- 3-1 I 19 



C H A P. III. 



FUNCTIONS OF VEGETABLES. 



erfpiration of Plants.* Circulation of the Fluids in.Plants, Property 

 in Plants of emitting vital Air ; of decomps/ing^atfr.^ Senftbility 

 to the Sun 's Light,**- Caufe of the Green Colour of Vegetables.*- 

 Bennetts "Experiments en 'Vegetable Perfpiration. Sexual Syjtcm.- 

 Growth and Nutriment of Vegetables, Manures.- Principles of 

 Agriculture. 



H J leaves of plants have been not improperly 

 compared with the lungs of animals. * Plants 

 as well as animals,' fays an author whom I have already 

 quoted with approbation, c perfpire, and in both 

 cafes this function is effential to health. By the ex- 

 periments of Dr. Haks *, and M. Guettardf, it ap- 

 pears, that the perfpirable matter of vegetables differs 

 in no -refpecl: from pure water, Excepting that, it be- 

 comes 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 furface, it is 

 natural to fuppofe, that the quantity of thefe will very 

 materially affect the quantity of the perfpiration. Ac- 

 cordingly, the experiments of Dr. Hales have afcer- 

 Iteined, that the perfpiration -of vegetables is increafed 

 or diminiftied, thiefly, in proportion to .the increase or 

 diminution of their foliage J. Th degree of heat in 

 which the plant was kept, according to the fame 



* Statical Effays, vol.i. p. 49. 

 f Mem. de 1'Academie des Sciences, 1748. 

 J Statical Effays, vol. i. p. 2-;. 



C a author^ 



