VINE-MILDEW 757 



generally. The mycelium forms brownish-white irregular 

 spots on the sheaths and blades of the lower leaves of young 

 crops. It is most prevalent in summer among rankly-growing 

 plants. 



The conidia are produced in long chains on short conidio- 

 phores, the fungus in this stage of development being formerly 

 known as Oidium tiionilioides Lk. The perithecia are brown, 

 somewhat flattened, and contain from six to twenty asci in each, 

 which set free their ascopores in spring after remaining dormant 

 on dead leaves and straw during winter. 



Pea-mildew (Erysiphe MarHi Lev.) is a common species 

 which attacks peas and other leguminous plants, especially in 

 dry seasons. Its mycelium frequently spreads over both sides 

 of the leaves of the host-plant, and damages the latter so much 

 that pod-production is reduced, or stopped altogether. The 

 fungus is most abundant on late varieties of peas. 



The perithecia, which have colourless appendages, are dark- 

 brown, and coiitain four to eight asci. 



Various other species of Erysiphe are met with on Compositae, 

 Umbelliferse, and BoraginaceEe. 



(iii) The genus Uncinula has perithecia containing several 

 asci, as in the genus Erysiphe; the appendages, however, are 

 branched in a fork-like manner and always curved at their 

 tips. 



Vine-mildew {Uncinula spiralis Berk, and Curt.). The coni- 

 dial form of this fungus was first noticed in England in 1845, ^nd 

 was first named Oidium Tuckeri by Berkeley : until quite recently 

 the corresponding ascocarp or perithecium was not recognised. 

 The oval conidia arise in short chains, only two or three being 

 produced by each conidiophore. 



The mycelium forms grey spots on the vine leaves, and after 

 a time the affected parts of the latter die and shrivel. The 

 fungus also attacks the young grapes and often kills them before 

 they are larger than peas. 



