EELATION OF TEEES TO THE SOIL. 



I HAVE spoken of trees as the purifiers and renovators 

 of the atmosphere, as regulators of its humidity, equalizers 

 of the electric fluid, and as safeguards against both drought 

 and inundations ; but I have not yet alluded to the fact that 

 they are, in dense assemblages, the actual creators, in many 

 places, of the soil upon which they stand. The trees by 

 means of their foliage are direct fertilizers of the ground 

 they cover, causing it to increase in bulk as long as they 

 stand upon it. But the leaves of trees are not the only 

 source of this increase of bulk and fertility. The lichens 

 and mosses, and various incrustations upon their bark, and 

 the offal of birds, insects, and quadrupeds, all contribute to 

 the same end. Hence the most barren situations vill pro- 

 duce good crops for several years after the removal of 

 their wood; and from these facts we may learn why a 

 forest is still vigorous, though it has remained for centuries 

 upon the same ground. . If it were fertilized only by the 

 decayed foliage of the trees, it would gradually lose its 

 fitness to promote the health and growth of the timber. 

 But the foreign matters I have enumerated, the decayed 

 cryptogamous plants, and the relics and deposits of ani- 

 mals which have lived and died there, supply the soil 

 with nitrogenous ingredients in which decomposed leaves 

 are wanting. 



But what are the sources of aU. the matters which are 

 furnished by the trees alone ? They are chiefly the atmos- 

 phere and the deeper strata of the soil. The roots of the 

 trees, penetrating to a considerable depth, draw up from 



