PHYSIOLOGY OF TREES. 257 



nature, viz. gravitation, attraction, positive and 

 negative electricity, &c. to make out a feasible 

 hypothesis. The matured sap is made to descend 

 from the topmost spray of the Lombardy poplar, 

 and to descend vp the pendant branches of the 

 weeping ash or willow ! But the practical eye 

 is not distracted by such anomalies. By a very 

 slight examination, we find the sap distributed, 

 at all times when in motion, over the whole sur- 

 face of the last yearns alburnum, on the highest 

 shoot as on the lowest part of the stem : and 

 when not in motion, it is equally apparent rest- 

 ing, in an inspissated state, in the tubes and 

 cells of the wood, and between the wood and 

 bark. This is an undeniable fact ; and if it be, 

 why should physiologists puzzle themselves by 

 inventing a peculiar system of vessels, for the 

 purpose of accounting for the fancied motions of 

 the sap, by conveying it unnecessarily from one 

 place to another? Can a topmost shoot or any 

 other part of a healthy plant be found at any 

 time divested of it ? Can the keenest eye, as- 

 sisted by the most powerful microscope, discover 



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