56 
James Small. 
possibility of something being added to our knowledge of polarisation 
in plants. At the same time the experiments seemed to involve no 
special technique and, if successful, could be repeated by anyone. 
Experimental. 
The experiments on the problematical reversal of geotropic 
curvature in stem and root were commenced in May, 1919, and the 
methods will now be described. 
Geotropic Response of the Root. 
The primary roots of Vicia Faba were studied first. Roots 
from one to two inches long were used. It was found that excess 
of ammonia vapour rapidly turned both testa and root quite black ; 
the roots excreted a clear liquid and shrivelled within a day or two. 
With very dilute ammoniacal water it was found that the vapour 
was too strong the first day and had all been given off within three 
days. In order to get a more or less constant supply of ammonia 
vapour at a low concentration the following procedure was 
Figs. 3-4. Secondary roots showing reversed geotropism ; Fig. 3, five 
rootlets ; Fig. 4a, ten rootlets, end view; Fig. 4b, ditto, side view. 
adopted—a piece of sheet cork was fitted into a flat museum jar 
so that about one third of the cork was below the level of the liquid 
filling the jar. The jar was filled with ammonia solution (-880) 
diluted to 1 in 10 with water. This was placed under a bell jar and 
allowed to stand for a few days; the ammonia was thus absorbed 
by the cork. The liquid in the jar was poured off and the jar was 
refilled with successive lots of tap water at intervals for about a 
month; the effect of the atmosphere under the bell jar on 
germinating beans was observed, until the vapour acquired the 
proper low concentration of ammonia. At this stage the vapour 
turned red litmus paper blue in about half-an-hour and, although 
