PERONOSPORA. 



133 



oospore-coat (oospores of P. viciac have a coat with a regular net- 

 work). It occurs on stems, leaves, and petioles of clovers, lucerne 

 and other Papilionaceae, often with disastrous effect. 



P. sparsa, Berk. (Britain and U.S. America). This parasite 

 on the rose was first observed in England. It injures indoor 

 roses, causing a fall of the leaf, preceded by the appearance of 

 lilac-coloured spots which, on the underside of the leaf, are closely 

 beset with a white coating of conidiophores.^ 



Fk;. i'i.—Pi:ronos,mra viciac. Coiiidiophurus and conidia. (v. Tubcuf del.) 



P. arborescens (Berk.). On leaves and shoots of wild and 

 cultivated i)oppies ; especially injurious to seedlings of garden 

 species. 



P. parasitica (Pers.) (Britain and U.S. America). This pro- 

 duces greater or less deformation of attacked stems of many wild 

 and cultivated Cruciferae. Amongst cultivated plants the most 

 liable to injury are the varieties of turnips and cabbage, radish, 

 rape, cress, wallflower, also the mignonette. It is generally found 

 along with Cystopus candidus on shepherd's purse {CapscUa). 



P. cytisi, Rostr.,2 attacks seedlings of hiburnum in Denmark, 

 causing death in a few days. The leaves become brown spotted, 



^ Zeitschrift f. P.-krank., ii., p. 386, (description of attack in Silesia.) 

 -Rostrup, Zeitschri/t f. Pflanzenkrankhtitai, 1892. 

 Magnus, JJedwigia, 1892. 



