AGARICUS ARVENSIS AND A. COMTULUS 
9 
It is interesting to observe that during the early growth of the 
young hymenophore, and of the gill cavity, their outline rises from 
the point next the stem at an oblique angle outward and upward. 
Epinastic growth of the hyphae in the margin of the pileus begins 
early so that the hymenophore at this point curves outward and down- 
ward over the upper angle of the gill "slit." As the fruit body en- 
larges, continued epinasty tends to move the whole pileus margin 
downward while the extreme margin is inrolled. At the same time 
elongation of the stem begins which tends to carry the inner angle 
of the gill slit and the hymenophore upward, so that the angle at 
which they formerly stood is reversed and they extend outward and 
downward. 
Origin of the partial veil. — Since the hymenophore is endogenous in 
origin, the partial veil originates from the fundamental tissue lying 
outside the annular cavity and is not clearly separated from the 
universal veil. It is thus connected with the margin of the pileus 
and the surface of the stem. This fundament of the annulus, or partial 
veil, increases in extent by tension resulting from the expansion of the 
pileus and stem, and also by growth of the elements, which growth, 
however, does not keep pace with that of the surrounding parts. In 
the older fruit bodies, as shown in figures 5 and 6, this veil is duplex 
in structure. The lower portion lying next the stem surface has a 
looser texture, is the principal aerating tissue, is derived from funda- 
mental tissue and increases by growth of its elements. The upper 
portion lying next the gill cavity is connected directly with the margin 
of the pileus. It originates partly from fundamental tissue and 
partly by growth from the margin of the pileus, the growth from the 
pileus probably forming the denser portion. The lower looser portion 
is torn off from the surface of the stem during further growth and 
expansion of the plant, and provides the looser lower portion of the 
duplex veil characteristic of Agaricus arvensis and some of the other 
species of Agaricus, like Ag. augustus Fr., etc. Its looser texture 
would permit of its being torn into angular, often radiating areas or 
patches, so striking a feature of the duplex veil of these species. In 
very robust specimens the increase in the fundamental tissue between 
the partial veil and stem appears sometimes to be very great and this 
very likely provides the looser tissue which forms the floccose scales 
on the stem below the annulus in the peronate forms. 
