ABSORPTION OF OXYGEN BY ROOTS WHEN THE SHOOT IS IN DARKNESS OR IN LIGHT

Abstract

Experiments were carried out on Salix laevigata and Helianthus annuus to determine whether the rate of oxygen absorption by the roots, when in distilled water for short periods, might be modified by changing lighting conditions of the shoot, particularly when the latter is exposed to sunlight, or to shade. The Thompson-Miller apparatus for the micro-determination of dissolved oxygen was used. Temp. control was affected by running tap water. In general the results showed that less O was removed from the water in unit time while the shoot was in direct sunlight than when it was in dense shade. This was found to be true in 69%, or more, of the tests. Preliminary studies on the exceptions indicate that such features as high temp., or possibly a high rate of transpiration, may be operative in producing negative results. The decrease in the rate of the absorption of oxygen by the roots, coinciding with the periods of insolation, seems to point to the utilization of photosynthetic 0 to a certain extent, at least during the period of insolation of the shoot. O of this origin is referred to, for convenience, as "internal" O. Possible ecological application of the results is suggested.