100 THE BIOLOGY OF FLOWERING PLANTS 



modified. He assumes that a second series of diffusion 

 shells forms over the leaf as a whole, and that this offers a 

 further resistance to diffusion. It is not very easy to 

 appreciate this, when we take into account the fact that the 

 stomata do not interfere mutually. Such a vapour dome over 

 the whole leaf would, however, be formed in any case by 

 the vapour transpired through the cuticle. The equation, 

 devised by Renner, taking this outer dome into account, is 



Q = d{p, - ^o) 



ttR 



27rR^ 



nnr 



^+?) 



• (7) 



where R is the radius of a circle having the same area as the 

 leaf. Using this formula, and taking cuticular transpiration 

 into account, Renner does, in fact, get a much closer agree- 

 ment between observed and calculated values in quiet air, 

 as may be seen from Table XXIV. 



TABLE XXIV 

 Transpiration from Various Leaves by Renner's Formula 



The effect of wind, according to Browne and Escombe's 

 formula, is not very great ; in the example quoted the 

 theoretical absorption of carbon dioxide is increased by about 

 20 per cent. Using Renner's formulae the difference is 

 much greater, for in wind the vapour dome for the whole 

 leaf disappears and equation (4) becomes applicable. The 



