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Remarques sur les tropismes et plus particulierement sur le phototropism


, : Remarques sur les tropismes et plus particulierement sur le phototropism. Ann Epiphyties Et Phytogenetique 9: 253-269

The author adopts the following definition of tropism: Tropism includes the reactions, either motor or not, by which an organism takes and maintains an orientation defined by the play of some external source of stimulation. He limits his study to phototropism. It is known that in higher plants this tropism is regulated by the diffusion of auxins. The zoospores of Chlorophyceae and the plasmodia of mycetozoa are likewise endowed with phototropism. Among the protista Stentor coeruleus and Euglena viridis are sensitive to light. This movement is due to a motor reflex set off by variations of intensity of the light. The physical agent is not the only thing which intervenes. The movement depends on physiol. factors. The analysis of the phototropism of Daphnia pulex shows the importance of these internal factors. In general, the analysis of the behavior of this crustacean is above all a psychological study. Each individual obeys a rigorous determinism. These psychological ideas alone make it possible to consider the reactions of living beings as being subject to the general regulation of behavior and explain likewise the reversal of tropisms obtained by conditioning. However, special physiological conditions (fasting, sexual impulse, etc.) may also reverse tropisms. Tropic behavior results from complex neuro-humeral physiological mechanisms which intervene between the excitation and the reaction, and are always coordinated.

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