UNCINULA. 



177 



appendages having hooked tips. Within the peritheeia are 

 found the ovoid asci containing the spores ; there are from four 

 to ten asci in each perithecium, and four to eight spores in each 

 ascus. 



The conidial stage was formerly known as Oidium Tiickeri. 

 The conidia are abjointed as oval colourless bodies from simple 

 septate conidiophores, to the number of two or three in each chain. 

 They germinate at once, and as they are formed in large numbers, 

 especially in moist weather, the disease spreads rapidly. The 

 mycelium is non-septate, or almost so, and attaches itself to the 

 epidermal cells of vine-leaves and young grapes, by lobed attach- 

 ment-discs, from which simple sac-like haustoria make their way 



Fig. 73. — V'ticinula aceris. Peritheeia. (After Tulasne.) 



into the cells. The mycelium forms white spots, but after a 

 time causes the death of cells near it, so that brown withered 

 spots appear. The leaves generally wither, the grapes, however, 

 continue to grow at the places not attacked, till rupture of the 

 coat ensues, then they shrivel up or fall a prey to mould-fungi. 

 Sulphur is the preventive generally used (See p. 170). 



Uncinnla aceris D. C. (Britain). This appears as white spots 

 on the leaves of species -of Acer, native and cultivated. When 

 attacked by this mildew, young unfolding leaves are stunted in 

 growth, while older leaves in autumn still retain their chloro- 



M 



