4. Ruteæ. Ruta (Figs. 465–467) graveolens is an herbaceous, glaucous, strongly smelling plant with bipinnate leaves and yellow flowers; the terminal flower is 5-merous, the others 4-merous (S. Eur.).—Dictamnus; zygomorphic flower. The individual carpels of the fruit separate from each other, and dehisce like follicles, upon which the internal layer is detached elastically and springs out, carrying the seeds with it. Several species are ornamental plants.

B. The ovary is entire or only slightly grooved; the style is terminal, undivided. The fruit is most frequently a drupe or berry.

7. Aurantieæ, Orange Group. Fruit a berry with a leathery external layer.—The most typical flower is found for example in Limonia: S5, P5, A5 + 5, G5 (2–5).—Citrus has 4–5–8-merous flowers, a gamosepalous, dentate calyx, free petals, one whorl of stamens which are split irregularly into several bundles (Fig. 470). The fruit is a multilocular berry provided with a thick, tough, outer layer. The juicy pulp, which fills up the loculi and envelopes the seeds, is formed from many large-celled, juicy hair-structures which arise on the inner side of the walls of the loculi and by degrees entirely fill them up; the dissepiments remain thin, and form the partitions so easily separating from each other (Fig. 469). The seeds in many instances are remarkable for containing several embryos. The blade of the leaf is separated from the frequently winged stalk by a node (and hence is a compound leaf with only the terminal leaflet developed?) (Fig. 468); in other genera, as Triphasia, there is a fully developed trifoliate leaf. Thorns are frequently developed.—The species of this genus, which is a native of the warmer parts of S. E. Asia, are very hard to separate. The differences are found in the forms of the fruit, the leaves and the leaf-stalks, and in the number of stamens. Citrus medica, “Cedrat” (Ind.); C. limonum, “Citron,” “Lemon” (introduced into Italy in the 3rd to 4th century). Officinal: the fruits and essential oil of Lemon. C. aurantium from E. Asia, the Orange (introduced into Italy in the 14th century). C. vulgaris (Fig. 468), Bitter Orange (introduced into Europe at the time of the Crusades); the unripe Bitter Oranges, and peel of the Bitter Orange is officinal; it is from the flowers of this species especially that the essence of Neroli is made. C. limetta, C. bergamia, Bergamot; essence of Bergamot is officinal. C. decumana, Pomalo, a native of the Islands of the Pacific. About 780 species; chiefly tropical.

Family 16. Aesculinæ.

The essential characters of this family are in the main the same as those of the Terebinthinæ and Gruinales. The flowers are hypogynous, perfect, with free petals, 5-merous (S5, P5, typically A5 + 5, all of which, however, are not generally developed; in our native orders there are only 7–8 stamens), and most frequently a 3-merous, 3-locular gynœceum (less frequently 2 or 5 carpels with as many loculi). In each loculus there are usually only 1–2 ovules. A deviation from the preceding families is the frequent zygomorphy of the flower, with, as a rule an oblique plane of symmetry (Fig. 471). When a disc is developed it is placed outside the stamens. The majority have no endosperm (Fig. 473).—The members of the family are nearly all trees.

Order 3. Sapindaceæ. Trees or shrubs, often climbing by tendrils (lianes with anomalous structure of the stem) and with compound leaves. The flowers, in most cases, are small, insignificant, and without scent, and in some polygamous and zygomorphic. S4–5, P4–5, A8 (less frequently 5–10) inside the nectary (disc); ovary generally 3-locular, with 1–2 ovules in each loculus (raphe ventral, micropyle turned downwards). Seed without endosperm, often with an aril. The embryo is often thick and curved (Fig. 473).

Æsculus (Horse-Chestnut). Trees with opposite, digitate, dentate leaves without stipules; the inflorescence is composed of unipared scorpioid cymes arranged in a pyramidal panicle (termed a thyrsus). The flowers are irregular, with an oblique plane of symmetry (through the 4th sepal, Fig. 471); there are 5 sepals, 5 free petals, of which the one lying between S³ and S⁵ is the smallest (see Fig. 471) and may be absent; stamens 7 (5 + 2), three being suppressed; gynœceum simple, 3-carpellary and 3-locular, with single style; of the two ovules one is ascending, the other descending (Fig. 472).—The fruit is a 3-valvate, sometimes spiny, capsule, with loculicidal dehiscence, the seed having a large hilum, a curved embryo without endosperm and united cotyledons (the radicle lies in a fold of the testa, Fig. 473). Æ. hippocastanum (Greece, Asia), introduced into cultivation about 300 years ago; the majority of the other species, e.g. Æ. pavia, etc., several of which are frequently cultivated in gardens, are from N. America. The flower of the Horse-Chestnut is adapted for bees, whose abdomen touches the anthers or style when visiting the flower. The flowers are protogynous.

Order 4. Aceraceæ. This order is so closely allied to the Sapindaceæ, that some authorities have classed it with them. The main difference is in the regularity of the flowers, and the 2-merous gynœceum (in abnormal cases several carpels occur).—They are trees, and, like the Horse-Chestnuts, have opposite leaves without stipules; in Acer the leaves are palminerved, but imparipinnate in Negundo, a plant frequently cultivated in gardens. The flowers are often unisexual, polygamous (some species have ☿-, ♂-and ♀-flowers); sepals 5, petals 5 free, stamens 8 (that is, 5 + 5, but the two median ones are absent) inside a large disc. Fruit a samara (schizocarp) with 2 winged, nut-like fruitlets (Fig. 474). In each of the 2 loculi of the ovary are 2 ovules. Embryo curved, with thin, folded cotyledons. Endosperm absent.—The inflorescences are racemes with a more or less elongated main axis and terminal flower (which sometimes has 10 stamens); when the lateral branches are developed they are similar to the main axis. In some species both corolla and petal-stamens are suppressed. Acer is pollinated by insects, Negundo by the wind.—88 species; North Temperate zone. Acer in the Tertiary from the Oligocene. The following are native plants: Maple (Acer campestre), Sycamore (A. pseudoplatanus, doubtful native). Important as avenue trees and timber. Sugar is obtained from the spring sap of the Sugar Maple (N. Am.).

Order 10. Polygalaceæ. Herbs or shrubs (some tropical species are lianes) with scattered (rarely opposite), simple and most frequently quite entire leaves, without stipules. The flowers are usually borne in terminal spikes or racemes, and are strongly zygomorphic (the plane of symmetry being median); they have 5 free sepals, the 2 lateral ones of which (4 and 5 in Figs. 475, 476) are very large, petaloid, and frequently project on each side like the “wings” of a Pea-flower; petals 5, of which the two lateral ones are wanting or rudimentary (dotted on Fig. 475), and the anterior “the keel” (Fig. 476 c) is large, hollow and boat-shaped, and frequently with a lobed or fimbriated edge (Fig. 476 A and B, c); stamens 8, the two median ones being absent, all united into a tube split along the back, which is also slightly united to the keel (the anthers, often 2 locular, open by pores, Fig. 476 B, st); the 2 median carpels form a bilocular ovary. 1 pendulous ovule in each loculus (Figs. 476 C, 475); capsule compressed with loculicidal dehiscence, rarely a nut. Polygala (Milk-wort).

Family 17. Frangulinæ.

The plants belonging to this family, with very few exceptions, are trees or shrubs. The leaves are usually simple; stipules may be absent or present. The flowers in almost all the orders are small, green or whitish; they are always regular, 4-or 5-merous with 2–5 carpels, but never have more than 1 whorl of stamens, which in Rhamnaceæ and Ampelidaceæ are placed opposite the petals (typically 5 + 5 or 4 + 4 stamens, of which however either the external or internal whorl is always wanting); hypogynous or slightly perigynous, in Rhamnaceæ only strongly perigynous or epigynous; generally ☿; the calyx is inconspicuous; petals free or slightly united. Gynœceum simple; ovary generally multilocular; style short or entirely wanting. A disc is nearly always developed in the flower, but is found sometimes inside the staminal whorl, sometimes outside it or between the stamens. The ovules are apotropous (anatropous with dorsal or ventral raphe).

Order 1. Celastraceæ. Euonymus europæa (Spindle-tree) may be chosen as a type. It is a shrub with simple, opposite leaves and small caducous stipules. The small, greenish-yellow flowers, borne in regularly-branched dichasia, are regular, ☿, with 4 whorls, 4-(or 5-) merous in regular alternation. There is a thick disc upon which the polypetalous corolla (imbricate in the bud) and the stamens are borne, with a slightly perigynous insertion. The style is short and thick; the ovary has 2 erect ovules in each loculus. The fruit is a red, 4-valvate capsule with loculicidal dehiscence; the seeds are few in number, and have a large, red-yellow aril (developed from the micropyle). Embryo green, in a large, fleshy, white endosperm. The dingy yellow flowers are generally visited only by flies and ants for the sake of the honey secreted by the disc, and while they run about on the flowers they touch the anthers and stigmas, now with one part of the body, now with another. The flower is protandrous. The stigmas are not developed till several days after the opening of the anthers.—Celastrus, Cassine, Catha, etc.

Order 3. Aquifoliaceæ (Hollies). The genus Ilex forms almost the entire order. (175 species out of 180; especially from S. Am.) They are shrubs or trees with scattered, leathery, simple leaves (in Ilex aquifolium, spiny) with very small stipules. The flowers are small, white, and borne in few-flowered inflorescences in the axils of the foliage-leaves; they are most frequently unisexual and diœcious. There are 4–5 sepals, petals, stamens and carpels in regular alternation; the calyx and corolla have their leaves slightly connate; stamens slightly adnate to the corolla; the ovary is generally almost spherical with a thick, sessile stigma (Fig. 477). This order deviates especially from Celastraceæ in the absence of the disc and in having only 1 (pendulous) ovule in each of the 4 loculi of the ovary, and in having a drupe with generally 4 stones. Embryo extremely small, at the apex of the large endosperm, with the radicle directed upwards.—3 genera.—I. aquifolium (Holly) principally on the coasts of European countries; from Norway to W. Denmark, and further westward. It is a common garden shrub with stiff, shining leaves and red fruits. Several South American species contain so much caffeine that they may be used as a beverage in the place of tea (I. paraguayensis, Paraguay tea, or Maté). The Holly does not contain caffeine.

Order 4. Ampelidaceæ (Vines). Shrubs with the stem swollen at the insertion of the petioles and climbing by tendrils borne opposite the leaves (Figs. 478, 479). The leaves are scattered (generally 1/2), stalked, stipulate, frequently palminerved and lobed, divided or compound. The small, greenish flowers are generally borne in paniculate inflorescences, whose position is the same as that of the tendrils (Fig. 478); they are hypogynous or slightly perigynous, ☿, with 4–5 sepals, petals, stamens (which, as in the Rhamneæ, are opposite the petals; Fig. 480 A, B) and 2 carpels. The calyx is very small, entire, or slightly dentate; corolla valvate, and in some falling off as a hood, since the individual parts remain united at the summit (Fig. 480 A). Between the stamens and gynœceum is situated an hypogynous disc, with 5 lobes alternating with the stamens (Fig. 480 A, B, E). In each loculus of the 2-locular ovary there are 2 erect ovules (E); the style is short or wanting. The fruit is a berry. The embryo is small and lies in a horny, sometimes slightly folded (ruminate) endosperm (Fig. 480 C, D).

Order 5. Rhamnaceæ. The stamens are placed opposite the petals as in the Ampelidaceæ (Fig. 482), but the flowers are much more perigynous or entirely epigynous. The trees and shrubs belonging to this order have simple, most frequently penninerved leaves with stipules; frequently thorny (modified branches). The flowers are inconspicuous, sometimes unisexual (Fig. 482), and have 5 (-4) sepals, petals, stamens, and generally 3 (2–5) carpels. The calyx has valvate æstivation. The petals are very small (generally less than the sepals), often spoon-like, hollow, and embracing the stamens; a disc covers the inner surface of the thalamus or the base of the style in the epigynous flower; gynœceum simple, with one style and one erect ovule in each loculus. The fruit is most frequently a drupe. The embryo is large, often green or yellow, with endosperm.

Rhamnus (Buckthorn) has a juicy drupe with 3 (2–4) stones, surrounded at the base by the persistent portion of the receptacle; the disc is thin. R. cathartica (common Buckthorn): diœcious, with opposite, serrate leaves. R. frangula (Alder Buckthorn): flowers ☿, with scattered, entire leaves.—Ceanothus (N. Am., with richly-flowered inflorescences and a fruit closely resembling that of the Euphorbias). Phylica, Pomaderris (Austr., fruit a capsule). Zizyphus, Paliurus, Colletia (S. Am.) are thorny shrubs; C. spinosa has thorny shoots with small, caducous leaves; the seedling has normal foliage-leaves. Others climb by tendrils as in the Ampelidaceæ, e.g. Gouania.

Family 18. Thymelæinæ.

Exclusively trees or shrubs with simple, entire, scattered leaves without stipules. They have a strongly perigynous, regular, 4-merous flower. The receptacle (often coloured) envelopes a simple gynœceum formed of 1 carpel and with, in most cases, 1 ovule, bearing on its edge 4 (or 5) petaloid sepals and, but rarely at the same time, small, scale-like petals. The corolla is most frequently entirely wanting (and hence these plants were formerly reckoned among the Monochlamydeæ); frequently only one of the 2 whorls of stamens, which are situated on the inner side of the edge of the receptacle, is developed. The fruit is most frequently a 1-seeded berry or drupe, or a nut which may be falsely berry-like, the partly persistent receptacle being fleshy and enveloping it.

Order 1. Thymelæaceæ. The flowers are most frequently ☿ (Fig. 483). The receptacle is high, generally tubular, coloured, and bears on its edge the 4-(or 5)-merous calyx, with imbricate æstivation. The corolla is wanting or is represented by small scales. The stamens are situated on the inside of the receptacle, and number 4 + 4 (or 5 + 5); stigma capitate. 1 pendulous ovule (Fig. 483 B), the radicle pointing upwards. The fruit is most frequently a berry. A disc is sometimes developed. Endosperm wanting or very slight.

Daphne (Spurge-Laurel, Fig. 483) has a deciduous receptacle, often coloured; sepals 4; petals absent; stamens 4 + 4. Berry.—Gnidia (corolla); Pimelea (2 stamens); Thymelæa; Passerina and others.

Order 2. Elæagnaceæ. Shrubs or trees, which are easily recognised by the covering of peltate hairs found upon almost all parts of the plant, causing them to assume a silvery or rusty-brown appearance. Stipules are absent; the leaves are simple, most frequently scattered. Flowers (Figs. 484, 485) frequently unisexual. The sepals are valvate, 2-4; the corolla is wanting; stamens 4 + 4 or 0 + 4. The ovule is erect and the radicle turned downwards (Fig. 486). The fruit is a nut, but becomes a false fruit, being surrounded by the persistent receptacle or the lower part of it, and thus assuming a berry- or drupe-like appearance (Fig. 486). Endosperm insignificant.—Shepherdia (opposite leaves) has 4 sepals, 4+4 stamens, as in Daphne. Diœcious.—Elæagnus (Silver-leaf) is ☿, has 4–6 sepals, and 4–6 stamens alternating with them. Hippophaë is diœcious; it has 2 sepals and 4 stamens in the ♂-flower (perhaps properly speaking 2+2 stamens); thorny (stem-structures).

Family 19. Saxifraginæ.

The flower is generally perfect, regular and polypetalous, usually perigynous or epigynous, eucyclic and 5-merous; most frequently S5, P5, A5 + 5 or 5 + 0 and G2-5, but other numbers are found, especially 4; the flowers are very frequently obdiplostemonous. The calyx is sometimes large and the corolla small; the carpels in some are entirely free, in others more or less united. Endosperm is found in the majority. The hypogynous forms approach the Cistifloræ, the others the following families, especially the Rosifloræ. This family is not, upon the whole, so well defined and natural as most of the others. The Saxifragaceæ proper, approach very near to the Rosaceæ, especially Spiræa, and form a transition to it. The forms with opposite leaves, as Philadelphus, etc., approach the Myrtifloræ, just as the Escalloniæ appear to be closely allied to Bicornes, especially Vacciniaceæ. Finally through Pittosporaceæ, they pass over to the Frangulinæ. The family terminates in very reduced forms, on the one hand in the arborescent orders with crowded inflorescences, on the other perhaps in the very remarkable order Podostemaceæ.

Order 1. Crassulaceæ. Nearly all are herbs or small shrubs with round, succulent branches and scattered, fleshy, often more or less round leaves, which are very rarely incised, and never have stipules. The flowers are generally borne in dichasia or unipared scorpioid cymes, which again may be arranged in racemes, umbels, etc.; they are regular, ☿, hypogynous or perigynous, and most frequently have free sepals and petals (gamopetalous corollas with sessile stamens are found in Cotyledon, Bryophyllum, Echeveria, and others); the floral formula is Sn, Pn, An + n, Gn, where n may have very different values, partly depending upon the size of the flower (e.g. 4–7 in Sedum, Fig. 487; 6–30 in Sempervivum; 4 in Rhodiola, Bryophyllum, and Kalanchoë; 5 in Echeveria, Umbilicus, Cotyledon). The carpels are free and are placed opposite the petals (Fig. 487). Fruit a syncarp composed of follicles containing many, small seeds without endosperm. Outside each carpel is found a small, nectariferous scale (Fig. 487). The northern genus, Rhodiola, is diœcious. The petal-stamens are wanting in some (Crassula, Bulliarda, and others). The floral-leaves are very often displaced upon their axillary branches. A multicarpellary gynœceum also occurs.

Sedum (Stonecrop) is generally 5-merous with 10 stamens; Sempervivum tectorum (House-leek), 12-merous, and with 24 stamens. The leaves of Bryophyllum calycinum very readily form buds, and also frequently exude water from the edges.