128 



The Canadian Horticulturist. 



This pest is known to attack at least eight species of the genus Prunus. 

 The appearance of the knot varies somewhat among the various species, but as 

 Dr. Halsted points out, '* it has been demonstrated by direct inoculation, that 

 the spores from the knots of the choke cherry will produce the quite dissimilar 

 excrescences common to the garden plum, a fact that in this connection it is 

 important to know. 



Fig. 650. 



RECAPITULATION. 



1. The fungus which causes the growth of the knots, was described by the 

 celebrated German mycologist, Schweinitz, some 70 years ago. He was of the 

 opinion, however, that the knots were caused by some gall-producing insects, 

 rather than by the fungus which he found upon them. 



2. Several species of insects have been observed, inhabiting the knots, but 

 none of them belong to the gall-producing kinds, and most of these insects are 

 also found upon other trees which never produce the knots. 



3. A characteristic fungus is invariably found in the end fronting on the 

 knots, from their earliest to their latest stage, and nowhere else. 



4. The life-history of this fungus was carefully worked out and published 

 by Dr. Farlow, in the Bulletin of the Bussey Institute, in 1876. At this tim^ 



jits communicability. between wild and cultivated forms of the plum and cherry 

 was proved by artificial inoculation. 



