224 
A. W. BLIZZARD 
manner similar to that described above and gradually changes to a 
broadly convex form with an incurved margin (Figs. 7-10). 
Hymenophore Primordium. — Simultaneously with the formation 
of the annular groove by epinastic growth of the marginal hyphae, 
the hymenophore primordium is differentiated by the rich content 
in protoplasm of the hyphae forming the external annular zone in the 
furrow. They are crowded, and stained deeply as shown in longitudi- 
nal section (Fig. 6). 
The annular region is composed of more or less blunt and cylin- 
drical ends of numerous hyphal branches which have their origin both 
in the stipe and pileus elements. Their growth direction is obliquely 
out and downward. The oldest are on the stipe and by centrifugal 
development new elements are added to this area near the margin of 
the pileus which continues to curve down over this surface. Figure 22 
is a median longitudinal section of the fruit body at this stage of devel- 
opment and shows this structure in detail. 
At first this annular primordial layer curves out and upward at an 
angle of about 45°. As the pileus expands and becomes more convex, 
new primordial elements are introduced by branching and interstitial 
growth in centrifugal succession as above described. This causes it 
to curve in the form of an arch (Figs. 7-8). 
Since the development is centrifugal it must be borne in mind that, 
at the time this layer is in the primordial stage at the margin of the* 
pileus, near the stipe it will be further differentiated. 
Palisade Layer; Origin and Development of the Lamellae. — The 
hyphae of the hymenophore primordium branch in a digitate manner. 
By this branching new elements are interpolated in the spaces between 
the older hyphae. This process continues gradually until a compact 
layer of short hyphae is formed. Simultaneously with this the cells 
enlarge, especially the terminal ones, and the surface smooths up into 
an even, compact layer (Fig. 23). This is the palisade layer and pre- 
cedes the origin and development of the lamellae, as has been described 
for a number of endogenous forms. The differentiation of the palisade 
layer appears first near the stipe and progresses centrifugally toward 
the margin of the pileus, as did the development of the hymenophore 
primordium. As the cellular elements of the palisade layer increase 
in size, a great pressure is produced within this structure. This 
pressure is released to some extent by the palisade layer being thrown 
into equally spaced, radial folds beginning near the stipe (Fig. 12). 
