624 RELATION TO ENVIRONMENT. 



to environment, and yet we know something of the halophytic 

 vegetation of some of the alkaline waters and of the soil shores 

 of the lakes and ponds in the arid regions. See alkaline marshes 

 and Bad Lands in Chapter L. The vegetation in the vicinity 

 of the Great Salt Lake is similar to that mentioned here. 



1112. Marl ponds. The water in marl ponds contains a 

 large percentage of carbonate of lime. Plant life is, therefore, 

 somewhat restricted. Certain species of Chara (one of the 

 algae), however, are often very abundant in the waters of marl 

 ponds, and the plants are very brittle because of the large amount 

 of carbonate of lime in their tissues. (See shores of marl ponds 

 in Chapter LV.) 



1113. Vegetation of hot springs. The vegetation of hot 

 springs is remarkable for the high temperatures at which cer- 

 tain bacteria and blue-green algae can grow. In America the 

 most notable instance is the vegetation of the hot springs and 

 geysers in Yellowstone National Park. Certain filamentous bac- 

 teria grow in hot water, the temperature reaching as high as 

 7o-82 C., or rarely as high as 89 C. In water slightly cooler, 

 65-68 C., or even scantily at 75-77 C., species of the Cyano- 

 phyceae, like Phormidium, occur, and in still cooler waters of the 

 hot springs are found Anabaena, Glceocapsa, etc. Some of these 

 waters are rich in carbonate of lime, which some of these plants 

 deposit, forming curious and often fantastic figures in the basins. 



II. Fresh-water, or Limnetic, Plant Societies. 



1114. Pond or inland-lake societies. These should be ob- 

 served in connection with swamp societies and the flora of soil 

 shores, since the semi-aquatic plants, like the bulrushes, cattail- 

 flags, arrow-leaf, etc., growing in the shallow water of the pond 

 or lake margin, are the transition forms from the lowland or 

 swamp flora to the truly aquatic plants. In general several 

 zones can be recognized from the shore lakeward (see Chapter 

 LV). The first is a littoral zone, and includes the semi-aquatics 

 like those mentioned above, and this is connected with the 



