654 Bulletin 8i. 



SUMMARY. 



I- The black-knot of plums and cherries was first trouble- 

 some in the Atlantic states. Page 637. 



2. Its presence west of the Alleghany mountains seems to be 

 due at least in part to plants introduced from the eastern states. 

 Page 637. 



3. The first swelling of the knot occasionally begins in the fall 

 but is generally first noticeable in the spring. Page 638. 



4. The young, growing knot is yellowish brown in color, but 

 this color changes to black as the season advances. Page 638. 



5. Knots most commonly form in the forks of young branches, 

 at the union of the growths of two seasons, and upon the small 

 spurs which commonly bear the fruit. Page 640. 



6. The cause of the black-knot is a fungus, Plowrightia vior- 

 bosa. Page 641. 



7. The fungus produces from each knot one crop of spores 

 during the early part of the season, and another during midwin- 

 ter, after which the central portion of the knot dies. Page 641. 



8. Black-knots are very generally infested by insects, but these 

 are not the cause of such swellings. Page 641. 



9. The time in which the spores produced by the fungus gain 

 an entrance into the branches is not definitely known, but it 

 seems probable that this occurs soon after the ripening of the 

 spores. Page 642. 



ID. The manner in which the spores penetrate the outer tissues 

 has not yet been observed ; but the fact that the layer of cork is 

 thinnest, or entirely wanting, in those places in which the greater 

 number of knots are found leads to the conclusion that the fun- 

 gus can penetrate the outer tissues at these points, but cannot 

 enter at all places. Pages 643, 644. 



11. Knots found upon old wood first obtained a foothold 

 upon younger wood, from which they spread to the older parts. 

 Page 646. 



1 2 . Many remedies for the black knot have been suggested 

 but none have proved to be efiicient. Page 647. 



13. The most generally recommended preventive measure is 

 to cut out the knots and destroy them. This work should be 



