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| Fig. 1. | |
1. Shoot of Euphorbia hypericifolia,about ½ nat. size. 2. A partial inflorescence, cyathium,bearing the petaloidglands. 3. A similar one at a later stage,cut open to show the single-stamened(monandrous) maleflowers and the central long-stalkedfemale flower. 4. A cyathium without petaloidglandular appendages. 5. A similar one at a later stagewith nearly ripe fruit. 6. An anther dehiscing. 7. Fruit dehiscing and exposingone of the three seeds. | 8. Seed. 9. Seed cut lengthwise exposingthe embryo. 10. Diagram of the inflorescenceof Euphorbia, illustratingthe dichasial cymose arrangementof the ultimatebranches. b, Bract subtending the centralterminal cyathium I. a′b′, Bracteoles of the firstorder subtending the secondarycyathia II. a″b″, Bracteoles of the secondorder subtending the tertiarycyathia III. |
| In the central cyathium I. are shown the details of the arrangementof the male flowers in monochasial cymes, m, and the centralfemale flower, f. | |
The form of the flower shows great variety. The most complete type occurs in Wielandia, a shrub from the Seychelles Islands, in which the flowers have their parts in fives, a calyx and corolla being succeeded in the male flower by 5 stamens, in the female by 5 carpels. Generally, however, only 3 carpels are present, as in Euphorbia; Mercurialis (fig. 2) has minute apetalous flowers with 3 sepals, followed in the male by 8 to 20 stamens, in the female by a bicarpellary pistil. In the large tropical genus Croton a pentamerous calyx and corolla are generally present, the stamens are often very numerous, and the female flower has three carpels. In Manihot, a large tropical American genus to which belongs the manioc or cassava (M. utilissima), the calyx is often large and petaloid. In a great many genera the corolla is absent. The most reduced type of flower is that described in [Euphorbia], where the male consists of one stamen separated from its pedicel by a joint, and the female of a naked tricarpellary pistil. The stamens are sometimes more or less united (monadelphous), and in castor-oil (Ricinus) (fig. 3) are much branched. The ovary generally contains three chambers, and bears three simple or more often bipartite styles; each chamber contains one or two pendulous ovules, which generally bear a cap-like outgrowth or caruncle, which persists in the seed (well shown in castor oil, fig. 3).
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| Fig. 2.—Dog’s Mercury (Mercurialis perennis). | |
1. Male plant. 2. Female plant; 1⁄3 nat. size. 3. Female flower. | 4. Male flower. 5. Fruit beginning to split open. 6. Seed cut lengthwise showingthe embryo. |
As the stamens and pistil are borne by different flowers, cross-fertilization is necessary. In Mercurialis and others with inconspicuous flowers pollination is effected by the wind, but in many cases insects are attracted to the flower by the highly-coloured bracts, as in many Euphorbias and Dalechampia, or by the coloured calyx as in Manihot; the presence of honey is also frequently an attraction, as in the honey-glands on the bracts of the cyathium of Euphorbia. The fruit is generally a capsule which splits into three divisions (cocci), separating from the central column, and splitting lengthwise into two valves. In the mancinil (Hippomane mancinella) of Central America the fruit is a drupe like a plum, and in some genera berries occur. In the sandbox tree (Hura crepitans) of tropical America the ovary consists of numerous carpels, and forms when mature a capsule which splits with great violence and a loud report into a number of woody cocci. The seeds contain abundant endosperm and a large straight or bent embryo.
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| From Bentley and Trimen’s Medicinal Plants, by permission of J. & A. Churchill. | |
| Fig. 3.—Castor Oil (Ricinus communis). End of shoot with flower-spike;about 1⁄3 nat. size. | |
1. Section of male flower, aboutnat. size. 2. Group of stamens. 3. Fruit. | 4. Seed. 5 and 6. Vertical and transversesections of seed showingembryo in position. |
Several members of the order are of economic importance. Manihot utilissima, manioc or cassava (q.v.), is one of the most important tropical food-plants, its thick tuberous root being rich in starch; it is the source of Brazilian arrowroot. Caoutchouc or india-rubber is obtained from species of Hevea, Mabea, Manihot and Sapium. Castor oil (q.v.) is obtained from the seeds of Ricinus communis. The seeds of Aleurites moluccana and Sapium sebiferum also yield oil. Resin is obtained from species of Croton and Euphorbia. Many of the species are poisonous; e.g. the South African Toxicodendron is one of the most poisonous plants known. Many, such as Euphorbia, Mercurialis, Croton, Jatropha, Tragia, have been, or still are, used as medicines. Species of Codiaeum (q.v.), Croton, Euphorbia, Phyllanthus, Jatropha and others are used as ornamental plants in gardens.
The box (Buxus) and a few allied genera which were formerly included in Euphorbiaceae are now generally regarded as forming a distinct order—Buxaceae, differing from Euphorbiaceae in the position of the ovule in the ovary-chamber and in the manner of splitting of the fruit.
EUPHORBIUM, an acrid dull-yellow or brown resin, consisting of the concreted milky juice of several species of Euphorbia, cactus-like perennial plants indigenous to Morocco. It dissolves in alcohol, ether and turpentine; in water it is only slightly soluble. It consists of two or more resins and a substance euphorbone, C20H36O or C15H24O. Pliny states that the name of the drug was given to it in honour of Euphorbus, the physician of Juba II., king of Mauretania. In former times euphorbium was valued in medicine for its drastic, purgative and emetic properties.