POTATO BLIGHT (PHYTOPHTHORA INFESTANS) 309 
A spray that is very commonly used is Bordeaux mixture.!. The 
odspores live over winter and may perpetuate the disease from 
year to year. Portions of diseased plants containing odspores, 
when hauled out in manure or scattered about by the wind, may 
be a means of spreading the disease. 
In some forms of the Peronosporales as in Albugo or White 
Rust, which forms white blisters on 
the leaves and stem of the Radish 
and other plants of the Mustard 
family, both the sex organs and 
conidiospores are produced internally. 
The hyphae form in clusters under 
the epidermis and form conidiospores 
in chains which push up the epider- 
mis, forming white blisters which 
finally rupture and allow the spores 
to escape. In this Fungus the 
conidiospore produces a number of 
zoOspores. 
In this order Pythium is some- 
times included, species of which at- 
tack seedlings in greenhouses, causing 
the rapid wilting known as damping 
off, when moisture and warmth are Tic. 310.—The lower 
abundant. Some species of Pythium — epidermis of a Potato leaf 
live in the water like the Saproleg- showing the conidiophores of 
niales in which order Pythium is the Late Blight protruding 
3 : . . through the stomata and 
often put, while other species live in hesmie Gouttosmares wt le 
the soil. tips of their branches. Many 
In contrast to the Water Molds, _ times enlarged. 
the Downy Muildews are chiefly para- 
sitic, much less aquatic and, having introduced the conidia, they 
depend less upon water for dissemination. But like the Water 
Molds the presence of zodspores and the character of the re- 
productive organs suggest a relationship to the Green Algae. 
1 The preparation as most commonly made consists of 5 pounds of copper 
sulphate and 5 pounds of stone lime dissolved in 50 gallons of water. Potato 
Spraying Experiments in 1906. Bulletin 279, New York Agr. Exp. Sta. Cer- 
tain Potato Diseases and their Remedies. Bulletin 72, Vermont Agr. Exp. 
Sta., 1899. 
