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Notes on the " Black Knot." 

 By C. H. Peck, Esq., of Albany, New York. 



What is black knot ? To tliis question Dr. Fitch, Entomologist 

 of the New York State Agricultural Society, answers : " It is a 

 large irregular black wart-like excrescence which grows upon the 

 limbs of plum and cherry trees, causing the death of all the branch 

 above it and extending down the limb farther and farther every 

 year till the whole branch is destroyed, other limbs at the same 

 time becoming affected in the same manner, and also the limbs of 

 other trees in the vicinity. If it is neglected, it in a few years 

 kills the tree." 



The late lamented B. D. Walsh, Entomologist of the State of 

 Illinois, thus defines it : " It is a black, puffy, irregular swelling 

 on the twigs and smaller limbs of plum and cherry trees, and in 

 one instance that came under my observation, of peach trees, mak- 

 ing its first appearance in the latitude of New York early in June, 

 and attaining its full growth by the end of July. Usually a tree 

 that is attached in this manner is affected worse and worse every 

 year until it is finally killed, and where one tree of a group is af- 

 fected, the malady usually spreads to them all in process of time." 



According to our own observations the death of the branch 

 above the excrescence is not always produced by the first attack. 

 In such cases the malady extends ujDwards as well as downwards. 

 The time of the first appearance of the excrescence is in late 

 autumn, although the external development of the fungus is not 

 manifest until the following May. We have never found it on 

 peach trees. 



Let us now see what is written concerning the origin of black 

 knot. Schweinitz, the botanist who wrote the original description 

 of Sphceria morbosa, the fungus that develops itself on the ex- 

 crescence, seems to have been in some doubt concerning the origin 

 of the tumour. In his description he uses these words : " Hcec 

 massa num sit effectus ictuum Cynipis nescimiis, videmus tamen hic 



