recognize this disease? This past summer Pennsylvania
has put into the field thirty or more men who have been trained to
recognize this disease, with the idea of locating the infections in
Pennsylvania. As perhaps all of you know, the legislature of
Pennsylvania has passed a law relating to this particular disease, and
has appropriated $275,000 to see if the disease can be controlled. Their
idea is that they have perhaps fifty million dollars' worth of
chestnuts, and if $275,000 can show whether or not this disease can be
controlled, it is economy to try it.

So far as Pennsylvania is concerned, it means possibly the saving of the
chestnuts in the middle and western parts of the state; but it also
means that if they can check it there, it is likely to save the great
area of chestnut growth along the southern Appalachians. I don't want to
make any prophecy as to how that experiment is likely to come out, but,
however it comes out, it will be a very great object lesson as to what
can be done on a large scale with a disease of this sort.

One of the first things which had to be considered in Pennsylvania was
to train a number of men to recognize the disease, so as to go over the
country and locate the diseased spots. The method of recognizing the
disease I will briefly outline. Of course, over a large country, many
hundreds of square miles, it is a long, and laborious operation to look
over every tree. It is perhaps impossible without a very much larger
force than $275,000 could put into the field. But there are certain
clues to the location of the disease which can be seen a long distance,
a quarter of a mile, at any rate. The means of recognition is by what I
commonly call danger signals. This fungus, when growing through the
bark, starts from the common point of infection and grows in all
directions, up the stem, down the stem, and around the stem. Wherever
this vegetative stage, technically known as mycelium, penetrates, the
bark is killed; and of course, you all know what that means. When this
has succeeded in reaching around a twig, branch, or trunk, everything
beyond that girdled area dies, not immediately, perhaps, but sooner or
later it dies; and it dies in such a way that the leaves change color
during the summer. The first obvious change which can be noted is a
slight wilting of the leaf; then the leaf assumes a pale green color,
and from the pale green it takes on a yellow stage; from this a reddish
yellow sta