26 



COMPARATIVE MORPHOLOGY OF FUNGI 



aceae to the Myxomycetes and flagellates would be premature; probably 

 they have arisen from these groups and have been much modified by their 

 parasitism. 



Woroninaceae. — Since the position of this family is obscure, its 

 classification here is provisional. It contains all biflagellate Archimy- 

 cetes. The assignment of definite phylogenetic lines is postponed until a 

 greater number of species is known. A representative of each of the 

 more carefully investigated genera will be described. 



The zoospores of Olpidiopsis Saprolegniae on Saprolegnia are ovoid 

 or reniform. The two flagella arise laterally somewhat toward the apex. 



eg 



■:0- 



.-■<=>•: 



if 



*fe"v 



°-i T " 



Si' 





.fcra.-. 



i&i'' 



m 



a.'-s-.-i--':'? 



^ „«>■', .'-^s.. : '&^- 



Fig. 15. — Olpidiopsis Saprolegniae. 1. The zoospore has formed a membrane and 

 allowed its content to slip into a hypha of the host. 2 to 5. Development of the young 

 protoplast to a zoosporangium. 6, 7. Development of the zygote. 8. Host hypha with 

 3 empty zoosporangia and 2 hypnospores. (1, S X 1,000; 2 X 890; 3, 6, 7 X 670; 4, 5 X 

 1,370; after Barrett, 1912.) 



A few minutes after swarming they come to complete rest and after a 

 short rest period, swim on. If they reach a filament of Saprolegnia, they 

 show some amoeboid movement, and surround themselves with a wall, 

 while the germ tube pierces the wall of the host hypha, into which the 

 uninucleate cell content is ejected (Fig. 15, 1). By streaming, the naked 

 protoplasm may be carried for a distance in the hypha; it grows rapidly, 

 becomes multinucleate, and after two or three days surrounds itself 

 with a wall and becomes a zoosporangium. At maturity several small 

 vacuoles form and these then flow together into a large central vacuole 



