io Odoriferous Exhalation from Plants. [Book VIII; 



author, varied the quantity of matter perfpired ; this 

 being greater, in proportion to the greater heat of the 

 ibrrounding armofphere. The degree of light has 

 Hkewife considerable influence in this refpeft : for Mr. 

 Philip Miller's experiments prove, that plants uni- 

 formly peripirermoft in the forenoon, though the tem- 

 perature ofthd'.air, in which they are placed, fhould 

 be unvaried. M. Guettard likewife informs us, that 

 a plant, expo fed to the rays of the fun, has its per- 

 fpiration increafed to a much greater degree, than 

 if it had been expofed to the fame heat, under the 

 lhade. Finally, the perfpiration of vegetables, is in- 

 creafed in proportion as the atmofphere is dry, or in 

 other words, diminimed in proportion as the atmo- 

 iphere is humid.' 



Dr. Hales found that a fun-flower, weighing three 

 pounds, perfpired twenty-two ounces during twenty- 

 four hours. Dr. Keil perfpired thirty-one ounces in 

 twenty-four hours. The quantity therefore perfpired 

 by the fun- flower was much greater, in proportion to 

 its weight, than that perfpired from the human body. 

 Dr. Kei! ate and drank four pounds ten ounces in 

 twenty-four hours. Seventeen times more nourifhment 

 was taken in by the root of the fun- flower, than was 

 taken in by the man. If the perfpiration of vegetables 

 is checked, they fpeedily fade. I: is checked from 

 glutinous fubftances adhering to their furface; hence 

 the advantage of wafhing them. The more healthy 

 and vigorous the plant, the more copious the perfpi- 

 ration j though an excefs, as well as a defect of it* 

 feems prejudicial and even deftruftive to vegetables. 

 Ik bears alto a proportion to: the quantity of leaves, 

 ^.efe being the principal organs of perfpiration. 



The odoriferous exhalation of leaves and flowers 

 forms an atmofphere around vegetables, which ftrikes 



our 



