12 CONNECTICUT GEOL, AND NAT, HIST. SURVEY. [Bull. 
be developed. Any failure to effect fertilization is of course 
a menace to the further existence of a species, and the probabil- 
ity of failure is especially great in the case of dioicous species, 
where the male and female plants are often far apart, neces- 
sitating a long journey for the sperms. To a certain extent 
the danger is overcome by the development of organs of vege- 
tative reproduction, known as gemme or propagula. The 
simplest of these consist of single cells or of small groups 
of cells without definite form, They easily become separated 
from the parent plant and develop into new individuals if 
supplied with the proper conditions. In many cases the 
reproductive bodies are more complex and already show, even 
before they fall away, some indication of the thallus or leafy 
shoot into which they will develop. Certain species reproduce 
largely if not entirely by means of these vegetative bodies. 
It is customary to divide the Bryophytes into two sub- 
classes, known respectively as the Hepatic, or Liverworts, 
and the Musci, or Mosses. This classification, however, as 
Underwood and others have pointed out, does not altogether 
represent the facts, and it is more convenient, if not more 
natural, to divide the group into the following six orders, 
which may be considered as approximately equal in rank: — 
I. MarcHanTIALes ; II. JUNGERMANNIALES ; III. ANTHOCERO- 
TALES; TV. SPHAGNALES; V. ANDREZALES; VI. BryaLes. By 
adopting this course it becomes much more practicable to 
assign definite characters to the various subdivisions. Of 
these six orders the first three comprise the Hepatice and 
the last three the Musci, as limited by the majority of botanical 
works ; and it is still often convenient to employ the terms in 
this general sense. 
THE MARCHANTIALES 
The present order includes about half of the thalloid Bryo- 
phytes known from Connecticut, and most of the species are 
large and conspicuous. Two are normally aquatic, floating in 
ponds or slow streams; the others are all terrestrial, and even 
the aquatic species tend to become terrestrial through the 
drying up of the water in which they live. Except in the 
aquatic forms the thallus clings closely to the substratum, 
