58 
ORGANOGRAPHY. 
BOOK I. 
any one may easily convince themselves, that their remaining 
open is not at all caused by a constant exterior influence, but 
very probably depends upon the momentary vitality of the 
plant, or of the organ, or perhaps only of the surrounding cel- 
lular tissue. The substances which are deposited near and 
upon the stomata are considered by some, with more or less 
plausibility, as sufficient evidence that these substances cannot 
be abstracted from the epidermis itself, and then they jump 
to the conclusion that such substances are secreted by the 
stomata. I have, however, in vain looked for any facts which 
might make it even probable, that those secretions should 
arise rather from the evaporation of the so called glandular 
cells, than from those of the other parenchymatous cells, and 
more especially from such as border upon the cavities into 
which the stomata lead; and it appears to me that this 
assumed function is, in the present state of our knowledge, 
a mere petitio principii. Let us take the Coniferae : here I 
find gum resin on the stomata; if I remove this by etherial 
oil, the stomata still remain wide open ; then I find a cavity 
(including the two cells of the stomata), and surrounded by 
cells which contain gum (schleim), some starch and chloro- 
phyll, but no traces of gum resin or turpentine ; on the 
contrary, I find, much deeper down, large turpentine ducts, 
and conclude now that the fluid turpentine oil escapes from 
these passages in the form of vapour, and following the in- 
tercellular passages, arrives in the cavities, and from here 
evaporates by means of the stomata into the atmosphere, by 
which, as follows from its nature, it leaves behind a certain 
quantity of resin,” &c. 
The surface of the epidermis is either perfectly smooth, or 
furnished with numerous processes, consisting of cellular tissue 
in different states of combination, which maybe arranged under 
the heads of hair, scurf, glands, and prickles. All these ori- 
ginate either directly from the epidermis, or from the cellular 
substance beneath it; never having any communication with 
the vascular or ligneous system. 
In Nepenthes the cuticle in the inside of the pitchers is 
pierced by a great number of holes, each of which is closed 
up by a firm thick disk of small cellular tissue, deep brown in 
