EXPERIMENT STATION BULLETINS. 



325 



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. The tender shoots and berries are also attacked by this fungus. 

 The disease is particularly favored in its development by cold, wet weather, 

 although any weakness of the vines caused by overbearing, soil exhaustion, 

 or similar causes, may both induce the development of the disease and 

 increase its inj urious effects. 



In many respects the 

 powdery mildew is quite 

 the reverse of the downy 

 form. It nourishes in 

 hot, dry weather; it is not 

 found within the tissues, 

 but forms powdery mas- 

 ses on the outside, obtain- 

 ing its food by means of 

 short suckers with which 

 " it pierces the epidermis. 

 Under favorable con- 

 ditions, the fungi wax 

 and grow strong, and at 

 length send up fruiting 

 hyphae (Fig. 2, ') on 

 which the summer spores 

 are produced by constric- 

 tion. The one at the tip 

 soon falls off and the 

 others follow. If they 

 fall on "good soil" they 

 at once germinate and 

 produce a new mycelium. 

 The winter spores are 

 formed in much the same 

 manner as those of the 

 downy mildews, but their 

 structure IS tar more Com- f ig . 2.— Powdery Mildews of Rose, Cheery, and Grape. 



piex. iilier me lertlliza- j i summer spore of rose mildew ; 2-4, development of carpogonium; 

 tioil of the Carpo°"Onium "• wipter spore (perithecium) with ascus, containing ascospores 

 c -I.-1 r is 'escaping; 6, summer spores of cherry powdery mildews; 7, winter 



nnger-llKe processes are spore of same; 10, mycelium with haustoria in cells; 11, 12, 13, the 

 developed around it ( Fi°" 8ame ' of tlle P owd ery mildew of the grape. —After De Bary. 



2, 3 ), and becoming segmented (Fig. 2, 4 ) they have a cellular or raspberry 

 appearance. From the exterior, appendages of various forms are devel- 

 oped. In some cases they are straight, in others forked at the extremities, 

 and in yet others are coiled as in the Uncinula of the grape (Fig. 2, 12 ). 

 Within these sporocarps or perithecia, one or more oval bodies ( asci ) are 

 developed, and inside these are the ascospores, varying in number from 

 two to eight. These winter spores remain in their cases on the fallen 

 leaves until spring, when the asci burst the walls of the perithecium, and 

 the ascospores escape through orifices at the extremities of the asci. They 

 soon germinate and the cycle is completed. As the vegetative or] growing 

 portion of the fungus is outside the host plant, it is easily destroyed by 

 any fungicide. If the vines are in fruit, it may be found best to use the 



