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 gemmcu 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 Hepaticae, 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 ; IV. Sphagnales ; V. Andre^ales ; 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 HepaticDS 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. 



