NOTE 
GEOTROPISM AND THE WEBER-FECHNER LAW.— Some recent 
experiments having demonstrated the truth of a statement made by the writer at the 
Newcastle meeting of Section K of the British Association that the perception of 
gravity in plants was purely a protoplasmic phenomenon and as such conformed to 
the Weber-Fechner Law, it has been considered advisable to make a preliminary 
statement of the work. All details with a description of the apparatus used will be 
published shortly. 
The main points are these : 
1. In 1905 Fitting 1 suggested that the Weber-Fechner Law might explain the 
results he obtained in an investigation with the oblique intermittent klinostat of the 
minimal angle-differences perceived by the epicotyl of various plants at varying angles 
to the vertical. He did not, however, develop the suggestion. 
2. In 1906 Darwin 2 repeated the suggestion with reference to Fitting’s 
observations on the differences in the presentation times required at varying angles to 
the vertical, but he did not develop the suggestion. 
3. As the Weber-Fechner Law holds good within certain limits for the percep- 
tion by animals of most stimuli, such as weight, light, sound, &c., and as protoplasm 
is the only substance common to the various organs involved in the perception, it 
occurred to the writer that the perception of gravity by plants involved only a proto- 
plasmic change. Changes in permeability seemed the most probable mechanism, and 
such changes involve changes in the electrical resistance of the tissue. 
4. Waller 3 has pointed out certain divergences from the logarithmic curve of 
the Weber-Fechner Law which convert that curve into an f or sigmoid curve. 
5. The writer has examined Fitting’s observations on the difference in presenta- 
tion time required at varying angles and finds that the results give a sigmoid curve. 
6. The writer has also examined Fitting’s observations on the minimal angle- 
differences perceived at varying angles to the vertical and finds that, on the hypothesis 
that 3*6 per cent, is the minimal angle-difference perceived by the plant, forty-eight of 
the fifty-eight experiments recorded by Fitting give a correct result, and of the ten 
results not in accordance with this hypothesis two are almost correct and six were 
repeated by Fitting and the results of the repeated experiments are in accordance. 
According to Weber the minimal difference in weights which is perceived by man is 
3*3 per cent. 
7. The writer has investigated, by measuring the changes in electrical resis- 
tance of the second millimetre of one side of the root-tip, the changes in permeability 
1 Fitting, H., Jahrbiich. f. wiss. Botanik, Bd. xli, 1905. 
2 Darwin, F., New Phytologist, 1906. 3 Waller, A. D., Brain, 1895. 
{Annals of Botany, Vol. XXXI. No. CXXII. April, 1917.I 
