The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

[VOL. 24

so in a sense the cheilocystidia are not hymenial elements. It seems appropriate,
however, to include them here and also to discuss caulocystidia and pileocystidia.
The caulocystidia in general represent variations of both pleurocystidia and
cheilocystidia and often vary greatly in form and size. They cause the pruinosity
over the apex of the stipe. In a few instances some distinctive morphological
types occur along with the usual pattern of clavate to fusoid-ventricose cells.
When the veil is heavy, caulocystidia are often absent or poorly represented.
Pileocystidia are unimportant in Psathyrella with the exception of the P.
conopilea group in which long setae occur which have ochraceous tawny or
darker walls (in KOH). At times some of the cells of the pileus cuticle may be
"cystidioid" (fusoid-ventricose) but they are usually only an integral part of
the cuticle-especially if the latter is hymeniform in structure. Consequently
they do not enter prominently into the taxonomy of the genus. At best, it may
be said that the various types of cystidia in Psathyrella do not show unusual
diversity as compared with other large genera of the Agaricales.
The Tissues of the Basidiocarp
The Hymenophore. In Psathyrella the hyphae of the gill trama are mostly
somewhat interwoven to subparallel. The latter condition is most often observed
on lamellae just reaching the sporulating stage and the former on old lamellae
that are completely expanded. The most pronounced feature is the degree to
which cell inflation occurs. The tissue may appear almost cellular in expanded
pilei of some species as seen in cross sections of the lamellae. Typically the
subhymenium is cellular (pseudoparenchymatous) but again, often does not
reach this condition until full expansion is attained. In some, however, it remains
filamentous and interwoven, but it was found impractical to emphasize more than
both extreme conditions in the taxonomy of the group. The most important features for taxonomic purposes are concerned with color reactions of the wall in
KOH. Three conditions are worthy of mention: (1) no reaction-the hyphal
walls are hyaline, thin and smooth. (2) The hyphal walls become tawny to
fulvous in KOH and may be smooth or have some pigment incrustations. (3)
The hyphal walls become distinctly vinaceous to vinaceous brown in KOH and
are likely to show incrustations when first revived.
It will be noticed very soon that on colored hyphae or incrustations the
color is often concentrated near and on the septa, often as thickenings in the
wall or as incrusted patches on it. This is pronounced enough in some species
to give a mottled effect as one views the sections. In most species showing
color it is most pronounced at about the time the veil breaks, and it diminishes
in intensity as the basidiocarp matures and ages-at which time it may be
hardly demonstrable. This difference in pigmentation has superimposed upon it
the fact that KOH has the feature of bringing out the pigment strongly at first
but in 15 minutes causes the color to fade, more so in some species than in
others. This behavior of the pigment in KOH caused me to abandon any serious
attempt to use it in the taxonomy of the genus. Melzer's solution with one
slight exception does not yield any significant color reactions either. A laticiferous
system of "oleiferous" hyphae is often present, as in most agarics, and is in the
form of scattered individual metallic-appearing (in KOH or Melzer's) practically
non-inflated hyphae sparingly septate. Although the pleurocystidia often arise
in the gill trama, their connection appears to be with the more or less uninflated
primordial or binding hyphae. A few exceptions occur, such as in P. rugoproxima