CLASSIFICATION OF FUNGI 41 



The conidiophores are somewhat evanescent. The 

 oospores are formed in great numbers. 



The genus Pkytophtliora contains many species 

 which are the causes of numerous diseases in both the 

 tropical and temperate zones. In general it may be said 

 that the mycelium penetrates the tissues of the host in 

 practically the same manner as other members of this 

 order. They also give rise to conidiophores and 



Fio. 25. Sporophores of late blight of potato, Phytophthora infestans 

 (after R. E. Smith). 



conidia, and these conidia in turn produce the zoo- 

 spores. The oospores are very common in some species, 

 and very uncommon in others, and in some species 

 unknown. Among the most important species of this 

 genus are Phytophthora infestans, (Mont.) De Bary, of 

 the potato and the tomato (Fig. 25) ; P. phaseoli, 

 Thaxt., of the bean; P. nicotianae, de Haan, of the 

 tobacco ; P. omnivora, de Bary on seedlings ; and P. 

 faber] ^Maub., on cacao, and Para rubber tree (Hevea 

 braziliensis). 



