OF THE LEAVES, &C. 87 



" nels foreign to that which nature had appointed 

 " for them. I have before said, that I have ever 

 " found nature disposed to such resources, in 

 " case of any unnatural impediment. I have 

 " myself proved it." 



The effect of grafting shows that the sap does 

 not circulate ; or, at any rate, if it does circu- 

 late, that it undergoes no change by the ascend- 

 ing and descending motion : and this also shows 

 the fact, that every part of a plant possesses the 

 power of selecting and transforming the portion 

 of fluid destined to its use as it passes up. 



If the sap be passed through the body of a tree 

 to its leaves, and there prepared and returned 

 back, that part of the tree which is uppermost, 

 and producing one variety of wood and fruit, must 

 possess the power of preparing the fluids for the 

 production of every other variety below it, unless 

 the sap be supposed to pass up and return in the 

 same state, which amounts to a superfluity of 

 motion, and an excess of exertion, seldom found 

 in nature. This subject has always excited con- 

 troversy among phytologists, and notwithstand- 

 ing the great variety of ingenious and elaborate 

 experiments that have been made, they not only 

 have not been sufficiently conclusive to produce 

 unanimity of opinion, but the subtle and prolix 

 arguments that have been adduced on both sides 



