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

INTRODUCTION

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usually become shorter and branching occurs to give rise to the hymenial elements. The diverging hyphae in most boletes are somewhat
gelatinous, which causes the whole hymenophore, to some extent, to
have a similar consistency. Because the texture is very pliant, good freehand sections of the tube layer are difficult to obtain. Also, the degree
to which the individual hyphae are separated from each other, or the
angle at which they diverge, is likely to be variable for a number of
reasons. First, the more gelatinized the hyphae become the farther apart
from each other they are separated in the trama because of the swelling
effect the intervening slime exerts. Second, if sections are made from
material killed and fixed in such solutions as FAA, one cannot be sure
the picture one gets actually represents the arrangement in the living
material even though the technique always gives the same result. Sections may be cut on a freezing microtome, but here again the freezing
may very well effect the degree of gelatinization of the hyphae. Finally,
the differences, even when shown to best advantage, are not sufficient
to be of material aid in distinguishing genera or species in the family.
The feature of bilateral hymenophoral trama is most valuable as a character to aid in distinguishing the Boletaceae as a family-especially from
the true polypores.
In the trama of the basidiocarp, in addition to the hyphae which
form the basic tissue (matrical hyphae), one often observes hyphae
distinguished in some way by a content different from that of the
matrical hyphae. The content is often in the form of globular material
or a dense homogeneous material which refracts the light differently
than do the other hyphae. Collectively, such hyphae are regarded as a
laticiferous system. We regard them as repository hyphae containing,
possibly, by-products of metabolism, and the system is best regarded as
a storage system rather than a system of "vascular hyphae" (which
implies the function of conduction). The degree of their specialization in
the boletes varies. Smith has seen the ends of some actually forming
basidia with spores attached. Rarely in the boletes do they actually
contain a latex that is exuded on injured places of the basidiocarp or on
the developing pore surface of the hymenophore.
THE STRUCTURE OF THE PILEUS
For taxonomic purposes the dermal layer of the pileus is the most
important and will be treated first. The important characters are in the
arrangement of the hyphae and, second, in their anatomical features.