84 



sooner or later I think I can give tbem plenty of data to convince any 

 reasonable man. In fact, if we can raise a bliglit-proof chestnut near 

 Piketown, Penn.^ it is sufficient proof. 



Last year I got into a discussion about immunit}'. A gentleman told 

 me a tree could not be artifically immunized. Also that the tojj of a 

 tree may be vulnerable^ but the root of a chestnut tree was immune. 

 I told him I did not concur in his belief. He gave as his reason for 

 believing that the chestnut root was ^immune that it did not become 

 blighted or die. As a matter of fact some of the roots do live but the 

 reason of that is that they are protected^ not immune. They are pro- 

 tected very much as a man's hands would be if lie should put on a pair 

 of gloves and go out in poison ivy. He is not immune, he is pro- 

 tected. The chestnut below the ground is protected by bacteria in 

 the ground which destroy the chestnut endothia. 



Question : Can you graft a native chestnut, pile up dirt around 

 it and escape the blight.^ 



Dr. Zimmerman: The immune chestnut, as it is referred to in my 

 work, is a chestnut in which an antigen has been injected into its sys- 

 tem and whose cells have developed a definite specific ferment which 

 will digest the endothia parisitica. 



With reference to grafting native chestnut stock with an immune 

 variety, that is one of the reasons why I have tried to get my trees on 

 their own roots. It is almost impossible to go into a blight-ridden 

 district and graft trees and not have them become infected, and a 

 great many of them will die from the infections before they have time 

 to develop a new top. It can be done and I have done it but it re- 

 quires a great deal of work. 



Mr. Bixby: Would you mind telling the audience how the anti- 

 gen is made. 



Dr. Zimmerman: Last year I went into that rather extensively. 

 There are about nine different methods of making the material. The 

 way I have been doing so far is to grow the germs in pure culture on 

 some suitable culture media, sterlizing them and preserving them with 

 trikresol or phenol. Then they are ready to inject. 



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