Hydrion Differentiation Theory of Geotrofiism. 211 
the electrical conditions to those which occur when a large bar 
magnet is placed horizontally near the opposite pole of a small 
erect cylindrical magnet. Then the lines of force can be demon¬ 
strated as arranged in Figure 1, with a small neutral area on the 
side of the “axis” magnet opposite or nearly opposite the bar 
magnet which takes the place of the lateral organ. It has been 
suggested that the polarisation of growth in the stem is due to the 
normal polarity current; the cells in that neutral area would, 
therefore, be freed from this polarising influence, and would grow 
out in all directions in the fundamental spherical form, giving the 
more or less hemispherical primordium of a leaf. The shape and 
size of the leaf primordium would depend upon the relative 
strengths of the two electric fields. 
Fig. 1. Combined 
electric field of a large 
bar magnet and a small 
cylindrical magnet as 
shown by iron filings 
Fig. 2. Combined 
electric field of one 
large bar and one 
smaller bar and one 
small cylindrical 
magnet. 
Fig. 3. Combined electric 
field of two equally large bar 
magnets and one small cylin¬ 
drical magnet. 
When the primordium has developed, an apical meristem is 
differentiated, with consequent loss of neutrality and acquirement of 
polarity, and a third electric field is developed (Fig. 2). The first 
leaf may be taken as the cotyledon, the second as a foliage leaf. 
The position of the third leaf or fourth electric field would then 
depend upon the rate at which growth caused the removal of the 
meristems of the first and second leaves away from that of the 
stem apex. Any slight inequalities of growth would result in 
tangential displacement, as in Fig. 2, and one primordium, not two 
primordia would be the result. Since these movements are part 
of a “ continuous energy expansion system ” (see 7, Chap. XX), the 
