﻿196 Nichols: The vegetation of Connecticut 



an insoluble form on the surfaces of the cells. At Twin Lakes this 

 alga is extremely abundant, more so than in any other lake or pond 

 in the state, so far as the writer's observations have extended. 

 Here, not only Chara, but the leaves and stems of Najas, Elodea^ 

 and various species of Potamogeton are incrusted by a thin, white, 

 flaky deposit of marl. Some of the blue green algae, notably 

 Zonotrichia, are likewise instrumental in causing marl formation.* 

 Because of the inability of most of the plants active in its pre- 

 cipitation to survive in competition with shallow water species, 

 the production of marl is largely restricted to the deeper parts of 

 lakes. 



The Floating Mat 

 Occurreyice and Importance of the Floating Mat. — In an earlier 

 paragraph the writer has alluded to the manner in which the shal- 

 low-water zones of vegetation in a lake tend to push out from the 

 shore and to encroach upon the deeper areas. In most lakes and 



irough the interventior 

 usual succession of plant societies. Sequence of Zones: i. Pondweed Zone; 2 

 Water-lily Zone; 3. Decodon Zone; 4- Cassandra— ^^ftagnwm Zone; 5. Cassandra— 

 S^/tagnutn— Sedge— Low Spruce Zone; 6. Tall Shrub Zone; 7. Bog Forest. F = 

 Marginal Ditch or "Fosse". 



* For detailed discussion of the relation of Chara and Zonotrichia to marl forma 



