28 SCIENCE PROGRESS. 



For some time after I proved, by the direct experiment 

 described in the previous section, that the absorption does 

 not take place through the astomatic surface, this result of 

 his was an enigma to me. 



That the cuticle of leaves was slightly permeable to C0 2 

 was well known, but how was one to explain the greater in- 

 take of C0 2 in the leaf with its stomata blocked than in the 

 leaf with its stomata open ? 1 1 occurred to me that the explana- 

 tion might lie in the large C0 2 content of the gas in which 

 Boussingault exposed the leaves. The CO a formed more than 

 30 per cent, of the mixture, and the less decomposition 

 of C0 2 in the leaf with stomata open might be due to its 

 receiving not less CO. than the other leaf, but more, indeed 

 so much more above the optimum for assimilation that it 

 decomposed much less than the leaf inside which the C0 2 

 was not so abundant. Within the latter, C0 2 would never 

 become very plentiful, diffusing slowly as it must through 

 the upper surface of the leaf, as the stomata were blocked 

 with lard. I then turned to Godlewski's well-known paper 

 ( 1 6) on the optimum strength of CCX for assimilation, and 

 found that he had worked on this same leaf, Nerium, and 

 that although his results are not very decisive, there was 

 evidence that the Boussingault result could be interpreted in 

 this way. Thus Godlewski found the optimum strength of 

 C0 2 for assimilation in Nerium to be decidedly lower than 

 the 8 per cent, which is the number for other leaves. 

 On looking through his experiments with Nerium there will 

 be found one, No. xxxiv., which just seems to fit the case in 

 question. In this experiment he exposed two leaves to the 

 light in 28 per cent. CO a and 3*6 percent. CO. respectively, 

 and the amounts of C0 2 decomposed were as 10 : 17 '8. 

 Assume that from an environment of 30 per cent. CO,, the 

 CO, diffuses through the cuticle of the leaf with blocked 

 stomata at such a slow rate that there is only as much CO, 

 inside the leaf as would result from about 3*6 per cent, outside 

 were the stomata open, and the whole contradiction is gone. 



The truth of the above explanation of Boussingault's 

 result will be confirmed if it be shown that in an atmosphere 

 which contains an amount of C0 2 that is but little, if at all, 



