LABORATORY FOR PLANT PHYSIOLOGY. 53 



fact that the rate of C02-emission is directly affected by the partial pressure 

 of the CO2 surrounding the plant, another factor seems to enter, namely, 

 that of the absorption of CO2 by the leaf material itself. 



The Absorption of CO2 by the Leaf Material, by H. A. Spoehr and J. M. McGee. 

 The classical investigations of Brown and Escombe established the quanti- 

 tative relationships governing the diffusion of CO2 into the leaf. Willstaetter 

 has shown that the killed leaf is capable of absorbing CO2 in quantities con- 

 siderably above the amount dissolved in the water of the leaf. An investiga- 

 tion has been begun to determine the nature of the substance which absorbs or 

 adsorbs these relatively large amounts of CO2. A large variety of plant 

 material, killed and dried by different methods, has been studied. Highest 

 C02-absorption was obtained by killing and drying in an oven at 100°. Dif- 

 ferent species of leaves vary considerably in their absorptive capacity. This 

 is less in leaves which have been illuminated than in those not illuminated. 

 Thorough extraction with cold water removes about 30 per cent of the absorp- 

 tive material, the concentrated extract also absorbing this quantity of CO2. 

 Extraction with hot water very greatly reduces the absorptive capacity of the 

 leaf material; the concentrated hot-water extract absorbs very little CO2. 

 Extraction with hot alcohol reduces the absorptive capacity but slightly. 

 Green leaves and stems absorb considerably more CO2 than the corresponding 

 etiolated portions. The investigations are being continued on the basis of 

 analytical separation of the mineral, carbohydrate, fatty, and proteinaceous 

 materials of the leaf. 



The Reduction of Carbon Dioxide, by Arthur Locke. 



Molecular configuration is determined by an equilibrium between attrac- 

 tive (or valence) forces and forces which may be described as instability 

 tensions. Any variation in the instability tension requires a counter variation 

 in the valence forces, which further requires the redistribution of these forces 

 throughout the molecule, residual or intermolecular attractions being sac- 

 rificed to preserve stability. When the instability tensions exceed the valence 

 capacity, decomposition ensues until a new equilibrium is reached. The more 

 closely the molecule has already approached its stability limit, the less energy 

 need be added to decompose it. On the basis of the quantum hypothesis this 

 is equivalent to the statement that a lower frequency of radiant energy is 

 required. There is thus a connection between stability and color. 



Carbonic acid, being very stable, is restricted to absorption in the ultra- 

 violet. Any activation which renders it sensitive to light of lower frequencies 

 is the result of the production of an increased strain along one of the valence 

 bonds. This involves the imposition of a reducing potential upon an oxygen 

 of the carbonic acid or the substitution of that oxygen by a reducing agent. 



There is some evidence that a purely chemical reduction (6) of carbonic 

 acid is associated with the photochemical reduction which takes place in 

 plants, in somewhat the following fashion: 



R-CX°~-. . , R-CC'°'--... , R-C=o "o 



//Z) "^^ "chloro- ,:rfh+ — 1^2 -chloro- _"-y=° . ?..-chIoro- 



