247 
The Hydrion Theory of Geotropism 
microscopic particles, but if the theory was from the first one which 
included the movement of visible cell granules an attempt to obtain 
direct evidence before putting forward the theory would seem more 
in accordance with the accepted canons of scientific procedure. The 
examination of meristematic cells with the microscope horizontal 
should soon supply proof as to whether the cell granules do, or do not, 
markedly “ cream ”; and the use of an electric field should accelerate 
their movement and also decide as to the nature of their charge. 
Until evidence of movement is available it would seem useless to 
discuss further the many difficulties which are still implicit in the 
theory. 
THE HYDRION THEORY OF GEOTROPISM 
By R. SNOW, B.A. 
The Botanical Laboratory, Oxford 
ith regard to Professor Small’s Hydrion differentiation theory 
V V of geotropic response, surely there is a difficulty in the electrical 
assumptions which has so far escaped notice. 
Let us grant for the moment that the creaming process in which 
various particles rise through the effects of gravity might lead to 
the production of potential differences. It is still not clear how any 
current would result even so. For let us consider, for simplicity, one 
cell in the root, instead of a series of cells. In this cell, we will suppose 
that there are free positively charged particles, which tend to rise 
under gravity. This they will do, then, until the forces on them due 
to gravity are balanced by the electrostatic attractions between them 
and the relatively negative remainder of the cell. At this point equi¬ 
librium will be reached, and there can be no current unless there is a 
return path for discharge. To suppose that a current will be pro¬ 
duced in the reverse direction down the cell is equivalent to supposing 
that when a Voltaic cell is set up with terminals unconnected, the 
production of positive and negative poles will cause a reverse current 
to flow from positive pole to negative in the cell ! 
Professor Small says that Bose has found in stems and roots 
currents of the required kind. Now it is true that when Bose connects 
