Dr. Bell en the Thyfwlogy of Plants. 425 



which increafe the growth of plants, by afting 

 as ftimuli on their moving fibres.* 



There are fome other funftions which belonsr 

 to vegetables, of which I (hall now endeavour 

 to give fome account. 



Plants, as well as animals, perfpire, and, 

 in both cafes, this fun(flion is eflential to health. 

 By the experiments of Dr. Hales, f and M. 

 Cuettardy % it appears, that the perfpirable mat- 

 ter of vegetables differs in no refpeft from pure 

 water, excepting that it becomes rather fooner 

 putrid. The quantity perfpired varies, according 

 to the extent of the furface from which it is 

 emitted, the temperature of the air, the time 

 of the day, and the humidity of the atmofphere. 

 As the leaves form the greateft part of the 



* The experiments here alluded to were made, to deter- 

 mine the influence of light, of fixed air, of inflammable 

 air, and of the vapour which arifes from the putrefaclion 

 of cabbage leaves, on the growth of vegetables. Dr. Bell 

 likewife tried the efteds of fome faline bodies, of which I 

 do not recolleft the particulars. When the different 

 vapours were applied to growing vegetables, the light was 

 accurately excluded. Neverthelefs, in that to which fixed 

 air was applied, there was fome degree of tafte and fmell; 

 and where the inflammable air was ufed, there was like- 

 wife a tinge of the natural colour. He often thought of 

 repeating thefe experiments, but death prevented this, 

 and many other fchemes. J, C. 



-f Statical Efiays, vol. I. p. 49. 



I Mem. de TAcademie des Sciences, 1748. 



furface. 



