1906] ATKINSON—AGARICUS CAMPESTRIS 245 
of the fact that at present few species have been cultivated artificially 
(exceptfin the genus Coprinus by BREFELD, /. c.) so as to obtain the 
stages df development, and because the feral species nearly all pass 
their early and critical stages of development within the substratum 
and therefore are difficult to find, and at the same time it is often 
difficult to be certain to what species they appertain. These difh- 
culties have probably played an important part in discouraging the 
further study of development of the Agaricaceae. 
It is rather surprising, however, that even in the present time we 
do not have a sufficiently clear, full, and accurate account of the 
development of the fruit body of Agaricus campestris, especially the 
origin and differentiation of the various parts of the plant. This 
is the more so because this species is so common and of such wide 
distribution, but especially because it has been cultivated for so 
many years under conditions in which large numbers of carpophores 
in all conceivable stages of development are so easily obtained. Per- 
haps the very commonness and richness of the material has been 
the chief reason of its having been passed by. 
Having given some attention to the study of the Agaricaceae for 
several years, especially as to their economic and biologic significance, 
as well as to the recognition of species and genera, the need of studies 
of development has been brought very forcibly to my attention, and 
I have been obtaining material for this study in several different 
genera, The meager and conflicting accounts which we have of the 
development of Agaricus campestris, as well as the ease with which 
material can be obtained, has led me to deal with this species first. 
DeBary" says the fruit body of many Agaricaceae (Agaricus 
campestris, A, praecox, Coprinus micaceus and relatives) is in its 
early youth a body interwoven out of delicate, dense, and uniform 
yphae. At a very early stage, through differentiation of the original 
homogeneous weft, the principal parts of the fruit body are outlined 
and limited. On the interior of the upper part of the body a small 
and narrow air space of the form of a horizontal ring arises through 
the separation of the tissue elements. The portion which lies above 
becomes the pileus, the tissue present surrounded by it and below it 
s ** Morphologie und Physiologie der Pilze, Flechten und Myxomyceten 68. 1866. 
ipzig. 
