case of this chestnut fungus, we have a fairly typical fungus in
certain respects. We have a vegetative stage of the fungus which is
nothing more or less than a lot of threadlike structures penetrating the
bark of the chestnut, the inner bark or the middle bark, and there
drawing the organic matter from the bark of the chestnut and
appropriating it to its own use. Fungi, like practically all other
plants, have two stages of existence, one the vegetative or growing
stage, the other the reproductive stage. Sooner or later the fungus will
produce the fruiting bodies, after it has obtained a sufficient amount
of food to justify the formation of these more highly organized
structures. In the case of the fruiting body of the chestnut fungus, we
have very small, pinhead-like structures, which come out to the surface
of the bark, the vegetative portion developing through the interior of
the bark. On smooth bark we find that these fruiting pustules are apt to
appear all over the surface. With bark that is sufficiently old to have
ridges and crevices, we find these fruiting bodies only in the crevices.

These fruiting pustules which you will see on this bark are the
structures which produce the reproductive bodies, these latter being
known as the spores. There are two types of spores which are produced by
this fungus. One is the type which is commonly spoken of as the summer
spore, the other the type which is spoken of as the winter spore. The
winter spore is known from the point of view of the mycologist as the
perfect stage of the fungus, that is, it is the more characteristic of
this particular fungus. If we should make a cross section of the bark,
we should find that the vegetative stage is running through the middle
bark, and commonly the inner bark, sometimes in one place only,
sometimes in the other only, sometimes in both. This vegetative stage
later sends up in various ways a mass of tissue which results in the
formation of pustules. These appear on the surface, sometimes more or
less regularly rounded, sometimes rather irregular. In the case of the
summer spore stage, we have inside the pustules a mass of tissue which
is formed into spores. The interior of the spore mass, or at least
portions of it, is somewhat mucilaginous, so that when moisture is
applied a swelling of the interior mass is produced at a certain stage
and something has to break. As a result, we have a mucilaginous mass
pressed out through the break in t