52 
James Small. 
in each cell but the lower side of the cell becomes differentiated 
from the upper side. The change is visualised as the “creaming” 
of the suspensoid protoplasm 1 ; the electrically charged particles 
are supposed to ascend and thus decrease the polarisation of the 
lower side of the cell, while increasing the polarisation of the upper 
side of the cell to an equal and opposite extent. 
Fig. 1. Diagram of root-apex. 
The more highly polarised surfaces are the upper ends of the 
cells while the lateral surfaces are increasingly polarised from 
bottom to top. Reduction in polarisation involves increase in 
permeability and decrease in turgor, and since these are relative 
terms, increase in polarisation involves decrease in permeability 
and increase in turgor. 
In the erect position the asymmetric polarisation of the cells 
has no apparent effect because these regions of different 
polarisation are symmetrically arranged around the axis of the root. 
Any electric current developed as the result of the potential 
differences between upper and lower surfaces of the cells must 
likewise flow symmetrically, either down the centre and up the 
cortex or up the centre and down the cortex. The longitudinal 
growth of the root might be explained in this way. 
In the horizontal position the asymmetric polarisation of the 
cells is arranged as in the diagram (Fig. 1). Even single cells are 
now recognised to be concentration cells with a definite though 
small electromotive force. This EMF in the normal resting 
condition is considered to be developed between the negatively 
charged outer layer and the inside of the cell which has a lower 
potential. In the root the outer layer was supposed to differ from 
the normal case in being electropositive instead of electronegative 
1 This “creaming” is dealt with very fully for particles of greater density 
the medium by Perrin (15). The laws governing the creaming of particles of 
lesser density than the medium are the same. The perceptive region and 
motor region differ in^the height available for the creaming which is governed 
by Stoke’s Law. 
