AGARICUS ARVENSIS AND A. COMTULUS 
19 
the stem. But later as the epinastic growth of the pileus becomes 
stronger, and the stem begins to elongate, the direction becomes 
reversed, and the outline of the gill cavity and the hymenophore 
extends outward and downward. 
4. Distinct organization in the pileus first appears at the margin, 
indicated by the parallel growth of the hyphae, under the influence of 
epinasty. The surface of the pileus proper can here be distinguished 
from the external, intricately interwoven fundamental tissue which 
constitutes the "universal veil," or blematogen layer. 
5. Stem organization can be observed in the more deeply staining 
portions of the stem fundament, as growth continues. At first it is 
broader than long, the outline of the stem cortex staining more deeply. 
6. The marginal, or partial, veil is first differentiated by the appear- 
ance of the annular gill furrow. It extends from the margin of the 
pileus to near the base of the stem, and is covered externally by the 
"universal veil," usually with no well-formed line of demarcation 
between the two structures. The tissue of the partial veil increases 
greatly by growth of this inner fundamental tissue, by growth also 
from the margin of the pileus, which forms a part of the inner (upper) 
more dense portion of the veil. Abundant increase occurs also next 
the stem on the lower (outer) side of the partial veil. Thus is formed 
a duplex partial veil of much looser, more spongy structure below. As 
the plant expands the partial veil is at first torn from the lower surface 
of the stem. As it is stretched by the expansion of the pileus the looser, 
spongy, lower portion of the veil is separated from the pileus margin 
and surface of the stem and torn into the scales characteristic for the 
species, while the firmer upper (inner) portion is later separated from 
the margin of the pileus. In very robust specimens this loose tissue 
of the under surface of the annulus may be so abundant as to leave 
many scales on the stem giving it a peronate character. 
7. In the very early stages of Agaricus comtulus, the first evidence 
of the differentiation into pileus and stem primordia is a dense, deeply 
staining, internal, annular area, appearing in longitudinal section as 
two deeply staining areas symmetrically disposed. This is the 
primordium of the hymenophore and probably also of the pileus 
margin. At the same time a less deeply staining dome-shaped area, 
the margin of which connects with the internal annular hymenophore 
primordium, or a general central area of larger extent, marks the 
differentiating pileus primordium. The stem fundament lies below. 
