CHAPTER XIV. — THE SPERMAPHYTA. 



373 



suspensor. This usually pushes its way downward through the 

 wall of the oospore into the cellular tissues of the embryo-sac, 

 and at its lower end forms a mass of cells from which the embryo 

 is developed. The time of pollination to the ripening of the 

 seed, comprises, in this and many other species of the Coniferae, 

 two entire seasons. The seed is albuminous, and the embryo, as 

 in many other species of Abietinae and in some other Coniferae, 

 is polvcotyledonous. The reproduction of Pinus sylvestris is 

 illustrated in Figs. 571 and 572. 



Fig. 573. — Welwitschia mirabilis, entire plant, about one-thirtieth natural size. After 

 Hooker. 



(C) The Gnetaceae, or Joint-Firs, constitute a small but 

 diversified order of plants, consisting of undershrubs, shrubs, 

 and small or moderate-sized trees. There are only about forty 

 species in all, and these are distributed into the three genera, 

 Ephedra, Gnetum and Welwitschia. The Ephedras are shrubs 

 or undershrubs with much the aspect of Equisetums, having 

 slender, cylindrical, jointed branches covered with a green rind, 

 and bearing at the joints a pair of opposite small leaves, which 

 are connate at the base, forming a two-toothed sheath. 



The Gnetums also have opposite leaves, but these are large, 

 broadly lanceolate or oval, entire, and pinnately veined. The 

 remarkable genus, Welwitschia, is represented by but one species, 

 Welwitschia mirabilis, a native of South Africa. It has a short, 

 thick stem, which rises but a few inches above the soil, and is 



