524 
W. H. SAWYER, JR. 
surface into downwardly projecting folds (fig. 24) which are the first 
gill salients. At the same time a more rapid growth of the hymeno- 
phore downward in radial, regularly spaced areas directs the formation 
of the folds, as described for Agaricus rodmani (5) and species of 
Coprinus (7), so that the gills are radially symmetrical with reference 
to the stipe. 
The origin of the lamellae is next the stem, and by continued 
growth and differentiation the lamellae develop toward the pileus 
margin. This centrifugal manner of formation enables one to study 
their development by means of serial longitudinal sections from the 
pileus margin toward the stem, since they are youngest near the former 
and become progressively older as they approach the latter. Figure 
23 represents a section near the pileus margin. The even palisade 
occupies the greater part of the hymenophore surface, with a little of 
the primordial tissue on either side. The gill cavity is well formed. 
The tissue below the latter belongs to the stem cortex and universal 
veil, together with some ground tissue belonging to the partial veil. 
Figure 24 represents a seccion a little nearer to the stem. The palisade 
is no longer level, but has an undulating surface, with two slight, very 
broad folds. In figure 25, still nearer to the stem, these two folds are 
more pronounced, and at the right the beginning of a third may be 
noted. The breadth of these folds, and their distance apart, can 
leave no doubt that they are the first salients of the lamellae them- 
selves. 
The trama of the mature gill (fig. 34) has its origin in the hyphae 
beneath the palisade layer which grow down into the young gill salient. 
Further growth takes place by the elongation and enlargement of 
these hyphae. Throughout the center of the lamella they are com- 
pactly interwoven, with their general direction of growth toward the 
edge (fig. 34). Laterally, however, they turn outward and form the 
hymenial layer of the lamella. 
The primary gills, because of their radial arrangement with the 
stipe as a common center, diverge as they approach the pileus margin. 
Continued growth of the hymenophore results in the production of 
shorter secondary lamellae between their outer ends in the same way as 
that in which they w^ere formed. Figures 28-32, however, show the for- 
mation of two gills in a somewhat different manner. In figure 28, a 
section near the stem, it will be noted that a gill salient occurs that is 
unusually broad. In the successive sections it can be seen that this 
