376 APPENDIX 



less thick and more or less deep, lying between the humid region of the surface and 

 the humid region below. 



One sees there, in a very clear fashion, the influence of the absorption of water by 

 roots of plants in the region where they are active, or in that immediately below where 

 the water can raise itself by capillary action after drying up the superior stratum. 42 

 This is a general fact for all ground covered with living plants; they present a dry 

 stratum more or less removed from the surface, according to the depth of the root 

 system of vegetation above. This depth being greater in the case of forest vegetation 

 than in others, it is clearly to be seen that at a similar level, within certain limits, the 

 soil of the forest will be poorer in water than an agricultural soil. 43 It has been con- 

 cluded from this that the forest absorbed more water by its vegetation than other 

 species of culture, and thus was harmful to the feeding of phreatic sheets of water. 



It must be admitted that there is no evident and necessary connection between the 

 humidity of the soil in its superficial parts and the alimentation of the subterranean 

 sheet. Other things being equal, the latter depends not so much on the degree of 

 dampness of the soil as upon its permeability. A stratum of coarse sand will allow 

 rain water to filter through rapidly, while a fine clay will keep it stagnant at the sur- 

 face and give it over to evaporation. And, nevertheless, the sand will be dry, while 

 the clay will always contain a quantity of hygroscopic water. 



An extremely interesting fact, which will perhaps throw some light on the relation 

 of the wooded condition of the surface with the feeding of phreatic waters, has been 

 quite recently brought forward. We think we ought to dwell on this with some detail, 

 borrowing what follows from the last publications of our learned colleague, M. Henry. 44 



The Imperial Free Economic Society of St. Petersburg undertook a series of re- 

 searches into subterranean hydrology in the forests of the steppes of Russia, the director- 

 ship of which was confided to M. Ototzky, curator of the Mineralogical Museum at 

 St. Petersburg. 



From borings effected in the forest of Chipoff (province of Voronez) and in the Black 



42 The depth of the system of our large tree species is much greater than has been 

 generally supposed. The tempest of February 1, 1902, having torn up by their roots 

 a multitude of fir trees of all ages in the Vosges, we took advantage of this opportunity 

 to ascertain the depth to which the roots, thus rendered visible, had penetrated the 

 Vosges sandstone formation. It varied from 5 to 11.5 feet. If one takes into account 

 that the extremities of the roots were still remaining in the soil, one can realize that 

 these trees were deriving nourishment from a stratum which must extend to a depth of 

 13 and perhaps of 16 feet. 



43 These researches of a very delicate nature only meet with reliable results when 

 they are conducted simultaneously for a very long period of time under the trees and 

 in the open. If one observes the soil after heavy rain one sees it saturated at the surface 

 to a greater or lesser depth. The rain having ceased, the free surface water sinks 

 down gradually into the soil under the action of its weight, saturating always a deeper 

 and deeper zone, above which the ground has become dry, until it comes in contact 

 with the phreatic sheet of water of which it raises the level. It is conceivable that 

 very varying amounts of water in the soil, at one particular season and depth, have to 

 be accounted for, according to the proximity and abundance of the latest rainfall, 

 that is to say, according to fortuitous circumstances which, up till now, observers 

 do not seem to have taken into account. 



44 M. E. Henry, professor of the "Ecole Nationale des Eaux et Fordts," was the first 

 to draw attention to the Russian borings, the results of which, up till then, had been 

 unnoticed both in France and Germany. He gave an account of these in a series of 

 articles, one after the other, from 1897 and February, 1898 (Annales de la Science 

 Agronomique), until 1903. In his article of 1903 M. Henry narrates for the first time 

 the complete result of his own researches undertaken in the forest of Moudon. The 

 few pages which M. Ebermayer devotes to the subject in his publication dated 1900 

 (Einfluss der Walder auf das Gumdwasser) only reproduce, almost word for word, 

 M. Henry's report of 1898. 





