THE VASCULAR CRYPTOGAMS 



27 



megasporangium, which takes place as in the micro- 

 Bporangium 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 



{-Ex. 



FIG. 15. Selaginella Martensii; longitudinal section through 

 old prothallus showing two embryos. p and p 2t 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 Pfeffer.) 



apical end, and so the upper part of the prothallus 

 becomes exposed, and grows a little beyond the limits 

 of the megaspore (see Tig. 15). 



Other archegonia are formed around the first one, 



