AGARICUS ARVENSIS AND A. COMTULUS 
13 
the pileus and stem is a broad zone of fundamental tissue character- 
ized by a more open mesh. It has already been noted that this tissue 
is composed of thick-walled hyphae quite distinct from the thin-walled 
h^^phae of the denser inner tissue, though at the border between the 
two there is more or less a merging of both elements. This zone of 
tissue is homologous with that in Amanitopsis vaginata which forms 
the volva or universal veil. In the young carpophores of Amanitopsis 
vaginata there is a similar loose-meshed tissue surrounding the primor- 
dium of pileus and stem which merges gradually into the denser 
tissue within, and which only at a later period is separated as the volva, 
by a zone of gelatinizing hyphae. This universal veil while still 
undifferentiated may be called the blematogen,'^^ or hlematogen layer, 
yet unfashioned as a volva. 
Relation of partial veil, universal veil'' {hlematogen layer) and 
primary universal veil. — When the annular gill cavity is formed in 
Agaricus, it separates from the stem at this point, the fundament of 
the marginal, or partial veil. Since the universal veil or blematogen 
layer at this stage of development envelops the young carpophore, 
the question arises as to the relation existing between marginal or 
partial veil and the universal veil. Is the marginal veil merely a 
section of the universal veil as Fayod states, or is it a structure partly 
sui generis, and partly consisting of the universal veil which is external 
at this region? These questions are difficult to answer precisely, since 
the universal veil, or blematogen layer, in the genus Agaricus, and 
in a number of other genera, is never clearly differentiated in structure 
from the carpophore as it is in the Amanitae. The delicate, floccose, 
loose scales sometimes present on the expanding and mature plants 
as shown in Agaricus campestris may be regarded as the primary 
universal veil, the protoblema, or protohlem}^ Beneath this primary 
veil or protoblem, in the young carpophore of Agaricus campestris, 
is the zone of loose-meshed tissue homologous with the undifferentiated 
universal veil, or blematogen layer in Agaricus arvensis, Ag. comtulus, 
and in Amanitopsis vaginata just described. But since, in these 
species of Agaricus, no distinct cuticle or cortex of the pileus of a 
definite cellular structure, markedly different from that of the blema- 
togen is developed, which releases the universal veil as is said to be the 
fiXrjfux = cover; yepr]s = producing. 
See Plate 10, and Plate 12, figure 18, in Atkinson, Geo. F. The development of 
Agaricus campestris. Bot. Gaz. 42: 241-264. pis. y-12. 1906. 
TrpwToj = first ; ^Xtjfia — cover. 
