TWENTIETH ANNUAL MEETING. 87 



gained suiScient strength, send down through the stomata or breathing 

 pores of the leaves, slender stalks (hyphce), which bear, on the tips of 

 their branches, oval bodies known as conidia or summer spores. These 

 give the under side of the leaves a whitish, downy appearance, while the 

 upper surface takes on a yellow and finally a brown color. 



The spores soon drop off, and, if they fall on a moist place, germinate with 

 great rapidity. The contents swell, become segmented, and finally burst 

 forth as ciliated swarm-spores. They move about for a time, and then, 

 having come to rest, they drop off their cilia and some throw out a 

 mycelial thread which developes into a new fungus if the conditions are 

 favorable. In this way the downy mildews rapidly reproduce themselves 

 during the summer, generation following generation in quick succession. 

 As winter approaches, the fundus sets about the development of spores, 

 with thick coverings that will enable them to withstand the winter's 

 extremes. These are developed at points where two threads cross or come 

 in contact. Each thread gives rise to a rounded protuberance, one 

 corresponding to the pistil and the other to the anthers of flowering 

 plants. The contents of one passes into the other, and the development of 

 the oogonium commences. It finally becomes covered with a thick cell 

 wall, and at the proper time in the spring germinates, either by at once 

 sending out a germ tube or segmenting and then pouring out its contents 

 as ciliated zoospores, much like those developed from the conidia. 



There is a long list of downy mildews, the most injurious, perhaps, 

 being those of the grape and potato. They flourish in cool, moist seasons, 

 and from their being endophytes, living in the tissues, are protected from 

 applications of fungicides after the germ tubes have entered the stomata. 

 For both of these forms, however, the Bordeaux mixture can be applied 

 with good success. To be entirely effectual it should be repeated, 

 especially in rainy seasons, as often as every two or three weeks. In the 

 case of the grape mildew, the lime sticks to the fruit and some other 

 copper mixture, as modified eau celeste, is preferable for the later 

 applications. 



