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

INTRODUCTION

9

reaction. It is most evident on species in the section Luridi of Boletus
and species of section Subtomentosi. Its significance still remains to be
evaluated. In spores mounted in KOH the colors are usually yellower or
more rusty brown than in water mounts.
THE HYMENIUM
The hymenium is composed mainly of the hyphal end-cells modified for spore production-the basidia. These (figs. 1, 6, 8) are arranged
in a palisade and typically are clavate in shape. There is considerable
variation in size-those from the part of the hymenophore nearest the
pileus usually being larger (both longer and wider) than those near the
tube mouths (pores). Most basidia of the hymenophore in Michigan
boletes are 4-spored. However, it is not uncommon in mounts to see a
few 2-spored basidia, and hence there is always the problem of whether
all the sterigmata develop simultaneously. Not many secondary characters of the basidium are important in the recognition of genera and
species in the boletes. Measurements of basidia are not particularly useful for the reasons stated.
One distinguishes the basidia in the hymenium from the sterile
elements by observing that sterigmata have developed on them (fig. 1).
Similar-appearing cells in the hymenium but lacking sterigmata are
termed basidioles (figs. 6,8)-meaning young basidia. If sterile elements
of different shape and more random distribution are present, they are
termed cystidia; pleurocystidia if on the hymenophoral surface and
cheilocystidia if on the edge (the pores). Those found on the stipe are
termed caulocystidia. These designations merely indicate position. As
pleurocystidia are commonly present in boletes, their presence versus
their absence has never become a major taxonomic feature per se.
Pleurocystidia in the Boletaceae are found in 4 simple shapes with
intergradations between types in some instances: In Boletus and Leccinum is found mostly the.fusoid-ventricose type (fig. 5), which is to
be regarded as a very simple and rather universal type in the fleshy
fungi. Two variations from it are important, first to a type with rounded
apex (fig. 9), termed utriform. If the cell is merely clavate but has a
short apical protuberance, it is termed clavate-mucronate (fig. 7). In
Tylopilus the contents of the cystidium in many species may be dextrinoid (dark reddish brown) or a dark yellow-brown in Melzer's. They
are a type of gloeocystidia termed chrysocystidia. In Suillus (fig. 25)
the cylindric to narrowly clavate type is often present in bundles, a very