HYDROPHYTE ASSOCIATIONS. 1S9 



those of the swamp association, although the amount of 

 water is approximately the same. Xot only are the plants 

 different in the sphagnum-moor, but they are not so 

 numerous, and, with the exception of the moss, do not 

 grow so densely. Creeping plants are common ; certain 

 kinds of sedges and grasses are found, but generally not 

 those of the swamps ; while heaths and orchids are espe- 

 cially abundant. It is in these sphagnum-moors, also, that 

 the curious forms of carnivorous plants are developed, among 

 which the pitcher plants, droseras, and dionaeas have been 

 described. In considering this strange collection of forms, 

 it is evident that there must be some peculiarity in the 

 conditions of living. Heaths and orchids are well-known 

 mycorhiza forms ; the carnivorous plants are so named 

 because they capture insects to supplement their food 

 supply; while the peculiar sphagnum mosses replace the 

 mosses of ordinary swamps. What causes have resulted in 

 an association of such marked physiognomy are unknown, 

 but the subject is attracting much attention. 



It seems evident that the problem is one of absorption 

 and that some condition is interfering with this important 

 function. One conclusion, based upon experimental work, 

 is that the greater coldness of the bog water is the cause of 

 diminished absorption, for the difference between the tem- 

 perature of bog water and of other waters is quite remark- 

 able. Another conclusion is that certain salts dissolved in 

 the bog water tend to check the power of absorption. In 

 any event, the assemblage of bog plants is made up of 

 forms that have learned to live with a diminished power of 

 absorption. 



It is usually stated that the water of the sphagnum- 

 moor is very poor in the food materials which are abundant 

 in the water of swamps, and that there is a special lack of 

 the materials which are used in the manufacture of pro- 

 teids. If this is true, it would be necessary to obtain some 

 proteid material already formed, and this might account 



