498 



A TEXTBOOK OF THEORETICAL BOTANY 



again divides transversely. Of the two cells formed from it, the upper one 

 produces the four rows of cells that form the neck. Since the neck is curved, 



Fig. 488. — Dryopteris filix-mas. Stages in the development of the 

 archegonium from a superficial cell of the prothallial cushion. {After 

 Kny.) 



the two rows on the convex side usually contain five to six cells, while those 

 on the concave side have only four. The lower or central cell grows up 

 between the neck cells and cuts off a narrow cell which is the neck canal 



