XI 



LEPTOSPORANGIATAl HETEROSPORE^ 



399 



and a smaller number of cilia than is usually the case in the 

 Filicinejc (Fig. 233, G). 



In Azolla the contents of the ungerminated microspore, 

 whose wall is thin and smooth, contain but little granular mat- 

 ter. The first indication of germination is the rupturing of 

 the exospore along the three radiating ventral ridges, and the 

 protrusion of a small papilla. This is cut off by a transverse 

 wall near the top of the spore cavity, and forms at once the 

 mother cell of the single antheridiuin fFig. 234, C). Belajeff 



Fig. 234. — Azolla filiculoides. A, Massula with enclosed microspores (sp), X250; gl, 

 glochidia; B-D, development of male prothallium and antheridium, X560; 0, oper- 

 cular cell; E, cross-sections of a ripe antheridium, X750; i, the top; 2, nearly 

 median section; x, second prothallial cell. 



((3)' P- 329) says the next divisions are nearly parallel and 

 divide the antheridium into three cells, one above the other, and 

 of these only the middle ones divide further. For some reason, 

 which is not quite clear from his account, Belajeff does not re- 

 gard the whole upper cell as an antheridium, but says that the 

 latter is only formed after five vegetative cells have been cut off. 

 ,Tt seems much more in accordance with the structure found 

 in the related homosporous Ferns to regard the whole 



