FERNS 



335 



terior) end. Among these are the sperm cases (antheridia). 

 The sperm case is in the form of a rounded protuberance from 



Fig. 314- 



Prothallium of fern, underside, showing rhizoids, antheridia scattered among and near 

 them, and the archegonia near the sinus. 



the underside of the prothallium. The wall consists of a single 

 layer of thin cells. The central portion develops a number 



of 



sperms 



The 



sperms are coiled in 

 the form of a screw, 

 with numerous deli- 

 cate cilia over the 

 smaller end. by the 

 vibration of which 

 the sperms swim 

 rapidly for a half 

 hour or so in the wa- 

 ter like a moving screw. The egg cases (archegonia} are borne also 



* The motile sperms of plants are sometimes called " anther ozoids." 



Fig. 315- 



Section of antheridia, showing sperm cells, and sperms 

 in the one at the teft. 



