Zeller : Development of Stropharia Ambigua 141 
show it to be made up of a pseudo-parenchymous tissue. In the 
upper part of the carpophore the hyphae seem to spread and their 
course is generally parallel with the surface. 
The first sign of internal differentiation of the previously hom- 
ogenous tissue appears in a plane a little above the center of the 
primordium of the carpophore. Here in medial vertical section 
two darkly stained patches of descending hyphae appear (Fig. 
2). These seem to be the regions of most active growth and are 
rich in protoplasm. In the remaining sections of the same carpo- 
phore these deeply stained areas can be traced as an annular area 
in the whole carpophore. This is the hymenial primordium. The 
hyphae of this region are very slender and pointed at first, but 
eventually they enlarge and become crowded, their lower ends 
forming an even surface. After this differentiation to form the 
primordium of the hymenium, an inverted cup-shaped layer of 
hyphae, rich in protoplasm appears. This extends upward from 
the outer edge of the hymenial primordium and over the top of 
the carpophore, remaining the same distance from the surface 
over the whole area. This forms the primordium of the pileus 
(Fig. 3). Simultaneously with the differentiation of the pileus 
the gill cavity is formed by the sagging of the neutral tissue below 
the hymenial primordium, due to the cessation of growth in that 
region. Figure 4 shows the primordium of the hymenium en- 
larged. The primordium of the hymenium increases in width at 
the outer edge, where the hyphae begin to grow downward and 
inward as if to form the incurved margin of the pileus. At this 
stage the partial veil can be distinguished as tissue of lighter 
stain, extending from the universal veil and the pileus margin to 
the outer surface of the upper portion of the stem, which is now 
clearly differentiated (Fig. 5). 
Next, a differential growth takes place in the hymenial hyphae. 
Radial plates of these hyphae grow downward rapidly and form 
ridges, which are the first signs of the lamellae. As soon as these 
appear, the hyphae of the gills spread laterally, leaving a groove 
along the edge of the lamella. In the very earliest stages of the 
development of the lamellae they are differentiated into a lightly 
staining central region, and the heavily staining lateral regions 
made up of the tips of the hyphae. The vertical tangential sec- 
