236 SELECTIONS FROM ADDRESSES. 



Naked fallows, then, are no longer necessary, except, perhaps, 

 occasionally for the extirpation of some troublesome weed. 



This improvement of the soil is seen quite strikingly in for- 

 ests. We there find, that very poor land, incapable, without 

 heavy manuring, of bearing crops, sustains a fall growth of 

 large trees, and, at the same time, improves from year to year. 



This appears very strange, but. when we consider the reasons 

 for such a seeming anomaly, we find that it is only a beautiful 

 exemplification of the law which we are considering. 



The growth of onr ordinary crops is sudden, and must be 

 completed within a single season ; that of trees is slow and con- 

 tinued through many years, — the demand upon the resources of 

 the soil is more gradual. Then, too, the roots of trees bring 

 their food from a very extended range ; spreading wide and de- 

 scending deep, they draw supplies from sources inaccessible to 

 annual plants. By a wise regulation of Providence, the wood, 

 which constitutes the great bulk of the tree, contains very little 

 inorganic matter, frequently not more than one-half or three- 

 fourths per cent. ; while the leaves oftsn contain, when dry, 

 from fifteen to twenty per cent., and even more. Thus, the 

 trunk derives nearly all its bulk from the air, while the leaves, 

 with their large proportion of organic matter, fall upon the soil, 

 and constitute an annual top-dressing, of a nature best calcula- 

 ted to improve its capabilities. Even when the trunks of the 

 trees are carried' away, a small portion of inorganic matter is 

 abstracted, compared with that which has been deposited on the 

 soil during their growth, in the shape of leaves and bark. 



The same thing is observed to a considerable extent, upon 

 grass lands, where the soil is of good quality. In situations 

 where grass has annually grown, and decayed undisturbed, for 

 a long series of years, a surprising degree of fertility is attained. 

 Many of our western prairies and cleared forest lands, are ex- 

 amples of this principle. We have instances where crops of 

 Indian corn and wheat have been grown, for many years in 

 succession, with scarcely a perceptible diminution in the yield. 

 Ordinary manure upon these soils is injurious, because it indu- 

 ces too luxuriant a growth ; they really seem inexhaustible. 

 Where, however, there is no source of supply to make good the 



