160 



Biology in America 



So too the deathbed of a lake is the birthplace of a new 

 cormminity of plants. In the sliallow margins of the lake 

 rises a niiniatnre forest of cat-tail, rnsh and sedge. With the 

 gradual shrinkage of the lake through evaporation or drain- 

 age, and the slow accumulation of wind-borne dust and debris 

 on its bottom, runners of rush and sedge press further from 

 the shore. Their decaying stems and leaves, together with 

 wdnd-borne sediments form ever-increasing mud in the shal- 

 low water, which with the recession of the lake forms a fer- 

 tile field for the advancing grasses along its shores. And 

 thus a meadow is formed into which soon come the moisture- 



A Glacial Pond in the Eocky Mountains 

 Showing the encroaching forest. Original. 



loving herbs, and then from near or far wind-driven catkins 

 come and willows grow from these, the vanguard of the for- 

 est ; which soon are joined by other trees, of various sorts, 

 dependent on proximity and ease of carriage of their seeds; 

 and thus a young forest takes its stand upon the old lake 

 bottom and meadow herb and grass give place to trees and 

 plants which love the dark — the victors in the "struggle for 

 existence." Where however forests are far away or soil and 

 climate are not adapted to growth of trees, the grasses per- 

 sist and a meadow marks the graveyard of the lake. 



The inter-relationships of the various members of plant 

 communities, both to one another and to their environment, 



