444 SELAGINELLA i i,.s>. 



nieristem, but in some species no apical cell can be distin- 

 guished. There are from one to three vascular bundles 

 running through the stem, each surrounded by a ring of 

 small air-cavities : from them a single bundle is given off to 

 each leaf. The presence of vascular bundles and of a well- 

 marked epidermis is enough to distinguish our present type 

 from the mosses, to which it bears a superficial resemblance. 



The peculiar forked branching is due to the development 

 of lateral branches alternately on each side of the stem. The 

 roots arise from peculiar leafless branches, sometimes mis- 

 taken for true roots. 



The branches terminate in cones (Fig. ii6, a, c, and Fig. 

 117, a) formed of small leaves {sp. ph\ which overlap in 

 somewhat the same way as the scales of a pine-cone. Each 

 of these leaves is a sporophyll, and bears on its upper or distal 

 side, near the base, a globular sporangium. The sporangia 

 are fairly uniform in size, but some are megasporangia 

 (Fig. 116, c, and Fig. 117, a, m^. spg), and contain usually 

 four megaspores ; others are micro.sporangia (Fig. 116, u, 

 and Fig. 117, a, mi. spg), containing numerous microspores. 



The microspore (Fig. 117, n) cannot be said to germinate at 

 all. Its protoplasm divides, forming a small cell (prth), which 

 represents a vestigial prothallus, and a large cell, the repre- 

 sentative of a spermary. The latter {spy) undergoes further 

 division, forming six to eight cells in which numerous sperm- 

 mother-cells are developed. The sperms are finally liberated 

 by the rupture of the coats of the microspore. 



A similar but less comi)lete reduction of the prothallus is 

 seen in the case of the megaspore (c). Its contents are 

 divided, as in Salvinia, into a small nia.ss of protoplasm at 

 one end, and a large quantity of plastic products filling up 

 the rest of its cavity. Tlie protoplasm divides and forms a 

 small prothallus {prili) and a process of division also takes 



