Page:Insectivorous Plants, Darwin, 1899.djvu/52

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tions of certain salts, and of too great heat, whilst weaker solutions of the same salts and a more gentle heat cause movement. We shall also see in future chapters that various other fluids, some vapours, and oxygen (after the plant has been for some time excluded from its action), all induce inflection, and this likewise results from an induced galvanic

current.[1]

  1. My son Francis, guided by the observations of Dr. Burdon Sanderson on Dionaea, finds that, if two needles are inserted into the blade of a leaf of Drosera, the tentacles do not move; but that, if similar needles in connection with the secondary cell of a Du Bois induction apparatus are inserted, the tentacles curve inwards in the course of a few minutes. My son hopes soon to publish an account of his observations.