Growth and tropic movements of plants / by Sir Jagadis Chunder Bose.

  • Jagadish Chandra Bose
Date:
1929
Catalogue details

Licence: In copyright

Credit: Growth and tropic movements of plants / by Sir Jagadis Chunder Bose. Source: Wellcome Collection.

    169/488 (page 133)
    DIA-PHOTOTROPISM AND NEGATIVE PHOTOTROPISM I have explained how under the unilateral action of light the positive curvature attains a maximum. There are, however, cases 'where under the continued action of strong light the tropic movement undergoes a reversal. Thus to quote Jost : ‘ Each organ may be found in one of the three different conditions determined by the light intensity, viz. (i) a condition of positive heliotropism, (2) a condition of indifference, (3) a condition of negative heliotropism.’ 1 No satisfactory explanation has, however, been found as to why the same organ should exhibit at different times a positive, a neutral, and a negative response. The exhibition of these different effects by an identical organ is incom- patible with the theory of specific sensibility, often assumed in explanation of characteristic differences of phototropic response. Oltmanns found that the seedling of Lepidium sativum assumed a dia-phototropic position under intense and long- continued action of light of 600,000 Hefner lamps. He regards this as the indifferent position. But the neutralisa- tion of curvature is, as will be presently explained, not due to a condition of indifference, but to antagonistic effects induced at the two opposite sides of the organ. Phenomenon of Neutralisation Neutralisation, partial or complete, is principally due to the transverse conduction of excitation across the stem.