Rate of oxygen evolution in photosynthesis was measured as the current from a polarized platinum electrode covered by a thin layer of Chlorella . The arrangement gave a reproducibly measurable rate of photosynthesis proportional to light intensity at the low levels used and gave rapid response to changes in illumination. Two phenomena have been explored. The Emerson effect was observed as an enhancement of photosynthesis in long wavelength red light (700 mµ) when shorter wavelengths were added. Two light beams of wavelengths 653 and 700 mµ when presented together gave a photosynthetic rate about 25 per cent higher than the sum of the rates obtained separately. Large and reproducible transients in rate of oxygen evolution were observed accompanying change in illumination between two wavelengths adjusted in intensity to support equal steady rates of photosynthesis. The transients were found not to be specifically related to long wavelength red light. Both enhancement and the transients have identical action spectra which are interpreted as demonstrating a specific photochemical participation of chlorophyll b .

1. The fluorescence spectra of the alga Porphyridium have been recorded as energy distribution curves for eleven different incident wave lengths of monochromatic incident light between wave lengths 405 and 546 mµ. 2. In these spectra chlorophyll fluorescence predominates when the incident light is in the blue part of the spectrum which is strongly absorbed by chlorophyll. 3. For blue-green and green light the spectrum excited in Porphyridium contains in addition to chlorophyll fluorescence, the fluorescence bands characteristic of phycoerythrin and of phycocyanin. 4. From these spectra the approximate curves for the fluorescence of the individual pigments phycoerythrin, phycocyanin, and chlorophyll in the living material have been derived and the relative intensity of each of them has been obtained for each of the eleven incident wave lengths. 5. The effectiveness spectrum for the excitation of the fluorescence of these three pigments in vivo has been plotted. 6. From comparisons of the effectiveness spectrum for the excitation of each of these pigments it appears that both phycocyanin and chlorophyll receive energy from light which is absorbed by phycoerythrin. 7. It is suggested that phycocyanin may be an intermediate in the resonance transfer of energy from phycoerythrin to chlorophyll. 8. Since phycoerythrin and phycocyanin transfer energy to chlorophyll, it appears probable that chlorophyll plays a specific chemical role in photosynthesis in addition to acting as a light absorber.

1. The quantum yield of oxygen liberation by spinach and Tradescantia chloroplasts suspended in solutions containing ferric oxalate and potassium ferricyanide varied from 0.013 to 0.080. 2. It was concluded that the nature of this oxygen liberation reaction is not fundamentally different from the formation of oxygen in normal photosynthesis, with respect to its light efficiency.

1. Photoxidation in leaves is measured by exposing them to light in an atmosphere free from carbon dioxide but containing varied percentages of oxygen. 2. Photoxidation is observed in living leaves as well as in dead ones and in plant juices. Its rate is only slightly enhanced by feeding the leaves with sugar, but the respiration (autoxidation) becomes considerably enlarged during the exposure and the following dark period. 3. The rate of photoxidation rises slower than linearly with light intensity; its dependence upon oxygen pressure has the character of a saturation curve. Oxygen saturation occurs at about 6/10 of an atmosphere of oxygen. A similar dependence on oxygen pressure has been observed by Gaffron for photoxidation in vitro sensitized by chlorophyll adsorbed on proteins and by Warburg for the depression of the saturation rate of photosynthesis. 4. The influence of photoxidation on photosynthesis and the chemical kinetics of photoxidation are discussed.

1. Photosynthetic bacteria in water suspension break open when treated with supersonic vibration thus liberating the cell contents, including a water soluble protein to which is attached the otherwise water insoluble pigments, bacteriochlorophyll and carotinoids. Both types of pigments appear to be combined with the same protein. 2. The protein pigment compound is insoluble in the region of pH 3.0 to 4.5 and in neutral solution can be completely precipitated by 0.5 saturated (NH 4 ) 2 SO 4 . It is soluble in distilled water and adsorbable on fullers' earth. 3. Supersonic extracts of photosynthetic bacteria do not have the ability to carry on photosynthesis, but will act as a photocatalyst for the oxidation of ascorbic acid with visible or infrared radiation. The rate of the photochemical oxidation is proportional to the light intensity.

Absorption curves have been obtained in the spectral region of 450 to 900 mµ for the water soluble cell juice of four species of photosynthetic bacteria, Spirillum rubrum (strain S1), Rhodovibrio sp . (strain Gaffron), Phaeomonas sp . (strain Delft), and Streptococcus varians (strains C11 and orig.). These curves all show maxima at 790 and 590 mµ due to bacteriochlorophyll, whose highest band, however, occurs at 875, 855, or 840 mµ depending on the species. The bacteria that appear red rather than brown have a band at 550 mµ due to a carotinoid pigment. An absolute absorption curve of bacteriophaeophytin has maxima at 530 and 750 mµ. The extraction of cell juice by supersonic vibration does not change the position of the absorption bands or of the light absorbing capacity of the pigment.

1. The relative absorption spectrum of the pigments in their natural state in the photosynthetic bacterium Spirillum rubrum is given from 400 to 900 mµ. The position of the absorption maxima in the live bacteria due to each of the pigments is: green pigment, 420, 590, 880; red pigment, 490, 510, 550. 2. The relative absorption spectrum of the green pigment in methyl alcohol has been determined from 400 to 900 mµ. Bands at 410, 605, and 770 mµ were found. 3. The wave length sensitivity curve of the photosynthetic mechanism has been determined and shows maxima at 590 and about 900 mµ. 4. It is concluded that the green bacteriochlorophyll alone and not the red pigment can act as a light absorber for photochemical CO 2 reduction.

1. The effect of H 2 tension, CO 2 tension, pH, time, light intensity, density of suspension, salt content of the medium, and certain spectral regions on the rate of photoassimilation of H 2 and CO 2 by Streptococcus varians has been studied. 2. The method of making light absorption measurements with thin suspensions of bacteria is described. 3. A light source, optical system, and filter for isolating 852 mµ with 894 mµ in sufficient intensity for photochemical work and an improved design of thermostat are given. 4. The photoassimilation of 2H 2 with 1CO 2 apparently involves little over all energy change but nevertheless requires 4 quanta.

The respiration of the green alga Chlorella pyrenoidosa , suspended in Knop's solution, has been studied in the dark as a function of time and of temperature. The rates of oxygen consumption and of carbon dioxide production (at constant temperature) decline for about 25 hours to a low, constant level. From an analysis of the curves it is suggested that two substances, A and B , are utilized, whose respiratory quotients are 1 and 0.65 respectively. The values of the temperature characteristics were found to be: for oxidation of A , 19,500 (0.6 to 11.5°C.) and 3,500 (11.5 to 28°C.); for oxidation of B , 5,600 (23.4 to 0.6°C.).

The decomposition of hydrogen peroxide by intact Chlorella cells follows a first order course at very low temperatures, but at higher temperatures gives falling first order constants. Between 0.6° and 20°C. the value of µ is 10,500 calories.

The temperature characteristic for the rate of O 2 consumption by Chlorella pyrenoidosa suspended in Knop solution containing 1 per cent glucose was studied between 1° and 27°C. with the Warburg technic. The value of µ was found to be about 19,000 ±1,000 cal. There is some indication of a critical temperature at 20°C., with shift to a lower µ above this temperature. The effect of sudden changes in temperature on the rate of respiration and the variation of the latter with time at constant temperatures are discussed. It is concluded that the "normal" respiration (in absence of external glucose) does not appear in the determination of this temperature characteristic.