150 DO STOMATES SECRETE ? [BOOK i. 



form an intercellular passage, not three or four ; examples of 

 which are not uncommon in the interior of plants. They 

 contain, like the surrounding parenchym, sometimes gum, 

 sometimes globules of mucus (schleim), 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 I remember having seen a few drops of oil. 

 The diversity of opinions as to whether the stomates be really 

 open, leads to the supposition, of the correctness of which 

 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 

 cellular tissue. The substances which are deposited near 

 and upon the stomates 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 stomates. 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 stomates 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 Coni- 

 fers : here I find gum resin on the stomates ; if I remove 

 this by ethereal oil, the stomates still remain wide open ; then 

 I find a cavity (including the two cells of the stomate), and 

 surrounded by cells which contain gum (schleim), some starch 

 and chlorophyll, but no traces of gum resin or turpentine ; 

 on the contrary, I find, much deeper down, large turpentine 

 vessels, and conclude now that the fluid turpentine oil escapes 

 from these passages in the form of vapour, and following the 

 intercellular passages, arrives in the cavities, and from here 

 evaporates by means of the stomates into the atmosphere, by 



