The veiled species of Hebeloma in the western United States / Alexander H. Smith, Vera Stucky Evenson, and Duane H. Mitchel.

8

The Veiled Species of Hebeloma

much more frequently in nonveiled species (subgenus Denudata). It is
correlated with the clumping of capitate cystidia, the concomitant development of slime over the surface of those cystidia, and the resulting
visible droplet formation.
Caulocystidia. In the veiled species, we have found caulocystidia
to be of little taxonomic value. They resemble the cheilocystidia in size
and shape and often exhibit considerable variation on a single stipe. It
seems likely that the veil in species of subgenus Hebeloma augments
the effect of caulocystidia-that of maintaining humidity in the region
of the developing basidia.
Pileocystidia. These are not common in subgenus Hebeloma although they can occasionally be found as very slender obtuse hyphal
end cells in an ixotrichodermium of a young pileus.
The Cuticle of the Pileus. Features of the surface of the pileus are
important in the taxonomy of the genus (see figs. A28-32). Nomenclature used here for the different patterns of hyphal arrangement has
been discussed at length in North American Species of Hygrophorous
(Hesler and Smith 1963).
The Ixocutis. A simple cutis (without slime) has not been observed by us in subgenus Hebeloma (see fig. A28). In many species,
the hyphae are appressed to the surface and to some extent embedded
in slime. The slime may result from the gelatinization of walls of the
cuticular hyphae or it may be extruded from the hyphal cells. If the
walls of the hyphae are gelatinized, a microscopic examination (in
KOH, Melzer's, or water) will show the hyphal walls in unclear focus.
On the other hand, if the slime is extruded from the hyphal cells, the
hyphae become + widely spaced but remain sharply defined as observed in the microscope. Both sources of slime can, apparently, be
found in a single basidiocarp so the place of origin of the slime is not
emphasized in the taxonomy of the subgenus unless it happens to be a
prominent and readily discernible feature (see fig. A29).
If slime is present in copious quantities, the surface of the pileus
will be slimy to the touch when fresh. If little gelatinization or slimeproduction takes place, the fresh pileus will be only slightly sticky
(viscid) to the touch. If the slime has dried in situ, the pileus surface
will be "dry" to the touch (not sticky or slimy), but the pileal surface
will appear + shiny as if varnished. Under the microscope, however,
the presence of the slime can still be demonstrated on sections
mounted in KOH, Melzer's, or in water. In such mounts, if slime is
present, the hyphae of the layer are more or less distinctly separated,
and the space between them has a translucence not seen in a simple
cutis.
The Ixolattice. The ixolattice may be a well-developed ixocutis in
which the hyphae have become very widely separated by the slime,