28 
F. Cavers. 
The primary division of the Higher Mosses into Cleistocarpi 
(capsule opening by irregular rupture or by decay of its wall) and 
Stegocarpi (capsule opening by a predetermined dehiscence line or 
zone which throws off the apical portion of the wall as a lid or 
operculum) appears to have been first proposed by Muller in 1849, 
and it has been maintained by the majority of bryologists to the 
present day, as has also the division of the Stegocarpi into Acrocarpi 
and Pleurocarpi (according to the position of the archegonial group, 
and therefore of the sporogonium, at the end of the main axis or 
that of a short lateral branch) which was made by Bridel in 1826. 
On various grounds, neither of these distinctions can now be 
regarded as forming a sound basis for the classification and 
phylogeny of the Bryales. Lindberg in 1879 distributed the 
cleistocarpous forms among the various stegocarpous families, to 
which he attached them according to their general resemblances 
apart from the absence of a lid. The cleistocarpous Bryales are 
mostly very small plants, often with the protonema persistent and 
more conspicuous than the leafy gametophyte and with the seta 
short or almost absent; the capsule wall at maturity consists 
usually of a single layer of cells, though (except in Nanomitrium ) 
bearing stomata ; and in some of the forms placed in this group 
there is a rudimentary annulus (. Nanomitrium ) and even a rudi¬ 
mentary peristome ( Mildeella ), though in the latter case this organ 
is functionless, since the rudimentary operculum does not become 
detached. Excepting Archidium, such of these cleistocarpous types 
as have been investigated ( Ephemerum , Pleuridium, Phascum, 
Nanomitrium) show the typical Bryinean embryogeny. Much more 
detailed work on the cleistocarpous forms appears to be required 
before one can venture an opinion on the vexed question whether 
they are primitive forms, lying at the starting-point of several lines 
of development leading up to the typical Bryales, or on the other 
hand degenerate forms derived by reduction from various distinct 
groups of the stegocarpous Bryales. 
The old distinction into Acrocarpi and Pleurocarpi must be 
abandoned, for many reasons. Many pleurocarpous forms occur 
among such acrocarpous families and genera as Leucobryacese, 
Fissidens, Pleuroweisia, etc.; not only do different species of the 
same genus differ In this respect, but in some cases the same plant 
may be both pleurocarpous and acrocarpous, e.g., species of Daltonia, 
Fissidens, Hypo pterygium. The division of the stegocarpous Bryales 
into Acrocarpi and Pleurocarpi is not only quite artificial, but it com- 
