EFFECTS' ©F AIR ON LEAVES. 165 



some remarks much more to our purpose. Dr. Hales 

 there clearly anticipates by conjecture, what succeeding 

 philosophers, more enlightened chemists, have ascer- 

 tained. His words are remarkable : 



" We may therefore reasonably conclude, that one 

 great use of leaves is what has been long suspected by 

 many, viz. to perform in some measure the same office 

 for the support of the vegetable life, that the lungs of 

 animals do, for the support of the animal life ; plants 

 very probably drawing through their leaves some part of 

 their nourishment from the air." p. 326. A little further 

 on he adds, " And may not light also, by freely entering 

 the expanded surfaces of leaves and flowers, contribute 

 much to the ennobling the principles of vegetables ?" 

 />. 328. (84) 



(84) [The surfaces of most leaves contain a large number of 

 small whitish points, scarcely apparent to the naked eye, but ea- 

 sily distinguished with a glass. These points were called cor- 

 tical glands^ by Saussure, and evafiorating fioresf by Hedwig. On 

 examination, they are found to consist of small fissures, sur- 

 rounded by areas. According to M. Jurine, a microscopic anat- 

 omist of Geneva, almost all leaves are penetrated with a great 

 number of these apertures. Their size varies in different plants. 

 Thus in the Orchis and Lily kind, they are very large ; in the 

 Jessamine and Oak, they are very small. Leaves are unequally 

 provided with them ; some having pores on both surfaces, others 

 only on one, while some are even destitute of them. These 

 pores which contain air only, are surrounded by a pair of cells, 

 which Jurine denominates conjugate utricles, and which contam 

 a greenish fluid, in common with the other cells of the leaf. 

 Through these pores and utricles, the communication appears to 

 be kept up between the external air and the juices of the leaf.] 



