herit immunization from their parents.

DR. SMITH: We vaccinate each generation of youngsters.

DR. ZIMMERMAN: I was speaking of the experiments with guinea
pigs.

DR. SMITH: Isn't smallpox vaccination against your theory?

DR. ZIMMERMAN: I don't think so. They are doing it with other
things. I found a human being giving the reaction for typhoid for
seventeen years after he had been immunized.

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.

DR. SMITH: Perhaps I should not have used the word ignorant. A
farm hand can spray and make a pretty good crop of apples.

DR. ZIMMERMAN: No, he can't do it. It hasn't been easy. I have
run into all kinds of obstacles. As soon as I injure the stock a little
bit the blight takes it. As soon as I can raise them on their own roots
it will be all right. That will come.

DR. SMITH: Have you seen chestnut grafts root as the apple
does?

DR. ZIMMERMAN: Yes, right below the surface. A couple of them
were that long. They will send out roots. Then I have noticed on some,
that at the place where I grafted the callus got quit