Page:Transactions of the Linnean Society of London, Volume 12.djvu/23

Rh exhibiting any proof of its being analogous to the epidermis of animals.

Such is the substance of M. Mirbel's opinion, against which he is aware that objections may still be urged. For it may be said. If this is the true origin of the epidermis, how comes it to separate so easily from the interior parts in the spring? To this objection M. Mirbel furnishes the following reply, namely, that its facility of detachment is owing to the disorganization occasioned in it by means of its exposed situation, which has even the effect of ultimately separating it from the plant altogether, as may be seen in the instances in which it bursts and exfoliates when it is not able to expand in proportion to the internal parts. And thus M. Mirbel presumes he has got rid of all difficulties.

But the above is by no means the most formidable objection to which the hypothesis is liable. For if it be true that the epidermis is nothing more than the pellicle formed on the external surface of the parenchyma indurated by the action of the air, then it will follow that an epidermis can never be completely formed till such time as it has been exposed to that action. But it is known that the epidermis exists in a state of complete perfection, in cases where it could not possibly have been affected by the action of the external air. If you take a rose-bud or bud of any other flower before it expands, and strip it of its external covering, you will find that the petals and other inclosed parts of the fructification are as completely furnished with their epidermis as any other parts of the plant, and yet they have never been exposed to the action of the air. The same may be said of the epidermis of the seed while yet in the seed-vessel, or of the root, or of the stem of the paper birch, which still continues to form and to detach itself, though the interior layers are defended from the action of the air by the layers that invest them.

Rh