International Review of Educational Cinematography (Jan-Dec 1931)

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— 819 — The film of a functioning clinosiat, may be shown, as a proof that the geotropic causes are provoked by forces of gravity. The geotropic curve of a germinating beech root should be taken according to the well known Sachs experimental method : that is to say, six equidistant lines (from 0-5), starting from the apex, will be drawn in china ink. The root will lie on a horizontal surface, with its top barely visible, parallel with the apex o : within 24. hours the growth of the root will have determined the geotropic curve, dispacing the equidistant lines, the slope of which will indicate which part of the root has the greatest powers of growth in length. The film on geotropism may be further developed if projected in a laboratory for physiological research on tropism, with the collaboration of a physiologist. Heliotropism and Phototropism. An exact idea of positive and negative phototropism may be given by pictures of phototropic movements of the atmospheric and root sections of a plant of Sinoepis alba, recently germinated and placed, with the roots, in a graduated glass vessel full of water. The dependence of the reaction of the plant on the luminous stimulus of the quantity and intensity of the light may be shown by comparative experiments with germinating oat plants, the coleoptilis of which have great phototrophic sensitivity, and by exposing them for some time to a luminous ray, the intensity of which can be regulated. The various activities of different radiations of the spectrum may also be shown . A demonstration of the movements of the leaves of Robinia pseudocacia, taken from the dark into the light, may also be used, to give an idea of the phototropic curve of plant organs influenced by variations of turgor, as compared with the curve deriving from a process of growth. To illustrate the theory of the unequal disposition of the organ under the unilateral stimulation of special substances determining the cellular division and consequent growth, it would be interesting to show a film reproducing the experiments of Dolk and of Went, Director of the Botanical Laboratory of the University of Utrecht. A detailed description of these experiments has been made by Went himself in the « Revue generale des Sciences pure et appliques », T. XLI, 1930, page 631. Chemotropism. The chemotropism of fungus. Repetition of some of Miyoshi's experiments with regard to the qualities of attraction and repulsion of some substances.