ON THE RESPIRATORY FUNCTION OF STOMATA. 31 



formation that takes place round wounds or openings in the 

 upper epidermis under these circumstances. I obtained the 

 best results with leaves of Vitis, Polygonum sacclialinense, 

 and especially with Sparmannia. In its suitability for 

 demonstration purposes this experiment should be of great 

 service in dispelling the established English view as to the 

 paths of gaseous exchange. 



In conclusion it must be noted that throughout only 

 the carbon dioxide of the gaseous exchange and not the 

 oxygen has been localised. Chemical analysis hardly 

 permits us to attempt any such work with this latter gas. 

 It can, however, hardly be doubted that its movement is 

 normally limited to the stomata as much as that of carbon 

 dioxide. For, on the one hand, it must theoretically 

 diffuse more readily through small openings such as 

 stomata, since its density is less, and, on the other hand, 

 it has been experimentally proved to pass through cuticle 

 less readily than carbon dioxide. 



The passage of CO, into the leaf during assimilation is 

 the most difficult and crucial of the four movements of 

 gases, two of respiration and two of assimilation, that take 

 place. In any of the other three the differences of tension 

 between the inside and outside of the leaf may increase to 

 almost any extent, while for this case the difference of 

 tension never exceeds o - 3 millim. Hg., and the cuticle of 

 land plants is practically impenetrable to this small tension. 



The internal structure of leaves is generally in accord- 

 ance with the view that all gaseous exchange takes place 

 through stomata, for the intercellular spaces narrow towards 

 the palisade cells, forming a sort of funnel with the wide 

 end at the stomatal region. The active cause of the divorce 

 which results in the palisade cells and stomata, whose united 

 action is necessary for vigorous assimilation, being usually 

 found on opposite surfaces of the leaf, is presumably the 

 double necessity for at once limiting transpiration and 

 illuminating the assimilating cells. 



BIBLIOGRAPHY. 



(1) DUTROCHET. Sur les organes aeriferes des vegetaux. Ann. 

 Sci. Nat., serie i., tome xxv., 1832. 



