To an observant person nothing is more evident than the change 

 of plant life, often abrupt, with change of soil. For miles along 

 the dusty road the same daisies and asters repeat themselves. 

 Then an unusually verdant spot, with specifically different 

 growths, appears, and unerringly indicates wetter soil, a spring, 

 a running brook, or a river. In its wake its own beloved flowers 

 tread, hugging its banks, refusing to stray back into the drier 

 fields or woods. The banks of streams are often marshy, with 

 overflowing and stagnant water. The dividing line, therefore, 

 between vegetation peculiar to river banks and swamp plants is 

 sometimes difficult to trace. A flower of wet soil- not found in 

 this chapter should be sought in the next. 



Says Thoreau, " Rivers and lakes are the great protectors of 

 plants against the aggression of the forest, by their annual rise 

 and fall, keeping open a narrow strip where these more delicate 

 plants have light and space in which to grow." 



