POTATO BLIGHT (PHYTOPHTHORA INFESTANS) 359 



A spray that is very commonly used is Bordeaux mixture.^ The 

 oospores live over winter and may perpetuate the disease from 

 year to year. Portions of diseased plants containing oospores, 

 when hauled out in manure or scattered about l)y 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 hj'phae 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 

 abundant. Some species of Pythium 

 live in the water like the Saproleg- 

 niales in which order Pythium is 

 often put, while other species live in 

 the soil. 



In contrast to the Water Molds, 

 the Downy Mildews are chieflj^ 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 zoospores and the character of the re- 

 productive organs suggest a relationship to the Green Algae. 



Fig. 310.— The lower 

 epidermis of a Potato leaf 

 showing the conidiophores of 

 the Late Bhght protruding 

 through the stomata and 

 bearing conidiospores at the 

 tips of their branches. Many- 

 times enlarged. 



' 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. 



