Patrick Keith

“ 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. ”

“ Accordingly the developement of the epidermis is found to keep pace with that of the plant which it invests, so that it "grows with its growth and strengthens with its strength," expanding in all its dimensions, and accommodating itself with wonderful facility to the augmentation of the inclosed parts, as may be seen in the case of trees and fruits of rapid growth. ”

“ Till a satisfactory answer can be given to these inquiries, that shall be at the same time compatible with the supposed action of the air in other cases, it is impossible to admit the hypothesis of M. Mirbel.
But so far is the action of the external air from being the cause and origin of the epidermis, that it is even detrimental to its formation. For the re-production of a part that has been accidentally destroyed, in cases capable of re-production, is always more easily efiected if the wound be covered closely up [2] . ”