THE FUNGI 



223 



Phytophthora, to which the Fungus causing the Potato 

 disease (P. infestans) belongs. Here, and also in a third 

 genus, Peronospora, the sporangia always become detached 

 from the hypha which bears them, before germination 

 (whether by the development of zoospores, or by the direct 



FIG. 94. Germination of the sporangia in various species of 

 Peronospora. A, P. nivea ; a, b, c, stages in the formation 

 of zoospores ; d, free biciliate zoospore ; e, zoospores 

 germinating. B, P. densa ; b, commencement of germina- 

 tion ; c, expulsion of undivided contents ; d, empty 

 sporangium ; e, first formation of a hypha from the 

 contents. C, P. Lactucce ; direct germination through the 

 apical papilla. D, P. Radii ; direct germination, hypha 

 formed laterally. Magnified 400. (After De Bary.) 



formation of a hypha) takes place. The illustrations in 

 Fig. 94 are taken from different species of Peronospora. 



In P. nivea (parasitic on Umbelliferse) the contents of 

 the sporangium divide up at once into a number of 

 biciliate zoospores, which escape by the opening of the 

 terminal papilla (Fig. 94, A). In P. densa (Fig. 94, B), 



