THE VASCULAR CRYPTOGAMS 



27 



megasporangium, which takes place as in the micro- 

 sporangium by a transverse slit, the megaspores are shed 

 onto the ground. The growth of the prothallus con- 

 tinues, the coats of the megaspore are ruptured at its 



a 



-4-Ex. 



FIG. 15. Selaginclla Martensii; longitudinal section through 

 old prothallus showing two embryos, p-^ and p 2 , prothallus ; 

 a, unfertilised archegonium ; r.h, root-hairs ; s, suspensors 

 of embryos ; larger embryo shaded, no cells shown ; r, root ; 

 /, foot ; st, stem ; I, I, cotyledons ; Ex, wall of megaspore. 

 Magnified 165 diameters. (After Pfeti'er.) 



apical end, and so the upper part of the prothallus 

 becomes exposed, and grows a little beyond the limits 

 of the megaspore (see Fig. 15). 



Other archegonia are formed around the first one, 



