Family 14. Tricoccæ.
The very large order Euphorbiaceæ and three smaller ones belong to this family. They have in common: unisexual, hypogynous, frequently regular flowers, the perianth most frequently single, rarely double, or entirely wanting; there is such a great variety in the structure and parts of the flower that one only can be cited as the rule: viz. the simple gynœceum composed of 3 carpels forming a 3-locular ovary, which is frequently more or less deeply grooved (hence the name, Tricoccæ); in the inner angles of the loculi are found 1 or 2 (never several) pendulous (except Empetraceæ), anatropous ovules, with upward and outwardly turned, frequently swollen, micropyle (Fig. [455]). The seed most frequently has a large endosperm and a straight embryo (Figs. [455] B, [464]).—The family approaches the nearest to the Gruinales and Columniferæ; it may perhaps be regarded as an offshoot from the Sterculiaceæ.
Order 1. Euphorbiaceæ. Flowers unisexual. In each of the loculi of the ovary, generally 3, there are 1 or 2 pendulous ovules with upward and outwardly turned micropyle. The placenta protrudes above the ovules (Figs. [454], [461] B). On the ripening of the capsule the 3 carpels separate septicidally, frequently with great violence, ejecting the seeds and leaving a central column. Endosperm copious.—For the rest, the flowers present all stages, from genera with calyx and corolla, to those which are the most reduced in Nature, namely the naked, 1-stamened flowers of Euphorbia.
The same variety which is found in the flower is also present in the vegetative parts. Some are herbs, as our Spurges, others are shrubs and trees; some African Euphorbia-species even resemble the habit of a Cactus. Leaf-like branches with rudimentary leaves are found in Phyllanthus (sub-genus Xylophylla) (Fig. [456]). The leaves are scattered or opposite, often stipulate; they are nearly always simple. Large, highly-branched cells containing a great quantity of pungent latex are found in many, and watery juice in others. Glands and glandular hairs are general.—Only a few genera can be considered in this book.
As an example of the most perfect flowers (which partly reproduce the Geraniaceous type) may be mentioned, Croton, Manihot, and Jatropha; 5 sepals, 5 petals, sometimes gamopetalous, andrœcium diplostemonous, or many-stamened, often monodelphous.
Figs. 453–455.—Ricinus communis.
Fig. 453.—♂-flower (magnified).
Fig. 454.—♀-flower in longitudinal section.