104 A Monograph of the Erysiphaceae 



Smlth^have considered that '^ Oidinm TuckcrV — the conidial 

 stage of U. necator — was originally brought from the vines of 

 America to Europe, and thus introduced at once spread over all 

 the Mediterranean vineyards, but that from some cause due to the 

 effect of the change of environment, the fungus lost the power of 

 producing perithecia. Several fungous diseases are now known to 

 have been introduced in this Avay from America to Europe, and so 

 long as America was the only native country known for U. 7i€cator, 

 the idea of the Ameriican origin of '* Oidinvi Tiickeri'^ was natu- 



■ 



ral, although it appears that no direct evidence on the point ex- 

 ists ; now, however, that we know that U, iiccator is native to the 

 Old World, occurring on native plants in Japan, it is a question 

 whether it may not have invaded Europe from the East. Viiis 

 vinifcra is wild in western temperate Asia (and perhaps in the 

 Mediterranean region), being especially frequent in Armenia, Cau- 

 casia, and the region round the Caspian Sea, and it is possible 

 that U, necator Avill be found to occur in wild vines in these coun- 

 tries. It is, of course, possible that '' Oidhim TiickerV existed on 

 European vines before the great outbreak of it in 1847-52 — and 

 there is some evidence favorable to this view — but that, at this time, 

 for some unknown reason it first increased to such an extent as to 

 form a dangerous disease. (For further details of the history of 

 " Oidiuui TuckcH'' reference can be made to the following authors : 

 Viala {I'JZ), von Mohl (250, 251, and 252) and Montague (254). 



As it appears that the formation of perithecia is exceptional in 

 U. necator on European vines, the question presents itself as to 

 how the fungus, in this absence of ascospores, bridges over the 

 period of winter. It has been stated this is effected by a hibernat- 

 ing mycelium ; other authors, e. g., Viala, suppose that the conidia 

 have acquired the power of being able to hibernate. 



It is worth noting that Viala tried many experiments with the 

 view of seeing if vines could be infected with the conidia of Ery- 

 siphe polygo7ii, and conversely, if the host-plants of E, polygoni 

 could be attacked by '* Oidinm Tuckeri,'' but with negative results 



in both cases. 



Galloway (139) has made some valuable observations on the 

 ripening of the perithecia m and the germination of the ascospores 



of the present species. 



'lop. 



