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THE THEORY OF GEOTROPIC RESPONSE 
By V. H. BLACKMAN 
I have read with some surprise Prof. Small’s reply in this Journal 
(20, pp. 73-81, 1921) to my criticism of his theory of geopercep¬ 
tion. I understood that the cell particles which “creamed” were the 
ultramicroscopic disperse phase of the protein sol of the protoplasm, 
a view which I find was taken generally by botanists. Prof. Small 
now tells us that we are all mistaken in our interpretation and that 
the theory applies to the much larger visible particles of the granular 
protoplasm. The basis of this misunderstanding appears to be the 
author’s somewhat peculiar application of the term “disperse phase.” 
On his assumption protoplasm consists of an “emulsion of protein 
or protein-lipoid particles in a colloidal protein medium.” The system 
postulated has thus two disperse phases; the author, however, applies 
the term “disperse phase” solely to the particles, and neglects altogether 
the disperse phase of the protein sol, to which on the ordinary col¬ 
loidal theory the special properties of protoplasm are due. It is, 
therefore, not surprising that confusion has occurred, especially as 
references to iso-electric points naturally lead one to believe that 
protein sols are being considered. His scientific colleagues can, I 
think, with some justice complain of the vagueness of outline and the 
lack of detail in the picture which Prof. Small presented to them. 
Apart from the difficulty of interpretation just mentioned, such im¬ 
portant points as the size of the particles which were to react, the 
rate at which they were to move, and the extent to which redistribu¬ 
tion would take place, were all left quite untouched although they 
were fundamental to the theory. 
The theory has now assumed such a different complexion that 
it would seem unnecessary to refer to Prof. Small’s misunderstanding 
of some of my criticisms. What is now required is direct evidence of 
“creaming 1 .” There might be some excuse for the publication with¬ 
out such evidence of a theory based on the movement of ultra- 
1 The rate of movement of the large particles cannot be deduced directly 
from Stokes’s well-known equation for, ex hypothesi, the particles are producing 
a difference of potential. They are, therefore, doing work and their movement 
will thus be retarded, and possibly markedly so. 
