CHAP. II. 
STOMATES. 
57 
The origin of stomates has always been very obscure, nor 
do I know of any one who has explained dieir origin in any 
detail except Schleiden, who considers them to be the last 
cytoblasts which the cuticular tissue forms (see page 19. for 
his theory of cytoblasts). He considers that in the begin- 
ning all the forms of tissue are, in shape, contents, and struc- 
ture, exactly the same, and that all the modifications of tissue 
take place later. He supposes that the exterior tissue of a given 
mass leaves off producing new cells in its interior sooner than 
that of the exterior, and that consequently epidermis is first 
completely organised ; but in the epidermis some of the cells 
retain longer than others the property of forming internal 
cells, and it is when the last pair of cells separate and absorb 
their parent that the stoma is produced. The cells forming 
the stomatic sphincter are in their origin exactly the same as 
the cells of the parenchyma, and they remain so in their 
functions throughout their whole existence. 
Some physiologists. Link for instance, adhere to the opi- 
nion that stomates are glands or secreting organs, and not 
mere passages in the cuticle for the transmission of gaseous 
matter. Upon this subject I quote the words of Schleiden : — 
“ These two cells (of the stoma) have been designated by 
the name of glands, but I do not see any reason for this 
denomination being given to them in preference to any of the 
other exactly similar cells of parenchyma. From these they 
do not differ at all in the abstract, and in their position only 
apparently, inasmuch as it is a law that only two cells form 
an intercellular passage, not three or four; examples of 
which are not uncommon in the interior of plants. They 
contain, like the surrounding parenchyma, sometimes gum, 
sometimes globules of mucus (sclileim), sometimes starch, 
these latter substances sometimes colourless, and sometimes 
coloured by chlorophyll, but always so that their contents 
are the same as those of the surrounding cells : but never, as 
I believe, does one find in them peculiar substances which 
might warrant the name of glands. In the single instance 
of Agave lurida 1 remember having seen a few drops of oil. 
The diversity of opinions as to whether the stomata be really 
open, leads to the supposition, of the correctness of which 
