20 THE SYNTHESIS OF CARBOHYDRATES 



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. per 

 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. Some of Brown and Escombe's conclusions have been 

 criticized by Jeffreys f who has made a mathematical study of 

 evaporation, the problems of which are much the same as 

 those of gaseous diffusion. He points out that further in- 

 vestigation is required and remarks that " it is not obvious 

 that the surrounding stomata will not interfere with the action 

 of any individual to an important extent, and a wind blowing 



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

 t Jeffreys : " Phil. Mag.," 1918, 35, 270. 



