The Rev. Patrick Keith on the Vegetable Epidermis. 7 



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 sepa- 

 rate so easily from the interior parts in the spring ? To this ob- 

 jection 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 Avhen it is 

 not able to expand in proportion to the internal parts. And thus 

 M. Mirbcl 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 epider- 

 mis is nothing more than the pellicle formed on the external sur- 

 face 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 cover- 

 ing, 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 ex- 

 posed 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 tlie 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. 

 * Traits d'Anat. et de Phys. Veg. i. 87- 



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