ON THE RESPIRATORY FUNCTION OF STOMATA. 15 



the contrary of the one supported by Garreau, and to 

 minimise the function of stomata in gaseous exchange. 

 He appeared to prove by trustworthy experiments that 

 the vigorous intake of carbon dioxide during assimilation 

 in bright light proceeded chiefly through the astomatic 

 cuticle. These experiments demand experimental criticism, 

 which must be reserved until the historical survey is com- 

 plete. It may be here pointed out that his critical experi- 

 mental proof consisted in showing of two otherwise similar 

 leaves, that the one which had its stomata mechanically 

 blocked did not decompose any less carbon dioxide than 

 the leaf with its stomata in open functionable condition. 



Barthelemy (4) published his first paper on this subject 

 in 1868. After premising on the strength of Boussingault's 

 researches that stomata only play a secondary role in gaseous 

 exchange, and that there exists no fixed relation between 

 number or size of stomata and assimilatory activity, he 

 brings forward for the first time the view that the cuticle 

 plays a definite specific part in gaseous interchange. This 

 view was suggested to him by Graham's (5) work on the 

 osmosis of gases through thin films of caoutchouc combined 

 with Fremy's (6) then accepted determination of the chemi- 

 cal constitution of cuticle, as being very similar to that of 

 caoutchouc. Carbon dioxide is transmitted through caout- 

 chouc with a rapidity far exceeding that of other ordinary 

 gases, and, of course, it is this gas that must make its way 

 with great rapidity to the internal cells of the leaf during 

 assimilation. Cuticle, then, according to Barthelemy, is to 

 be regarded as a membrane specially fitted by its physical 

 colloid properties to transmit carbon dioxide into the interior 

 of the leaf. Nothing is suggested as to the path by which 

 the equally large quantities of oxygen formed are passed 

 out of the leaf. 



In support of his theory he adduced experiments on the 

 osmosis of gases through leaves, which yielded him numbers 

 almost the same as those obtained for caoutchouc by Graham. 

 The experiments are, however, absolutely valueless. C0 2 , 

 he concludes, enters leaves almost entirely through the 

 cuticle. As for the stomata, he enunciates the view that 



