THE DEVELOPMENT OF CORTINARIUS PHOLIDEUS 523 
body there is present at the same time the paHsade condition of the 
hymenophore and a considerable amount of primordial tissue. 
The Annular Prelamellar Cavity 
When the pileus and stem areas become differentiated from the 
primordial tissue of the basidiocarp, in the angle formed by the junc- 
tion of these two structures a small amount of primordial or ground 
tissue is left. The primordia of pileus, stipe, and hymenophore grow 
more rapidly than does this ground tissue and as a result tensions are 
produced which cause it to become loose in texture and to tear apart. 
This results in the foimation of a cavity in the form of a ring around 
the apex of the stem, beneath the surface of the hymenophore. In 
this species the formation begins very soon after the origin of the 
hymenophore, as shown in figures lo and ii, where the tissue immedi- 
ately below the hymenophore primordium is becoming loose through 
the lateral and upward pull exerted on it by the margin of the expand- 
ing pileus. In figures 14 and 15 the development has proceeded 
further, so that an actual cavity is formed, although still weak and 
spanned by hyphal threads. By the time the level palisade stage is 
reached the gill cavity is well differentiated and entirely free from 
intervening tissue, as shown in figures 16, 17 and 23, Like the pri- 
mordium of the hymenophore and like the palisade, its development is 
from the stem toward the pileus margin, so that its earliest appear- 
ance is close to the stem. The two tangential sections represented by 
figures 12 and 13 show this fact; in figure 13 the cavity, while not com- 
plete, is more strongly developed than in figure 12, a section of the 
same fruit-body nearer to the pileus margin. 
The Origin and Development of the Lamellae 
At the time of the beginning of gill formation the pileus and stem 
are completely formed and the gill cavity is well defined. The hy- 
menophore is in the stage in which there is an even palisade layer extend- 
ing from the junction of the stem and pileus nearly to the pileus margin ; 
near the latter the palisade grades off into the primordial condition of 
the hymenophore. The palisade is composed of small hyphae with 
blunt and crowded ends (fig. 23). The continued growth of these 
hyphae and the intercalation of new elements from the hymenophore 
above gives rise to sufficient lateral pressure to throw the palisade 
