36 



in which I have principally brought together all that we ac- 

 tually know respecting the structure of this substance at the 

 present day. I showed that even Ludwig was acquainted 

 with the cuticle and first started this term ; that further, this 

 term must, it is true, be retained in vegetable anatomy, but 

 that the cuticle is decidedly no distinct membrane enveloping 

 the surface of the cells of the epidermis, and much less can it, 

 as M. Valentin endeavoured to demonstrate, be considered 

 as an intercellular substance. I referred to cases in which it 

 might be distinctly seen, that even the cuticle, be it ever so 

 thick, is composed of the upper sides of the cells of the epi- 

 dermis, for the lateral lines of union of those cells are seen to 

 traverse the cuticle, and indeed quite to the surface. This is 

 best seen on any well-prepared horizontal section of the 

 leaves of Aloe candicans. I have also drawn attention to an 

 aperture peculiar to the cuticle*, and which is situated imme- 

 diately above the true stomates of the epidermal glands. In 

 the genera Aloe and Agave this peculiar formation is very com- 

 mon. I call it a prostomate (Vorspalte)', between it and the 

 true stomate of the epidermal gland there exists a greater or 

 less space, which is also filled with air, and is continued through 

 the stomate into the respiratory cavity. 



I also drew attention f to some peculiarities in the epidermis 

 of various Orchidea. In Pleurothallis and Stelis the epidermis 

 of the leaves exhibits peculiarly formed funnel-shaped cavities, 

 which traverse the whole layer of the cells of the epidermis, 

 and project as deep again into the subjacent cellular mass. 

 Pleurothallis and Stelis offer epidermal glands with stomata 

 only on the under surface of the leaf; these cavities, however, 

 occur on both surfaces, on the upper surface more frequently 

 than on the under. The cells, more immediately connected 

 with the formation of these cavities, mostly contain large drops 

 of oil, which are sometimes found in almost all the cells of 

 the epidermis of the upper surface of the leaf. As I imagined 

 I had observed that these cavities were not closed, but open, 

 and might thus effect a free communication between the atmo- 

 spheric air and the diachyma of the leaf, I regarded them as 

 representatives of the stomata. M. Schleiden, in the following 



* Pflanzen-Physiologie, Tab. V. fig, 1. 

 f Wiegmann's Archiv, 1837, p. 421. 



