V. H. Blackman 
38 
of equality. Thus out of a total of 75 cases 28 per cent, are early, 
67 per cent, late and 5 per cent, are equal. 
It should be noted that among the early cases a majority occurs 
between March 3 and April 11. 
In conclusion, it may be pointed out that there is a general re¬ 
semblance between 1920 and 1918, inasmuch as the springtime 
flowerings are early in both these years. And this fact we must con¬ 
nect with the relatively high temperatures ruling in the spring of 
these two years. Thus from the week ending Jan. 26, 1918, to week 
ending Feb. 16 we have deviations from the normal of + 6*2 to 
+ 9-8. And, again, from March 16 to April 13 the deviations are + 
though not so well marked as those quoted. 
The early spring flowerings of 1920 also correspond with the 
relatively high temperatures ruling from the week ending Jan. 10, 
1920, to that ending Feb. 21, 1920. 
THE THEORY OF GEOTROPIC RESPONSE 
By V. H. BLACKMAN 
I N recent numbers of this journal ( 19 , pp. 49-63 and 208-212) Pro¬ 
fessor Small has put forward a theory to explain the geotropic 
response in plants, and particularly the difference in the behaviour 
of the stem and the root. This theory rejects the movement of com¬ 
paratively large cell particles (such as starch grains) as the first step 
in the chain of processes which lead to geotropic curvature, and 
relates the response to changes in the plasma itself under the action 
of gravity. The particles or drops forming the disperse phase of the 
colloidal protoplasm are supposed to be lighter than the surrounding 
fluid (continuous phase) and to rise to a marked extent under the 
action of gravity, a phenomenon which is described as “ creaming.” 
As these particles are electrically charged their movement should 
produce a difference of potential or alter the difference of potential 
already existing in the cell. The particles are supposed to be electro¬ 
positive in the root and electro-negative in the stem; the differences 
of potential produced, and the electric currents to which they give 
rise, would thus be in opposite directions in the two organs. These 
currents are supposed to affect the permeability and growth of the 
cells and so bring about the geotropic curvature. 
The nature of the geotropic response (even if the statolith theory 
be accepted) is one of the most obscure of physiological phenomena, 
