Page:An introduction to physiological and systematical botany (1st edition).djvu/47

 Rh of this membrane continually peeling off from the Birch, we see a resemblance to the scales which separate from the shell of a Tortoise. By maceration, boiling, or putrefaction, this part is separable from the plant as well as from the animal, being, if not absolutely incorruptible, much less prone to decomposition than the parts it covers. The vital principle, as far as we can judge, seems to be extinct in it.

The cuticle admits of the passage of fluids from within as well as from without, but in a due and definite proportion 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 constructed, 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