AGARICUS ARVENSIS AND A. COMTULUS 
7 
campestris,"^ except that in the specimens of the latter species studied 
there was no morphological differentiation of the fundamental tissue 
indicating the pileus and stem fundaments distinct from the surround- 
ing fundamental tissues, as in Ag. arvensis, until some time after the 
first evidence of the hymenophore primordium. In the young fruit 
bodies of Agaricus campestris examined, there appears an annular 
region of more deeply staining hyphae before any evidence of the 
annular cavity is seen, and just above the region where this is formed. 
Median longitudinal sections of these very young carpophores of 
Agaricus arvensis show that the hyphae in the pileus primordium have 
in general a radiate direction. But the central ones show this char- 
acter only in a slight degree, the hyphae are much interwoven and 
over the central area where the pileus primordium passes over into 
the external fundamental tissue they are intricately interwoven, no 
radial direction is evident and they show no evidence of specially 
active growth. 
The lateral hyphae, however, show distinctly a radial direction and 
curve outward at the same time somewhat like the lateral stalks in a 
sheaf. The outer and lower ones curve more strongly, and the 
terminations of the lower ones curve downward next the outer funda- 
mental tissue and directly above the looser mesh where the annular 
gill cavity is forming. These hyphae stain more deeply than the 
remaining elements of the pileus primordium, but the contrast is not 
very striking, and they lie very close to the external fundamental 
tissue which is deeply stained. Consequently this primordium of the 
hymenophore and pileus margin is not differentiated in the photograph 
of the entire section, figure i. But in figure 8 more highly magnified, 
it can be seen that just above the more open mesh there is a narrow 
area next the external fundamental tissue where the hyphae compacted 
together have a downward direction. The external fundamental tissue 
presents a very distinct texture since the walls of the hyphae are thick 
and the mesh is open though not so open as that where the gill cavity 
is forming. 
The primordia of the hymenophore and of the pileus margin are 
merged in the early stages. — In slightly older stages, as shown in figure 
2, the gill "slit" is distinct though narrow, and the primordium of the 
hymenophore is very distinct, not only by the deep stain of the 
^Atkinson, Geo. F. The development of Agaricus campestris. Bot. Gaz. 42: 
241-264. pis. 7-12. 1906. 
