THE FOREST AND SPRINGS 375 



acre during the season of growth would be 24,112,000 pounds for beech (5.6 yards 

 per diem); 18,568,000 pounds for spruce pine (47 yards per diem); 6,424,000 pounds 

 for Scotch pine (1.6 yards per diem). 



It is to be remarked that these quantities do not include the water incorporated in 

 the tissues of the trees for the purposes of their growth, but only that emitted by evapora- 

 tion from leaves. 37 



Other figures have been published by Th. Hartig, V. Hohnel and Wollny; they differ 

 sometimes so much from those quoted above that one is necessarily very sceptical as to 

 the value of the results obtained. As M. Henry remarks very justly: 38 "If it is easy 

 to determine, by means of weighing, the evaporation on a sapling in a pot, or of a square 

 of young forest trees, of grass or corn; if one can calculate, strictly speaking, according 

 to those results, without fear of too great discrepancies the evaporation on an acre 

 covered with grass, with corn, or young forest trees of equal height, 39 it is far too rash 

 to apply the results obtained by experiments on an isolated sapling grown in a 

 pot to a forest comprising many tangled and superimposed stages of growth, whose 

 leaves giving more or less shade are doing their work with different degrees of 

 intensity." 



In the present condition of science it is not therefore possible to determine by con- 

 trast in a sufficiently precise manner the difference between the volume of water under 

 the trees and in the open which goes to feed the subterranean sheets. 



In view of the great interest this question presents, and of the diversity of opinions 

 on the subject, the greatest efforts have been made in an indirect manner to arrive at a 

 clear idea of the action of clumps of trees on the feeding of the subterranean sheet. 



A primary series of researches has been undertaken with a view to determine com- 

 paratively the quantity of water which filters through a stratum of earth enclosed in 

 a box without drainage, its surface being covered with different kinds of plants. 



It has proved that the bare earth allows more water to pass than that which is 

 covered with vegetation, dead leaves, moss, etc. This is almost the only definite result 

 obtained, and even this is controvertible. We do not lay much stress on these experi- 

 ments which, it would seem, can give us no definite information as to what occurs under 

 natural conditions. 40 



An attempt has been made to measure directly the quantity of water contained in the 

 soil under the trees and in the open at different depths. 



Experiments undertaken in Germany 41 and in Russia have brought to light the 

 following facts which appear to be properly established: 



The humidity of forest soil is very great at the surface, but diminishes rapidly to a 

 depth varying in degree which does not go beyond 31.5 inches under plantations of 

 spruce pine, according to Ebermayer, and which reaches a depth of 10 or 13 feet, 

 according to Russian experiments. Below this level the amount of water keeps on 

 increasing with the depth. There exists in the ground, therefore, a dry zone more or 



37 The quantity of water remaining annually in the tissues of trees may be estimated 

 at 2,640 pounds per acre. 



38 "Annales de la Science Agronomique," 2nd Series, 4th year, 1898, pp. 20 et seq. 



39 It is doubtful if even this is admissible. 



40 For the measurements made in Switzerland see Bulletin IV of the " Mitteilungen " 

 of the Research Station of Zurich; for the Bavarian works, see the various publications 

 of M. Ebermayer, etc. 



41 "Einfluss des Waldes," etc., an article by M. Ebermayer which appeared in the 

 January 1888 number of the "Allgemeine Forst und Jagd Zeitung." A good trans- 

 lation has been published by M. Reuss in the first volume of the "Annales de la Science 

 Agronomique," 1889. A complete resume of all the works published up till then is 

 inserted in the account of the "Congres International de Sylviculture a Paris en 1900," 

 pp. 328 et seq. (Communication byJM. Henry to this Congress). 



