The Effect of Air Supply on Apparent Photosynthesis.

It has beeni recogniized for a lolng tiiiie that the rate of absorption of CO2 by a greein plant shoot or leaf enclosed in a vessel is affected by the rate at whieh air is supplied. Much attention has been given to the problem of miaintaining a "normal" air supply; that is, a CO2 supply comiiparable to that foundl under natural conditions. The early literature was reviewed and discussed by HEINICKE and HOFFMAN (5), who presented results showing that the rate of photosynthesis was below normal when the air supply was less than approximately two liters per hour per square centimeter of leaf area. VERDUIN and LOOMIS (9) presented results from which they concluded that photosynthesis of corn leaves "was affected surprisingly little" by 70%o depletion of the CO2 within the leaf chambers. BROWN and ESCOMBE (1) presented results which they interpreted as inidicating an approximate proportionality between the rate of apparent photosynthesis and the mean CO2 concentration. They pointed out that "in all cases where the illumination of the leaf was good, although the amouint of intake of CO2 into the leaf was approximately proportional to the increased partial pressure, the photosynthetic work was always somewhat in excess of what might be expected from the increased amount of CO2. " They were obviously expecting strict proportionality and had overlooked some of the following facts. Proportionality implies a linear relationship. General linear relationship is described by the equation y = a + bx; but strict proportionality exists only when a = 0 and y = bx. Apparent photosynthesis becomes zero at a measurable CO2 concenitration (the compenisation point) therefore a #' 0, and strict proportionality cannot exist. The data of BROWN and ESCOMBE actually contain very little information concerning the real relationship between photosynthesis and CO2 coneenitratioin. They made only two observations on each planit, one at high CO2 concentration and one at low coiieenitratioii. Thuts only two poinits were established for each plant, and a liniear ftunetion can be derived from any two points whether established experimentally or selected at random. Further, a variety of functionis other thanl linear canl be fitted to alny two poinits, for example, y = axn, y = a+ I/x. Data presented by DENEKE (4) indicated that the rate of photosynthesis increased with the velocitv of air over the leaves and apparently approached a maximum limit at an air velocity of approximately 100 meters per miinute. He circulated air over a plant in a closed system and nieasured the timiie required for a certaini reductioni of CO2 content. One set of data, his figure 8, is reproduced here as figure 1. This and similar curves suggested to 561