Organization of Leaves. 5 



I was able to separate a pellicle, which carried with it only 

 the exterior face of these utriculae, as seen fig. 3 and 4.* 



To find tlic epidermis of Saussure I repeated the same 

 processes which he employed, varying them different ways ; 

 but instead of epidermis 1 always observed that the surface 

 of the leaves was formed only by the external face of the 

 exterior utricula; ; tliat this face was distinguished by slight 

 rug^E, produced, no doubt, by exposure to the air ; that it 

 was indeed a little thicker than the other faces of the same 

 utriculae, and on that account exceedingly proper for dis- 

 charging the functions of an epidermis. It needs not be 

 objected that this thickness supposes -an epidermis con- 

 nected with the exterior face of the utriculse, for in this 

 manner we ought to admit nothing which is not supported 

 by rigorous proof: but though I was never able to separate 

 the C'pideiniis from the surface of the leaves, I am in doubt 

 whether I sliould thence conclude that it does not exist. 



C. Mirbel entertained the same opinion as I do f in re- 

 gard to the non-existence of the epidermis in leaves, and 

 expresses it in the following manner : — " The exterior cells 

 (which are my utriculfe) closely united exhibit contiguous 

 surfaces, which many authors have considered as an epi- 

 dermis. It was natural that they should believe in the ex- 

 istence of this organ, since they considered the vegetable 

 as composed of fibres, vessels, and utricuUe. All these 

 parts, in their opinion, being only joined or weakly united, 

 ought to have a connnon connection or covering to retam 

 them in their respective places : but, according to the facts 

 which I have established, the existence of the epidermis does 

 not appear to be necessary ; and the more I observe, the 

 more I am convinced that it does not exist. The sides of 

 the cells exposed to the contact of the air and of the light 

 undergo an alteration to which the interior parts are not 

 exposed ; they become dry, and are even separated some- 

 times from the cellular tissue. It is thus that they become 

 a distinct covering, and it is then that they are destroyed : 

 but if this pretended epidermis be carefully removed in the 

 green parts, its continuity with the cellular tissue will be per- 

 ceived ; the vascular reticulation of Saussure is seen adher- 

 ing to that exterior membrane ; and this reticulation, when 

 better ol>served, appears to be only the lateral sides of the 

 cells, wliile the epidermis or membrane, which serves them 



* Tlic difTrcnt figurts referred to in lliis article will be found in 

 Plitcs I and II. 



t Journal Ue Physique, Prairial. nn. 9, p. 44.3. 



A 3 as 



