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 



D 



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. dcnsa ; 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 Umbellifera) 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), 



