>ECT. I. ELEMENTARY ORGANS. 205 



disorganization occasioned in the epidermis by means 

 of its exposed position, which has even the effectof ulti- 

 mately detaching it from the plant altogether, as may 

 be seen in the instances in which it bursts and exfo- 

 liates when it is not able to expand in proportion to 

 the internal parts. And thus M. Mirbel presumes he 

 has established his position. But this is by no 

 means the most formidable objection to which his 

 hypothesis is liable ; for if it be true that the epider- 

 mis 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 epider- 

 mis 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 com- 

 plete perfection in cases where it could not possibly 

 have been affected by the external air. If you take 

 a rose-bud, or bud of any other flower, before it ex- 

 pands, 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 paper birch, which still continues to form 

 and to detach itself, though defended from the 

 action of the air by the exterior layers. In herbs 

 and in the annual parts of woody plants, such as the 

 leaves and flowers, the epidermis never detaches 



