88 C. H. PECK ON THE *^ BLACK KNOT." 



sometimes being attacked while cherry trees in their vicinity escape, 

 or til e 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 neighbours' cherry trees are 

 swarming with black knot, and cherry growers need not be 

 alarmed when their neighbours' plum trees are infested 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 cannot spread upon our cultivated cherry, and 

 still less ujDon our cultivated plum trees ; but black knot un- 

 doubtedly 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 observa- 

 tions 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 fruit- 

 ing specimens of the black knot fungus, taken from the choke 

 cherry tree, Prunus Virgitiimia ; 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 dif- 

 ferent 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 

 that the black knots of both plum and cherry trees are produced 

 by the same species of fungus, viz., Sphceria morhosa, Schw., and 

 that it can and does spread from cherry to plum trees, and from 

 plum to cherry trees, and therefore that there is no safety for some 

 cherry trees in the vicinity of affected plum trees, nor for some 

 plum trees in the vicinity of affected cherry trees. We admit that 

 there are certain species, both of cherry and of plum trees, that 

 do not seem to be liable to the attacks of this fungus, which per- 

 haps is the origin of the theory of distinct species of black knot. 



