192 



FIXATION OF CARBON DIOXIDE 



CHAP. 8 



Spoehr and Newton observed that leaves of sunflower arid nettle 

 absorb about twenty times more carbon dioxide than those of alfalfa, 

 rhubarb, spinach, and hydrangea. However, the properties of sunflower 

 are not exceptional, as shown by the later data of Smith (1940), some 

 examples of which are given in table 8.X. 



Table 8.X 

 Carbon Dioxide Absorption by Fresh Leaves 



In all species listed in table 8.X, "chemical" absorption of carbon 

 dioxide enhances the solubility under atmospheric pressure by 20-50% 

 (in agreement with the 100% increase under 150 mm. pressure found by 

 Willstatter and Stoll). The absorption is fully reversible — in fact, a little 

 more carbon dioxide is usually removed by evacuation than has been 

 absorbed under high pressure (obviously because of respiration). Acidi- 

 fication liberates an additional quantity of carbon dioxide by the de- 

 composition of neutral carbonates. 



Table 8.XI 

 Carbon Dioxide Content of Helianthus Leaves " 



" All figures refer to 10 g. fresh leaves or material derived therefrom. 



' Amount of carbon dioxide absorbed when CO2 pressure is increased from to 1 atm. 



' Amount of carbon dioxide released by cold dilute acid, minus the "reversible" CO2. 



