60 ON VEGKTABLE PHYSIOLOGY. 



a kind of net work, having externally the appear- 

 ance of laminae or scales, which, in old trees, may 

 be seen in a loose and decaying state. In others 

 less advanced, it is often so compact as to resem- 

 ble a solid mass; while in delicate shoots, it pre- 

 sents, as we have before stated, a fine membranous 

 texture. 



The vegetable epidermis, which like that of 

 animals, consists only of condensed cellular mem- 

 brane, is not vascular, though, as in animals, it is 

 endowed in every part with very minute pores, 

 and with terminating ducts to admit the ab- 

 sorption of the atmosphere, and the transpiration 

 of the superfluous fluid of the plant; while, like 

 the shells of crustaceousfish, itdefends theinterior 

 parts from injury. In the larger trees and shrubs 

 the bodies of which in themselves are strong and 

 of firm texture, the latter property is not of so 

 much importance ; but in the reeds, the grasses, 

 the canes with hollow stalks, and in the various 

 farinaceous seeds, where it is most essential that 

 their structure should be protected from the ac- 

 tion of insects ; nature, to render it more strong 

 and resisting, has given it a glassy kind of net 

 work, composed principally of a silicious earth, 

 which Sir Humphrey Davy has ascertained in 

 many instances, is capable of striking fire upon 

 the application of the steel. 



Immediately below the epidermis is the cutis, 

 real skin, or true bark, consisting of two parts 



