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Oh the Theory of Ve'gdallon. 155 



absorption of moisture is owing to the contraction of the 

 air in the same vessels, which occasions the exterior vessels 

 to dilate. Now a potatoe kept in a cool cellar of uniform 

 temperature cannot perspire very freely; and probably the 

 similar roots, placed in water and exposed to changes of heet 

 and cold in the open air would have thrown off by perspi- 

 ration, twenty times the quantity oT water, which those did 

 In the cellar. At' the same time, a vegetable confined to a 

 dark room will flourish but indliferently, as It is deprived 

 of an essential part of its food, phlogiston. 



Whether this communication contains any thing new or 

 sufficiently interesting to deserve the notice of the\merican 

 Academy of Arts and Sciences, is left wholly for you to 

 determin. All I know for certainty is that it proceeds from 

 a sincere desire to serve the agricultural Interest of my coun- 

 try, and that I am, Sir, with great respect, 



your obedient and 



very humble servant 



Rev. Dr. Willarp. 



NOAH W:f:BSTEB, Jl.y 



Ti 



MEDICAL 



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