New York Agricultural Experiment Station. 315 



develops into a spore. While this spore is developing at the tip 

 the branch is growing longer and the formation of new spores is 

 begun in the same way lower down. As soon as the tip spore 

 ripens it drops off, and as the branch is continually growing and 

 forming new spores, there is a succession of ripe spores scattered 

 broadcast to spread the disease. When these spores alight on 

 the leaves or fruit with proper conditions of moisture and tem- 

 perature present, growth immediately takes place; and since 

 thousands of these spores are formed daily the disease is spread 

 very rapidly. 



The fertilization and development of the winter spores corre- 

 spond to the fertilization and development of seeds of higher 

 plants but are quite different and usually take place late in the 

 season of growth of the fungus. In certain instances where two 

 threads come near to or cross each other an enlargement or cell 

 forms on each, one partaking of the functions of the male organs 

 and the other of the female organs of a flower. At a certain 

 stage of the development protoplasm passes from the male cell 

 to the female cell and the latter is thus fertilized. Growth imme- 

 diately begins and by the time the fungus assumes a brownish 

 color black specks may be seen upon it; these specks are the 

 winter spore cases (perithecia). Within the dark covering of the 

 winter spore case will be found an inner spore case (ascus) which 

 contains eight of the winter spores. In this double covering of 

 spore cases the winter spores live over winter. By spring the 

 cases break open and the spores escape. They are blown about 

 by the wind and when they reach the leaves or fruit of the goose- 

 berry bush under favorable conditions growth takes place and 

 the pest is started for the season. 



As a rule only the English varieties and their seedlings are 

 attacked by mildew, although the American varieties are not 

 always exempt. A comparison of the susceptibility to mildew of 

 the English varieties as grown at this Station is given in Bulletin 

 No. 114. 



