87 



This tiling is much more important than I realized at that time, for 

 it means that immunization in this district is pretty nearly a matter of 

 treating blighted trees and curing them. Trees that are so nearly nor- 

 mal that one cannot judge them to be otherwise, become badly infected 

 just as soon as the top is removed for grafting purposes. Then there 

 is another consideration. It is perhaps possible that some of the scions 

 placed on certain stock are more or less incompatible and do not 

 {jroperly nourish the stock, and, after grafting, the plant performs very 

 much as one does that has most of the top removed. Such cases would, 

 according to experiment No. 100, immunize with considerable difficulty, 

 if they did not die altogether. 



I stated above that I was convinced that a plant would immunize 

 under induced antigen. I just want to cite two reasons for believing 

 this. First, when an endothic antigen is placed in the pocket of the 

 plant for the first time, it practically invariably kills the cambium, espe- 

 cially on a pure American chestnut. Succeeding doses act with less 

 destruction, until after several have been given there is very frequently 

 no destruction whatever. This means that something has happened to 

 give the cambium more resistance. 



Second, the blighted area heals over under the influence of an active 

 antigen, frequently covering the wound as evenly as if there had been 

 no infection. I am submitting to you a small branch of a blighted tree, 

 on which the blight area is healed over, and under no influence other 

 than an injected antigen. In all the blighted chestnuts I have ex- 

 amined I have never seen this happen under any other condition. I 

 have seen some healed areas but they have always been associated with 

 a lot of callus and presented a warty, rough looking appearance, spoil- 

 ing the timber for lumber purposes. 



Another reason for believing this is that trees injected seem to hang 

 on after infection beyond the point that one would naturally expect. 

 To illustrate this, last summer I came to two trees of the native Amer- 

 ican chestnut, both blighted at the root. I picked out the worse of the 

 two, this one being blighted in several places, and injected into it a 

 dose of antigen. Two more doses were given during the season. The 

 other tree was left untouched. These trees are about the same size 

 and stand about fifty feet apart. Examination on Sept. 2, '27, showed 

 the uninjured one entirely surrounded at the root, the area just above 



