46 



by the same vessels which absorbed it, for the reason 

 above given : and, therefore, the existence of other 1 

 peculiar vessels for the emission of air, ought like- 

 wise to be proved. By the common absorbents of 

 the leaf, it cannot be supposed to enter ; for they 

 are employed in taking up fluids, and are besides si- 

 tuated on the inferior surface (23.), while the changes 

 on the air are effected by the superior only. To 

 suppose that it gains admission through inorganic 

 pores, is contrary to all sound physiology ; for we 

 have no example of any healthy function being car- 

 ried on by animated beings, otherwise than by a li- 

 ving action, and by a peculiar organization destined 

 to perform that action. 



37- Rejecting, therefore, the opinion that any 

 aeriform fluid obtains admission into the vascular 

 system of plants by any process resembling the living 

 function of absorption, let us next inquire how far 

 the supposition of chemical affinity will help to re- 

 move the difficulty. The juice of the leaves, w r hich 

 is supposed so powerfully to attract the oxygen gas 

 of the air, is contained within its peculiar vessels, 

 and these vessels are likewise covered by the green 

 colouring matter, over all which is spread the efiider- 

 mis. The minute structure of these parts has been 

 lately described by M. Jurine, as it appeared on mi- 

 croscopic examination * ; but the appearances ob- 

 ser v ed by him are so different from those represent- 

 ed by other authors, as to justify, in his opinion, the 

 adoption of new names, in almost every instance, to 



* Phil. Mag. vol. xvi. 



