SECT. I. OR6ANOGRAPHY AND GLOSSOLOGY. 



27 



posed of two lunate vesicles (fig. 18. a), which may 

 be detached by maceration in water, but in the epi- 

 dermis are in close contact at their extremities, and thus 

 form a sort of border round the area occupied by the 

 slits in the outer pel- 

 licle. The space be- 

 tween these vesicles 

 may be contracted or 

 completely closed, by 

 an alteration in their 

 position. Some sto- 

 mata appear to con- 

 sist of a single annular vesicle (6), which may pos- 

 sibly be occasioned by the blending of two ; or thi s 

 may be owing to an optical illusion. In some cases* 

 the stomata are square (c) ; in others, the orifice ap- 

 pears dark, but whether from the interposition of a 

 peculiar membrane, or merely by the deposit of se- 

 creted matters, seems to be doubtful. As the vesicles 

 of the stomata contain granular matter, they appear to 

 be more nearly related to those of the cellular tissue 

 in the substance of the leaf beneath the epidermis, 

 which contain a similar matter, than to the flattened 

 cells which compose this organ itself, and which are 

 generally without grains, and perfectly transparent. 

 Stomata do not occur on flower less plants, excepting 

 among their higher tribes, and which also possess tra- 

 cheae (art. 23.). They are also absent on the sub- 

 merged parts of aquatics, and are not to be found on 

 certain parasitic plants. 



(31.) Pubescence. There are great varieties in the 

 forms under which certain prolongations of the cellular 

 tissue occur, on the surface of different parts of plants. 

 To the naked eye, such appendages to the epidermis re- 

 semble hair, silk, bristles, scales, &c., and have received 

 these names in descriptive botany. Under the micro- 

 scope, they are all found to be composed of cellular 

 tissue ; sometimes of a single vesicle, at others of 



