LECT. III.] EPIDERMIS. 101 



flakes of epidermis which are cast off annually 

 by the Plane tree, and some other trees, consist 

 of cellular substance also, yet, the cuticle is already 

 formed under the flakes before they fall, and 

 therefore it cannot be in these cases produced by 

 the action of the air, and light. On examination 

 of these flakes, the epidermis appears to be dis- 

 tinct from the plate of cellular substance which 

 separates with it. Mirbel himself, indeed, is 

 obliged to modify his objection, and adds, But, 

 although the epidermis of vegetables does not 

 resemble that of animals, and is certainly the 

 external part of the cellular substance, yet, it is 

 no less true that secondary causes modify its 

 nature, and it consequently becomes an organ 

 the functions of which are very distinct and im- 

 portant *. Such a concession is all that can be 

 demanded. That the human cuticle is a distinct 

 organ has never been denied, and yet we know 

 that it is equally without vessels and nerves. On 

 the same principle, therefore, the vegetable epider- 

 mis must be admitted to be a distinct organ ; and 



* " Mais, quoique Pepiderme des vegetaux ne ressemble 

 " pas a celui des animaux, et qu'il soit forme certainement par 

 " la partid exterieure du tissu cellulaire, il n'est pas moins vrai 

 " que des causes secondaires modifient sa nature, et qu'il 

 " devient par le fait un organe dont les fonctions sont tres- 

 " distinctes et tres-importantes." Physiologic vegetate, vol. i. 

 p. 89. 



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