Dr. Smith: Have you any evidence for or against the decline of immunity in the tree?
Dr. Zimmerman: I think it will decline.
Dr. Smith: Then we have got to keep on immunizing like spraying. I didn't mean necessarily annually. I mean perhaps it is not a permanent achievement.
Dr. Zimmerman: I imagine that the tree will be sufficiently attacked by blight to keep the immunity up. It is wise to have it attacked once in a while.
Mr. Hershey: Isn't this only carried on until you get natural resistance?
Dr. Zimmerman: I know that it will be a long time before I can have chestnut trees to produce like Mr. Harrington's. But I am going ahead. I can't wait 17 years. All I need is some time and I will produce chestnuts of the finest varieties, as Mr. Harrington has.
Dr. Smith: How long will it take?
Dr. Zimmerman: They will hold their immunity as well as the Chinese. The ones I have are worth planting right now. I have trees that are standing up better than any Chinese chestnuts are. It takes a long time before the immunizing principle is so disseminated that every part of the tree will have an equal resistance. I can easily see that by cutting off a scion and grafting it I may get hold of one that has not had its immunization distributed as it should be.
Dr. Smith: A fairly ignorant man can take machinery and spray an orchard. Can he do the same with immunizing?
Dr. Zimmerman: No sir, he can not.