3:2 OF THE CUTICLE OR EPIDEIIMIS, 



The cuticle admits of the passage of fluids from within 

 as well as from without, but in a due and definite pro^ 

 portion in every plant : consequently it must be porous ; 

 and the microscope shows, what reason would teach us 

 to expect, that its pores are different in different kinds of 

 plants. In very succulent plants, as Aloes, a leaf of 

 which being cut off will lie for many weeks in the sun 

 without drying entirely, and yet when partly dry will 

 become plump again in a few hours if plunged into 

 water, the cuticle must be very curiously construct- 

 ed, so as to admit of ready absorption, and very tardy 

 perspiration. Such plants are accordingly designed to 

 inhabit hot sandy countries, where they are long expos- 

 ed to a burning sun, with very rare supplies of rain. 



This part allows also of the passage of air, as is prov- 

 ed 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 ceconomy. 



But though this fine membrane admits extraneous 

 substances, so as to have their due effect upon the veg- 

 etable 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 feeble defence ; but 

 when clothed with hair or wool, it becomes a very 

 powerful one. Against the undue action of the atmos- 

 phere 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 Ani- 



