D}\ Bell on the Thyfiology of Plants. 42 1 



poflefled of vafa aeria, and, when a plant is 

 placed under the exhaufted receiver of an air- 

 pump, the air enters through the cuticle, and 

 only iffues from the wood, in which the va/a 

 aeria are fituated. From thefe circum fiances 

 taken together, and confidered attentively, wc 

 have reafon to conclude, that the air's {iroper 

 entrance to the va/a aeria is through thefe cuti- 

 cular veflels. Thus, in the early part of the 

 fpring, the gentle heat expands the mouths of 

 thefe veffels, before contradled by the winter's 

 cold. Into thefe orifices, the external air rufhes 

 and prelTes down to the roots. To thefe it gives 

 energy, as it does to the moving fibres of ani- 

 mals J and, by its prcffure, it may afTift in pro- 

 pelling the juices upwards. An additional 

 quantity of air is evolved by the internal motions 

 of the plant, and the whole pafTes ofi^with the 

 perfpirable matter. In this way, there feems to 

 be a circulation of air through plants, affifling 

 and afTifted by the powers which move the 

 juices. 



The two following fads confirm the above 

 •opinion, and, at the fame time, fbew, that in 

 plants, as well as animals, impeded refpiration 

 impedes the motion of the fluids, and inter- 

 rupted refpiration deftroys it. 



I. In the winter feafon, I covered feveral 

 young trees with varnifh, and at the fame time 

 wrapt them in wax-Cloth, leaving the tops of 



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