COMPOSITION OF SOILS. M 



them • the plant may, indeed, under such circumstances, become 

 a 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 mixed with a considerable quantity of clay ? 

 It is because these soils do not contain alkalies and certain other 

 ingredients in sufficient quantity, the growth of wheat being ar- 

 rested by this circumstance, even should all other substances be 

 presented in abundance. 



It is not mere accident that we find on soils of gneiss, mica- 

 slate, and granite in Bavaria, of clinkstone on the Rhone, of 

 basalt in the Vogelsberg, and of clay-slate on the Rhine and in 

 the Eifel, the finest forests of oaks, which cannot be produced on 

 the sandy or calcareous soils upon which firs and pines thrive. 

 It is explained by the fact that trees, the leaves of which are re- 

 newed annually, require for their leaves six to ten times more 

 alkalies than the fir-tree or pine, and hence they do not attain 

 maturity when placed in soils containing very small quantities 

 of alkalies.* When we see oaks growing on a sandy or calca- 

 reous soil — or the red-beech, the service-tree, and the wild-cherry, 

 for example — thriving luxuriantly on limestone, we may be as- 

 sured that alkalies are present in the soil, for they are necessary 

 to their existence. Can we, then, regard it as remarkable, that 

 oak copse should thrive in America, on those spots on which 

 forests of pines which have grown and collected alkalies for cen- 

 turies, have been burnt, and to which the alkalies are thus at 

 once restored ; or that the Spariium scoparium, Erysimum latifo- 

 Hwn, Blitum capitatum, Senecio viscosus, plants remarkable for 

 the quantity of alkalies contained in their ashes, should grow 

 with the greatest luxuriance on the localities of conflagrations ?f 



* One th* 1 \sand parts of the dry leaves of oaks yielded 55 parts of ashes, 

 of which W parts consisted of alkalies soluble in water ; the same quantity 

 of pine lea* es gave only 29 parts of ashes, which contain 4'C parts of solu- 

 ble salts. (De Satjsstjre.) 



f After the great fire in London, large quantities of the Erysimum lati- 

 folium were observed growing on the spots where a fire had taken place. 

 On a sim'lar occasion the Blitum capitatum was seen at Copenhagen, the 

 Senecio viscosus in Nassau, and the Spartium scoparium in Languedoc. 



