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 p],ants. 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 [iai, upon, and Ssp/to 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- 



