A STUDY OF DEVELOPMENT IN THE GENUS CORTINARIUS 325 
Spaced radial areas. The palisade layer is thus pushed out into folds, 
which allows room for the expansion of the ends of the hyphae, now 
considerably swollen. Subadjacent to the stratum of young salients, 
there appears a thin growth zone, very conspicuous on account of its 
abundant nuclei. In the center of each gill, it extends down into 
the trama, but between the gills it remains as a thin layer^^ (hgs. 13- 
15, 18). It maiks the boundary of the pileus and the hymenophore 
and probably represents the region where cleavage takes place in such 
forms as Paxillus, in which the hymenophore separates readily from 
the flesh of the pileus. As we approach the stem, we find the salients 
more mature. The median section of figure 12 shows that the hymeno- 
phore, when cut radially, is more or less crescent shaped, due to the 
inrolling of the edge of the pileus and the decurrence of the gills along 
the slanting surface of the stem. As the knife passed through the 
plane represented by line 13, it cut through the junction of the de- 
current gills with the stem and nearly perpendicular to their direction 
of growth. For this reason, the space between them, a part of the 
main gill cavity, appears as a little pocket. In a similar manner, 
the peculiar appearance of figure 16 may be explained. The curving 
inward of the margin of the pileus caused the hymenophore primor- 
dium to be cut twice. 
Structure of the Pileus and Stem. — The pileus and stem are both 
composed of a very homogeneous and yet firm tissue, containing 
very large air spaces. Toward the outside of the pileus, the tissue 
becomes more and more dense until it passes into the firm cortex, 
spoken of above. On the outside of the cortex, we frequently find 
large, thick-walled hyphae undergoing disintegration and giving the 
pileus surface the viscid character common to this sub-genus. In 
the cortical region of the pileus, the hyphae are filled with large oily 
drops, remaining unstained. At the apex of the stem the tissue is 
very dense, but it becomes more and more open towards the base, 
thus providing for aeration of the tissues. In this region also the 
hyphae are stouter and have thicker walls than those above near 
the pileus. The general direction of the hyphae in the stem is longi- 
tudinal or slightly oblique. They are somewhat interwoven. On the 
This recalls the distinct zone from which the hymenophore originates in 
Polyporus fumosus as described by Miss Ames (p. 225, figs. 38, 39). See Ames, A. 
A consideration of structure in relation to genera of the Polyporaceae. Ann. Mycol. 
11: 211-253. pis. 10-13. 1913- 
