Page:Transactions of the Linnean Society of London, Volume 12.djvu/25

Rh expansion is circumscribed, however, by certain bounds or limits which it cannot pass. For, when it has become indurated with age, or when vegetation is too luxuriant, it refuses or is unable to expand further, and consequently bursts. But if it does not burst spontaneously, where it does not expand freely, it is then thought to check or retard the growth of the plant, by operating as a sort of tight roller or bandage; as may be exemplified in the case of the cherry-tree, the epidermis of which the gardener is often obliged to lay open by means of a longitudinal incision, in order to facilitate the growth of the parts inclosed.

With regard to the disavowed analogy between the animal and vegetable epidermis, it is of no consequence to the above argument whether it holds good or not. But there are several important respects in which an analogy between the two cuticles is sufficiently striking. They are both capable of great expansion in the growth of the subject. They are both easily regenerated when destroyed, (with the exceptions above stated,) and seemingly in the same manner. They are both subject, in certain cases, to a constant decay and repair; and they both protect from injury the parts inclosed. Whence we feel ourselves entitled to draw a conclusion directly the reverse of that of M. Mirbel, namely, that the epidermis of the vegetable is not an accidental scurf formed on the surface of the parenchyma by means of the action of the air; but a distinct and individual organ formed by the agency of the vital principle, at the period of the generation of the plant, and destined to the discharge of peculiar functions in the vegetable œconomy, as well as exhibiting a close analogy to the epidermis of the animal.

Stow Maries, Dec. 22, 1814.

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