STRUCTURE.] NATURE OF THE EPIDERMIS. 138 



delicate membrane, but in some plants it is so hard as almost 

 to resist the blade of a knife, as in the pseudo-bulbs of 

 certain Orchideous plants. The most usual form of its reti- 

 culations is the hexagonal (Plate III. fig. 11.) : sometimes 

 they are exceedingly uncertain in figure ; often prismatical ; 

 and not unfrequently bounded by sinuous lines, so irregular 

 in their direction as to give the meshes no determinate figure 



(fiff- 50 



Botanists were formerly not agreed upon the exact nature 

 of this epidermis; while some inclined to the opinion that it 

 is an external layer of cellular tissue in a compressed state; 

 others, among whom were included both Kieser and Amici, 

 considered it a membrane of a peculiar nature, traversed by 

 veins, or lymphatic vessels. 



By the latter it was contended, that the sinuous direction of 

 the lines in many kinds of epidermis is incompatible with the 

 idea of anything formed by adhesions of cellular tissue : that 

 when it is once removed, the subjacent tissue dies, and does 

 not become epidermis in its turn, and that it may often be 

 torn off readily without laceration. 



On the other hand, it was replied, that the reticulations of 

 the epidermis are mostly of some figure analogous to that of 

 cellular tissue, and that the sinuous meshes themselves are not 

 so different as to be incompatible with the idea of a membrane 

 formed of adhering bladders. We are accustomed to see so 

 much variety in the mere form of all parts of plants, that an 

 anomalous configuration in cellular tissue should not surprise 

 us. The lines, or supposed lymphatic vessels, are nothing 

 more than the united sides of the cells, and are altogether 

 the same as are presented to the eye by any section of a mass 

 of cellular substance. It is certain that the epidermis cannot 

 be removed without lacerating the subjacent tissue, with how- 

 ever much facility it may be sometimes separable : on the 

 under surface of the leaf of the Box, for instance, there has 

 plainly been some tearing of the tissue, before the epidermis 

 acquired the loose state in which it is finally found. 



There is now no anatomist who doubts the fact of epider- 

 mis being composed of cellular tissue. In many plants the 

 cellular state is distinctly visible upon a section (Plate I. 



