OF THE FERTILITY OF SOILS. 151 



it does not contain them ; the plant may indeed, 

 under such circumstances, become an herb, but 

 will not bear fruit. 



Again, how does it happen that wheat does not 

 flourish on a sandy soil, and that a calcareous soil 

 is also unsuitable for its growth, unless it be not 

 mixed with a considerable quantity of clay ? It is 

 because these soils do not contain alkalies in suffi- 

 cient quantity, the growth of wheat being arrested 

 by this circumstance, even should all other sub- 

 stances be presented in abundance. 



It is not mere accident that only trees of the fir 

 tribe grow on the sandstone and limestone of the 

 Carpathian mountains and the Jura, whilst we find 

 on soils of gneiss, mica-slate, and granite in Bavaria, 

 of clinkstone on the Rhone, of basalt in Vogelsberge, 

 and of clay-slate on the Rhine and Eifel, the finest 

 forests of other trees which cannot be produced on 

 the sandy or calcareous soils upon which pines 

 thrive. It is explained by the fact, that trees, the 

 leaves of which are renewed annually, require 

 for their leaves six to ten times more alkalies than 

 the fir-tree or pine, and hence, when they are 

 placed in soils in which alkalies are contained in 

 very small quantity, do not attain maturity.* When 

 we see such trees growing on a sandy or calcareous 



* One thousand parts of the dry leaves of oaks yielded 55 parts of 

 ashes, of which 24 parts consisted of alkalies soluble in water ; the same 

 quantity of pine leaves gave only 29 parts of ashes, which contained 

 4-6 parts of soluble salts. (De Saussure.) 



