322 
GERTRUDE E. DOUGLAS 
Amanitopsis.^^ The loose character of the tissue is due to the less 
active growth of this region, the hyphae elongating but producing 
no new elements. As in the case of the species mentioned, the exact 
limits of this region are impossible to define in the early stages. In 
the right-hand object of figure i this internal growth area has reached 
the apex of the young fruit body. The upper end of this probably 
represents the pileus primordium, though there is no evidence of its 
differentiation from the stem. 
It is not until the buttons reach the stage of figure 2 that we can 
distinguish the separate fundaments of the different regions. At the 
top of the central growth region, there is differentiated a dome-shaped 
area, which takes the stain more deeply at its margin. This dome- 
shaped area represents the fundament of the pileus (fig. 2) and the 
deeply stained margin, the primordium of the hymenophore. As 
soon as the latter appears, the fundament of the stem is delineated as 
that part of the central dense area below the pileus. At the same 
time the ground tissue between the margin of the pileus and the 
stem becomes the fundament of the partial veil. From this time on 
expansion of the fruit body takes place in all directions, particularly 
in the longitudinal one, and the mesh becomes more and more open 
(figs. 3 and 4). 
The Development of the Hymenophore. — ^The margin of the pileus 
fundament (fig. 2) forms an annular zone of very actively growing 
hyphae, which are becoming very crowded and are turning downward 
and obliquely outward. They are very rich in protoplasm and con- 
tain very prominent nuclei. This annular zone stains deeply and is 
shown in section in figure 2 as two deeply staining areas one on either 
side. This annular zone is the fundament of the hymenophore. The 
hyphae are provided with very sharp ends, thus enabling them to 
penetrate the ground tissue below the more easily (fig. 10). The 
hyphae first appear near the stem fundament and as the pileus expands, 
they are continually being formed at the margin. At the same time, 
by the branching of the hyphae, new ones are interpolated between 
the original ones, causing the tissue to become more and more compact. 
Origin of the Palisade Layer and Gill Cavity. — When the primordium 
of the hymenophore is first formed, the growth of the hyphae is very 
unequal and consequently the lower surface presents the very irregular 
Atkinson, G. F. The development of Amanitopsis vaginata. Ann. Mycol. 
12: 369-392. pis. 17-19. 1914. 
