TERRESTRIAL BOGS 501 



occupy the drier spots, but the others generally grow in the water. 

 The projecting knees of cypress and the arched roots of Nyssa are 

 much in evidence. The knees are formed only where the cypress 

 grows in water, and serve as a sort of breathing organ or pneuma- 

 tophore. They are excrescences from the roots, rising above the 

 water, of a subcylindrical form, and crowned by a cabbage-shaped 

 expansion of bark, rough without and often hollow within. When 

 through a rise of water these knees are submerged the trees will 

 die. 



Extensive cedar swamps (CJiaincccyparis thy aides) occur on the 

 Atlantic coastal plain of the United States north of Florida. The 

 peat increases in thickness inward from the shore to perhaps 15 

 feet, and is full of tree trunks buried at all depths, these having 

 either rotted away or become uprooted. The peat is very pure, con- 

 taining only 3.35 per cent, of ash. The trees on the surfaces of 

 these marshes have broad, spreading roots, which do not penetrate 

 very far into the ground, but rely upon the great horizontal extent 

 of their shoots, which penetrate very deeply. 



Terrestrial Bogs. 



These include the forest bogs or moors and the high moors. 

 They may be the regular successors of the lake and river swamps, 

 but more often they develop independently upon a rocky or sandy 

 substratum. Such are the familiar upland moors, covering the hill- 

 sides in Great Britain and Scandinavia, as well as large parts of 

 northern Germany, and broad areas of northern Asia, and of Can- 

 ada and the northern United States. 



Forest Moors. Beeches, pines and spruces succeed the tamarack 

 and alders, and form the transition to the high moors. Here the 

 ground is dry, and a wood flora appears, often characterized by 

 orchids. In these woods dry peat or forest peat results from the 

 falling and partial decay of the trunks, branches and leaves of the 

 trees. The character of the resulting peat varies with the type of 

 vegetation, especially with the predominant arboreal types. Decay 

 is partly accomplislicd tin'ough the influence of microorganisms. 

 The destruction of the dry peat and its conversion into earthy mold 

 or its entire decay are furthered by the growth of a number of 

 grasses, especially the common hair-grass, DescJiainpsia Hexuosa 

 Trin. The growth of peat mosses among the trees in the transition 

 of the bogs to the high moor type will result in killing these trees 

 through increasing moisture. Decay at the point of exposure above 



