Homology of the “universal veil” in Agaricus 19 
lamellae are beginning to show as low folds. The outline of the surface of the stem 
is very distinct as a downward and outward sloping dark area below the partial veil. 
The surface of the primordial pileus is nearly organized, its elements interlacing with 
the inner layer of the “universal veil”, or blematogen which still shows the coarser 
mesh. The partial or marginal veil shows a section of the blematogen or “universal 
veil”, as its outer surface, but the bulk of it is formed by the growth of threads 
from the margin of the primordial pileus and increase of its own elements. The 
duplex character is beginning to show, the lower portion showing a more open mesh, 
increase having come chiefly from growth of fundamental tissue between the blematogen 
and stem surface. 
Fig. 6. Section of a somewhat older basidiocarp of Ag. arvensis , the gill cavity 
slopes downward still more due to continued epinasty of the pileus margin and the 
elongation of the stem; the duplex character of the veil is more distinct; the bulb of 
the basidiocarp has broadened greatly but has not elongated appreciably so that the 
stom surface here is horizontal while the main part of the stem is elongating which 
brings the surface nearer a perpendicular position. The open mesh character of the 
medulla is beginning to show due to a lagging behind in growth. The primordial 
surface of the pileus has become concrete with the inner zone of the blematogen, or 
“universal veil”, so that its outer zone really becomes the surface of the mature pileus. 
Fig. 7. Section of a young basidiocarp of Ag. comtulus showing in the upper 
portion the roundish primordial area of the pileus, on either side the more densely 
staining primordium of the hymenophore and pileus margin; below the nascent prim- 
ordium of the stem. Enveloping stem and pileus fundaments is the coarse meshed 
blematogen, or “universal veil”. 
Fig, 8. Ag. arvensis , highly magnified portion of fig. 1 showing details of 
structure and differentiation in the region of the early primordium of the hymenophore 
and pileus margin. This is located at the intersection of lines perpendicular to a, a. 
At the right note the coarse meshed tissue of the blematogen with its thick walled 
hyphae, in strong contrast with the dense area at the left with thin walled hyphae. 
At the angle of this tissue (intersection of lines from a, ä) note curving downward of 
the elements of this primordium. The open meshed tissue heneath is the beginning 
of the gill cavity, and the threads of this tissue form the primordium of the inner 
portion of the partial veil, the hyphae are thin walled and distinct from those of the 
blematogen lying outside. 
Fig. 9. Ag. arvensis. Highly magnified portion of a section from the same 
basidiocarp as fig. 2, showing young gill cavity, the hymenophore primordium just 
above; the primordium of the pileus margin above and slightly to the right, at inter¬ 
section of perpendicular lines from b, on the right, the open meshed tissue of the 
blematogen, or “universal veil”, below the margin of the pileus and the gill cavity is 
the now more abundant tissue of the partial veil of finer texture than that of the 
blematogen. 
Fig. 10. Ag. comtulus. Section of well advanced basidiocarp, showing the 
hymenophore primordium with nascent lamellae; the distinct primordial margin of the 
pileus, the less differentiated area of the pileus primordium above; the loose meshed 
blematogen, or “universal veil”, the well advanced partial veil of duplex structure 
below the gill cavity covered externally by a section of the blematogen; the conical 
primordium of the stem below. 
Fig. 11, Ag. comtuhis. Section of a nearly mature basidiocarp, slightly tan¬ 
gential, showing nearly mature lamellae; duplex partial veil; surface of stem; and 
pileus surface “concrete” with the “universal veil”, or blematogen; a section of the 
latter forms one-third to one-half the thickness of the portion of the partial veil ex- 
tending from margin of pileus to its junction with the lower portion. 
Fig. 12. F rom photograph of young cluster of basidiocarps of Ag. campestris , 
showing on the older specimens the tearing apart of the delicate floccose protohlem 
on the surface of the blematogen. 
Fig, 13, From photograph of a cluster of mature individuals of Ag. campestris. 
showing white patches of the protoblem on the surface of the pileus. 
2* 
