115 



(2) Tlio caiiso of tho dning iii) of the soil by the plants is to be 

 foMiul in the very considerable transpiration of aqueous vapor by 

 their leaves. 



(8) The plants deprive the soil of water in proportion as they 

 stand eloser together and have developed their tops more luxuriantly. 

 V (4) The influence of the vegetation on the moisture of the soil 

 extends to the deeper layers of soil. 



^ (5) The moisture of the soil under a layer of inert objects, such 

 as dead plants, manure, straw, pieces of wood, windfalls, etc., is 

 always greater than that of the uncovered soil. 



(6) The retention of the moisture in the soil under a cover of dead 

 matter is a consequence of the protection a Horded l)y the latter against 

 the influences that favor evaporation. 



(7) The quantity of moisture in the soil is, wnthin certain limits 

 and to a depth of about 5 centimeters, or 2 inches, greater in propor- 

 tion as the covering of dead matter is thicker, 



\ (8) The soil shaded by living plants is, under otherwise similar 

 conditions, driest during the growing period, but that covered by 

 dead objects is the moistest, while that which is not cultivated, not 

 covered with plants and naked, is midway between the two previous 

 in reference to its relations to moisture. 



Wollny has also studied the influence of plants and shade upon the 

 drainage of water from the soil. His conclusions are : 



v(l) A notably smaller quantity of water drains through the soil 

 supporting living plants from the same quantity of rainfall than 

 through a naked soil during the growing season. 



1/(2) The quantity of drainage in cultivated fields is less in pro- 

 portion as the plants stand more closely together and in proportion 

 as they have developed themselves more luxuriantly. 

 ^ (3) The quantity of drain water from a soil covered by inert 

 objects is increased in comparison with that from fallow land in 

 proportion as the covering layer is thicker, up to a certain limit, up 

 to about 5 centimeters, beyond which a further increase in the thick- 

 ness of the covering steadily diminishes the quantity of drainage 

 water. 



^ (4) For the same quantity of rain and under otherwise similar 

 circumstances, the soil covered with dead leaves and similar objects 

 furnishes the greatest quantity of drainage water up to a covering 

 of about .5 centimeters thickness; the naked, fallow land furnishes 

 the next smaller quantity of water; the soil covered with livnig plants 

 furnishes the least quantity of drain water. 



