Vol. 40 No. 3 
BULLETIN 
OF THE 
TORREY BOTANICAL CLUB 
er ee - 
MARCH 1913 
Development of the peristome in Ceratodon purpureus 
ALEXANDER W. EvaNs AND HENRY D. Hooker, Jr. 
INTRODUCTORY 
In his recent work on the Bryophyta, Cavers (11, p. 182) 
divides the Bryales, or true mosses, into the four following groups, 
based on distinctions emphasized by Fleischer: Tetraphidales, 
Polytrichales, Buxbaumiales, and Eu-Bryales. In this division 
the peristome is the organ from which the most important differ- 
ential characters are derived. In the Tetraphidales and Poly- 
trichales the teeth of the peristome are composed of entire cells; 
in the Buxbaumiales and Eu-Bryales they are composed of 
thickened cell walls. Leaving the Encalyptaceae out of con- 
sideration, the Eu-Bryales may be further divided, following the 
example of Philibert (’84, p. 67), into the Diplolepideae and the 
Haplolepideae.. The Diplolepideae with few exceptions have two 
peristomes, while the Haplolepideae have single peristomes, if 
such structures are present at all. 
In the Diplolepideae the two peristomes are derived from two 
concentric layers of cells in the opercular portion of the capsule. 
The development of the peristome has been described in several 
species of this group but is especially well known in Funaria 
hygrometrica (Goebel, ’87, p. 188; Campbell, ’05, p. 211) and 
Mnium hornum (Strasburger, 02, p. 491), which may be considered 
typical representatives. In both these species the outer per- 
istomial layer is composed of thirty-two longitudinal rows of cells 
and the inner of sixteen rows. These rows form sixteen groups, 
[The BuLtetin for February 1913 (40: 43-96) was issued March 18.] 
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