Note . 
3H 
produced in the root of Vicia Faba on exposure to varying angles, and finds that the 
permeability increases with the angle to the vertical according to the Weber-Fechner 
Law, showing the same divergences as found by Waller for the physico-chemical 
changes in retina, muscle, and nerve in response to various stimuli. 
8. The permeability of the cortical cells of both upper and under sides of the 
root-tip increases, but that of the under side does so to a greater extent. The conse- 
quent relatively greater turgidity of the cells of the upper side explains the curvature. 
The increased permeability, giving decreased turgor, on both sides of the root explains 
the retardation of elongation of the axis shown by Sachs 1 to take place during 
curvature. 
9. If statoliths or other bodies acted at all their effect would be dependent on 
four factors : 
a. The size of the grains. 
b. The number of grains. 
c. The angle of the plant. 
d. The viscosity of the medium. 
Alone, these four factors could never give a resultant which would conform to the 
Weber-Fechner Law, and if they acted in conjunction with the changes in permeability 
their effect would be to distort the sigmoid curve considerably. Statoliths are present 
in considerable numbers in the root-tip of Vicia Faba , but the curve is always what 
would be expected if the excitation due to gravity were a purely protoplasmic 
phenomenon. 
10. The negative geotropism of the shoot is explained by the obvious fact that if 
the protoplasm has the property of producing ‘stem’ cells it is different from that 
which produces ‘ root ’ cells, and another of its properties is to react to gravity by 
changes in permeability which are the reverse of those which take place in the root. 
JAMES SMALL. 
Bedford College, 
December 28 , 1916 . 
1 Sachs, J. v., Physiology of Plants (Eng. trans.), 1887. 
