* 9 
pletely obscures the phylogeny of the group, for there can be no doubt 
that the pleurocarpous forms have arisen independently from various 
acrocarpous groups—a line may be traced, for instance, from the 
acrocarpous Orthotrichaceae through intermediate forms like the 
Hedwigiaceae and Cryphaeaceas to such typically pleurocarpous 
forms as Eurhynchium and Hylocomium, while another line leads 
upwards from the Bartramiaceae to the Spiridentaceae. Moreover, 
the characters of the peristome are practically identical in detail, 
as well as in the general structural plan, in such families as the 
Bryaceae and Hypnaceae, which, on the generally accepted classi¬ 
fication, are widely removed from each other. 
The most striking feature in the organisation is the evolution 
of the peristome, and it is upon the characters of this organ that 
something approaching a natural classification must be founded. 
Here again much remains to be done on the developmental side, for 
there are many gaps in our knowledge of the origin of the peristome 
and the annulus, despite the excellent memoirs of Lantzius-Beninga, 
Philibert, Goebel, Dihm, and others. Moreover, as pointed out by 
Loeske (31) in his recent interesting book on the Morphology and 
Classification of Mosses, welcome aid in the attempt to trace out 
the main lines in the evolution of the Bryales may come from 
practically every piece of research undertaken on the histology, 
physiology, and ecology of the various families, and there is room 
for careful monographs of many of the orders and genera. 
Detailed treatment of the Bryales would unduly extend the 
scope of the present series of articles, and must therefore be left 
over for another occasion, but in order to draw together some of the 
more important results of recent work a brief summary will be given 
regarding the phylogeny of the Bryales. In this group we can 
distinguish four sharply marked types of peristome-structure, upon 
which it is probably justifiable to split up the higher Mosses into 
four independent series co-ordinate with the Sphagnales and 
Andreaeales. The division suggested here is a compromise between 
the systems recently proposed by Lorch (32) in his fine monograph 
of the Polytrichaceas, and by Fleischer (14) in his great work on 
the Mosses of Java. According to Lorch, the Bryales should be 
broken up into the four groups Polytrichales (Polytrichaceae and 
Dawsoniaceae), Buxbaumiales ( Duxbaumia ), Diphysciales (. DipJiy - 
scium), and Bryales (or Eu-Bryales). Fleischer, on the other hand, 
unites the Buxbaumiaceae and Diphysciaceas into one group 
(Buxbaumiineae), and splits off the Tetraphidaceae as a second group 
