Lecture XXI. 



175 



from the sporangium, but it is usually continued on the moist 

 soil. The microspore begins by its division into two very un- 

 equally sized cells, the larger one practically occupying the whole 

 spore while the smaller one is very minute. This latter one 

 undergoes no further development and is the only somatic or vege- 

 tative cell of this reduced gametophyte. The large cell segments 

 and produces a layer composed of eight cells lying against the inside 

 of the spore coat and a mass of rounded cells occupying the space 

 surrounded by the eight. Within each of the cells forming the 

 central mass a sperm develops in a manner resembling the de- 



FIG. 48. Selaginella, germination of microspores. A, section of microspore 

 showing sperm-mother-cells surrounded by the cells of the antheridium. 

 The blackened cell below on the right is the somatic cell of the gameto- 

 phyte. B, bursting of the spore-coat and liberation of the sperms. A 

 and B, x about 1250 ; C, more highly magnified. (After Lyon.) 



velopment of the sperms of the Ferns and Mosses, but the sperm 

 of Selaginella is club-shaped with a corkscrew bend in it, and it 

 possesses two cilia only, resembling in this respect the sperms of 

 the Mosses and not those of the Ferns. When the sperms are 

 approaching maturity the cells forming the enclosing capsule and 

 the remnants of the sperm-mother-cells disintegrate and become 

 mucilaginous. By large absorption of water they swell up, burst 

 the spore-coat, and set free the sperms. 



Meantime the germination of the megaspores is taking place. 

 The original single nucleus of the spore divides repeatedly and its 



