CHYTRIDIALES 



39 



spore membrane and infection tube degenerate. Zoospores soon develop 

 in the zoosporangia, remain for a short time lying before the opening of 

 the emission collar, there undergo some amoeboid alterations in form and 

 finally swim away (Fig. 22, 4 and 5). In a related species, P. Oedogo- 

 niorum, the whole content of the zoosporangium may pass out of the emis- 

 sion collar and be differentiated into individual zoospores. 



In the sexual plants, the germ sac is divided into a smaller male and a 

 larger female sexual cell (Fig. 22, 6). The content of the male passes 

 over into the female. This as a whole (?) becomes a hypnospore, 

 thickens its wall, so that the male cell, as in Olpidiopsis, remains attached 

 as an empty cell. Germination follows by zoospores which escape 

 through the emission collar (Fig. 22, 7). 



Fig. 23. — Harpochytrium Hyalothecae. 1. Young parasite on Spirogyra filament. 2. 

 Mature individual. 3. Swarming of zoospores and lateral growth of zoosporangium. 

 4. Empty zoosporangium showing the beginning of proliferation. (After Atkinson, 1903.) 



The Harpochytrieae, because of their unusual habitat and the peculiar 

 proliferation of the zoosporangia, known elsewhere only in the Clado- 

 chytriaceae, are unique in the Chytridiales. 



In Harpochytrium Hyalothecae, which is parasitic or saprophytic on 

 numerous green algae (Atkinson, 1903; Dangeard, 1903), the germinating 

 zoospore forms a small germ tube which swells to a hapteroid structure 

 between the lamellae of the cell wall of the host or within the cell (Fig. 

 23, 2). Rhizoids are absent. The young thallus is uninucleate. 

 Nuclear division begins later and the plant divides into a short stipe 

 cell and a long sporangium which discharges the zoospores through an 

 opening at the tip (Fig. 23, 3). After evacuation, the stipe cell grows 

 into the empty sheath of the sporangium, and develops a new sporangium, 

 repeating the process several times. Resting stages are unknown. 



