EXPERIMENT STATION BULLETINS. 



377 



Fig. 27. — A, Concord grapes diseased with black rot, and found hanging on vines in March; 



b, small portion of surface, magnified, of diseased grapes, showing ^pimples or pustules; 



c, section of a pustule, showing formation of numerous minute, spore-like bodies (sper- 

 matia); d, section of another pustule which produces tlie summer spores which are seen 

 oozing out of the protruding mouth; e, separate spores; f, a spore sac (ascus), contain- 

 ing eight winter spores, which are produced in a pustule, similar to d, on the diseased 

 grapes which lie on the ground over winter, (d, e, f, after Scribner, in part, the others 

 original.) 



enlarge until the whole berry Is involved. Wrinkling of the fruit due to drying, 

 then takes place, the affected berries remaining attached to the stems. Such 

 fruits possess a black, strongly wrinkled surface studded with minute points 

 or pustules which lie just under the skin. These little pustules are spore-forming 

 organs and have a small projecting mouth through which the spores are dis- 

 charged when the grape is wet. On becoming dry these microscopic spores may 

 be carried to other parts of the plant or vineyard thus serving to disseminate 

 the disease during the growing season. Other spores produced in another man- 

 ner also serve the same purpose. 



The old grapes and diseased leaves, moreover, when left on the vines or lying 

 on the ground give rise to another spore form, the spores being produced in spore 

 sacks (asci) contained in little cavities (perithecia). This spore form remains 

 dormant until spring thus carrying the disease through the winter. 



Treatment. The fact that the old diseased leaves and grapes are the hiber- 

 nating places of this fungus points out the need of destroying them before growth 

 begins in spring else the disease is almost sure to reappear. Raking and burning 



48 



