The North American species of Pholiota, by Alexander H. Smith and L. R. Hesler.

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The North American Species of Pholiota

upper portion of the stipe. This ring of fibrils is commonly brownish
from spores which have lodged on them. The ring or zone of veil-remnants is usually inconspicuous and often evanescent. Its color (often
either white or yellow) in the early stages of the basidiocarp should be
noted. When strongly developed, the veil may be membranous and persistent, as in P. albivelata. In one species, P. velaglutinosa, the elements
are gelatinous, and the veil is described as glutinous. In other species,
the veil breaks so that remnants cling to the margin of the pileus, a condition described as appendiculate. Finally it appears that in some species
the inner veil is absent. In P. nigripes for example, no trace of such a
veil was found, even in young basidiocarps. With the exeception of the
glutinous veil, and the veil which forms a membranous persistent annulus, the color of the inner veil is its most valuable feature for taxonomic
emphasis.
Outer veil. The development of the veils was studied by Sawyer
(1917) for P. adiposa and P. flamanans. It is now apparent that the
species he studied were P. squarroso-adiposa and P. flammans. The outer
veil, or blematogen as he used the term, may be regarded as part of the
ground tissue within which the active differentiation of the basidiocarp
occurs, and the amount to which this layer develops varies with the
species. In such species as P. squarrosa this layer continues to grow along
with the differentiating basidiocarp to the point that at maturity conspicuous aggregations of its hyplae persist as scales. As Sawyer pointed
out the hyphal arrangement in the blematogen tissue is at first perpendicular to the developing cap surface. Hence as these hyphae elongate
they become decumbent and by the expansion of the cap become aggregated into separate fascicles oriented toward the cap margin away from
the disc, but often standing straight up (squarrose) on the disc. These
scales are innate (firmly attached to the pileus). At maturity they appear
to be a direct outgrowth from the pileus. When the gelatinous layer
forms underneath them however, there is no solid connection to the cap
and they can be easily washed away by rains. It is difficult in Pholiota to
distinguish at all times between a partial and an outer veil as in most
cases over the stipe the two tissues appear grown together and the fibrils
assigned to each are better identified by their position on the stipe. As
already pointed out those of the inner veil leave the zone nearest the
apex of the stipe. Veil material left on the stipe below this is likely to be
mostly outer veil material. For the species without well developed scales
on the pileus it must be recognized that the development of the outer
veil is reduced. In the subgenus Pholiota, in keeping with the derivation
of the name, the central feature is the presence of numerous scales on the
pileus and these scales are to be interpreted as remains of the blematogen.
However, the structure of the scales themselves is important taxonomically. In some the end-cells of the hyphae may be somewhat cystidioid, in
some the hyphal walls may be slightly thickened, colored or encrusted,
etc.