604 



RELATION TO ENVIRONMENT. 



rush in where new opportunities present themselves by changed 

 conditions or by newly made soil. The permanent drainage of 

 ponds or marshes brings changed conditions, and the flora there 

 undergoes remarkable transformations. The deposits of the 

 washings of streams in protected places along the shores, or at 

 their mouths, where deltas or lateral plateaus are made by the 

 accumulations of soil scoured off the banks of the stream, or 



Fig. 526. 

 Sycamores, grasses, and weeds, starting in crevices on a rock bed, New York. 



washed off the fields during rains, make new ground. With such 

 banks of newly made ground are deposited seeds carried along 

 with the soil, or dropped there by the wind, by birds, or other 

 agencies of seed distribution. 



Plants vary greatly in their capacity to occupy and hold new 

 territory and to invade occupied territory and displace the inhabit- 

 ants. The first plants to get a foothold are not always the ones 

 to endure longest, and a royal struggle takes place during years 



