194 AM ERIC AN POMOLOGY. 



it is neither a disease nor a gall, we may infer by the 

 method of exhaustion that it must be a fungus, or rather 

 an assemblage of funguses. In confirmation of this theory 

 may be adduced the very remarkable analogies between 

 the structure of the Black-knot and that of the fungus, 

 described above as occurring on Red Cedar. That this 

 last is really and truly a fungus and not a gall, is shown 

 by the fact, that it is scarcely ever inhabited by insects ; for 

 out of hundreds of specimens that I have cut into, both 

 green and dry, not more than two or three contained the 

 larvae of the moths, but one contained what was prob.ibly 

 the larva of an Ichneumon-fly, and all the rest were per- 

 fectly solid and unbored. On the other hand, Black-knot 

 is so infested by insects, that it is almost impossible to 

 find a mature specimen that is not all bored up by them. 

 The cause of this remarkable difference may be attributed 

 to. the well-known repugnance of almost all kinds of in- 

 sects for Red Cedar. 



"If, then, Black-knot is a fungus, and if, as I think I 

 have shown, it is an annual plant propagating itself by 

 seed or the so-called ' spores,' and the ' spores ' make their 

 appearance about tlu> end of July in latitude 41 30', then 

 it must be obvious that if all the Black-knot on a parti- 

 cular tree is cut off and destroyed in the fore-part of July, 

 or a little earlier or later as you go further south or further 

 north, an effectual stop will by put to its. further propaga- 

 tion. It is true that the ' spores ' are in the form of an im- 

 palpable powder, so that they may be carried some con- 

 siderable distance from other infected trees by the wind ; 

 and it may possibly be further true, that certain c spores ' 

 may lie dormant in the bark for over a yeur, as the seads 



