54 
James Small. 
Explanation of the Upward Curvature of the Stem. 
According to hypothesis 6 the protein-lipoid particles of the 
disperse phase of the plasma membranes in the perceptive region 
of the stem apex are electronegative (instead of electropositive as 
in the root) because the continuous phase of the plasma membranes 
in that region is of an acidity less than that of the proteins 
concerned. The medium or continuous phase is not necessarily or 
even probably alkaline, but it is supposed to be on the basic side of 
the isoelectric point of the proteins and is probably slightly acid. 1 
In the perceptive region of the vertical stem there is the same 
creaming effect as in the root, giving a symmetrical distribution of 
polarised areas as in the vertical root, but the polarisation of the 
. upper and lower surfaces of the cells is arranged in the opposite 
way to that in the root. The upper ends instead of being of a 
Fig. 2. Diagram of stem-apex. 
higher electropositive potential than the lower ends of the cells are 
of a higher electronegative potential. This gives an arrangement 
of potential differences which are symmetrical about the axis of the 
vertical stem, and may at the same time account for some of the 
polarity of growth shown by the rootless, subaerial cryptogams. 
When the stem is placed horizontally these potential differences 
again cease to be symmetrically arranged about the axis. The 
potential differences produce an EMF which gives a current from 
the under to the upper side of the perceptive region (Fig. 2); the 
direction of the current in the stem is the reverse of that in the 
root. Resistance is present in the stem as in the root, therefore 
the greatest effect will be produced in the upper side. The 
effect of the current on the cells of the motor region will again be 
an increase in the permeability, which will be greatest in the upper 
1 The H-ion concentration of plant cells as shown by Haas (8) varies in 
the cases he investigated from PH 3 to PH 8 (PH 7 being the true neutral point), 
while the PH of proteins as given by McClendon (12, p. 77) varies from 3-52 
to 9-3, the majority and especially the plant proteins varying only from PH 4 
to PH 5 5. The H-ion concentration of at least some plant proteins is there¬ 
fore such that the variation actually found in the acidity of plant cells would 
be sufficient to produce electropositive and electronegative protein particles. 
