Societies and Academies

    Abstract

    LONDON. Royal Society, March 4.—Sir J. J. Thomson, president, in the chair.—Dr. F. F. Blackmail: The protoplasmic factor in photo-synthesis. The centre of interest in problems of the photo-reduction of CO2 in green photo-synthesising cells is shifting from the chlorophyll to the protoplasm. The quantitative control of photo-synthesis in the normal green eeli is determined protoplasmically. This is illustrated by the temperature relations, which are not those, of a photo-chemical reaction, but of a dark reaction. The photo-synthetic activities of leaves of different varieties (green υ golden leaves) and at different stages of development show no relation to the amount of chlorophyll that they contain, as is brought out by the “assimilation numbers“ of Willstätter. The relation between chlorophyll development and photo-synthesis development, described in the next communication, furnishes another instance of the dominance of factors other than the pigment. In many lower organisms we find the power of reducing CO2 to forni organic matter by chemical energy in the absence of pigment or light. This chemo-synthesis may be the sole or only an alternative source of the carbon for the living cell. The process involves, of course, no cosmic gain of energy. In these cases the efficiency of energy transference from the oxidation of various substances to the reduction of CO2 seems to be as great as or greater than in the utilisation of light energy for photo-reduction of CO2.—G. E, Briggs: The beginning of photo-synthesis in the green leaf. In young leaves development of the power of photosynthesis is found to lag behind development of chlorophyll, so that a green leaf when young may exhibit very slight or zero photo-synthetic power. This means that photo-synthedc activity demands development of some other internal factor than chlorophyll. The potentiality of this other factor rapidly increases with age day by day, even when the leaf is kept in darkness continuously. By keeping a leaf in a very low partial pressure of oxygen, further development of chlorophyll can be completely arrested, even in continuous light. Here also, starting with a leaf of feeble green tint, there is similar day-by-day increase in photo-synthetic power, in spite of there being no further greening. Experiments were carried out by means of a new apparatus designed by Dr. F. F. Blackman for measuring a small output of oxygen in photo-synthesis. The leaf is illuminated in a closed circuit in an atmosphere of hydrogen and carbon dioxide. In part of the circuit gases are carried over palladium black, so that oxygen produced unites with two volumes of hydrogen. The threefold reduction of volume resulting is measured by a gas burette in the circuit. In this apparatus oxygen pressure is kept so low that no further development of chlorophyll takes place, while photo-synthetic production of oxygen can be measured with great accuracy. If a leaf is cut from a seedling growing in the dark at an early stage of development, and then partially greened by exposure to light in air, its photo-synthetic activity when transferred to the apparatus will be very small or nothing. If exactly the same procedure is repeated a few days later, the photo-synthetic activity may be nearly as great as in the normallv developed leaf.—Dr. B. Moore, E. Whitley, and T. A. Webster: Sunlight and the life of the sea. [Studies of the photo-synthesis in marine algæ, (1) Fixation of carbon and nitrogen from inorganic sources in sea-water; (2) increase of alkalinity of sea-water as a result of photo-synthesis and as a measure of that process; and (3) relative photo-synthetic activity of green, brown, and red seaweeds in light of varying intensity.] The vernal outburst of green life which occurs at the spring equinox is occasioned by the rapid change in intensity of daily illumination. A study of the seasonal variations in plankton around Port Erin, Isle of Man, has now been carried on for many years by Prof. W. A. Herdman and his co-workers. In many years the great outburst of diatoms Occurs before the temperature of the water has even begun to move from its winter level. It thus becomes clear that it is the longer, brighter day, with increased altitude of the sun, which is the primary factor in the sudden dawn of the life of the sea each spring. This is illustrated by a chart upon which are shown for each month (1) temperature of the sea, (2) number of diatoms, (3) hours of bright sunshine, (4) total radiant energy, and (5) the amounts of nitrogen peroxide present in the air (formerly called “ozone of the air” or “active oxygen”), as taken at Radcliffe Observatory, Oxford, by Schönbein's “Ozone“ papers. A sudden rise in radiant energy in March is accompanied by (1) the diatomic outburst and (2) increased nitrite content. It has been shown that the growing diatoms capture this enormous increase of light, and utilise it for building both carbon and nitrogen into their organic substances. The source of the nitrogen is the atmospheric elemental nitrogen dissolved in the sea-water, and not ammonia, nitrites, or nitrates. The source of the carbon is the carbon dioxide of the bicarbonates of calcium and magnesium dissolved in sea-water. As this carbon is removed in photo-synthesis the sea becomes always more alkaline, and the change of reaction can be used as a rough measure of the marine crop. Although the increase of alkalinity is small, yet the volume of sea-water is so immense that, as has been pointed out by Moore, Prideaux, and George Herdman, supposing this to happen to a depth of 100 metres over the surface of the sea, then the crop of moist plankton per square kilometre would amount to about 1,500,000 kilograms. This corresponds roughly to about 10 tons per acre.

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    Societies and Academies. Nature 105, 89–91 (1920). https://doi.org/10.1038/105089b0

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