SUBKINGDOM SPERMATOPHYTA 



345 



E 



scales about the joints. The plants are usually dioecious. The male 

 flower (Fig. 311, C) consists of two to eight sessile stamens at the apex 

 of a bare axis, which is surrounded at the base by scalelike leaves. 



The female flowers 

 have a single ovule, sur- 

 rounded by a membrana- 

 ceous integument which 

 projects beyond the peri- 

 anth. The ovule (Fig. 

 311, B) is either solitary 

 at the end of a shoot, or 

 there may be two or three 

 in the upper axils of a 

 cluster of bracts, the lower 

 bracts being sterile. In 

 the species figured, these 

 bracts are thin and 

 membranaceous, but they 

 usually become thick and 

 pulpy. 



The female gameto- 

 phyte in Ephedra is 

 much like that of the 

 Conifers, and the arche- 

 gonia are well developed. 

 After fertilization, several 

 free cells are formed in 

 the egg-cell, each one of 

 which produces an em- 

 bryo. The embryo, in all 



FIG. 311. A-B, Ephedra trifurca. A, fragment 

 of plant, of natural size, showing where the 

 flowers, ?, have fallen off. B, seed, o, sur- 

 rounded by the imbricated scale-leaves (X Is). 

 C, staminate flower of E. allissirna. D, Gnetum 

 latifolium (Xj); 6, staminate flowers. E, fe- 



male flowers, or youug fruits, of G. gnemon 

 (XI). (C, D, after EICHLEK ; E, after LOTSY.) 



the Gnetaceae, has two 

 cotyledons. 



The genus Gnetum (Fig. 311, D) comprises a number of plants 

 which are either trees or climbers. The broad, opposite leaves are 

 strikingly similar to those of the Dicotyledons, with which Gnetum 

 is possibly related. The flowers (E) are borne in whorls at the ends 

 of the shoots, usually upon different plants, and structurally are 

 similar to those of Ephedra. According to Lotsy (Coulter, 4) there 

 is but a single integument and a double perianth, the latter becoming 

 fleshy in the fruit. 



Embryo-sac. The embryo-sac shows certain resemblances to that of the 

 lowest Angiosperms. While the basal part becomes filled with prothallial tissue, 

 the nuclei of the upper portion remain free, and any one may become the egg- 

 nucleus, as there is.no archegonium developed. The zygote resulting from 

 the fusion of a generative nucleus from a pollen-tube with an egg-nucleus, 



