THE VASCULAR CRYPTOGAMS 



25 



call this angle the apex of the megaspore. The first 

 sign of germination is the division of the nucleus into 

 two. The divisions are repeated many times, and soon 

 cell-walls begin to appear in the protoplasm, between 

 the daughter - nuclei. The cell - formation is at first 

 limited to the apical part of the spore, but it gradually 



FIG. 13. Selaginella Martensii; germinating megaspore. 

 c, cellular tissue of prothallus, only complete in upper part of 

 spore ; n, free nuclei ; p, undivided protoplasm of spore ; 

 i, inner, e, outer, layer of cell-wall of spore. Magnified 

 335 diameters. (After Heinsen.) 



spreads downwards and inwards. In Fig. 13 a 

 megaspore is shown which is already nearly half-filled 

 with tissue. As a rule, the cell-division extends so 

 far that the tissue fills the whole cavity of the spore. 

 In some cases this process is completed even before 

 the megaspores are set free from the sporangium, while 

 in other cases the lower part of the tissue is developed 

 after the spores have fallen on to the ground. 



