ON THE RESPIRATORY FUNCTION OF 



STOMATA. 



TH E part played by the stomata of a leaf in the gaseous 

 exchanges essential to respiration and assimilation 

 has been much debated, and at the present time leading 

 text-books express entirely opposed views. Yet it would 

 seem to be a question of primary biological importance 

 whether the vast quantities of carbon dioxide that are 

 taken up by assimilating green leaves enter through the 

 stomatic openings or are absorbed by the much more 

 extensive, cuticularised, exposed surfaces of the epidermal 

 cells. Until this is decided no very definite conception 

 of the physiological significance of the leaf structure is 

 possible. 



It is proposed to give in this article, firstly, an historical 

 sketch of the conflicting theories and experiments that have 

 been advanced in the attacks on this problem ; then a brief 

 account of a complicated apparatus that the author has 

 designed, capable of obtaining direct experimental evidence 

 from the living leaf on this function ; and finally a resume 

 of the results so obtained, which it is trusted furnish a final 

 solution of the problem. 



The earliest paper that must be noticed is by Dutrochet 

 (i), 1832. He draws attention to the extensive system of 

 intercellular spaces to be found in leaves, especially in the 

 lower strata, and demonstrates by injection the connection 

 with the stomata. From determinations of the composition 

 of the gas normally contained within these spaces he con- 

 cludes that this internal air has a real physiological signifi- 

 cance, and that the leaf of the plant has a lung-like function, 

 handino- on to the outer air the carbonic acid formed within 

 the bulk of the plant, and returning oxygen in exchange. 



Interest in the role played by cuticle, then newly in- 

 vestigated, in absorption and exhalation by the aerial parts 

 of the plant, stimulated Garreau (2) in 1850 to carry out a 

 series of researches on these points. 



