Nov., 1922] LEVINE LAMELLAE IN AGARICUS CAMPESTRIS 52I 
do not become globular at this stage, but that the tips seem to converge 
toward the apex of the small button. The tip cells are more densely filled 
with cytoplasm and take the stain more heavily. It is interesting to note 
that the carpophore shown in figure 85 arose below the surface of the agar, 
and it appears in this figure as if a number of hyphae were involved in the 
initial development of the plant. Sections of small knob-like projections, 
which give rise to carpophores and which appear on the stipes of older but 
attenuated specimens of C. stercorarius, consist at first of an undifferentiated 
mass of hyphae, as shown in figure 86. Here it may be observed that, while 
the cells of the old stipe are large and generally highly vacuolated, the 
cells from which the young carpophore seems to take its origin are small and 
stain heavily. This type of young carpophore is somewhat more compact 
in structure, and the base of the plant stains less strongly than the apical 
region. In C. stercorarius, unlike C ephemerus, the first change in the 
undifferentiated carpophore consists in the formation of a pilear region 
which answers the description of Fayod's (1889) couche pileogene (fig. 87). 
It appears to be an inverted flattened hemispherical mass of tissue con- 
sisting of very much entangled, deep-staining hyphae. The stipe region at 
this stage also stains somewhat deeply, and between the two a layer of 
undifferentiated, delicately stained tissue remains. The apical terminal 
cells of this plant are thick- walled ; they lose their cytoplasm and fail to 
stain. It is quite likely that it is these cells which form the flaky structures 
on the surface of the mature pileus later in the development of the plant. 
In both C. ephemerus and C. stercorarius, these early stages are followed 
more gradually by the development of pockets of palisade-like hyphal tips 
immediately below the pilear region. In C. ephemerus the undifferentiated 
primordium of the hymenophore region gives rise to these pockets of 
palisade cells, no distinct pilear region having been formed ; in C. stercorarius 
they are formed on the outer part of the lower surface of the pileus rudi- 
ment. Previous to this stage, and during the development of subsequent 
stages, there is no indication of a general annular gill cavity such as is 
described by Atkinson and his students for other species of agarics. As I 
have pointed out above, the matter of successful fixation is of prime im- 
portance at this stage of development. It appears that the hyphae that 
are continuous between the stipe fundament and pilear region, the future 
trama, are very easily ruptured by shrinkage in fixation. 
Gill Cavities 
The palisade pockets of hyphal cells arise primarily from the pilear 
region and appear in longitudinal sections in distinct groups with the 
downward-growing hyphal tips slightly converging toward a common center 
within the group. The hyphae on the boundaries of such groups, the future 
trama cells, are continuous, as noted above, between the hyphae of the 
pilear and stipe rudiments. 
