Report on Botany. 



adduced which consists in plum trees sometimes being 

 attacked while cherry trees in their vicinity escape, or the 

 reverse. Then these words follow : " The practical infer- 

 ence to be drawn from the above theory is, that plum growers 

 need not be alarmed when their neighbors' cherry trees 

 are swarming with black knot, and cherry growers need 

 not be alarmed when their neighbors' plum trees are in- 

 fested in the same manner; for the disease can only spread 

 from plum tree to plum tree and from cherry tree to cherry 

 tree. * * * It would further seem to follow that 

 black knot growing upon the wild choke cherry can 

 not spread upon our cultivated cherry, and still less upon 

 our cultivated plum trees ; but black knot undoubtedly can 

 and does spread from the wild plum tree on to the tame 

 plum tree, and probably from the wild red cherry on to 

 our tame cherry trees." 



We are not disposed to dispute the correctness of the 

 observations from which this inference was drawn, but we 

 do believe the inference to be incorrect and calculated to 

 lull fruit growers into a feeling of false security. We have 

 carefully examined good fruiting specimens of the black- 

 knot fungus taken from the choke cherry tree, Prunus Vir- 

 giniana, the cultivated cherry tree, Prunus Cerasus, and the 

 cultivated plum tree, Prunus domestica, and we are prepared 

 to state that there is no essential difference between the black 

 knots of these trees. The spores in all are essentially alike 

 and mature at the same time. There is a slight difference in 

 the general external appearance of the black knots of the 

 different trees, but this is all, and no good botanist would 

 venture to consider such a difference to be alone of any 

 specific value. We have time and again observed plum 

 trees and cherry trees along the same fence and in the 

 same enclosure alike infested by black knot. We have 

 seen plum trees badly infested in localities where the wild 

 plum tree does not occur at all. We therefore conclude 



