NOTES FROM THE BIOLOGICAL DEPARTMENT OF THE 

 ONTARIO AGRICULTURAL COLLEGE. 



PEACH YELLOWS, 



'/OR several years investig^ators have 

 been trying- to determine the nature 

 1^ of this malady of the peach orchard. 

 Dr. Erwin F. Smith, of Washington, 

 worked carefully and patiently but reached 

 no conclusive result as to the real cause. 

 Although no positive conclusion was arrived 

 at, yet many valuable additions were made 

 to our knowledge of the conditions surround- 

 ing the Peach Yellows. For example, Dr. 

 Smith showed that although the disease was 

 communicable to other peach trees of the 

 orchard, yet the manner in which the infec- 

 tion spread was very erratic. Young trees 

 planted in the places of those destroyed 

 otten escaped infection, and trees nearby 

 diseased ones often remained healthy; more- 

 over, it was determined that neither the age 

 nor the vigor of the trees was a predisposing 

 factor in the matter of infection, as would 

 naturally be expected if the cause were bac- 

 terial ; besides, apparently the ravages of 

 disease were not influenced by the nature of 

 the soil nor the variety of the peach tree. 



It was noticed also as a characteristic fea- 

 ture of the Yellows that the fruit ripened 



prematurely, but here again a difficulty arose 

 in trying to explain how it was that all 

 diseased peaches of a tree did not prema- 

 turely ripen at the same stage of maturnity. 



It is very evident, then, that the disease 

 must be produced by some cause operating 

 independent of such factors as the age and 

 variety of the tree or the nature of the soil in 

 which the tree is growing. The cause, what- 

 ever it may be, must be sufficient to explain 

 the fact of the communicability of the 

 disease by budding, the irregular premature 

 ripening of the fruit and the periodicity in 

 the severity of the attacks. 



In a recent number of Science(Dec. 7, 1900) 

 Mr. O. F. Cook, of Washington, proposes 

 a theory of the Peach Yellows, which should 

 naturally attract some attention on the part 

 of peach growers. In his own words, "the 

 yellows may be the result of the poisoning 

 of the protoplasm of the living cells by the 

 bite of a small arthropod, probably a mite 

 of the family Phytoptidae." 



In support of his theory Mr. Cook brings 

 forward well-known cases of leaf-spot, or 

 yellowing of the tissues, which are plainly 



