292 THE BRYOPHYTES 



parts of the plants die and form a deposit below, called peat. 

 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 parts of Germany. There are regions of the northern United 

 States, Canada, Europe, and Asia, where the peat-forming plants 

 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 often becomes rich in certain toxic organic sub- 

 stances that result from the partial decomposition of the vegeta- 

 tion. The accumulation of these substances 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 soft or quaking bog becomes firmer, grasses may appear 

 and some characteristic orchids (Calopogon, Pogonia, Arethusa, 

 Cypripedium, etc.), the insectivorous plants Sarracenia (Fig. 311) 

 and Drosera (Fig. 312), such heaths as the swamp cranberry, 

 swamp blueberry, swamp azalea, and Labrador tea, and certain 

 trees, as the larch or tamarack (Larix), black spruce (Picea), 

 arbor vitae (Thuya), white cedar (Chamcecyparis), alders, and the 

 red maple. These plants and others, in various combinations 

 with the peat mosses, form very characteristic associations, and 

 furnish some of the best illustrations of what the ecologist calls 

 plant formations. The northeastern United States and Canada 

 are full of examples of this interesting feature in the natural 

 history of the Sphagnum swamp. 



