THE NATURE OF PHOTOSYNTHESIS 65 



established. These quantities were then correlated to the number of 

 stomata on each surface. A similar procedure was followed in order to 

 establish the path when carbon dioxide is taken up by the leaf in the 

 light. It was concluded that in both cases the carbon dioxide passes 

 primarily through the stomata. 



Jorgensen and Stiles ^- have summarized the result obtained by Black- 

 man of the quantities of carbon dioxide emitted from the two surfaces of 

 various leaves in proportion to the number of stomata on each surface. 



TABLE 8 



Amounts of Carbon Dioxide Given Out from the Two Surfaces of Leaves. 



(From Jorgensen and Stiles.) 



Stomatic Ratio. CO2 Respired. 

 Upper Surface Upper Surface 



Plant Peculiarity Lower Surface Lower Surface 



Neriuni oleander Very thick cuticle 3 6 



100 100 100 



Primus laurocerasus " " " 4 



100 100 100 



Hedera helix " " " _0_ J_ 



100 100 



Plantanus occidentalis Thin cuticle 3 



Too 100 



Ampelopsis hcderacea " " 3 



loo 100 



Polygonum sacclialinense . . " " 6 



loo 100 



135 120 



^r , A ■ , >r 100 100 



Alisma plantago Aquatic plant. More J35 



stomata on upper -rp^ 



surface ^ ^ 



100 100 



Iris germanica Isobilateral leaf 100 105 110 



iOO 100" 100 



Populus nigra Stomata on both sur- 100 100 



faces, fewer on upper 575 375 



Helianthus tubcrosus " 100 100 



240 273 



Tropceolum majus " 100 100 



200 265 



From Table 8 it can be seen that the quantities of carbon dioxide 

 emitted by the various leaves in most cases is in direct proportion to the 

 stomatic ratio, at least within the experimental error. Similar experi- 

 ments were carried out by Blackman with illuminated leaves, in which 



"Jorgensen and Stiles, Carbon Assimilation. London, 1917, p. 53. 



