68 



PHARMACEUTICAL BOTANY 



moving through the water are drawn by a chemotactic influence to 

 the archegonia of another prothallus, pass down the neck canals of 

 these and fuse with the ova, fertilizing them. The fertilized egg or 



Fig. 37. — Dryopteris filix-mas — Plant and section through sorus. {From Sayre.) 



oospore divides and redivides and soon becomes differentiated into 

 stem bud, first leaf, root, and foot. The foot obtains nourishment 

 from the prothallus until the root grows into the soil, when it atrophies 

 and the sporophyte becomes independent. Unequal growth and di\-i- 



