LECT. III.] EPIDERMIS. 95 



other part of the plant ; and for this purpose I 

 would recommend to the student the leaf of any 

 of the Lily tribe, before the stem shoots up ; or of 

 the Lettuce (Lactuca sativa}, or that of Sorrel 

 (Rumex acetosa) ; but even in these, some of the 

 cellular matter is always detached in separating 

 it ; and to this circumstance is perhaps to be at- 

 tributed the variety of opinions which phytologists 

 have advanced regarding its structure. 



The epidermis appears at first of a green co- 

 lour on the young stems and branches of almost 

 all plants ; but it changes to different hues, ac- 

 cording to the age of the part it covers. Accord- 

 ing to Du Hamel, it is composed of fine, but 

 tough fibres, which are interwoven "together ; and 

 every where interspersed with pores, which per- 

 mit the mouths of the absorbing, transpiratory 

 and air vessels to open to the atmosphere. Com- 

 paretti also describes it as composed of fibres, in- 

 terwoven so as to form hexagonal meshes, the 

 areas of which are filled up with opaque or dia- 

 phanous vesicles, inflated as if extended with 

 air or water, and having a small black point in the 

 centre. Mr. Bauer, on the contrary, conceives 

 the structure to be altogether cellular, and vary- 

 ing in different plants*. My own observations 

 lead me to adopt the opinion of the elder Saussure, 



* Tracts relative to Botany. Lond. 1805. 



