Uncixula 103 



distinctive names proposed by Riley for these two diseases, and 

 now generally in use in America, viz., powdery vine mildew for 

 U. necator {Oidium Tuckeri) and downy vine mildew for Pcrono- 



spora viticola. 



Although Oidium Tuckeri was so terribly prevalent in Europe 

 since its appearance in 1845-6, no perithecia were found associ- 

 ated with it for the first 47 years of its occurrence, and during this 

 time its true systematic position was much questioned. Berkeley 

 (32), recogn-zing its close resemblance to the conidial stage of 

 species of ^/^.y^/Z/r, changed the name in 1855 to Erysiphe Tuckeri. 

 When, however, the Uncinula on the American vines became 

 generally known, it began to be suggested that " Oidium Tuck- 

 eri'' might be merely the conidial stage of this fungus ; and Far- 

 low (121) and Viala and Ravaz (375) among others pointed out 

 the exact resemblance of the American and European Oidium 

 forms. Many mycologists, however, would not admit the iden- 

 tity of the two, contending that the Oidium Tuckeri of the Old 

 World had larger conidia than those of the American U necator. 



Fuckel considered Oidium Tuckeri to be the conidial condition of 

 a variety of Sphacrotheca Castagnei ; whilst others believed it to 

 be that of Erysiphe commuids [E. polygoni). In 1 844 Berkeley 

 recorded {^-j^ the occurrence of a species of Erysiphe, apparently 

 identical with E. communis y growing with U. necator on Vine 

 leaves^ sent from Washington. [This was probably either a stray 

 perithecium of E. polygoni, or probably immature examples (with 

 young straight appendages) of U. necator.] However, in 1892 

 Couderc (93) discovered in several places in France, perithecia on 

 vines attached by " Oidium Tuckeri," and showed that they were 

 identical with those of 17. necator. In the following year Viala 

 (1894) reported an abundant formation of perithecia of U. necator, 

 or diseased vines in many parts of France. This unusual pro- 

 duction of the perithecial stage has been attributed to the sudden 

 alternation of high and low temperatures which took place in 

 these years. Through the kindness of IMr. Jaczewski I have seen 

 specimens (now in the Kew Herbarium) of French examples of 

 U. necator and have found them to agree in everyway with Amen- 



can examples of this species. 



Mycologists, e. g., de Bary, von Mohl, Viala. Worthington G. 



