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

INTRODUCTION

19

Let us consider Suillus in the light of these comments. Its species
for the most part are readily recognized by their aspect in the field, and
this "thumbnail" characterization can be backed up by reliable morphological and anatomical features. In any natural genus we find a core of
those species "typical" of the genus as well as some lacking 1 or 2 of
the important features. In other words evolution as a process leaves in
its wake certain nonconformist populations as well as those which
conform to the genetic pattern of the group. The nonconformists often
end up as genera containing only the one species-as does Pulveroboletus. It is a matter of judgment as to whether an odd species is
distinct enough to deserve being placed in a separate genus, or whether
it should be placed in a section or subgenus of a previously described
genus. So it is with Suillus. We have a large core of clearly related
species and then a certain number of "Anhang" (hangers on) species
which do not have all the characters of the genus, but are "closer" to it
than to any other genus. Any truly natural genus will show this pattern,
since evolution as a process became highly refined long before man
began to try to plot its course by studying the populations that it left in
its wake. In order to make our assessment of the course of evolution as
objective as possible, we must select some characters as a working basis
for recognizing groups or our classification becomes "intuitive" to a
dangerous degree (by intuitive is meant that an investigator insists that 2
groups are closely related though he cannot give good reasons for his
opinion).
In Suillus some very concrete characters support the impression
both the amateur and specialist readily detect in the field, namely, that
two different fungi belong in the same genus. The features are:
1) A characteristic yellow coloration usually over the pileus
tubes and stipe.
2) A viscid pileus.
3) A dull cinnamon to olive spore deposit.
4) Subcylindric to narrowly clavate pleurocystidia, often in
bundles, which often undergo color changes with KOH or
have incrusting material around the bundles when revived in
KOH.
5) Caulocystidia in fascicles or patches which become colored
as the basidiocarp develops, producing what are termed
glandular dots.
The above characters also show a pattern of evolution within the
genus. In addition to these features, certain others also show a progression of development within the genus, but their pattern of occurrence is