Cassia (Figs. 508–510) is the largest genus (about 200 species); it has an almost hypogynous, zygomorphic flower with 5 free sepals and petals; of the 10 stamens the 3 posterior are generally barren, the others are of very unequal length and open at the apex by pores (Fig. 509). In some (the Senna group) the fruit is a flat, short, thin, dehiscing pod; in others (Cathartocarpus) it is round, long, woody or fleshy, indehiscent, and divided internally by more or less fleshy transverse walls into as many cells as there are seeds.—The following also have DEHISCENT FRUITS: Bauhinia (often lianes, tropical climbers with tendrils [stem-structures] and anomalous stems), Copaifera, Hæmatoxylon (whose pod does not dehisce along the suture, but laterally), Cercis (simple leaves; the corolla resembles that of the Papilionaceæ, but the posterior petal is the smallest, and is enveloped by the 2 lateral ones, which are enveloped in their turn by the 2 anterior).—Fruit Indehiscent: Tamarindus indica; the pod is almost round, often a little abstricted between the seeds; the wall is formed by a thin, brittle external layer, enclosing an acid pulp; well-developed septa are present, between the seeds; the most internal layer is parchment-like. Calyx 4-merous by the coalescence of 2 sepals. Only 3 fertile stamens.—Ceratonia siliqua (Carob-bean, Locusts); the pod is long, compressed, with thick sutures, and has a wall, the central part of which is more or less leathery, fleshy and sweet; there are transverse septa between the seeds, as in the Tamarind. Embryo greenish in endosperm. The flower is without a corolla, 5 stamens.—Pterogyne (winged fruit), etc.—Kramerieæ with Krameria is an anomalous group.

Order 2. Papilionaceæ. The flower (Figs. 511, 512) is strongly zygomorphic and somewhat perigynous (Fig. 512 B; most frequently more on one side than the other). The calyx is gamosepalous and persistent. The polypetalous corolla has descending imbricate æstivation, the posterior, large leaf, the standard (Figs. 511 f; 512 B’, e), covering in the bud the two lateral ones, the wings (Figs. 511 v; 512 B’, a), which again cover the two anterior; these are united in the form of a boat, the keel (k and c); the wings and the two petals of the keel are very unsymmetrical. That the keel is formed of two petals is seen by its position (in front of one sepal) and by the two often more or less free claws. The 10 (5 + 5) stamens (monadelphous) are either all united into one bundle, or into two bundles (diadelphous), the posterior one being free (Fig. 512 C). The ovules are curved and also the embryo (Fig. 512 G), especially the hypocotyl, so that the radicle assumes a position close to the edge of the thick, fleshy cotyledons. Endosperm wanting; the cotyledons are very rich in proteid reserve material. The forms of the fruit and exceptions are described under the genera.

3. Astragaleæ. Herbs or shrubs, less frequently trees, with imparipinnate leaves (without tendrils). The flowers are generally borne in racemes or spikes. Stamens monadelphous or diadelphous.—Astragalus (Milk-Vetch) has the legume incompletely divided longitudinally into 2 loculi by a septum formed by the incurved dorsal suture. Diadelphous.—Glycyrrhiza (Liquorice); Colutea (Bladder-Senna) from S. Europe; Robinia (the false Acacia) with thorny stipules; Indigofera (the Indigo plant); Amorpha (which has only one petal, namely the standard, and the fruit a nut), Caragana, Wistaria (a climbing shrub), Galega. Carmichælia australis, when old, produces flat branches with scale-like leaves.

4. Vicieæ. Climbing herbs with paripinnate leaves, the midrib ending in a point or frequently in a tendril, which generally is branched, representing lateral veins without mesophyll; stamens diadelphous; the cotyledons remain underground on germination.—Vicia (Vetch) has a filamentous style, hairy towards the tip, and a pod with many seeds; climbing by means of tendrils; the leaves have many leaflets.—Faba (F. vulgaris, Horse-bean) is erect, without tendrils; its pod is thick with spongy septa between the seeds.—Ervum (Lentil) has a pod with only 1–2 seeds, and sweeping hairs (stylar-brush) on the inner side of the style.—Pisum (Pea; Fig. 512) has very large stipules, the bent style has a hollow groove on the anterior side. P. sativum (Common Pea), P. arvense (Grey Pea).—Lathyrus (Sweet Pea) generally has an angular, winged stem and most frequently only a few pairs of leaflets. The style is flattened, with sweeping hairs on the back. In L. aphaca the stipules alone are developed into foliage-leaves, while the remainder of the leaf is modified into a tendril.—Cicer has a nearly straight embryo and imparipinnate leaves with dentate or incised leaflets. C. arietinus (Chick-pea).—Abrus (precatorius, etc.); the seeds (“Crab’s eyes,” “Paternoster peas,” “Jequirity”) are scarlet with a black spot round the hilum.

5. Phaseoleæ. Herbs, twining or erect, but not climbing by tendrils; the leaves are imparipinnate, generally ternate, and bear small, linear bodies resembling stipules at the base of the stalks of the leaflets. The inflorescences are most frequently compound, groups of few flowers being situated on short, nodose, lateral axes borne on a longer stem. On germination the cotyledons are raised a considerable distance above the ground, and become greenish, but do not become leaf-like; in P. multiflorus they remain underground. Stamens as in the Vetches.—Phaseolus (Kidney-bean): the keel with the stamen and style is spirally twisted (to the right). Herbs, twining to the left.—The “Calabar-bean” (Physostigma venenosum), Erythrina, Clitoria, Glycine, Soja, Mucuna, Apios, Canavalia, Vigna, Dolichos, Cajanus, Rhynchosia, etc.

6. Trifolieæ (Clovers). Herbs with ternate leaves, the leaflets are often dentate with the veins prolonged into the teeth; stamens diadelphous; fruit 1-locular, 1–few-seeded, pyxidium-like, irregularly dehiscent, or more frequently a nut. The flowers are generally borne in capitula, racemes, or spikes.—Trifolium (Clover). The corolla is gamopetalous. The calyx persists, together with the corolla, round the ripe fruit. The inflorescence is a spike, capitulum or capitate umbel; the leaves are ternate, and have adnate stipules.—Medicago (Medick). The corolla falls off after flowering; fruit curved like a sickle or spirally twisted; it is a nut, and opens with difficulty. Leaves ternate.—Melilotus (Melilot) has a small, spherical or lanceolate, thick and wrinkled fruit, which as a rule is indehiscent. The inflorescence is a raceme, often long, or a spike, sometimes a capitulum. Leaves ternate.—Ononis (Rest-harrow) differs in having monadelphous stamens and in being more shrub-like and bushy, and in having a normal, 2-valved pod, by which characteristic it approaches the Genisteæ. The flowers are generally rose-coloured, solitary, or in few-flowered racemes in the leaf-axils. Thorns (branches) are often present; the leaves are compound with only one small leaflet (the terminal one), or ternate with adnate stipules.

7. Loteæ. Herbs with ternate or imparipinnate leaves, with entire leaflets. In the latter case, when the lowest pair of leaflets is placed quite close to the sheath, the stalk is wanting, and apparently a trifoliate leaf with large stipules is developed. Flowers in an umbel or capitulum. Stamens monadelphous or diadelphous, the filaments (either all of them, or only the 5 sepal-stamens) are widened at the top.—Lotus (Bird’s-foot-trefoil) has a long, round pod.—Tetragonolobus.—Anthyllis (Lady’s-finger); the fruit is a nut, which is distributed by the wind by means of the membranous, bladder-like calyx, which completely encloses and falls off with it.

8. Genisteæ. The majority are shrubs or trees with apparently simple leaves, i.e. compound leaves with only one leaflet (the terminal leaflet), or ternate leaves; the stipules in most instances are very small or are entirely wanting; stamens monadelphous.—Genista (Dyer’s-weed) has apparently simple leaves; the branches often terminate in a thorn. The strongly-winged stems in G. sagittalis are its most important organs of assimilation. Bossiæa rufa has flat branches, its leaves being reduced to small, pointed stipules.—Sarothamnus (Broom) has switch-like, angular branches and often both the apparently simple and ternate leaves on the same shoot; style spirally rolled.—Cytisus (Laburnum). Ulex (Furze; in U. europæus, the seedlings bear a few foliage leaves, but the leaves succeeding these are modified into thorns); Spartium; Crotalaria, etc.—Lupinus (Lupin) is allied to this group; it has a thick, often somewhat fleshy pod, and digitate leaves with adnate stipules.—Retama.

9. Hedysareæ are especially recognised by having the ovary divided by transverse septa into as many cells as there are seeds, the fruit thus becomes a lomentum, dehiscing transversely into nut-like joints (Fig. 513).—Ornithopus (Bird’s-foot); Coronilla; Hippocrepis; Onobrychis (Sainfoin) has a fruit with only 1 joint (i.e. a 1-seeded nut); Desmodium; Alhagi; Hedysarum, etc.—Arachis hypogæa (Earth-nut) has a pod which is abstricted between the seeds, and is indehiscent, but is not multilocular nor a true lomentum; it is reticulately wrinkled externally, and ripens underground; the basal part of the ovary is prolonged after flowering, attaining a length of several inches, and buries the young fruit in the soil. The embryo is straight.—Desmodium gyrans is well-known for its motile leaflets.

Order 3. Mimosaceæ. The flowers are most frequently hypogynous and regular, the æstivation of the corolla is valvate and, in the majority of instances, that of the calyx also. The flower is 4-merous, less frequently 5- or 3-merous.—The flowers are generally small, but are always borne in compact, round capitula or spikes (Fig. 514); they are hypogynous or perigynous. The calyx is generally gamosepalous and the corolla gamopetalous, the latter being frequently wanting. The stamens are equal or double the number of the petals (Mimosa, etc., in M. pudica, e.g. S4, P4, A4, G1) or (in Acacia, Inga, etc.) in a large, indefinite number, free or monadelphous, often united to the corolla (Fig. 514 b). The colour of the flower in most cases is due to the long and numerous stamens. The fruit is various. The embryo is straight as in the Cæsalpiniaceæ. Entada and many species of Mimosa have a flat, straight, or somewhat sickle-like pod, which resembles the siliqua of the Cruciferæ in that the sutures (in this instance, however, dorsal and ventral suture) persist as a frame, but the intermediate portion divides, as in the transversely divided siliqua, into as many nut-like portions as there are seeds. Some species have a pod of enormous dimensions. The seeds of Entada gigalobium are often carried from the West Indies to the N. W. coasts of Europe by the Gulf Stream.—The fruit of Acacia in some species is an ordinary pod, in others it is transversely divided, or remains an undivided fruit, a nut.—This order includes both trees and herbaceous plants, which are often thorny; the leaves are usually bipinnate (Fig. 514) and are sensitive, and also possess sleep-movements.—Many Australian Acacias have compound leaves only when young, but when old have phyllodia, i.e. leaf-like petioles without blades, placed vertically. A large number have thorny stipules, which in some (Acacia sphærocephala) attain an enormous size, and serve as a home for ants, which in return protect their host-plant against the attacks of other, leaf-cutting ants.

Other genera besides those mentioned are: Adenanthera, Desmanthus, Parkia, Inga (with rather fleshy, indehiscent fruit), Calliandra, etc.

Family 22. Passiflorinæ.

The flowers are most frequently regular, 5-merous in the three most external whorls, eucyclic and perigynous or epigynous, less frequently hypogynous. A characteristic feature is that the ovary is tricarpellary, unilocular, and with 3 parietal placentæ which sometimes meet in the central line (Cucurbitaceæ). The styles are generally free and bifid. To all these characteristics, however, there are exceptions. The Cucurbitaceæ are sometimes placed among the Sympetalæ, close to the Campanulinæ, but they are not allied to the Sympetalæ, from which they differ especially, for instance, in the structure of the ovule. The position of the Begoniaceæ in this family is also open to doubt.

Order 1. Passifloraceæ (Passion-flowers). The majority are herbs which climb by means of tendrils (modified branches) and have scattered, stipulate leaves, often palminerved and lobed (Fig. 515). The flowers, which are often large and beautiful, are regular, ☿, with S5, P5, A5, G3; the calyx and corolla are perigynous, and immediately inside the corolla is the “corona,” consisting of numerous, tapering, filamentous bodies, or sometimes united in rings, most frequently petaloid and coloured; the stamens are raised on a long, round internode above the cup-like receptacle; immediately above these is the gynœceum with its 3 free styles and capitate stigmas; the ovary is unilocular with 3 parietal placentæ. Fruit most frequently a berry. The seeds have an aril.

Order 2. Papayaceæ. The best known representative is the Papaw (Carica papaya), a Tropical American tree whose stem is usually unbranched, and bears at its summit several large, palmilobed leaves on long stalks. The stem and leaves have latex. The large, Melon-like berries are edible, and for this reason it is cultivated in the Tropics. Flowers unisexual, with slightly different structure in the ♂-and ♀-flowers, besides intermediate forms. The ♂-flower has a gamopetalous, the ♀-flower a polypetalous corolla.—The milky juice contains a substance with similar action to pepsine. 10 stamens. 5 carpels.

Order 5. Loasaceæ. Herbaceous plants seldom shrubs, sometimes climbing, and nearly always studded with stiff hairs, in some instances stinging or hooked. The leaves are most frequently palmilobed and without stipules. The flowers are regular, ☿, polypetalous, entirely epigynous, with 4–5 sepals, petals and stamens, or more frequently (by splitting) many stamens, those which are placed before the sepals being generally barren and more or less petaloid; carpels most frequently 3, united into an inferior, unilocular ovary with 3 parietal placentæ, above which the receptacle is generally more or less prolonged. Fruit a capsule; in Gronovia an ovary with 1 ovule and fruit a nut.

Order 6. Datiscaceæ. 4 species, especially in the Tropics.—Datisca cannabina (Asia Minor) resembles the Hemp in external appearance. The flowers are diœcious, insignificant; ♂-flowers: a low, gamosepalous calyx, no corolla, and an indefinite number of stamens; ♀-flowers; epigynous; ovary unilocular with free, mostly bifid, styles, and generally 3 parietal placentæ. In most cases the ovary is not entirely closed at the top (as in Reseda).

Order 7. Begoniaceæ. This order principally comprises herbs or under-shrubs with succulent stems (having scattered vascular bundles in the pith); the leaves are arranged in two rows (a divergence of 1/2) and are asymmetrical, as a rule more or less obliquely cordate, or ovate with cordate base (Fig. 516); large, caducous stipules are present. Inflorescences dichasial, or unipared scorpioid cymes; the flowers are unisexual; the first ones (the oldest) are ♂-flowers, while ♀-flowers are found especially on the younger axes. The ♂-flowers have most frequently 2 + 2 coloured perianth-leaves, and many stamens collected into a head in the centre of the flower; the ♀-flowers are epigynous with 5 coloured perianth-leaves (placed spirally with a divergence of 2/5) and a trilocular ovary, bearing 3 bifid styles and 3 wings (the wings usually of unequal size); in the inner angle of each loculus there is one large projecting placenta, or two plate-like placentæ (the bent back edges of the carpels) studded with ovules. Fruit a capsule, with many extremely small seeds.—Begonia.

Order 8. Cucurbitaceæ. The flower is epigynous, and, as a rule, is also provided with a leaf-like, cup- or bell-shaped receptacle above the ovary, to which the perianth and stamens are attached; the flowers are regular, unisexual, with rudiments of the other sex, and 5-merous: sepals 5, narrow and pointed, with the median sepal posterior (Fig. 517), petals 5, stamens 5, and carpels 3 (rarely 4–5); the corolla is gamopetalous in the majority, polypetalous in some; generally plicate-valvate in the bud. The anthers in the ♂-flowers are extrorse, and monothecious, i.e. only one half of each of the anthers of the 5 stamens is developed, the pollen-sac having frequently a peculiar [**rtilde]-shaped curve (Fig. 518 A, B); the stamens are either all united into a column (e.g. in Cucurbita), or they are united in pairs, so that only one remains free (Figs. 517 A; 518 A); in the latter case there appears to be one small stamen with a ~-shaped, curved pollen-sac and two larger ones, each with two curved pollen-sacs placed as in Fig. 517 A. The original form appears to be Fevillea with free petals and 5 free stamens. Sometimes the rudiment of a gynœceum is present. The carpels are united into an ovary with 3 (4–5) placentæ formed by their united edges. These are thick, fleshy, and bifid, bearing a number of ovules on each side (Figs. 517 B; 518 C, D); in general the placentæ are so large that they not only meet in the centre, but also fill up the ovary as far as the wall of the pericarp. The whole interior of the fruit thus becomes a juicy mass in which three lines may be seen, meeting in the centre (the boundaries of the individual placentæ), and near the circumference 6 groups of seeds (Fig. 518 D). When the carpels are equal in number to the petals they alternate with them. The style is short and thick, and generally divided into 3 (4–5) branches, with a horse-shoe shaped stigma on each branch (Fig. 518 C). The fruit is most frequently a many-seeded berry; in some it attains a considerable size and has a firm external layer (Cucurbita, Lagenaria, etc.). The embryo is straight, has no endosperm, but contains a large quantity of oil. The exceptions to the above characters will be found under the genera.

Exclusively herbs, generally with stiff hairs and yellow flowers. Many species are annuals, others are perennial, having tuberous roots or hypocotyls. The leaves are scattered, long-stalked, in most cases more or less heart-shaped, palminerved, palmilobed, and exstipulate; in their axils are found both flowers (singly, or in an inflorescence) and a vegetative bud, and outside the axil, on the anodic[37] side of the leaf, a simple or branched tendril, by which the plant climbs (exceptions: e.g. Ecballium).

Cucurbita (Pumpkin, Marrow) has branched tendrils; the flowers are monœcious, and are borne singly; the corolla is bell-shaped, and divided almost as far as the middle. The stamens are all united into a tube; the compressed seeds have a thick, blunt edge.—Cucumis has (generally) unbranched tendrils; the ♀-flowers are borne singly, whilst the ♂-flowers are borne in groups: the corolla is divided nearly as far as the base, and the stamens are united 2-2-1. The connective is elongated above the anthers. The seeds have a sharp edge.—Citrullus (Fig. 518) has a corolla similar to Cucumis, but ☿-and ♂-flowers are borne singly; the stigma is only 3-lobed, the fruit most frequently spherical.—Ecballium (Squirting Cucumber, only 1 species, E. elaterium) has no tendrils, and is therefore not a climber. The oblong fruit is pendulous from the apex of its stalk, and when ripe is distended with an acrid, watery fluid; on being touched the fruit is detached, and the seeds, together with the watery fluid, are violently ejected through the aperture formed at the base of the fruit. The ♂-flowers are borne in racemes near the solitary ♀-flowers (Fig. 517).—Bryonia (White Bryony) has chiefly unbranched tendrils and small, greenish-yellow, usually diœcious flowers with rotate corolla, in many-flowered inflorescences; the small, spherical berry has no specially firm outer layer, and generally only few seeds. The tap-root and a few of the other roots are tuberous. B. alba (berry black; monœcious) and dioica (berry red; diœcious). Among other genera may be mentioned: Lagenaria (Gourd); the fruit has a woody external layer which, after the removal of the pulpy integument, may be used as a gourd. Luffa has a polypetalous corolla; the fruit is dry, and consists internally of a network of vascular bundles; it opens by an aperture at the summit. Benincasa; the fruit has a close, bluish coating of wax. Trichosanthes (Snake Cucumber) has a thin, round, long and curved fruit. Momordica; the fleshy fruit opens and ejects the seeds. Cyclanthera takes its name from the staminal column which is found in the centre of the ♂-flower, bearing a bilocular, ring-like anther which opens by a horizontal cleft. The fruit is unilocular by suppression, has 1 placenta, and when touched opens and ejects the seeds. Sicyos and Sechium have only unilocular ovaries with one pendulous ovule. Sechium has, moreover, 5 free stamens, of which only one is halved, the other 4 having both halves of the anther. Fevillea and Thladiantha also have 5 free stamens. Dimorphochlamys has dimorphic flowers.

Family 23. Myrtifloræ.

The leaves are most frequently opposite, simple, entire (rarely dentate), and exstipulate. The flowers are regular and epigynous (perigynous in Lythraceæ and a few others), ☿, polypetalous; the number of members in a whorl is generally 4 or 5 (S, P, A, or most frequently A 2, G), but sometimes it becomes (e.g. Myrtles and Lythraceæ) very large in the andrœcium by splitting, and in the gynœceum also is often different. (When suppression takes place it is principally in the corolla and petal-stamens.) In nearly all instances the calyx is valvate. Gyncœceum multicarpellary, multilocular, with only one style (except Haloragidaceæ). In the majority the ovules are situated on an axile placenta in the multilocular ovary. Endosperm is wanting in the majority.—Less important exceptions: Rhizophoraceæ and Gunnera have stipules. Haloragidaceæ have several styles and endosperm. Rhizophora also has endosperm.

Order 1. Lythraceæ. Hermaphrodite, perigynous flowers which are most frequently 6-merous, viz. S 6 (often with a commissural “epicalyx,” Fig. 519 c), one segment posterior, P 6, A 6 + 6 or 6 + 0 and G 2–6, forming a 2–6-locular ovary with many ovules in the loculi, style single, and capitate stigma. The gynœceum is free at the base of the tubular, or bell-shaped, thin, strongly veined receptacle, which bears the other leaf-whorls on its edge and inner side. Fruit a capsule. No endosperm.—To this order belong both herbs, shrubs and trees. The branches are frequently square, the leaves always undivided, entire, and without stipules, or with several very small stipules, and often opposite. The calyx is valvate. The flower is regular (except Cuphea) and frequently large and beautiful. The stamens are generally incurved in the bud, and the petals irregularly folded.

Lythrum (Loose-strife). The flower is diplostemonous and 6-merous, with a long, tubular receptacle with epicalyx-teeth (Fig. 519 c). The 12 stamens are arranged in two tiers on the inner side of the receptacle. The gynœceum is bicarpellary. The flowers are borne in small dichasia in the leaf-axils, and their number is increased by accessory inflorescences beneath the main inflorescence.—The native species, L. salicaria, is trimorphic (long-styled, mid-and short-styled forms, Fig. 520). Cross-pollination is chiefly effected by humble-bees and bees, which seek the nectar formed at the bottom of the receptacle. Other species are only dimorphic, or even monomorphic.—Closely allied are, Nesæa, Diplusodon, Lagerstrœmia, and Cuphea, whose flower resembles that of Lythrum, but is zygomorphic. In Cuphea the receptacle is oblique and at the back prolonged into a spur, in which the nectar, secreted by a gland situated behind the ovary, is collected; the calyx and corolla gradually become reduced in size toward the anterior side of the flower; the reverse, however, is the case with the 11 stamens (the posterior one is absent); the posterior loculus in the bilocular ovary is sometimes barren; the fruit, when ripe, dehisces along the posterior side, the ovary as well as the wall of the receptacle being ruptured by the placenta, which expands and projects freely. The flowers stand singly in the centre of the stem, between the pairs of leaves. This may be explained as follows: of the two foliage-leaves in each pair, one supports a foliage-shoot, the other a flower; the foliage-shoot remains in the axil, but the flower is displaced through the length of an entire internode to the next pair of leaves, and then assumes a position between these two leaves. All foliage-shoots stand in two rows, the flowers in two other rows.

Order 4. Œnotheraceæ (or Onagraceæ). The flowers are arranged in racemes or spikes, ☿, epigynous, regular, polypetalous, 4-merous in all 5 whorls (1 whorl of sepals, petals and carpels, 2 of stamens); 2–3–5–6-merous flowers are less frequent; the calyx is valvate, the corolla twisted in æstivation (the left edge being covered). Gynœceum simple with multilocular ovary; the style is undivided, filiform, and bears a capitate or 4-partite stigma; endosperm wanting; embryo straight.—The majority are herbs, especially water- and marsh-plants; several are shrubs. No essential oils. The leaves are alternate or opposite, always single, and without (or with very small) stipules. The odourless flowers sometimes have a coloured calyx. In some instances (e.g. Œnothera, Fuchsia) the receptacle is prolonged more or less beyond the inferior ovary, and finally falls off. The stamens are obdiplostemonous (carpels epipetalous); the petal-stamens are sometimes suppressed. The anthers in some genera are divided into storeys. The well-pronounced, triangular pollen-grains are connected together by viscous threads. Small stipules are sometimes found, e.g. Fuchsia, Lopezia.