5i8 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
with the undamental tissues after fixing in picro-acetic or chrom-acetic 
acid, as my experiments show. They explain this structure by assuming 
that this continuity of tissue is merely contact of the young gill with the 
rudimentary stipe due to the force exerted on the fundamental tissue by 
the involute margin of the pi eus, bringing this tissue in close contact with 
the young gill. 
Buttons that showed no increase in size and that had been on the surface 
of the substratum for 48 to 72 hours after they failed to show signs of 
growth, and fresh buttons of approximately the same age, showed stages 
in which the young gills were well formed. In those specimens that were 
already beginning to turn brown, the stretching and expansions of the 
tissues were retarded. These plants show but slight evidence of an involute 
margin (PI. XXX, figs. 59, 60, 61), yet the fundamental tissue of the stipe 
region is continuous with the gills. In the sections shown in figures 59 and 
61, the sagging of the tissue below the gills causes the formation of the 
deeply stained line which in a photograph tends to give one the impression 
of an artefact, but under the microscope hyphae can be traced from the 
fundamental tissue into the young gills. This sagging or collapse of the 
tissue is associated with loss of turgescence and necrosis. In all three 
cases the palisade cells are devoid of cytoplasm, and in figures 60 and 61 
they seem to have broken down, giving a ragged appearance to the layer, 
which is generally even and smooth at this stage. 
In a study of buttons of Agariciis campestris that have turned brown 
after they had been on the surface of the substratum for 96 hours without 
showing any signs of growth, we find conditions such as are represented in 
figures 56, 57, Plate XXIX, and figure 58, Plate XXX. The first of the 
series (fig. 56) represents a longitudinal tangential section toward the margin. 
This plant, as we can judge from the median section (fig. 58), has no marked 
involute margin and is similar to normal buttons of this size and age before 
death. There is no incurved margin, yet we see deeply stained tramal 
elements attached firmly to the fundamental tissue (fig. 56). Faint indi- 
cations of the palisade cells bounding the gill cavities can be seen in this 
figure. Though these buttons are dead, these sections offer further evidence 
of the continuity of the gill elements with the pileus region above and with 
the fundamental tissue of the stipe below. In this preparation and in 
stages of living plants of the same age we find quite conclusive evidence 
that the palisade layer is not followed by a region toward the periphery of 
the hymenophore primordium which subtends an annular gill cavity, as 
maintained by Atkinson and his students, but that this region is closely in 
contact with the fundamental tissue below it, as shown here. As our 
sections approach the median we find that the gills have already become 
separated from the fundamental tissue, which evidently develops into the 
annulus. It is of interest to note in these sections near the stipe the furrows 
of the fundamental tissue which are well shown in figures 57 and 58 directly 
