I 

 120 STRUCTURE AND USES OF THE STOMATA. , 



cuticle, which is dense, be shaved off with a sharp, thin scalpel) on the 

 ^buds and expanded leaves of the Ficus elastica, when contrastively 

 .examined, the following distinctive features can be readily determined. 

 Previously charred, the cuticle from the younger leaves will present 

 stomata, which consist of two or more elliptically disposed vesicles, 

 enclosing apparently a membrane, darkened by the charring, which can 

 be distinctly observed to be bisected by a diaphanous line longitudi- 

 nally traversing the oval space of the stoma. These appearances can 

 likewise be distinguished in the wwcharred cuticle, with the difference, 

 however, that the membrane here appears more like flattened cells, 

 studded in their interior with granules of chlorophylle, which impart to 

 the oval space a shaded or dark character ; and this latter circumstance 

 explains away the error of the idea which some microscopists have 

 entertained, that the dark appearance is caused by the presence of air 

 in the cavity beneath. In the epidermis of the -older leaves, on the 

 contrary, charred or uncharred, unequivocal perforations can be dis- 

 covered bounded by transparent vesicles. Between these two extremes 

 of the foetal and adult formations, numerous intermediate conditions 

 are presented. The transparent line, which I have satisfied myself to be 

 a fissural aperture between the two apposed, darkened vesicles, with 

 advancing development, acquires greater breadth, until ultimately it 

 assumes the character of an oval orifice. By comparing the stomates 

 on the bases and apices of the leaves of the Hyacinthus orientalis, the 

 distinctions here indicated may be conclusively determined. Subse- 

 quently to the settlements of these points, my attention was directed to 

 the observations of M. Hugo Mohl* on the development of these organs, 

 in which allusion is made to the views of M. Mirbel. f While no 

 positive statement is made in regard to the persistent condition of the 

 stomata, it may be obviously seen that the account which is here pre- 

 sented, derives confirmation from their labours. These observers 

 conducted their examinations upon the leaves of the Marchantia poly- 

 morpha, stalks of Gourds, and on the cuticle covering the articulations 

 of Tygnema. Although their opinions are somewhat different, they 

 agree upon the principle, that the orifices of these organs result from 

 the graduated separation of the vesicles, which are nothing more than 

 ordinary epidermoid cells, modified into a specific form. These facts, 

 then, obviously point to the general inference, that the normal condition 

 of the stomata is that of complete perforation, and that when the ap- 



* Annales des Sciences Naturelles, 1840, p. 222. 

 t Comptes Rendus, Tom. iii., p. 568. 



