DEVELOPMENT OF EXOGENOUS SPECIES OF AGARICS 
43 
Hygrophorus nitidus B and C 
(Figs. 48-66) 
Young Stages. — In the earliest stage obtained of this form, a 
button about 5 mm. in length (fig. 48), differentiation of the pileus 
and stem regions had already begun to take place. In the photo- 
graphs, the actively growing region appears by its deeply staining 
property to be at the tip, where the longitudinal hyphae are now 
multiplying profusely and growing outward in the forrhation of the 
pileus fundament. By the time development has reached the stage 
shown in figure 49, not only is the pileus primordium well delineated 
from that of the stem but we also have in the annular furrow between 
them the primordium of the hymenophore. Even though the whole 
surface of the fruit body is clothed with a layer of outwardly directed 
hyphae which take the stain deeply, this, layer is differentiated by a 
still deeper stain and by somewhat smaller hyphae (about 2 in 
diameter as against those 3 or 4 at the margin of the pileus) . These 
differences appear more sharply in an older stage (figs. 50, 51, 52). 
The hyphal ends on the surface appear to be disintegrating. This 
species is a viscid one and these deliquescing hyphae furnish the slime 
which covers the plant. 
The Palisade Layer. — Although the hymenophore elements become 
crowded into a palisade-like layer, the surface of the gills never 
becomes smooth as it does in most of the endogenous forms studied 
and in the early stages of the two preceding species. Their hyphal 
ends are variously directed and uneven in length (figs. 53-57). This 
character is retained even in fairly mature stages (figs. 59-63, 66), 
whose surface in consequence is always uneven. The layer is, how- 
ever, a very definite one and is homologous with the more even layers 
of the other species. 
Formation of the Gills.- — The first evidence of gill salients appears 
in the fruit body at a stage represented in figures 53-58, which shows 
the palisade layer being pushed out into very low undulations. In 
the next series (figs. 59-63), the gill character shows more clearly 
and it becomes quite evident that the method of formation is identical 
with that of Hygrophorus miniatus, previously described. The sec- 
tions were taken from a fruit body which was growing close beside a 
second one of the same age, the margins of the two at the point of 
