THE NATURE OE PHOTOSYNTHESIS 



71 



Brown and Escombe having thus determined that, "when a condi- 

 tion of static equiHbrium has been estabhshed in a diffusing column of 

 gas, vapor, or sokite, as the case may be, the amount of diffusion, under 

 Hke conditions, is proportional to the sectional area of the column, . . ," 

 they proceeded to apply these findings to conditions which simulate those 

 existing in the leaf. They discovered that when a septum with a circular 

 aperture is interposed in the line of flow, diffusion is modified in a re- 

 markable manner. It was found that when the aperture was reduced to 

 a certain point, the carbon dioxide i>assing through unit area of aperture 

 in a given time showed a marked increase, "which could not be satisfac- 

 torily accounted for by the mere difference in the gradient of i)artial pres- 

 sures of the gas inside and outside the covered disk." The experiments 

 were carried out with great care and the apparatus consisted, in brief, of 

 flasks containing sodium hydroxide to absorb the carbon dioxide. Over 

 the mouths of the flasks were cemented septa with apertures of differ- 

 ent diameters. After observing all precautions to maintain all experiments 

 under precise conditions of carbon dioxide-content, temperature, freedom 

 from convection currents, etc., the amount of carbon dioxide absorbed 

 by the sodium hydroxide was determined. Thus it developed that as the 

 size of the restriction decreased the flow per unit area of aperture rapidly 

 increased, and as the aperture was diminished below a certain size rela- 

 tive to the cross-section of the column, the amount of carbon dioxide 

 which passed became i>roportional to the linear dimension of the apertures. 



The following table is taken from Brown and Escombe's pai>er and 

 with the exceptions of Nos. 2 and 3 the results show that the rates of diffu- 

 sion follow very closely the ratios of the diameters of the openings as 

 well as the relative increase of carbon dioxide diffused, per area of the 

 aperture per hour. In Nos. 2 and 3 the diameter of the aperture was 

 more than one-half that of the unrestricted opening of the flask in which 

 case other conditions prevail. 



TABLE 12 

 Rate of Diffusion of Carbon Dioxide through Apertures. 

 (Brown and Escombe.) 



