THE GREAT GROUPS OF BRYOPIIYTES HQ 



gametophyte ; the Jungermannia line has differentiated 

 the form of the gametophyte ; the A^ithoceros 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) 



72. 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 sub- 

 stance called peat, which may accumulate to considerable 

 thickness by the continued upward growth of the mass of 

 moss. 



The gametophyte body is differentiated into two very 

 distinct regions : (1) the prostrate dorsiventral thallus, 

 which is called protonema in this group, and which may be 

 either a broad flat thallus (Fig. 104) or a set of branching 

 filaments (Figs. 81, 102) ; (2) the erect leafy branch or 

 gametophore (Fig. 82). This erect branch is said to be 



