SECT. I. VEGETABLE EPIDERMIS. 303 



inspecting that of the lower part of the petals of 

 Crocus vcrnus. 



In the permanent parts of woody and perennial 

 plants the old epidermis often disengages itself spon- 

 taneously, as in the Currant, Birch, and Plane-tree, 

 in which it seems to be undergoing a continual 

 waste and repair ; and in such parts it is again re- 

 generated, even though destroyed by accident. 

 But in herbaceous plants, and in the leaf, flower, 

 and fruit of other plants, it never disengages itself 

 spontaneously, and is never again regenerated if 

 once destroyed. 



Du Hamel, who seems to have been the first to 

 institute any very minute inquiry into the structure 

 of the vegetable epidermis, describes it as being 

 formed of a multiplicity of fine and delicate fibres 

 placed in a parallel direction, and inosculating at 

 regular intervals, or united by means of small and 

 lateral fibres, so as to constitute a net-work, the 

 meshes of which are filled up with a thin and trans- 

 parent pellicle ; thus forming a membrane that con- 

 sists either of a simple and individual layer, as in 

 the epidermis of most plants, or of several distinct 

 and separate or separable layers, as in that of the 

 Paper Birch ; in which he counted six or more. 

 He studied it chiefly as it occurs in the bark of 

 trees, and adds that it was sometimes to be met 

 with so very compact, as to exhibit no traces of net- 

 work, even under the microscope, but merely a 

 smooth and uniform surface.* 



* Phys. des Arbres, liv. i. chap. ii. 



