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operate ; but in the animal system these agents are 

 made subservient to a superior principle. To give the 

 argument in plainer language, there are few philoso- 

 phers who would be inclined to assert the existence 

 of any thing above common matter, any thing imma- 

 terial in the vegetable ceconomy. Such a doctrine is 

 worthy only of a poetic form. The imagination may 

 easily give Dryads to our trees, and Sylphs to our 

 flowers ; but neither Dryads nor Sylphs can be ad- 

 mitted in vegetable physiology ; and for reasons near- 

 ly as strong, irritability and animation ought to be ex- 

 cluded. 



As the operation of the different physical agents 

 upon the sap vessels of plants ceases, and fluid be. 

 comes quiescent, the materials dissolved in it by heat, 

 are deposited upon the sides of the tubes now consi- 

 derably diminished in their diameter; and in conse- 

 quence of this deposition, a nutritive matter is provi- 

 ded for the first wants of the plant in early spring, to 

 assist the opening of the buds, and their expansion, 

 when the motion from the want of leaves is as yet 

 feeble. 



This beautiful principle in the vegetable cecono- 

 my was first pointed out by Dr. Darwin ; and Mr. 

 Knight has given a number of experimentaj elucida- 

 tions of it. 



Mr. Knight made numerous incisions into the al- 

 burnum of the sycamore and the birch, at different 

 heights ; and in examining the sap that flowed from 

 them, he found it more sweet and mucilaginous in 

 proportion as the aperture from which it flowed was 



