244 Studies in Forestry [CHAP. xi. 



greatly improved, and the previously extracted nutrient salts are 

 again largely restored in a convenient, easily absorbed, soluble 

 form, and secondly, in the more thorough aeration of the soil 

 by means of the root-systems of the underwood. It is true that, 

 even when forming undergrowth and enjoying only compara- 

 tively limited exposure to light, air, and warmth, Beech under- 

 growth still transpires enormous quantities of moisture drawn 

 from the soil, and intercepts a high percentage of the precipita- 

 tions before they reach the ground ; but against this must be 

 duly weighed the greatly advantageous influence exerted by 

 the strongly hygroscopic humus in retaining the moisture 

 reaching the surface, and in allowing it facilities for entering 

 and percolating the soil, in place of running rapidly off into 

 the nearest water-channels, and of being quickly evaporated by 

 insolation and the freer play of winds. As a matter of practical 

 result Ramann found that, on the areas where Riinnebaum's 

 experiments were conducted, from the middle of May till the 

 end of August there was always more moisture immediately 

 underlying the humus in the Pine woods underplanted with 

 Beech than in those with no undergrowth ; and that, down to 

 2 ft. below the surface, the soil was moister in the former for 

 the first half of that time but drier throughout the later half, 

 whilst at a depth of about 28-32 inches the soil under the 

 pure Pine woods was always moister *. His deductions there- 

 from were that, under the light shade of the Scots Pine, the 

 spontaneous growth of berries, grass and other weeds exhausted 

 the superficial supplies of moisture to a greater extent than the 

 Beech underwood, whilst the layer about 20 to 24 inches below 

 the surface was called upon to furnish supplies to both Beech 

 and Pine ; whereas in pure Pine woods the lower soil received 

 larger quantities of moisture from above after the grasses had 

 completed their development than when a soil-covering of 

 Beech underwood existed. Wollny 2 also found, in independent 



1 Zeitschrifi fur Forst- und Jagdwesen, 1885, p. 172. 



2 Forschungen auf dem Gebiete der Agricultur-Fhysik, vol. x. p. 261. 



