56 TEXTURE OF VEGETABLES. 



some which absorb water with facility, exhale it very 

 sparingly, a fact, which renders them well adapted to 

 sustain the privations which they were designed to en- 

 counter. The Houseleek is a plant of this description, 

 and therefore we frequently see it flourishing on walls, 

 where other vegetables would wither and die. The 

 Aloe and Ice plants, those splendid ornaments of the 

 sandy desert are other examples, whose cellular tex- 

 ture is filled with fluids, which the peculiar formation 

 of their epidermis enables them to absorb and retain. 

 The epidermis usually appears like a simple mem- 

 brane, but those of the Paper Birch and Currant, are 

 composed of several layers which may easily be sepa- 

 rated from each other, and the number of its epider- 

 midal coats has acquired for an American shrub, the 

 popular name of Nine bark.* But there are cases in 

 which the several layers are obviously so incorpora- 

 ted as to form in the aggregate only an individual epi- 

 dermis. This may be exemplified in the rind of an 

 apple, of which the layers are two in number, the ex- 

 terior being thin and transparent, the other being more 

 succulent and tender, and tinged with a peculiar shade, 

 giving colour to the fruit. In most cases when recent- 

 ly formed, it is transparent as well as porous, so as to 

 admit the free access of light and air, while it excludes 

 every substance which would prove injurious to vege- 

 tation. Not only does it protect the young tree from 

 external injury, but it preserves our choicest fruit 

 from premature decay, and without it the leaf would 

 lose its verdure, the flower its fragrance, and their 

 transitory beauty would become still more evanes- 

 cent. 



* Barton's Elements, 



