he shape of a twisted thread, much the
same as if you take a collapsible tube of paste and pinch it.

Now, one of those summer spore threads may contain anywhere from one to
five million spores. I have tried to estimate the number in a thread of
this sort which was about an eighth of an inch long, and by taking a
certain portion of that thread, mounting it in a drop of water, and then
counting over a certain measured area under the microscope, I have
estimated, by multiplying, that there were 2,400,000 spores in that one
thread. So you can imagine how many of these spores may be produced by a
single diseased area which has produced perhaps four or five hundred of
those pustules, each pustule containing anywhere from one to twenty
threads. Each one of those spores may develop a new diseased area,
provided it is transported to a fresh break in the bark of a chestnut
tree. Fortunately, only a very small fraction of one per cent ever
reaches the proper place for growth.

This last is what I alluded to as the summer spore stage. There is a
winter spore stage, or technically, the ascospore stage, which comes, as
a rule, later in the development of the fungus. In this same pustule,
later in the season, certain sacs are formed. These have long necks
which extend to the top of the pustule. These sacs are sufficiently
large to be seen with the naked eye. They are dark colored. Inside
these, we have a lot of smaller transparent sacs or cases in each of
which we get eight spores, sometimes in one row, sometimes in two rows.
Each spore can propagate the fungus.

We have, then, two types of spores, either one of which can reproduce
the fungus under suitable conditions. There is still another way by
which the disease may be kept going. The vegetative stage can survive
the winter and continue growing the following year.

I will say right here that I am planning to give you merely an outline
of this disease, and have time afterwards for questions which I think in
a meeting of this sort are one of the most productive sources of
information.

In regard to the rapidity of spread of this disease, I will merely call
your attention to two cases as illustrations, or to certain facts,
rather. One is that the disease, so far as our attention has been
directed to it, has developed over the area indicated on the map since
the fall of 1904. Another case is one which has occurred in Rhode
Island, where I have had a chance to watch its developme