POTATO ' WART ' 



;i3 



round. All produce resting oospores which are developed within 

 the tissues of the host, and set free when the latter decays ; some 

 of the oospores arise without a definite fertilisation act. 



Plasmopara viticola Berk, causes the ' downy or false mildew ' 

 on the vine, a disease far more destructive, and quite different 

 from, the ' true vine-mildew,' mentioned on p. 757. The fungus 

 attacks the leaves, young shoots and berries of the vine, causing 

 these parts to turn brown and fall off. 



Bremia Lactvca Kegel, is a parasite frequently met with upon 

 various species of Compositse and 

 especially destructive to forced 

 lettuce. 



Peronospora TrifoHorum de Bary, 

 on clover ; P. Vicice Berk., on vetches, 

 peas and beans (Fig. 238); P. 

 parasitica Pers., on crucifers; and 

 P. Schleideni Ung., on onions, are 

 all common, very injurious fungi 

 belonging to the Oomycetes. "" 



Spraying with Bordeaux mixture, 

 or other solutions of copper salts, is 

 the most efiScient method of directly 

 checking the ravages of these pests. 



In several species the oospores 

 are usually produced in autumn and 

 remain dormant until the following 

 spring. As these reproductive bodies 

 enable the fungi to pass from one 

 year to another, it is important to 

 pay special attention to the disposal 

 of refuse containing them. Where- 

 ever feasible, the burning of all diseased plant-debris should be 

 practised. 



The genus Albugo ( = Cysiopus) differs from those of the 



Fig. 238. — Conidlonlioreof /'tfr(7«(;- 

 spora Vicm Berk. (Enlarged loo 

 diameters.) 



