PLANT DISEASES 



381 



outer cells have been killed by the fungus so that it is easy 

 for decay-producing fungi to enter. The fungous body is 

 very much like that of the downy mildew fungus, excepting 

 that the short branches that enter the host cells are also 

 thread-like and much more delicate than the main branches. 

 The spores also are very much like those of the downy mil- 

 dew fungus, and the large, thick-walled zygotes are very 

 rarely found. The disease may be kept under control by 

 the use of the Bordeaux mixture, making from three to five 

 applications at intervals of about two weeks. Some varieties 

 of potato seem to be more 

 resistant than others, but 

 their resistance appears 

 to depend partly upon 

 conditions in the locality 

 in which they are grown, 

 because potatoes de- 

 scribed as resistant in 

 one region may prove 

 very susceptible in an- 

 other. 



385. Brown Rot. — 

 This disease attacks the 

 peach, plum, cherry, 

 apricot, and related 

 plants. The damage 

 done by the brown rot 

 fungus (one of the sac 

 fungi) is enormous, a con- 

 servative estimate plac- 

 ing the annual loss in past 



years at over $5,000,000. It usually attacks the fruit, but 

 may cause damage to flowers, leaves, and small branches. 

 On the fruit, the disease first appears as a small, dark, decayed 

 spot which gradually enlarges until it covers perhaps the 



Fig. 216. — A branch bearing peaches 

 afiected by the brown rot. 



