96 EPIDERMIS. [LECT. in. 



that the true epidermis is a fine, transparent, un- 

 organized pellicle *. The pores, by which the in- 

 sensible perspiration escapes, are so minute, that 

 they are quite invisible, and with difficulty permit 

 the passage of air through them. Thus, if an 

 apple be put under the receiver of an air-pump, 

 and the air withdrawn, the cuticle of the apple 

 will be lacerated by the dilatation of the air con- 

 tained in the pulp of the fruit. There are oblong- 

 pores also in the cuticle of herbaceous plants in 

 particular, as was first observed by Decandolle, 

 who named them cortical pores. The size of these 

 is considerably greater than that of the former ; 

 and varies in different plants. 



The epidermis seems to be entirely destitute 

 of longitudinal vessels. In herbaceous plants, 

 and in young and succulent twigs, it is, with a 

 few exceptions, colourless and transparent ; the 

 apparent colour being produced by that of the 

 juices in the cellular substance immediately be- 

 neath it, in the same manner as that of the hu- 

 man cuticle is produced by the colour of the 

 capillary web which it covers, and which is filled 

 with different coloured fluids in different races of 

 men ; white in the inhabitants of the temperate 

 zones, and black, or brown, in those of the torrid 



* Obs. stir VEcorce des Feuilles. 



