292 THE BRYOPHYTES 



parts of the peat mosses die and form a fibrous deposit below. 

 These deposits may grow to be many feet in thickness, and 

 finally become so firm that they can be cut out in blocks. Such 

 blocks when dried are used for fuel, especially in Ireland and 

 in the Highlands of Scotland. There are regions of the north- 

 ern United States, Canada, Europe, and Asia where the peat 

 mosses cover immense territories, and there are innumerable 

 bogs filled with deposits of peat which may sometime become 

 important sources of fuel supply. 



Peat bogs are generally poorly drained or not drained at all, 

 and the water becomes very rich in certain organic acids that 

 result from the partial decomposition of the vegetation. The 

 accumulation of these acids renders the water unfit for the 

 growth of bacteria and is largely responsible for the preservation 

 from decay not only of the remains of the peat mosses but of 

 other plants with them. It is said that whalers and other ships 

 from the New England coast when starting on long voyages 

 preferred to take their supplies of drinking water from peat 

 bogs because of its keeping qualities. Occasionally the bones 

 of extinct animals, such as the mammoth and mastodon, are 

 found in peat, since these gigantic creatures became mired in 

 the soft bogs of former periods. 



As a quaking bog becomes firmer, other plants begin to grow 

 among the peat mosses. Certain grasses appear, some charac- 

 teristic orchids (Ccdopogon, Pogonia, Aretkusa, Cypripedium, 

 etc.), the insectivorous plants Sarracenia (Fig. 311) and Drosera 

 (Fig. 312), such heaths as the swamp cranberry, swamp blue- 

 berry, swamp azalea, and Labrador tea, and certain trees, as the 

 larch or tamarack (Larix), black spruce (Picea), the arbor vitse 

 (Thuya), and the white cedar (Chamcecyparis). These plants, in 

 various combinations with the peat mosses, form very character- 

 istic associations, and thev furnish some of the best illustrations 



V 



of what the ecologist calls plant formations. The northeastern 

 United States and Canada are full of examples of this interest- 

 ing feature in the natural history of the Sphagnum swamp. 



