350 



Mr. J. Small. Changes of Electrical 



logarithmic in the centre and shows divergences at the extremities, the 

 ordinates being tlie ratios of the times of exposure at 90° to the times at 

 other angles to the vertical, and the abseissse being the angles with the' 

 vertical. In this way we get the strength of the reaction, which -varies 

 directly as the time of exposure, plotted against the strength of the stimulus, 

 which varies directly as the angle with the vertical. The resulting graph is 

 the typical sigmoid curve obtained by "Waller (9) for the response by animals 

 to various stimuli. This more or less logarithmic relation is also proved by 

 the fifty-eight experiments on the perception of minimal angle differences by 

 the epicotyls of Viria Faba and Pliaseolus multifiorus and by the hypocotyls 

 of Heliantlms annuns, which Fitting (3, Teil I, pp. 306-310) has published 

 (fig. 2). 



I0-' 



9- 

 8- 

 7- 

 6- 



X = CURVATURE 



o = NO curvature: 



X X 



"io 30 40 50 60 to" 

 ANGLE WITH VERTICAL 

 Fig. 2. 



60 



From these published results of other investigators the hypothesis was 

 formed that the proximate mechanism of geotropic response in plants is a 

 change in the permeability of the protoplasm in the cells of the perceptive 

 region. Such changes involve changes in the electrical resistance of the 

 tissue [ep. McClendon(5) and Osterhout (6&)J. 



