94 



ease is American in its origin and occurs more or less 

 abundantly throughout the United States, but is es- 

 pecially prevalent in the Eastern States, where it seems 

 to have first appeared. In some sections of the East 

 growers of plums and cherries have been forced from 

 time to time to abandon the industry in consequence of 

 the ruinous effects of its work. Cases are on record 

 showing that orchards that paid handsomely one year 

 were completeh^ destroyed the following year or two. 



The more intelligent growers are fully aware of the 

 injuries they are liable to suffer from its attacks, and 

 whenever it appears on their premises they lose no time 

 in removing it by cutting off affected parts or rooting 

 up the diseased trees. Through such wise measures the 

 disease has not been allowed to get beyond control. 



Hoto to detect it. — Some fully formed knots are illus- 

 trated in figure 3. These are large, rough, black ex- 

 cresences, due to the growth of a fung-us {Ploivrightia 

 morhosa) in the cambium layer of the branches or twigs 

 These crusty enlargements may extend entirely around 

 the branch or grow lengthwise on one side. The first 

 swelling usually begins in the spring, when the sap be- 

 gins to flow; it may, however, occasionally be noticed 

 in the fall. Th first indication is a slight enlargement, 

 usually longitudinal, which rapidly increases in size 

 as the season advances. The bark is soon ruptured and 

 finally scaled off, exposing a yellowish brown crusty 

 surface. In May the fungus bears a crop of infecting 

 spores on the surface of the knot, which gives it a vel- 

 vety appearance. These spores are soon scattered by 

 the Avind or other natural agencies furnishing infection 

 for other trees and thus disseminating the disease. The 

 knot then becomes hard and black as fall is approached. 



