174 



GROWTH HABITS OF PLANTS 



Another very interesting type of habitat which seems to be 

 physiologically dry, although there is an abundance of water present, 

 is the bog (Fig. 79). Bogs are formed in places where lack of drain- 

 age, and consequently lack of aeration, leads to an accumulation of 



Fig. 78.— a mangrove thicket. Halic plants. (Photograph by H. L. Shantz. 

 Courtesy of H. L. Shantz and the U. S. Department of Agriculture.) 



Fig. 79.— Cordova bog, Alaska. (Photograpli by George B. Rigg.) 



