The boletes of Michigan, by Alexander H. Smith and Harry D. Thiers.

12

THE BOLETES OF MICHIGAN

Two arrangements are most commonly encountered; in one the hyphal
elements are short and are in a more or less upright palisade. This we
term a trichodermium (fig. 86). As the pileus expands the trichodermial
elements become aggregated into tufts exposing the context of the
pileus between them, and the pileus is said to have become areolate-rimose.
The second type is represented by a layer of appressed interwoven
hyphae generally termed a cutis, or if the hyphae are gelatinous, a
pellicle. The two types, upright elements contrasted to appressed elements, appear to be sharply distinct at first glance, but in many species
the layer appears to have been trichodermial in origin but as the elements elongated they became tangled and appressed. Hence in working
with individual species some difficulty in interpreting the dermal layer is
to be expected. Whenever possible sections should be made from young
pilei.
Though hyphal detail is very important taxonomically, one can
expect some difficulties to arise in using the various characters. The
simplest type of trichodermial element is an unmodified hypha 2-4 cells
long with the terminal cell essentially tubular like the rest and lacking
wall thickenings, incrustations on the wall, or distinctive content in the
cells such as amyloid granules. One of the most important modifications
is in the shape of the cells of the element. They, or some of them, may
inflate and become nearly globose. In some species the distal 3-4 cells
become nearly globose, and if they become so inflated that they are
packed tightly together a cellular layer (fig. 111), or "epithelium," is
said to be present. In such cases the trichodermial origin of the layer
may be all but obscured. Sometimes only the apical cell becomes greatly
enlarged, and sometimes the basal cells become more inflated than the
others. On the other hand most of the differentiation may take place in
the terminal cell of the trichodermial element, and the cells beneath
may be so reduced in number and length that the pileus surface appears
to be mainly a tangled turf of terminal cells (fig. 90).
Incrustations on the hyphal walls may or may not be present, and
if they are, they may be very conspicuous to almost invisible depending
on the species. We also find the hyphal cells reacting in various ways to
chemicals, such as weak KOH, by the production of blisters, or the
outer layer of the wall separating into thin plates (fig. 15) as the inner
wall swells (see Leccinum insigne). We also find the pigment which gives
color to the pileus located in the dermal hyphae. Hence it is important
to observe their color (which is usually dissolved in the cell content) in
both KOH and in Melzer's. In some species mounted in Melzer's the
pigment rounds up into globules and the hyphal cell resembles a tube