222 
F. Cavers. 
INTER-RELATIONSHIPS OF THE ANACROGYN/E. 
With the exception of the Calobryacere, the four families into 
which we have here divided the Anacrogynae are somewhat artificial. 
The classification and phylogeny of the Anacrogynae present great 
difficulties. It might he expected that the great diversity in both 
gametophyte and sporophyte shown by the genera of Anacrogynae 
would make it comparatively easy to arrange them in a natural 
classification, but it is just this diversity, together with the frequent 
occurrence of parallel developments in different lines, that baffles 
our attempts to frame a satisfactory arrangement. For instance, 
the genera Aneura and Pellia present the simplest type of gameto¬ 
phyte along with the most advanced type of sporogonium, if one 
may assume that the undifferentiated thallus is really the primitive 
type of plant-body and that the sporogonium which shows the 
earliest and most extensive sterilisation of “ potentially sporogenous 
tissue ” is the highest type of sporophyte. Both of these assumptions 
have been challenged, the former by Wettstein and the latter by 
Goebel and others, but the questions raised will be considered later 
when discussing the general phylogeny of the Bryophyta. 
Various writers have attempted to draw sharp distinctions 
between “ thallus-lobes ” and “true leaves” in the Anacrogynae, but 
these supposed distinctions are based upon somewhat narrow 
morphological ideas derived from the study of the Acrogynae. 
For instance, Stephani (66) describes Blasia, and even Treubia (62) 
as having a “ lobed thallus,” though he applies the term “leaves” 
to the appendages of the axis in Fossoinbronia and Noteroclada. 
Yet in all four genera the appendages arise in essentially the same 
way at the growing-point, an appendage being formed from each 
lateral segment cut from the apical cell and having therefore a 
definite position with reference to the axis. 
In the Anacrogynae the growth of the plant-body is always 
referable to a single apical cell, the form and mode of segmentation 
of which show great diversity in the various genera and even differ 
in different species of the same genus. Still, the mode of apical 
growth is of interest and even of value, in helping us to understand 
the morphology of the plant-body, with special reference to the 
