PHYSICAL AND LITERARY. 73 



every inch of the flaple comes In fuccef- 

 fion to be at the furface, and gets the 

 benefit of the fun and fro ft. 



Secondly^ By deep ploughing, the flaple 

 is doubled or tripled. I do not fay that 

 this doubles or triples the fertility of 

 the foil ; becaufe I imagine, that a plant 

 receives thegreatefl proportion of its nou- 

 rifhment from the roots neareft the fur- 

 face. But, as I have little doubt that 

 fome nourifliment proceeds from the deep- 

 eft roots, I conjecture, that, all other cir- 

 cumftances being equal, the fertility of 

 the foil bears a proportion to the deepnefs 

 of the ftaple. 



Thirdly, I lay great weight upon the 

 following confiderations : I am greatly 

 inclined to a theory that of late years is 

 creeping into reputation, 'uiz. That moi- 

 fture is the pabulum of plants : That the 

 earth ferves no other purpofe but to be a 

 receptacle for moifture; and that the 

 richefl foil is^that which furniOieth a due 

 proportion of moifture to its plants. Now, 

 let us compare a fliallow and a deep 11a- 

 ple with refpe(5l to moifture. Where the 

 Vol. III. K ftaple 



