The Path of Gaseous Exchange. 



53 



those where the stomata were hmited to the lower surface only and 

 those where the stomata were present on both surfaces. Usually 

 the carbon dioxide evolved from the leaf into a current of air free 

 from that gas was the quantity measured, but results were also 

 obtained for the intake of carbon dioxide which show the path 

 traversed by the gas is the same whether it is travelling into or out 

 of the leaf. 



In the following table we have summarised the results obtained 

 by Blackman for the ratios of the amounts of carbon dioxide given 

 out from the two surfaces of the leaves of various plants. 



Table III. 



The numbers in the foregoing table show hj^w constantly the 

 path of carbon dioxide from the leaf follows the distribution of the 

 stomata. Similar results were obtained in the case of carbon dioxide 

 absorbed in assimilation. Thus, in the cases of Ampelopsis 

 hederacea, Platanus occidentalis and Polygonum sacchalinense, 

 where all the stomata occur on the under surfaces of the leaves all 

 the carbon dioxide was found to enter by the lower surface. None 



