158 PHYSIOLOGY [BoT. Absts., Vol. IX, 



activity and led to the conclusion that in this process there are 2 variable factors: 

 (a) the green pigment, and (b) a factor associated with the protoplasmic activity. 

 The temperature coefficient depends upon the nature of the leaf and is probably variable for 

 different species. Leaves poor in chlorophyll are more dependent upon variations in the light 

 intensity while those rich in chlorophyll show greater variations with temperature. — III. 

 The absorption of carbon dioxide by the unilluminated leaf. Leaves absorb CO 2 from a 10 per 

 cent gas mixture. The absorption is independent of the pigment content. The leaf sub- 

 stance absorbs more CO2 than the water in the leaf. The difference between the absorption 

 by water and by the leaf substance is greater with decreasing partial pressure of CO2. Leaves 

 which have been killed and dried and then moistened again absorb CO2 as do living leaves. 

 The old statement that lecithin absorbs large quantities of CO2 was found to be entirely 

 erroneous. — IV. The behavior of chlorophyll toward carbon dioxide. Chlorophyll in organic 

 solvents does not react with CO2, but in colloidal aqueous solutions reaction takes place. 

 CO2 is absorbed and given off again when the partial pressure of the CO2 is reduced. It is 

 suggested that there is formed a combination of chlorophyll with performic acid or formalde- 

 hydperoxide which then splits off O2. The absorption spectra of colloidal solutions of chloro- 

 phyll and of leaves are very similar. At 0°C. the addition of CO2 to chlorophyll is most effec- 

 tive and decomposition into phaeophytin and MgCOs is lower. The aqueous colloidal solu- 

 tions were allowed to absorb CO2 and the amounts thus absorbed were determined by (a) 

 passing C02-free air through the solution and determining the CO2 liberated, (b) taking up 

 in ether and determining the Mg content, (c) adding alcohol to make an 80 per cent solution 

 and drawing off the gas. Each method shows that the CO2 produces a certain amount of 

 decomposition of chlorophyll. The decomposition of aqueous colloidal chlorophyll solutions 

 can be greatly diminished by the addition of MgCOs, and to a lesser degree by the addition 

 of CaCOs. These substances as well as gelatin also decrease the rate of addition of COj 

 to chlorophyll. Glycocoll, glucose, and starch exhibit no protective action. — V. The 

 constant photo synthetic coefficient during augmented photosynthesis. The value of the 



CO 

 photosynthetic coefficient, -pr-, for oxalic acid as the first reduction product = 4; for formic 



O2 



acid = 2; for glycollic acid = 1.33 for formaldehyde = 1. The difficulty of separating pho- 

 tosynthetic from respiratory activity has made accurate determination of the photosynthetic 

 coefficient impossible. By sufficiently increasing photosynthetic activity, with high CO2 

 content of air (5 per cent) and intense illumination, the inaccuracies incident to determining 

 the respiratory activity become negligible in the determination of the photosynthetic coeffi- 

 cient. In experiments lasting 1-6 hours at 10-35°C. the coefficient was found to equal 1 con- 

 stantly. In succulents, Opuntia, the coefficient equals 0.44 at first and after continued illu- 

 mination reaches 0.85. — VI. The dependence of photosynthesis upon small quantities of oxygen. 

 Removal of O2 from the atmosphere greatly influences photosynthetic activity. Some species 

 (Pelargonium zonale) lose the power to fix CO2 when kept in an atmosphere of about 0.01 

 per cent O2 and do not regain it in the presence of O2. Other species, for example. Cyclamen 

 beropalum, show slight photosynthesis in such an atmosphere, the rate increasing slowly with 

 continued exposure. The longer the exposure to an 02-free atmosphere, the lower is the photo- 

 synthesis and the more incomplete is the recovery of the leaf. — VII. Investigations on the 

 intermediate steps in photosynthesis. This is a critical discussion of the experiments of others 

 on the formation of CH2O in the leaf and with chlorophyll preparations. Schryver's 

 experiments were repeated with pure preparations of chlorophyll and no CH2O was found. 

 Colloidal chlorophyll solutions do not take up CH2O. The experiments of Usher and Priest- 

 ly and of Chodat and Schweitzer were repeated with pure colloidal chlorophyll preparations 

 and with and without catalase; CH2O was never found. Chlorophyll is relatively stable 

 towards O2 in the light; the first steps in photooxidation do not yield aldehydes nor lower 

 peroxides. These latter substances found by other workers are products of the photooxida- 

 tion of impurities accompanying the chlorophyll. — H. A. Spoehr. 



