INFUSION OF CARBON DIOXIDE 



21 



diameter of a perforation, each will act independently without 

 interference by its neighbours and conform to the law of 

 diameters. When situated more closely together, it was 

 found that the obstacle to diffusion was much less than the 

 actual obstruction of area by the solid portions of the septum. 

 To quote concrete examples, Brown and Escombe calculated 

 that in Helianthus the leaves could absorb 2*578 c.c. of carbon 

 dioxide per sq. cm. per hour in moving air and 2-095 c - c - P er 

 sq. cm. per hour in still air, assuming that the stomates are 



circular in shape. By actual measurement it was found that 

 in this same plant * in diffused light at a temperature of 19 C, 

 0*434 c.c. of carbon dioxide, per sq. cm. per hour was absorbed, 

 an amount much less than the capacity of the stomates to 

 supply. Those conditions, humidity of atmosphere, tem- 

 perature and illumination, which affect the size of the stomates 

 obviously will affect the infusion rate of carbon dioxide, f 

 Under natural conditions carbon assimilation is limited by the 



* Brown and Escombe : " Proc. Roy. Soc.," Lond., B. 1905, 76, 29. 

 fSee Darwin: "Phil. Trans. Roy. Soc.," Lond., B. 1898, 190, 531; 1916* 

 207, 413. Knight: " Ann. Bot.," 1916, 30, 57- 



