: gen, a8 shown in fig. 13. a. 
_ Formation OF PALISADE LAYER.— Following the stage when oo a 
: ged it in irregular tufts, the hymenophore pri 
re ompact ie ie ees eee of ae 
210 BOTANICAL GAZETTE [SEPTEMBER 
apex, and the two groups of threads grow into each other and inter- 
mingle to form the common mass of the “volva.”’ In P. squarrosa 
there is a material difference from the condition just described for 
C. lagopus, since in this case there are no hyphae on the stem sur- 
face which grow upward and unite with the downward growing 
threads. Figs. 2, 3, and 7 show the central strand of hyphae just 
mentioned; in fig. 5 the character of the blematogen hyphae may 
be seen. 
ORGANIZATION OF PILEUS.—Coincident with an early stage in 
the development of the hymenophore primordium, median longi- 
tudinal sections show that the fundament of the pileus is becoming 
differentiated from the surrounding tissue (fig. 8). The hyphae 
become richer in protoplasm and by interstitial growth form a more 
compact structure. This organization proceeds from the center 
outward in a centrifugal manner, the margin of the pileus keeping 
pace with, and contributing to, the growth of the hymenophore 
primordium. During the early stages of differentiation of the 
pileus some of the hyphae arise from the stem, but its later growth _ : 
is probably due entirely to interstitial and marginal increase of its 
own elements, which are interwoven in all directions, thus differing 
from the hyphae of the stem, which in general run parallel to the 
stem axis. The pileus elements merge gradually with the blemato- 
gen and there is no sharp line of division between the two struc-_ 
tures. The cells of the blematogen hyphae, however, are swollen 
and have thick walls, which stain deeply, while the pileus hyphae 
are slender and do not take a deep stain after the pileus is well 
Organized, so that a general distinction is evident. In ens ae 
ie peripheral threads of the eases ‘composing. = ote 
i 
