t bombs) was also an additional implicating
circumstance on the latter occasion.

What then were the results of the survey? They may be stated briefly as
follows:

1. No immune trees were found.

2. For the most part the older trees (from 20 years upward) were
entirely dead, and had been so for a long period, as attested by the
bare trunks, weathered a characteristic gray color which only time can
produce.

3. However, large numbers of seedlings and young saplings were located,
both healthy and diseased.

4. _The most important result was the finding of three well defined
colonies of living mature trees; all of which, by virtue of characters
to be presently described, are offering more or less resistance to the
disease._

SEEDLING TREES

It is well known that seedlings and young saplings are naturally immune
for a certain period, which varies in extent from 8 to 15 years beyond
germination of the seed beginning, of course with the first formation of
the seedling. Such immunity depends, however, not on any inherent
characteristic, but on the fact that at this period the bark is usually
smooth, sound, and free from wounds of any sort where Endothia spores
and mycelium might enter. Of course, when wounded from any cause
whatever during this period of youth, this immunity ends, so that the
condition might perhaps be termed physical, in contrast to physiological
immunity.

As I have already said, large numbers of seedlings, for the most part
still unattacked, were found in many places in the area surveyed. There
are of course no grounds for believing that such seedlings, descended as
they are from non-resistant trees, are physiologically immune. Where
they are free from disease, this exemption is due merely to the physical
immunity I have just mentioned. Since they therefore represent
non-resistant stock, they were used for comparative inoculation work,
which will be referred to later.

I may as well say here as anywhere, that by resistance, I do not mean
total resistance, for that would be immunity. There are, of course,
degrees of resistance, in the plant world just as in the animal world.
One person may resist a cold germ or the influenza bacillus better than
another, that is, it will cause him only a little discomfort. Another
person may not be affected at all, that is, he is totally resistant or
immune. I say this because I have misunderstood when I have used the
term resistance. The trees in the New York