LECT. III.] EPIDERMIS. 97 



regions of the globe *. When the epidermis is 

 applied very closely to the cellular layer below it, 

 which is the case in herbaceous plants, and in the 

 young twigs of trees and shrubs, the greater por- 

 tion of the light is transmitted through the cuticle, 

 and reflected from the cellular layer, and not from 

 the substance of the cuticle ; so that the colour of 

 the herbaceous stem, or of the twig, is, in this 

 case, that of the cellular layer, and not of the 

 cuticle itself; yet in trees and shrubs, which an- 

 nually renew the cuticle, as the Plane, the Birch, 

 the Currant and many others, the epidermis, when 

 it begins to peel off, becomes more opaque and 

 does not transmit the light, but reflects it from its 

 own surface. Thus the old cuticle of the Plane is 

 dark coloured, while the new is of a light green 

 hue ; the stem of the Birch, from which layers of 

 epidermis are continually peeling off, is white, 

 while the young branches are brown ; and the old 

 branches of the Currant are dark brown, while 

 the young shoots are of a very light green hue. 

 In some plants, instead of being thrown off in 



* " On peut done concevoir le corps reticulaire comrae 

 " un systeme capillaire general, entourant 1'organe cutane, et 

 " formant avec les papilles une couche intermediate au corion 

 " et a 1'epiderme. Ce systeme ne contient, chez la plupart des 

 " hommes, que des fluides blancs. Chez les negres, ces fluides 

 " sont noirs. Us ont une teinte intermediate chez les nations 

 " basanees." Bichat, Anat. Gcnerale, $c. tome 4 me , p. 657. 



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