THE NATURE OF PHOTOSYNTHESIS 



75 



percentage of the oi>en tube diffusion. It is, moreover, evident that as 

 the distance between the holes is increased, the efficiency of the holes, 

 i.e., the area of perforations increases. For the optimum efficiency of 

 each perforation, these should be about ten diameters apart. Under these 

 circumstances the rate of diffusion is about forty times the amount it 

 would be if the diffusion were proportional to the area of the cross-sec- 

 tion of the tube. 



The results are summarized in the following table : 



TABLE 13 



Diffusion of Carbon Dioxide Through Septa with Holes 0.380 mm. in Diam- 

 eter. The Distance between the Septa and the Sodium Hydroxide Solu- 

 tion IN THE Two Experiments was 1 cm. and 4 cm. (Brown and Escombe.) 



cc. CO2 Percent- 



Brown and Escombe picture this phenomenon as shown in Figure 6. 

 This is simply a multiplication of the case shown in Figure 5. Assuming 

 perfectly quiet air at some distance from the septum the lines of -flux 

 in a diffusive column are approximately parallel. As the stream lines 

 approach the aperture they converge and gradually assume parallelism 

 again on the lower side of the septum. The ellipsoidal shells come closer 

 together at the edges than in the center which would indicate that in 

 these regions the gradient of density is greater and results in greater 

 rate of flow per unit area. The lines of flow, which are at right angles 

 to the gradients of density, thus also converge at the edges of the aper- 

 ture, and after passing through the opening, again diverge. The lines 

 of flow from adjacent apertures cannot cross each other, as there would 

 then be shells of dift'erent density crossing each other, which is impos- 

 sible. The lines of flow must, therefore, bend around the aperture and 

 again become parallel, the velocity of the flow decreasing at the same 

 time. As is shown in the tallies there is an acceleration of flow per 



