cruickshank's practical planter, 313 



lage, which is, that the leaves of the trees are sufiPered 

 to decay and rot where they fall, and, by this means, 

 an annual addition is made to the depth of the ve- 

 getable mould. Now, the leaves of a tree may be 

 considered as bearing the same proportion to the 

 trunk and branches, in respect to the nourishment 

 which they require, as the straw of com bears to the 

 grain. But the manure which cultivated land re- 

 ceives, is, in general, little more than the straw 

 which grows on it after it has served for food or lit- 

 ter to cattle. Ground in wood, then, actually re- 

 ceives, in the annual fall of the leaves, as much en- 

 richment as the farmer bestows on his land under 

 tillage. 



" Ground employed in agriculture is exposed at 

 almost every season of the year to the full action of 

 the atmosphere ; and in the drought and heat of 

 summer, much of its strength is evaporated. In 

 land covered with wood, the case is entirely different, 

 as from the shade afforded by the leaves and branches, 

 very little evaporation takes place. This, then, 

 is another reason that serves in some measure, at 

 least, to explain the seemingly paradoxical fact in 

 question. For, that evaporation has a very powerful 

 tendency to exhaust land, by drawing off and dissi- 

 pating the more volatile part of the matter which 



