DISTRIBUTION OF ASCOMYCETES 403 



and vetches, but may also seriously involve tobacco, flax, cotton, 

 and watermelon. Collection records indicate its presence in Cen- 

 tral Asia, the Philippine Islands, Queensland and New South Wales 

 in Australia, the British Isles, Russia, Turkey, Rumania, Hungary, 

 Czechoslovakia, Germany, France, Switzerland, Italy, Puerto Rico, 

 the United States, and Canada. 



Distribution of powdery mildews. Of the 60 species and 

 varieties of Erysiphaceae listed by Salmon (1900), 22 are confined 

 to the Old World and 19 to the New World, leaving 19 that are 

 common to both hemispheres. This situation is accounted for in 

 part by the limitation of certain mildews to particular hosts and 

 to the seemingly almost complete lack of specialization in other 

 species. Erysiphe tortilis, confined to Cormis sanguinea, Uncinula 

 geniculata, to Morns rubra, and Podosphaera biuncinata, to Hania- 

 nielis virginiana, are examples of highly restricted species. Unci- 

 nula aceris is limited to species of Acer, U. flexitosa to Aesculus, 

 and Spaerotheca lanestris to Quercus. Less restriction is exhibited 

 by Erysiphe graminis, which occurs only on various Gramineae, 

 by Uncinula salicis on Salicaceae, and by Sphaerotheca pannosa on 

 Rosaceae. On the other hand, Erysiphe cichoracearum, E. poly- 

 gon! , and Phyllactinia cor y lea are world-wide and attack a wide 

 range of hosts. Phyllactinia corylea, for example, is recorded on 

 48 host-genera in 27 families of plants. Continental distribution 

 of powdery mildews has been summarized by Salmon (1900) as 

 shown in Table 29. 



DlSTRBUTION OF PyrENOMYCETES AND DlSCO.MYCETES. Bisby 



(1933) indicates that about half of the species of Pyrenomycetes 

 listed from Manitoba [Bisby et al. (1929)] are known to occur 

 in Europe. Moreover, only about 12% of those in the list from 



