30 STRUCTURAL BOTANY 



tissue of the prothallus (see Fig. 15). The embryonic 

 cell undergoes segmentation, and very soon the first 

 organs of the embryo are marked out. The apex of the 

 stem lies at the end opposite the suspensor, but not 

 quite in the middle ; the two cotyledons lie on either 

 side of it. One side of the hypocotyl grows out into a 

 temporary organ, the foot, which grows so rapidly as to 

 force the apex of the stem to one side (see Figs. 1 5 and 

 16). This organ serves to absorb food for the young 

 plant from the tissues of the" prothallus. The first root 

 appears a little later, between the foot and the suspensor. 

 Fig. 15 gives a general idea of the position of these 

 organs, and their relation to the prothallus. In Fig. 16 

 a slightly more advanced embryo is shown in greater 

 detail. At this stage the young stele, consisting of pro- 

 cambial tissue, can already be traced from the apex of 

 the stem to that of the root. It will be noticed that 

 the cotyledons, like all the other leaves of the plant, 

 possess ligules. 



The stem begins to branch while the embryo is still 

 enclosed in the prothallus. A young plant of Selaginella 

 Kraussiana after germination is shown in Fig. 2. It is 

 still attached by its foot to the megaspore, or rather to 

 the prothallus inside it. 



In possessing a suspensor, Selaginella resembles the 

 Gymnosperms and most other Flowering Plants. The 

 position of the organs of the embryo, however, is different. 

 Although the embryo is dicotyledonous, like that of 

 many Gymnosperms as well as of the Dicotyledons, 

 properly so called, the apex of the stem is displaced 

 towards one side, and the first root, though it arises near 

 the suspensor, is not in a line with it (cf. Part I. Figs. 

 114, F, and 115, pp. 279, 280). The peculiarities 



