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XXVII. ON THE STRUCTURE AND USES OF THE STOMATA.* 



By Thomas Williams, M.B., M.R.C.S., Lecturer on Forensic 

 Medicine, #c. 



THE ultimate organization and functions of the Stomata of Plants have 

 long formed the subject of hypothesis and dispute among high autho- 

 rities in vegetable physiology. 



The best informed of the earlier observers regarded them as folli- 

 cular pouches of the epidermis, through which the aqueous portions of 

 the elaborated sap were exhaled. In his more recent work, it is stated 

 by De Candolle, that they constitute the spaces where the spiral vessels 

 end, and through which the latter obtain their supply of air ; and hence 

 has probably originated the title of " breathing holes," under which 

 they are popularly known. By many modern botanists, they are de- 

 scribed as definitely organized openings leading into cavities which 

 freely communicate with the spaces between the cells of the paren- 

 chyma. There are not wanting others, by whom the patulous state of 

 the stomata has been denied, who consider them to be closed by a mem- 

 brane, described as a continuation of the epidermis, and which from its 

 delicacy and transparency is invisible under ordinary circumstances. The 

 mode adopted by the Rev. Mr. Reade to render evident this pellicle under 

 the microscope, consists in charring the leaf to be examined, between two 

 pieces of glass. Anxious to determine practically the relative merits of 

 these conflicting observations, I submitted the leaves and green parts 

 of several plants to this charring process ; and unquestionably succeeded 

 in rendering appreciable, in many instances, the existence of a pellicle 

 over the stomata. But in order to be certain that this membrane was 

 not the result of heat employed in preparing the leaf, of which I had 

 some suspicion, I contrived a modification of the process suggested by 

 the Rev. Mr. Reade. After having determined, by repeated observa- 

 tion, that some of the stomata in the spatha of the garden rhubarb 

 appeared open, it was immersed in warm water, after which air was 

 gradually forced into the parenchymatous interspaces, under the receiver 

 of an air-pump, the success of the injection being indicated by the ex- 

 trication of minute bubbles of air from the inferior surface of the leaf. 

 The escape of the air was evidently made through the stomatal orifices 



* Read at the Microscopical Society of London, August 18, 1841, and communi- 

 cated to that Society by the Editor. 



