Sect. VI. Agriculture and Vegetation. 175 



fluence of the fun, muft keep the nutri- 

 tious juice in a continual motion ; fo that it 

 muft be continually applied to the roots of 

 plants deftined for the admiffion of nou* 

 rifhment. 



THE firft queflion which can raife any 

 doubt here is, In what manner do the juices 

 arife to the tops of plants and trees ? Mal- 

 pighius thinks, this is owing, in a great 

 meafure, to the air-bladders which he difco- 

 vered in the fkucture of plants, and which 

 he thought behoved to dilate and contract, 

 according to the different changes of heat 

 and cold which happen in our atmofphere. 

 To me it does not appear, that the dilatation 

 of fuch vefTels would force it more upwards 

 than downwards. I mould rather imagine, 

 that fuch a dilatation would ftop the motion 

 altogether. 



THE .caufe commonly afcribed, viz. the 

 action of capillary veflels, appears to me 

 fufficient for that end. Hales has demon- 



ftrated 



