PERONOSPORALES 205 



the literature. It is hoped that the following resume will serve 

 to put the reader in touch with the general situation. 



Phytophthora infesians (Mont.) de Bary (1876) is the cause of 

 the widely disseminated and extremely destructive late blight of 

 potato, and, from the economic standpoint, is the outstanding 

 species of the genus. It is now found wherever the host is grown. 

 The early home of the potato is not certainly known. When 

 first introduced into Europe it was apparently free from the blight 

 but later the disease appeared there in epiphytotic form, and two 

 outbreaks, one in 1845 (cause of the Irish Famine) and another 

 in 1875 are now historical. In the latter year the celebrated 

 German mycologist Anton de Bary undertook the study of the 

 disease, and the pubhcation (1876) of his results constitutes the 

 first paper of importance on any species of the genus. In it he 

 erects the genus Phytophthora on this species. He describes the 

 sporangial stage, but did not find oospores. He states that the 

 fungus hibernates in the tuber in the mycelial condition, and 

 grows up through the young shoots the following spring giving 

 a systemic infection of the plant above ground. The English 

 mycologist, Worthington G. Smith (1875; 1876 a, b, c) described 

 and figured the oospores stating that he had discovered them in 

 the leaves. His observations were not substantiated by others 

 and his account fell into disrepute. For many years mycologists 

 regarded the species as lacking the sexual stage. Finally Clinton 

 (1911 a, 6) announced that he had obtained oospores in pure 

 culture on oat agar, and others have since succeeded in duplicat- 

 ing his results (Briiyn, 1923). Clinton also obtained hybrid 

 oospores between mycelia of Phy. infestans and Phy. phaseoli 

 Thaxter. More recently Murphy (1927) has found oospores on 

 the surface of tubers in nature The species is not confined to 

 the potato. It occurs also on tomato, eggplant, and other solana- 

 ceous hosts. According to Berg (1926) the fungus on tomato is a 

 different biological strain from that on potato. Important papers 

 on the species have been published by Jones (1912), Clinton (1905 

 6; 1906 a), Melhus (1915 b), and Pethybridge (1911 a; 1912; 

 1913 c). Although Phy. infestans is grouped with the species 

 characterized by amphigynous antheridia, the oospores are in 

 fact usually developed in the complete absence of antheridia. 

 The spores are then termed by some authors chlamydospores. 



Phytophthora phaseoli Thaxter (1889) parasitic on the lima 

 bean, Phaseolus lunatus, is fully treated by Clinton (1906 b). 



