i8 
GEORGE F. ATKINSON 
Agaricus rodmani Peck^^ (which may be identical with the variety 
edulis), the annulus has a double edge. Since the lower edge slips 
off from the under surface of the pileus margin, it might be regarded 
by some as a volva. But in robust specimens of Agaricus campestris 
where the double margin of the annulus is often marked, there is 
frequently, in addition, a delicate ring at the base of the stem, the 
lower remnant of the primary universal veil or protoblem. The 
annulus with its duplex edge is situated above the base of the stem, 
and its lower limb is separated from the surface of the stem during 
expansion. These two facts in connection with what is known as to 
the considerable increase of the fundamental tissue from which the 
partial veil originates, argue against the volva nature of the lower 
limb of such an annulus, and also speak in favor of regarding the 
partial veil of Agaricus as distinct from the "universal veil" and not 
merely a section of it. 
SUMMARY 
1. In Agaricus arvensis the very young carpophores show an 
internal differentiation into a pileus and stem primordium, the pileus 
primordium appearing as a small rounded projection from the broad 
stem primordium, and there is a very slight constriction at the point 
of junction of the two. At the point of constriction the fundamental 
tissue presents a more open mesh indicating the tension from expansion 
of the surrounding parts which eventually forms the annular gill 
cavity. The fundaments of the pileus and stem at this stage stain 
faintly in contrast with the deep stain of the surrounding fundamental 
tissue. Nevertheless there can be discerned at the lower margin of the 
pileus fundament, just above the point where the annular gill cavity 
is to be formed, a small area of compact parallel hypae which form 
the fundament of the hymenophore and pileus margin. 
2. Enveloping the primordia of the stem and pileus is a zone of 
fundamental tissue. The walls of the hyphae are thicker than those of 
the pileus and stem fundaments, and stain deeply but the mesh is 
more open. An outer, ill-definable zone of this represents the "uni- 
versal veil," or blematogen layer, homologous with a similar layer in 
Amanitopsis vaginata. 
3. The outline of the annular gill cavity, and the young hymeno- 
phore during the early stages, rises outwardly at an oblique angle from 
2448th Rept. N. Y. State Mus. Nat. Hist. 137. 1897. 
