. EVANS AND HOOKER: PERISTOME IN CERATODON PURPUREUS 99 
The material, which was collected in the vicinity of New Haven, 
Connecticut, was studied by means of microtome sections. 
The mature peristome of Ceratodon purpureus has been 
repeatedly described in taxonomic treatises, but a brief account 
of its peculiarities will make the description of the development 
more intelligible. It consists of sixteen teeth which arise from a 
continuous basilar membrane. Each tooth is divided almost to 
the base into two slender tapering branches, which show much the 
same structure throughout their entire length (FIG. 17, 18). 
The outer portion of each branch forms a subcylindrical ridge, 
distinctly contracted at its union with the inner portion, which 
is broader and more flattened toward the base. Four or five 
corresponding transverse ridges extend across the branches of 
each tooth, being close together at the base but farther apart 
toward the apex. They correspond with the transverse walls of 
the outer peristomial layer. On the inner surface also vestiges of 
transverse walls can be detected, but these are unaccompanied 
by ridges (FIG. 19, 24). Just above the basal undivided portion 
of each tooth one or more of the transverse ridges extend across 
from branch to branch, thus leaving median perforations (FIG. 21). 
The basal portion is especially thick and bears several crowded 
transverse ridges, which in longitudinal section give the tooth a 
serrated appearance (FIG. 24). The entire surface of the teeth 
is covered over with minute spicules. The basilar membrane of 
the peristome is in the form of a hollow cylinder, sixteen cells in 
circumference and three or four cells high, representing a part of 
the outer peristomial layer. The thickened walls in this portion 
of the peristome are smooth throughout. 
The early development of the sporophyte in Ceratodon purpu- 
reus was studied by Kienitz-Gerloff (’78, p. 42), who detected in 
very young stages a two-sided apical cell cutting off two rows of 
segments, just as in other members of the Eu-Bryales. Each of 
these segments, as he further showed, soon became divided into 
quadrants by an anticlinal wall and then underwent divisions 
ace to the so-called ‘‘Grundquadrat” or ‘fundamental 
square” method described below. The embryonic development 
of Ceratodon is discussed also by Goebel (’87, p. 178), but the most 
complete account of the process is that published by Kuntzen 
(12), who, however, pays but little attention to the peristome. 
