PLASMOPARA. 129 



the Vine. This parasite was introduced into Europe from 

 America.^ It makes its appearance in early summer as white 

 patches on the under surfaces of leaves, sometimes also on stalks 

 and fruit. In the course of the summer the leaves show brown 

 spots and dry up. 



The white patches consist of tufts of branched conidiophores, 

 from which ovoid conidia are abjointed. These on germina- 



FiG. 40. — Ptasmopara viticola. Conidiophores, much enlarged, (v. Tubeuf deL) 



tion in rain-drops discharge six to eight swarming cells from 

 which germ-tubes grow into the epidermis of the host-plant ; 

 thus the disease spreads rapidly during moist weather and a 



Peronospora viticola, 1890. Magnus, Wittmack's Gartenzeit, 1883. Soribner, 

 Report of U.S. Dept. of Agriculture for 1886, pp. 96-105; this contains an 

 excellent account of this mildew. Articles on this subject dealing with remedial 

 measures are frequently published in the U.S. Amer. Department reports and 

 bulletins, in the bulletins from experimental stations, and in the horticultural 

 journals. 



^ Seymour and Farlow give it as occuring on every American species of Vitis. 



I 



