150 



FOREST INFLUENCES. 



penetration, which we will see is not the case, the influence of the fof^ 

 est upon the intensity of water absorption would be in the direction of 

 diminishing superficial flow and facilitating- subterranean drainage; 



This factor is of tlie utmost importance in the discussion of the 

 causes of floods. Without a consideration of the water capacity, and 

 still more of the intensity of water absorption, it will never be possible 

 to draw conclusions as to probable floods from the amount of precipita- 

 tion alone. 



The influence of various soil conditions and soil covers upon the 

 amount of water that will filter through has been investigated by 

 Wolluy and Ebermayer in an extended series of experiments. 



Experiments of this kind which will yield results a])plicable to nat- 

 ural conditions are exceedingly difficult to arrange, and require not 

 only many precautions, but must be continued for a long time before 

 generalizations can be attempted. One of Wollny's series of experi- 

 ments was intended to show the influence upon filtration of a grass 

 cover on different soils. The results calculated for 1 acre are as follows : 



Kinds of soil. 



Calcareous sand with humus 



Quartz saud * 



Loam .soil ' 



Peat soil 



Amount of filtration. 



Fallow 

 field. 



Po%inds. 

 h 593. 216 

 3, 044, 250 



1. 529, 671 



2, 018, 124 



Grass 

 covered. 



Pounds. 



782. 334 



661,548 



59 105 



405. 162 



* From May to November. 



The grass cover, therefore, reduced considerably (by 50 per cent and 

 more) the percolation of water. Ebermayer experimented with boxes 

 43 square feet surface (4 square meters) and 4 feet deep, filled with 

 garden soil, leaving one bare, covering another with moss, and two 

 others each planted with 6-year-old plants of beech and of spruce, with 

 the following results, arranged according to seasons: 



In these experiments it is remarkable how small a percentage of the 

 rainfall was filtered through, which would lead us to look at the results 

 with caution, namely: 



