A rmillaria mucida , Schrad. 
505 
presented a homogeneous tissue ; the hyphae ran longitudinally, interweaving 
freely. Soon, the tissue at the apex becomes looser in texture, leaving, 
however, an unaltered layer round the periphery (PI. XXXV, Fig. 1). The 
hyphae near the apex, which hitherto all ran in the same direction, now 
begin to display a tendency to radiate towards the periphery, and rapidly 
form a subcuticular layer of hyphae at right angles to the outer surface 
(Fig. 2). These hyphae, which are somewhat closely packed to form a sort 
of palisade tissue, are not differentiated, but are rich in protoplasm, and take 
a deeper stain. The universal veil can be clearly distinguished now as 
a layer of hyphae, two or three deep, traversing the ends of the hyphae 
composing the palisade tissue (Figs. 3 and 4). The veil generally takes 
a brown stain with haematoxylin and orange G, contrasting well with the 
violet tint of the adjacent cells. 
Hartig considered that A rmillaria me Ilea was devoid of a universal veil, 
but Fayod ( 3 ) has shown that such a tissue always exists, though it is some- 
times so tenuous as to escape attention. 
We have seen that the differentiation of tissues begins at a very early 
stage and marks off the stipe from the pileus, the latter being defined 
by the palisade layer. This layer rapidly becomes more confirmed and 
spreads inwards from its outer and lowermost edge, at the same time 
assuming a marked palisade character. By this time, too, the pileus is 
externally distinguishable as a minute cap. The radial palisade layer 
spreading inwards forms the primordium of the hymenium. 
Strong surface-growth now causes the pileus to assume greater con- 
vexity, at the same time, owing to cessation of growth of the tissues 
immediately below, the primordium of the hymenium becomes separated 
from them and a small air-space is formed, which is the origin of the ‘ gill 
cavity’. Meanwhile, the outline of the future stipe has become more 
clearly defined by the outer layers growing looser in texture, so that a mass 
of lacunae filled with air arises, whereas the future stipe remains densely 
felted. This, no doubt, assists in supplying the necessary air for the 
formation of the gill cavity, as pointed out by Atkinson (Fig. 5). 
Up to this stage the universal veil has kept pace with the growth 
of the inner tissues, now, however, its hyphae begin to disintegrate and 
break up, not only over the surface of the pileus, but also down the sides of 
the stipe (Figs. 6 and 7). 
It may be noted here that at this time the decomposing universal veil 
is very delicate and apt to be torn off even by the microtome blade, so that 
in some of the sections no veil can be seen. Further, the pileus has taken 
a more rounded form and is growing in diameter more rapidly than the 
stipe, so that it bulges somewhat beyond the latter. The disappearance of 
the veil accentuates this overlapping (Fig. 7). It would seem possible that 
these phenomena combined to mislead Hartig. 
Mm2 
