EXOGENOUS OK DICOTYLEDONOUS PLANTS. 



471 



involucre, but entirely destitute of calyx and corolla ; stamen one 

 (or rarely two), hypogynous, with a slender filament, and a reni- 

 form confluently one-celled anther ; the ovary four-lobed, four-celled, 

 indehiscent in fruit ; the seeds albuminous. 



908. Ol'd. PodostemaceiE {River-weed Family) comprises a few 

 (chiefly American and Asiatic) aquatics, in rivers, with the aspect 

 of Mosses, Hepaticse, &c. ; their small flowers arising from a spathe ; 

 the calyx often entirely wanting ; the stamens frequently unilateral 

 and monadelphous ; the ovary two-' or three-celled, with distinct 

 styles ; in fruit forming a ribbed capsule, containing numerous ex- 

 albuminous seeds attached to a central column. — Ex. Podostemon. 



909. Ord, Enphorbiaceffi {Spurge Family). Herbs, shrubs, or 

 trees, often with a milky juice : in northern temperate climes chiefly 

 represented by the genus Euphorbia ; which is remarkable for hav- 

 ing numerous staminate flowers, reduced to a single stamen (487), 

 enclosed in an involucre along with one pistillate flower, this reduced 

 to a compound pistil, and also achlamydeous, or with an obsolete 

 calyx. But other genera have a regular calyx both to the staminate 

 and pistillate flowers ; and a few are likewise provided with petals. 

 Ovary of two to nine more or less united carpels, coherent to a cen- 

 tral prolongation of the axis : styles distinct, often two-cleft. Fruit 

 mostly capsular, separating into its elementary carpels, or cocci 

 (usually leaving a persistent axis) : these commonly open elastically 



FIG. 1136. Callitriche vema, about the natural size. 1137. Perfect flowers, magnified. 

 1138. A staminate and pistillate flower, magnified. 1139. The fruit. 1140. Cross-section of 

 the fruit. 1141. Vertical section through the pericarp, seeds, and embryo. 



