50 
James Small. 
Preliminary Theories. 
In an endeavour to find an explanation of the difference in the 
increase of electrical conductivity shown by the upper and under 
sides of a horizontally placed root (18-19), certain hypotheses were 
used. These included as a corollary a preliminary explanation of 
the difference in the geotropic response of stem and the root. 
Hypotheses. 
1. The increase in electrical conductivity is due to increased 
permeability of the protoplasm to ions. This hypothesis is 
supported by the work of McClendon, Osterhout, Stewart and 
Waller (see 12, pp. 103, 122), and particularly by that of Clowes 
(2-3). In spite’of the criticism by Stiles (22) of the “ assumption ” 
that conductivity is a measure of permeability, this “ assumption ” 
is very widely used and very strongly supported by experimental 
evidence. The work of Hober and others makes^it seem probable 
that “ the chief impermeable layer of all cells is the plasma 
membrane” (12, p. 92). Lillie (11) also states that it has been 
found that the process of stimulation is always accompanied by an 
increase in permeability and probably is often dependent upon it. 
2. The increased permeability was assumed to give decreased 
turgor. 
3. The protoplasmic layer governing the permeability was 
assumed to contain rapidly moving (i.e., exhibiting the Brownian 
movement, cp. Price, 16, p. 602-3) colloidal particles of a protein 
nature. This layer is probably of a suspensoid structure at 
least partly denatured) rather than of a purely emulsoid character. 
The protoplasm was conceived to be an'emulsion of protein or 
protein-lipoid particles in a colloidal protein medium. It has been 
shown by Pischer (4) and confirmed by Roon and Oesper (17) that 
a hydrated colloid is an essential part of an emulsion. It has also 
been shown by Fischer (4) that, while neutral casein is not a good 
emulsifyingagent, alkaline or acid casein emulsify equally well, either 
becoming the hydrophilic colloid necessary as a dispersing agent. 
The permeability was considered to depend on adsorption of 
the ions and salts by the active particles and not to be a chemical 
phenomenon as suggested by Stiles (21) nor a more or less static 
phenomenon as suggested by Fischer [(5-6), and cp. Henderson (10)] 
and Free (7) and Tolrnan (23) 1 . It was considered to be kinetic 
and dynamic. 
1 The views of the last author on the influence of the H-ion concentration and 
amphoteric colloids are very similar to those outlined below. The differences 
are those between a spongy structure which would not be affected by gravity, 
and an emulsion which creams under the influence of gravity and centrifugal 
force. The latter is the structure observed by Price (16). 
