112 DISEASES OF CULTIVATED PLANTS 



The mildew forms dense, dingy lilac, broadly effused 

 patches on the under surface of the leaves. 



Conidiophores stout, repeatedly branched, ultimate branch- 

 lets pointed and curved downwards, conidia elliptical, 

 25-35x15-24 fji. Oospore globose, brown, wall irregularly 

 wrinkled, 25-38 //. diam. 



As spraying is practically impossible in the case of spinach, 

 diseased plants should be promptly removed before the leaves 

 fall, otherwise the numerous oospores present in the tissues of 

 such leaves may infect plants the following season. 



Peronospora violacea (Berk.) occurs on the petals of Scabiosa 

 arvensis, where it forms pale lilac tufts. 



Conidiophores very short, repeatedly branched, terminal 

 branchlets short, erect, conidia elliptical, 30-40X16-20 //. 

 Oospores globose, brown, wall irregularly wrinkled, thick, 

 20-26 //. diam. 



This species has vesicular haustoria. 



Peronospora Candida (Fuckel). This fungus forms delicate 

 white, effused patches on the under surface of primrose 

 leaves. 



Conidiophores repeatedly branched, ultimate branchlets 

 spreading, often slightly curved, conidia elliptical, 15-18 X 

 10-14 A*- Oospores globose, wall wrinkled, brown, 30-36 /* 

 diam. 



This fungus has occurred in Germany on the leaves of 

 Anagallis arvensis, var. coerulea. 



Violet mildew, caused by Peronospora violae (De Bary), 

 sometimes attacks the Neapolitan and the sweet violet under 

 cultivation, and is also not uncommon on most of our wild 

 violets. The under surface of the leaves becomes more or 

 less covered with a somewhat dense coating of a dingy lilac 

 mould. Such diseased leaves soon dry up and die, and the 

 disease spreads rapidly in a dull, moist atmosphere. Oospores 

 are quickly produced in the dying leaves, hence all diseased 

 material should be removed and not allowed to be on the 

 soil. 



Conidiophores rather short, repeatedly branched, ultimate 

 branches pointed and turned downwards, conidia elliptical 

 with a short apiculus, about 25X18 /x; oospore with a 

 yellowish-brown, wrinkled epispore. 



Recedes from Peronospora in having the conidia furnished 



