Geotropism and Phototropism in the absence of free oxygen

All experiments were carried out with a stimulus of definite, known intensity. In order to determine the influence of oxygen withdrawal, no complete or partial vacuum was used, but the air was always replaced by nitrogen by means of gradual diffusion. Thus the seedlings always remained under a pressure of one atmosphere. When seedlings, which have been long enough removed from the influence of oxygen, are stimulated geotropically or phototropically, likewise in the absence of oxygen and are then at once placed in atmospheric air, they are unable to execute a reaction. If the seedlings are given a similar fore-period in an oxygen-free atmosphere, but if the stimulus is administered in air, in which the plants are also left subsequently, a reaction does occur. In an oxygen-free environment the perception of a stimulus cannot therefore take place, provided that the condition of a sufficiently long fore-period has been satisfied. If, after perception of a geotropic or phototropic stimulus, the seedlings are left in the oxygen-free atmosphere, they do not react, so that the presence of oxygen is also necessary for the occurrence of the reaction. In an atmosphere with low oxygen-content the seedlings remain for a long time able to perceive normally, but a prolonged stay in such an atmosphere weakens the power of perception. There are no indications that, on complete or partial withdrawal of oxygen, the reaction of seedlings to a geotropic stimulus differs from their reaction to a phototropic one.