15 OF THE CUTICLE OR EPIDERMIS. 



exposed to a burning sun, with very rare 

 supplies of rain. 



This part allows also of the passage of air, 

 as is proved by experiments on the functions 

 of leaves. Light probably acts through it, 

 as the cuticle is a colourless membrane. We 

 know the effects of light to be very important 

 in the vegetable oeconomy. 



But though this fine membrane admits 

 extraneous substances, so as to have their 

 due effect upon the vegetable constitution, 

 according to fixed laws, it no less powerfully 

 excludes all that would be injurious to the 

 plant, either in kind or proportion. Against 

 heat or cold it proves, in general, but a fee- 

 ble defence ; but when clothed with hair or 

 wool, it becomes a very powerful one. Against 

 the undue action of the atmosphere it is so 

 important a guard, that, when any tender 

 growing part is deprived of it, the greatest 

 mischiefs ensue. It forms in the Vegetable, 

 as well as the Animal, a fine but essential 

 barrier between life and destruction. 



Some have imagined that the cuticle gave 

 form to the vegetable body, because it some- 

 times being over tight causes contractions on 



