4 '24 ^^' ^^^^ ^^ ^^^ Phyjlology of Plants. 



attra6lion, how happens it, that the fap of the 

 vine flows from an incifion made in the fpring, 

 and not from one made in fummer ? In 

 this cafe, as the vefifels i-emain the fame, and 

 the heat is at lead not diminiflied, the efflux of 

 fap ought to be equally copious in fummer as 

 in fpring. 6. Capillary tubes, filled with li- 

 quor, do not difcharge their contents when 

 broken acrofs. But from the ftem of a vine, 

 cut tranfverfely, a large quantity of fluids is 

 difcharged, as has been demonftrated by Dr. 

 Haks. 7. The analogy between vegetables and 

 animals, which was formerly pointed out, gives 

 a reafonable prefumption, that the fluids of both 

 arc moved by fimilar powers. In animals, the 

 powers of circulation are refpiration and mufcular 

 aftion : of thofe powers in plants we have al- 

 ready treated, and what has been faid on the 

 fubjetfl, fccms to fhew, that the motion of the 

 juices in plants is rather to be afcribed to them, 

 than to capillary attraftion. 



I might draw fome arguments, in addition to 

 thefe, from fome experiments I have lately 

 made, to afcertain the effedls of air impregnated 

 with various efiluvia, of light, and of faline 

 folutions, on the growth and qualities of vege- 

 tables ; but thefe, being as yet incomplete, 

 I forbear to detail. In general, however, it 

 appeared, that there are particular fubflrances 



which 



