XIV 



L YCOPODINE^E 



489 



occurs, and this takes place in a manner identical with that 

 found in Isoetes, or in the endosperm - formation of most 

 Spermaphytes. Fig. 254, C shows a cross-section of the apex 

 of the spore shortly after the first cell walls are complete. 

 The extremely regular hexagonal form of the cells toward 

 the centre of the prothallium is very noticeable. At the 

 margin, and below, the cells are larger, and often contain 

 several nuclei. 



The cell -formation does not extend at this stage to the 

 base of the spore, as in Isoetes, but is confined to the apex, 

 where a definite cellular body is formed. This is three-layered 



Fig. 2$s-—Selagi>iella Kraitssiana (A. Br.). A, Longitudinal section of a nearly ripe macrospore, 

 with the primary prothallium (pr) complete, but still showing a large vacuole in the centre of the 

 spore, X65 ; B, similar section of a younger stage, before the diaphragm has been differentiated, 

 X 400 ; n, nuclei. 



in the middle, but at the margins but one cell in thickness. 

 The lower cells have the walls which are in contact with the 

 spore -cavity much thickened at a later stage, and thus is 

 formed the diaphragm which is so conspicuous in most species, * 

 and which led Pfeffer to suppose that the first division in the 

 young prothallium was by a cell wall which separated the 

 prothallium proper from the lower part of the spore, in which 

 later the " secondary endosperm " is formed. 



Scattered through the protoplasm of the spore-cavity are 

 numerous very small nuclei. The protoplasmic layer becomes 

 rapidly thicker (Fig. 255, A), and finally completely fills the 



