5i6 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
fixing agents they showed no annular gill cavities and did not differ from 
the unfixed living or unfixed dead specimens (figs. 23-28). 
It appears that the already inert cells are less likely to shrink in fixation 
than are those of the living and growing plants. For this reason fixed 
material of dead plants was studied, the living plants shrinking too much 
to give a true picture of the conditions even with the fixing agent generally 
conceded to be the best for fungi. Figures 29-51 represent free-hand 
sections of living buttons approximately of the size and age in which gill 
primordia are developing after having been fixed for 24 hours in the fol- 
lowing fixing agents: chrom-acetic, Bouin's picro-formol, picro-acetic 
Carnoy's, Gilson's, Kaiser's, Flemming's strong, medium, and weak, Juel's, 
and Merkel's. It appears from these figures that the chrom-acetic, picric 
acid, and Flemming's strong solutions produce the greatest amount of 
tearing of the fundamental tissue just below the lamellar region. 
Flemming's weak solution produced the least shrinkage of all fixing 
agents (figs. 29-34), but still sufhcient shrinkage to vitiate the results. 
For this reason it was found that detailed histological studies were best 
made from fixed dead carpophores simultaneously with a study of free-hand 
sections of fresh ones. The dead carpophores after being fixed were carried 
through the alcohols to parafifin with the greatest care and then sectioned. 
As to the early development of Agaricus species my results from the 
fresh and fixed dead plants confirm those of De Bary (1887), Hoffmann 
(i860), and others. The development of the gill primordia is essentially 
similar to that in the Coprinus species I have described. The gill cavities 
originate separately and not as a continuous annular or ring-shaped opening. 
They arise as arched series of palisade cells which appear very early between 
the vertically arranged radial plates, the trama primordia, so as to form a 
series of wide archways, the rudimentary gill cavities. The tramal elements 
are in connection with the fundamental tissue of the stipe region below. 
In Agaricus campestris the rudimentary gills differ in shape from those of 
the Coprinus species I have studied, in that they are broader near the 
pileus and more or less wedge-shaped as they approach the fundamental 
tissue of the stipe region; so that, when shrinkage of the tissue occurs, 
one studying a tangential longitudinal section is given the impression that 
the gills grow downward into a large cavity. 
Sections of fresh buttons together with prepared dead carpophores of 
approximately the same age and size show that the wedge-shaped gill 
primordia are attached to the fundamental tissue of the stipe region, and 
very often the gill cavity Anlagen are invaded by fundamental tissue from 
below giving a picture similar to those described by De Bary (1866), Brefeld 
(1877), and Atkinson (1914c) for Amanita and Amanitopsis species. These 
stages were reproduced satisfactorily only by photographic methods from 
carpophores that were dead and which were put into Flemming's weak 
solution, sectioned, and stained, although similar figures were obtained 
from free-hand sections of the living carpophores. 
