Distribution 25 



4 varieties ; to the New World, 14 species with 5 varieties ; leav- 

 ing 17 species and 2 varieties common to both. 



In deahng with the features of distribution, however, w^e must 

 remember that while Europe and the United States have been 

 well-worked for the Erysiphaccac, little has yet been done in in- 

 vestigating the family in Africa, Asia and Australia. 



An interesting fact is the occurrence in Japan of two species, 

 Unciniila Clintonii and U. polychaHa^ hitherto supposed to be en- 

 demic to America, Sphaerothcca uiors-uvae, widely spread in the 

 ynited States on species of Ribes, appears to be identical with the 

 European species S. tomoitosa growing on species of Euphorbia, 

 Microsphacra cuphorbiae is not uncommon in the United States 

 on EupJwrbia and Astragalus^ and appears in Asia (Turkestan) on 

 Cohitea and Astragalus {M. coluteae). Uncinula ticcator, long sup- 

 posed to be endemic to North America, was discovered in 1892 in 

 Erance. and has now been found in species of Actinidia in Japan. 



'lifolia 



Japa 



Most 



variation in their characters, and the description of each species 

 given in the following pages will usually be found to be much 

 wider than that hitherto given by authors. 



Examination of a large amount of material has shown con- 

 clusively that such characters as the persistence or evanescence of 

 the mycelium, the size of the perithecium, the number of asci, 

 and in many cases the number of spores are far more variable 

 than is generally supposed. On the other hand, just as we find 

 that a classification based on differences in the shape of the ap- 

 pendages divides the family into natural genera, so also we find 

 that frequently the best specific characters are those derived from 

 the appendages. The minute differences in the shape, mode of 

 branching, etc., of the appendages are specifically constant, and 

 usually show far less variation than other cTiaracters. It is im- 

 portant to note, however, that the mature condition of the ap- 

 pendages is necessary to show these specific characters ; many 

 erroneous descriptions have arisen from the examination of only 



immature stages. 



At the end of the synonomy of each species, a list of exsic- 



