LIFE CONDITIONS IX THE FRESH-WATER MARSH. 



441 



Other important life factors are — 



'■]. Abundant precipitation and atmospheric humidity, as through- 

 out the region. 



4. A soil containing abundant moisture, and abundant nitrogenous 

 matter, but relatively cold, poor in oxygen, and probably more or 

 less acid. 



This exposure to direct light and the accompanying and resulting 

 heat, as well as to the drying effect of the wind, creates a tendency to 



Fk;. S4 -Ciji 



i/throrhizos along the Dismal Swamp Canal 



excessive transpiral ion from i he foliage. The coldness, and doubtless 

 acidity, of the substratum, moreover, reduces the power of the roots 

 to absorb water, although so abundant in the soil. Therefore it is 

 not surprising that the vegetation of the fresh-water marshes, like 

 that of the salt marshes, exhibits in a certain degree those peculiari- 

 ties which are often termed "xerophytic." Indeed, there is but one 

 important point of difference between tl nvironmenl <>\' the fresh- 

 water marsh vegetation and 1 hat of the salt marsh, the absence in the 

 former of any considerable amount of sodium chloride in the soil and 



