316 PLANT STUDIES 
gametophyte ; the Jungermannia line has differentiated 
the form of the gametophyte ; the Anthoceros line has 
differentiated the structure of the sporophyte. It should 
be remembered that other characters also serve to distin- 
guish the lines from one another. 
Musci (Mosses) 
206. General character. Mosses are highly specialized 
plants, probably derived from Liverworts, the numerous 
forms being adapted to all conditions, from submerged to 
very dry, being most abundantly displayed in temperate 
and arctic regions. Many of them may be dried out com- 
pletely and then revived in the presence of moisture, as is 
true of many Lichens and Liverworts, with which forms 
Mosses are very commonly associated. 
They also have great power of vegetative multiplica- 
tion, new leafy shoots putting out from old ones and from 
the protonema indefinitely, thus forming thick carpets and 
masses. Bog mosses often completely fill up bogs or small 
ponds and lakes with a dense growth, which dies below 
and continues to grow above as long as the conditions are 
favorable. These quaking bogs or "mosses," as they are 
sometimes called, furnish very treacherous footing unless 
rendered firmer by other plants. In these moss-filled bogs 
the water shuts off the lower strata of moss from complete 
disorganization, and they become modified into a coaly 
substance called peat, which may accumulate to consid- 
erable thickness by the continued upward growth of the 
mass of moss. 
The gametophyte body is differentiated into two very 
distinct regions : (1) the prostrate dorsi ventral thallus, 
which is called protonema in this group, and which may 
be either a broad flat thallus or a set of branching fila- 
ments (Figs. 275, 290) ; (2) the erect leafy branch or 
gametophore (Fig. 276). This erect branch is said to be 
