Report on Botany. 



195 



as Dr. Burnet supposed, or by the irritating punctures of 

 insects, which is the prevailing opinion, they form an appro- 

 priate bed for the growth of numerous little parasitical 

 plants or fungi." 



Dr. Fitch claims to have made a careful investigation 

 of this subject and as his observations are quite accurate 

 we again quote from his address : " There has been much 

 speculation as to the cause and true nature of these 

 excrescences. * * Most persons suppose them to be 

 of insect origin. The larvse of the curculio are almost 

 always found in them, and these larvse consume nearly all 

 the spongy matter of the warts, but do not touch the little 

 fungus growing on their surface, which remains, forming 

 a kind of shell, after the whole inside is devoured. But as 

 these excrescences are sometimes found wholly free from 

 curculio larvse and all other worms, it is obvious they are 

 not the cause of their growth. * * Suffice it to say that 

 now having carefully examined these excrescences from 

 their commencement onward through their subsequent 

 growth, I am prepared to say, with the fullest confidence, 

 that the microscope shows nothing whatever about them, 

 externally or internally, indicating that an insect has any- 

 thing to do with causing them." Then after giving his 

 views as to what constitutes a fungus, he says : " We arrive 

 at the conclusion that these excrescences are not of insect 

 origin, and are not a vegetable fungus, but are properly a 

 disease of these trees, in many respects analagous to the 

 cancer in the human body." 



Mr. Walsh, whose definition of black knot we have 

 already quoted, agrees with Dr. Fitch in concluding that 

 the excrescences are not of insect origin. He also claims 

 to have carefully watched the black knot through all its 

 stages from its earliest commencement to its complete 

 maturity. He affirms that he bred from the galls five dis- 

 tinct species of insects beside the curculio, but that not one 



