OOMYCETES 



75 



is discharged as zoospores. Most of the forms belonging here are aquatic. 

 The only parasite of land plants is P. Indigoferae which rarely forms 

 zoospores and reproduces almost exclusively by oospores, wasteful of 

 material. 



In the subgenus Nematosporangium, the sporangia are filamentous, 

 but separated from the rest of the mycelium by a septum. In the sub- 



-if *i 



10 



.••y-rjt^-. 



m 



11 



Fig. 45. — Pythium. Forms of sporangium. Pythium gracile. 1. Filament of Vau- 

 cheria with parasite. 2, 3. Vegetative hyphae which have swollen terminally. 4. The 

 protoplasm has passed into a germ sac. 5. Zoospore formation. Pythium proliferum. 

 6. Zoosporangia. 7. Proliferating zoosporangiferous hyphae. 8 to 11. Germination of 

 zoosporangia. Pythium diacarpum. 12. Habit of fungus on decaying wood. Pythium 

 intermedium. 13, 14. Formation of zoosporangia. Pythium palmivorum. 15. Germinat- 

 ing oospores. (1 X 565; 2 to 5 X 330; 6, 12 X 67; 7 X 100 8 to 11, 13, 14 X 200; 15 X 

 270; after Butler, 1907.) 



genus Sphaerosporangium, the characteristic spherical sporangia lead to 

 true conidia; in the section Orthosporangium, e.g., P. proliferum., they 

 always remain attached to the mycelium and germinate in situ (Fig. 45, 

 6 and 7) ; here they behave as ordinary sporangia. In the section M eta- 

 sporangium, e.g., P. debaryanum and P. intermedium (Fig. 45, 13 and 14), 

 they may fall off and be disseminated by wind or water as true conidia. 

 In their manner of renewal, also, these two sections may be distinguished. 



