North American species of Lactarius / L. R. Hesler, Alexander H. Smith.

46

North American Species of Lactarius

are they amyloid, see above) occur through the mount. This situation
is strongly reminiscent of that reported by Smith and Zeller (1966)
for Rhizopogon. We have recorded the occurrence of these globules,
but have not established a basis for evaluating their taxonomic significance.
In a number of groups in the Agaricales (e.g., some species of
Mycena) the layer or zone of tissue between the cuticle and the pileus
trama is differentiated, for instance, by cell enlargement. This layer or
region has been termed a hypodermium (see Singer 1962, pp. 59, 63).
We have avoided the use of the term in this work because it appears
to us that the layers or zones of distinct hyphal differentiation are
better grouped as the cuticle proper (the covering layer, zone, or
layers over the pileus trama). A hypodermial region is difficult to distinguish from the trama in Lactarius because rosette formation in this
region is irregular; at times rosettes are observed to have been initiated
in the basal region of the cuticle. In thick-fleshed species there may
be a wide zone of matrical hyphae lacking rosettes between the cuticle
and the heteromerous tissue, but one can never be sure the feature is
not just an expression of the degree of development of the basidiocarp
at the time it was collected. Even with this characterization of the
cuticle and the pileus trama some taxonomically awkward situations
are encountered.
The Pileus Cuticle. As already mentioned, the cuticle as here
defined includes all the differentiated layers forming the covering of
the pileus trama. The simplest cuticle, but not necessarily the most
primitive, is the cutis. We define the cutis as a layer of repent hyphae
oriented mostly in a radiating pattern from the center of the pileus
toward its margin, but this pattern varies to one of interwoven or
periclinal hyphae in some species. Typically the hyphae are tubular
or nearly so, have distinctly long cells, and branching occurs in varying frequency depending on the species. The hyphae are thin-walled
and lack any extensive pattern of incrustations except that in the subgenus Tristes small patch-like or collar-like incrustations occur (see
p. 44) on some of the hyphae in the cuticular region. In a simple cutis
there is often little difference between the hyphae of the cutis and
those adjacent to it. Ordinarily, however, cutis hyphae are narrower,
less interwoven in their arrangement, and the cells are generally more
strictly tubular. In a cutis of this type, hyphal ends may be upright or
ascending at the surface, but are ~ widely scattered and not organized
into a turf of lattice. In our terminology, the cutis rests directly on
the pileus trama or merges with it.
A simple type of further differentiation of the cutis results from
the secretion of slime by the hyphae, or their walls gelatinize producing some slime. In either case, the slime causes the hyphae to become