THE FUNGI : ARCHLMYCETES AND PHYCOMYCETES 205 



nuclei zoospores are differentiated. Thus from the original zoospore which 

 entered the host cell some 1,500 zoospores are developed. 



The mature sorus, which is the name given to the group of sporangia, 

 now absorbs water and swells, rupturing the wall of the host cell and forcing 

 out the separate sporangia, which thus come to lie near the surface of the 

 potato. Through slits, or sometimes through definite projections of the wall, 

 termed papillae, the zoospores escape. 



Reproduction 



The behaviour of these zoospores depends upon the environmental 

 conditions (Fig. 197). If they are liberated from the sporangium immediately 



Fig. 197. — Synchytrium endobioticum. A, Young prosorus in enlarged host cell. B, Mature 

 prosorus. C, Passage of nucleus from the prosorus. D, Two sporangia of a sorus 

 above and empty prosorus membrane below. E, Mature zoospores. F, Gametes in 

 contact, left, and after fusion, right. G, Resting sporangium after division of host 

 cells. H, Surface view of resting sporangium during the formation of zoospores. 

 J, Young zoospore from resting sporangium. {After Curtis.) 



