18 
G. F. Atkinson, 
3. The partial or marginal veil in the above species of Agaricus is 
not merely a sector of the “universal veil". It is largely a structure sui 
generis, the upper and inner portion being formed by the down ward 
and inward growth of the margin of the pileus primordium; the lower 
portion being formed by increased growth of the hyphae on the surface 
of the pileus; there is but a sliglit external contingent which is derived 
from the thick walled hyphae of the blematogen layer at this point, which 
may be largely or completely sloughed off or only remain as scattered 
portions on the margin of the annulus. 
4. In some species of Agaricus , for example in the early stages of 
Agaricus campestris , there is an additional “universal veil", the proto- 
blem, which lies outside of the blematogen, and consists of a delicate 
floccose, loose layer, soon becoming torn into floccose patches, sometimes 
present after the complete expansion of the plant. 
College of Arts and Sciences, Cornell University. 
Description of Plates. 
The photomicrographs were made as follows: Figures 1 — 6 with an extension 
camera and Zeiss lenses, x 15 diameters. Figures 8 — 11 were made with a Zeiss 
microscope, the object being 370 mm from the sensitive plate. Figs. 7, 10 and 16 
with ocular ^ 4 and objective 16 mm. Fig. 8 with ocular =j= 8 and objective ^ 
3 mm; fig. 9 with ocular 4- 12 and objective =}- 16 mm. 
Fig. 1. Longitudinal section of very young basidiocarp of Ag. arvensis showing 
earliest origin of gill cavity as two symmetrically disposed light spots, separating pileus 
fundament above from the stem fundament helow, indicating a constriction between 
them. External to the fundament of the pileus and stem is the fundament of the 
“universal veil“, or the blematogen layer. It is easily recognized in this figure by 
the more open mesh of its tissue compared with the denser tissue of the pileus and 
stem fundaments, and stains darker because the thick walls of the hyphae take up the 
stain readily. The base of the young basidiocarp is lighter colored than the stem 
fundament indicating that growth is more active in the latter. The rhizomorph is 
attached to the base. 
Fig. 2. Same in a little older stage, the gill cavity is evident, the hymenophore 
primordium is well organized as also the primordium of the pileus margin shown by 
the deeper stain over the gill cavity. Note the oblique position of the gill cavity 
rising outward and upward, also shown in fig. 3. 
Fig. 3. Same in a still more advanced stage. The pileus margin is more defi¬ 
nite and the inner limit of the blematogen layer is more distinct. The outline of the 
stem is more distinct showing its present form to be shorter than broad. In figs. 2 
and 3 there is shown the exfoliation of a very thin layer from the basidiocarp. This 
may represent the primary universal veil, or protoblem, present sometimes on young 
basidiocarps of Ag. campestris in addition to the blematogen, or it may represent 
merely a dead outer layer of the blematogen which was in contact with the substratum; 
it is difficult to determine this point on basidiocarps developed in the substratum. 
A similar exfoliating layer is shown in figs. 6 and 10. 
Fig. 4 is a section of a young basidiocarp of Ag. arvensis or a closely related 
species, collected in the edge of the forests south of Pontarlier in 1905. If it is not 
Ag. arvensis it is probably Ag. ßavescens as young basidiocarps of this species were 
collected, but the number became detached. It dif'fers from fig. 1 chiefly in the very 
deep stain of the hymenophore primordium, and shows also a dome-shaped primordium 
of the pileus connecting with the primordium of the hymenophore and pileus margin. 
though not so deeply stained. The blematogen layer is very deeply stained due to 
the absorption of the stain by the thickened hypha walls. The section was not 
decolorised to the extent of that of fig. 1, but if it were the primordium of the 
hymenophore would stand out strongly as compared to that in fig. 1. The reactions 
here are more like those in specimens of Ag. campestris studied. 
Fig. 5. Sections of an older stage of Ag. arvensis than shown in fig. 3. The 
Position of the gill cavity is now reversed, sloping downward. The fundaments of the 
