FRESH-WATER SWAMPS 



495 



Lake Sivamps. Around the margins of lakes and fresh water 

 ponds a variety of plants are found more or less submerged. The 

 number of species of flowering plants having such a habitat is com- 

 paratively small, the endogenous plants predominating, with the 

 water lily family, especially Potamogeton, as the leading class. Of 

 the flowerless plants Hypnum and Sphagnum, two mosses, and the 

 alga Chara are the most significant. The depth at which seed plants 

 will grow ranges from 15 to 25 feet, very few, such as the water 

 lilies, being able to establish themselves in depths greater than 10 

 feet. As the 25-foot limit is approached the number of species 

 rapidly diminishes, this being apparently due to the decrease in 

 light and heat available. Of the plants growing in deeper water, 

 the algae, especially the species of Chara, should be mentioned as 



Fig. III. Diagram of plant zones in small lake near Merryman's Lake, Mich- 

 igan. (After Davis.) o, Chara; i, floating bladderworts ; 2, 

 yellow pond lily ; 3, lake bulrush ; 4, Sartwell's sedge ; 5, 

 bottle sedge; 6, spike rush; 7, cat-tails. 



significant. These are instrumental in raising the bed of the lake 

 or pond by the formation of marl {ante, p. 471). Floating or 

 planktonic plants also abound in most fresh water ponds and lakes, 

 especially in the stagnant portions. The most important of these 

 are the Bladderworts (Utricularia), of which there is a number 

 of species, and Myriophyllum which may cover whole surfaces of 

 the ponds. 



The most important species of peat-forming plants in lakes do 

 not grow in water over two feet in depth. These comprise, among 

 others, the cat-tail flags (Typha), the Bur reeds (Sparganium), the 

 Water Plantain (Alisma), the Arrow-heads (Sagittaria), some 

 grasses (Zizania), the wild or Indian rice (Phragmites), Reed 

 grass, and several sedges, in addition to the pond lilies. Hypnum 

 and Sphagnum grow near the surface. 



In lakes more than 25 feet in depth, filling by the formation of 



