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AMERICAN JOURNAL OF BOTANY * [Vol. 9, 
Atkinson reports a primitive annular gill cavity for Agaricus campestris 
(1906), A. arvensis, and y4. comtulus (1914a), and Lepiota clypeolaria (1914Z?). 
In L. clypeolaria the hymenophore primordium is described as at first 
smooth. Later, folds are formed which develop into gills. His sections of 
this material are conspicuous and particularly interesting for the absence 
of a palisade layer at the time the annular gill cavity is formed (1914&, 
figs. 7-9). In this respect, L. clypeolaria is made to differ from all other 
forms he describes. This appearance is clearly due to the abnormal rup- 
turing of the fundamental tissue below the hymenophore as I am describing 
it later in this paper. 
Prior to 1915, Atkinson classifies the agarics, in which the lamellae 
arise endogenously, into two groups: those forms in which there is a so- 
called well-marked annular gill cavity formed below the primordium of the 
hymenium, as in ^4. campestris, etc., and those in which there is no general 
gill cavity but rather a series of cavities as in Amanita, Amanitopsis, and 
in Coprinus described by me. For Agaricus Rodmani, Atkinson (1915) 
finds a new type of annular gill cavity. In this case the general annular 
gill cavity is interrupted by strands of fundamental tissue which extend 
from the hymenophore primordium to the stipe region below. These 
strands are conspicuously attached and are continuous with the tissues of 
the stipe and pileus and remain attached to the gill fundaments until well- 
differentiated lamellae are formed. Atkinson is unable to give any adequate 
explanation of these conditions on his theory that the gill cavity should be 
annular from the first. 
In 1916, Atkinson reports finding a weak prelamellar gill cavity in 
Coprinus micaceus and C. atramentarius . In C. comatus a well-marked, 
"strong" annular prelamellar gill cavity is reported. In the same year, 
Atkinson (1916Z)) reports in Lepiota cristata a ''weak" annular prelamellar 
cavity, and in L. seminuda a very strongly developed annular gill cavity. 
Douglas (191 6) studied five species of Cortinarius^ to determine the 
origin of lamellae and also the development of the universal veil, but gives 
no data as to the origin of the gill cavity. 
Sawyer (1917a) found in Pholiota squamosa, P.flammans, and P. adiposa 
the appearance of "weak" annular prelamellar gill cavities, although the 
degree of "weakness" varies in the different individuals. The gills which 
he finds partially attached to the fundamental tissue become free very late, 
just before the gills are exposed by the rupturing of the partial veil. Sawyer 
fails to show the critical stages in the development of the gill salients. 
His preparations are made of plants too old, and in many cases probably 
dead, before fixation, although he failed to recognize this fact. His work 
on Cortinarius pholideus (1917&) shows nothing further as to the origin of 
the gill cavity. 
Walker (191 9) reports on the development of Pluteus admirahilis and 
^ Cortinarius distans, C. cinnamomeus, C. armillatus, C. lilacinus, and C. infractus. 
