ROOT KNOT 585 



Gumming is, therefore, not considered in itself a disease, but rather 

 an indication of conditions unfavorable to the thrifty growth of the 

 tree. It has been usually found by investigation that trees in perfect 

 condition of health, with the moisture just enough and not excessive, 

 are not troubled with gumming; but there are cases in which this 

 statement does not wholly apply. There is very much in this con- 

 nection which is not fully demonstrated as yet and the University 

 Plant Disease Laboratory, at Whittier, is undertaking careful and 

 wide studies of which preliminary results appear in the University 

 Bulletin No. 200. When there is an outbreak of gum where it can 

 be treated it is desirable to cleanly remove all the unhealthy bark 

 cutting clean to sound bark and covering the wound with paint or 

 wax to exclude the air. 



Root Knots. These are excrescences upon the roots or at the 

 root crown of various trees and of grape-vines, and they have been 

 a serious trouble in this State for a good many years. Some of the 

 knots have been studied by experts in plant pathology and the cause 

 of the trouble demonstrated to be a fungus and the disease infec- 

 tious. A satisfactory treatment has, however, been discovered. If 

 the knot has not increased in size sufficiently to seriously interfere 

 with the growth of the tree it can be smoothly removed, the wound 

 treated with the Bordeaux Mixture, and the knot will not reappear 

 at the same place. Success has also been had with boring a hole 

 into the knot and filling the hole with bluestone solution, but some 

 trees have been killed in this way. Bluestone can be used with least 

 danger when the tree is dormant. 



