42 MASSACHUSETTS HORTICTJLTURAL SOCIETY. 



The knots on the choke cherry when compared with those on the 

 phim and cultivated varieties of cherry are seen to be shghtly differ- 

 ent in general appearance, but when viewed with the microscope all 

 prove to be identical, the difference noticeable to the naked eye 

 being due to more favorable circumstances for its growth afforded 

 by one species of Prunus than another. 



Dr. Schweinitz was the prst to describe the fungus causing the 

 black knot, under the name of Sphceria morbosa. 



The black knot is far from being of recent origin, and has fur- 

 nished a subject about which vastly more has been written than was 

 known. Many, especially the early writers, held it to be of insect 

 origin, while, later, others have looked upon it as a vegetable growth, 

 and still others include in its production both these forms of life. 

 During the last thirty years the insect theory has been gradually 

 given up by the entomologists, but it still remains for many fruit 

 growers to accept the knot as being of fungous origin. The proof 

 given by Dr. Farlow is very conclusive on this long disputed point. 

 " Fu'st, the knots do not resemble the galls made by any known 

 insect. Secondly, although insects or remains of insects, are gen- 

 erally found in old knots, in most cases no insects at all are found 

 in them when young. Thirdly, the insects that have been found by 

 entomologists in the knots are not all of one species, but of several 

 different species which are also found on trees that are never affected 

 by the knot. On the other hand, we never have the black knot 

 without the Sphceria morbosa, as was admitted by Harris, and the 

 mycelium of that fungus is found in the slightly swollen stem long 

 before anything which could be called a knot has made its appear- 

 ance. Furthermore, the Sphceria morbosa is not known to occur 

 anywhere except in connection with the knots." 



With a knowledge of the nature of this contagious disease, the 

 remedy at once suggests itself, namely, to cut off the knots, together 

 with the swollen portions of the branches, whenever and wherever 

 they are found. In autumn, as soon as the leaves fall, the knots 

 can be most easily seen, and all branches bearing them should be 

 cut off and burned at once. Though the- sexual spores do not ^rm 

 until late in winter, it was carefully observed that were the knots 

 left undcstroyed they would ripen after the branch was cut from the 

 tree. The choke cherry, bird cherry, and wild plum furnish means 

 for rapid propagation of the knot, and they should be gladly sacri- 

 ficed for the good of their more worthy allies. Knowing the cause, 



