Communications. 299 



fungus begins its destructive work. In the spring the swollen 

 portion of the branch increases in size, and the mycelium soon 

 reaches and bursts through the baric, so that by the time the 

 choke cherry is in flower the knob has reached nearly its full size, 

 though differing from an old one in being still greenish in color 

 and solid or pulpy in consistency. 



"With a hand lens one can see small hemispherical protuber- 

 ances which are the beginning-^ of the " perithicea," or pits in 

 which the sexual spores are to form. The whole surface of the 

 protuberances is covered with filaments, which are somewhat flex- 

 uous and branched. At the terminal joints, or frequently a little 

 to one side, conidial spores are borne. These spores continue to 

 be formed until near the close of summer, when the filaments dry 

 up and only their shrivelled remains are to be seen. The knots 

 now assume this black color, the inner pulp being either destroyed 

 by insects or reduced to a powdery mass, with only the hard 

 outer shell which contains the perithicea left in place. About 

 the middle of January the spores in the saos in the perithicea 

 begin to ripen. 



The knots on the choke cherry when compared with tho?e on 

 the plum and cultivated varieties of cherry are seen to be slightly 

 different in general appearance, but when viewed with the micro- 

 scope 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 first to describe the fungus causing the 

 black knot, under the name of Sphceria morhosa. 



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 vege- 

 table growth, and etill 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. "First, the knots do not resemble the 



