THE EPIDERMIS AND ITS APPENDAGES. 19 



tuting the true epidermis or skin. These two superposed 

 membranes are intimately united and pierced by a number of 

 apertures, called stomata or pores. 



The presence of the cuticle on the exterior surface of the 

 epidermis, may be detected by a simple chemical process. If a 

 transverse section of the epidermis be treated with a dilute 

 solution of iodine, the cells of the epidermis will remain colorless, 

 whilst the cuticle will assume a yellowish or brownish tinge. 



Some writers consider the cuticle to be a mere secretion 

 from the epidermic cells on which it is deposited ; but the 

 recent investigations of M. Gareau, a distinguished French 

 physiologist, who succeeded in effecting its quantitative analy- 

 sis, would seem to prove that it is a distinct organ, formed 

 from cellulose of a special matter distinct from that which 

 constitutes the epidermis. 



The cuticle is the only part of the epidermis which covers 

 the surface of the stem and leaves of aquatic plants. It is 

 developed in the form of a glaucous bloom or vegetable varnish, 

 which renders the surface of the plant a perfect water shed, 

 preventing it from obtaining an injurious amount of the fluid 

 in which it floats. 



The epidermis (i*i upon, and gep^a skin). In flowering 

 plants, the epidermis may be readily perceived to be a mem- 

 brane perfectly distinct from the cellular and fibrous tissue 

 which it covers, on account of the magnitude and peculiar 

 arrangement of its cells. The epidermic cells contain ordi- 

 narily no traces of chlorophyl, and therefore the epidermis may 

 be readily separated from the parenchymatous tissue, with which 

 it contracts but a feeble adhesion, as a colorless layer. 



The epidermis of plants is clearly intended to guard their 

 subjacent vascular' and cellular systems from injury, to pro- 



