The majority of Grasses are annual or perennial herbs; tree-like forms being only found in the Tropics, for example, the Bamboos; they branch (in tufts), especially from the axils of the basal-leaves, while those which are borne higher on the stem are separated by longer internodes and have no vegetative branches in their axils, though a few forms, like Bambusa and Calamagrostis lanceolata, produce branches in these axils.