ON THE RESPIRATORY FUNCTION OF STOMATA. 29 



above the optimum for assimilation, the reverse result is ob- 

 tained and the leaf with open stomata decomposes more C0 2 

 than the one with the stomata blocked. I have, therefore, 

 performed a series of experiments similar to Boussingault's, 

 but with leaves of Nermm in varying percentages of C0 2 , 

 and have found that in a high percentage the leaf with its 

 stomata blocked always decomposes more than the normal 

 leaf, while in low percentages it decomposes less. 



These experiments were all performed, with slight 

 modification, by the method brought to perfection by 

 Pfeffer, and described in detail with all its possible sources 

 of error in his paper, "Die Wirkung farbigen Lichtes auf 

 die Zersetzung der Kohlensaure in Pflanzen " (17). 



I append a synopsis of the experiments arranged accord- 

 ing to the strengths of C0 2 in which they were carried out. 



While in 6 per cent. C0 2 the leaf with blocked stomata 

 decomposes only one-seventh as much as the normal leaf, 

 in 50 per cent. C0 2 the relation is completely reversed and 

 it decomposes one and a half times as much. 



Boussingault's work then, thus explained, ceases to sup- 

 port the cuticular exchange theory and yields but a con- 

 firmation of the view that the stomata offer a far easier 

 entrance for gases into the leaf. 



A due consideration of the differences in assimilation 

 between leaves with stomata open and leaves with stomata 

 blocked brings out the relativity of that which we speak of 

 as the optimum percentage of CO a for assimilation. The 



