522 
W. H. SAWYER, JR. 
Almost simultaneously with the formation of the pileus margin the 
hyphae of its under surface begin to grow outward and downward very 
rapidly. These hyphae are slender, very rich in protoplasm, crowded 
together, and with terete ends. Their outward growth while under 
the influence of epinasty causes them to curve strongly, so that the 
ends point downward, or even inward toward the stem. This ring of 
new growth surrounding the stem apex is the hymenophore primordium. 
A median longitudinal section at this stage shows it as a deeply stained 
region on either side, as in figure lo. Since the primordium of the 
hymenophore is formed from hyphae of the pileus margin, and at 
practically the same time with the latter, it is extremely difihcult to 
point to the exact stage at which it originated. As has been stated, 
the hyphae of the pileus margin stain deeply and by new growth in- 
crease the density of its structure, and the beginning of this period of 
increased activity probably marks the origin of the hymenophore 
primordium. 
The appearance of this new fundament definitely marks off the 
pileus area from the stem primordium. As development continues, 
the pileus broadens centrifugally and becomes more compact by in- 
terstitial growth. At the same time the hymenophore primordium, 
by the intercalary growth of new hyphae from the pileus, and by the 
increase of its own elements, likewise develops centrifugally, and keeps 
pace in its growth wnth the pileus margin. 
Formation of the Palisade Layer 
For a time the growth of the hyphae composing the hymenophore 
is very rapid and uneven, the pointed ends of some of the threads grow- 
ing down beyond the others, so that the surface is rough and jagged 
(figs. 12 and 13). Gradually, however, the hyphae acquire a more 
uniform rate of growth, and the ends reach the same level, becoming 
clavate and crowded. This condition of the hymenophore in which the 
hyphal ends form an even, compact surface is the palisade stage. Such 
a condition is shown in figure 23. In this species, as in others pre- 
viously investigated, its development is centrifugal, from the stem 
toward the pileus margin. Here however it develops very uniformly, 
so that at one time in the same fruit-body the palisade occupies the 
whole area of the hymenophore except the extreme margin. In all 
the species that have had this phase of their development described, 
the formation of the palisade is more gradual, so that in the same fruit- 
