636 Waring ton .— The Effect of Boric Acid and Borax on 
turning yellow and falling off, death proceeding from below upwards. It 
would seem, therefore, that the period when the withering appears varies 
with the individual plant, but given sufficient time the ‘dying off’ phe¬ 
nomenon inevitably occurs. 
The contrast between the shoots of plants treated with different con¬ 
centrations of boric acid (except in extreme cases) was hardly evident 
towards the close of the experiment, 
while the difference in the growth of 
the controls from all the others was 
more clearly emphasized (PI. XIII, 
F 'g- 5 )- This gave support to the 
idea that the presence of boric acid 
was of fundamental importance, 
though the actual concentration 
within certain limits, approximately 
1 : 25,000-1 : 12,500,000, was of little 
consequence. 
ic) Discussion of dry weights. 
The dry weight figures for these 
first three experiments on broad 
beans substantially support the con¬ 
clusions which have already been 
drawn by inspection of the plants. 
Consideration of Table I and 
Text-fig. 2 shows clearly that such 
a minute quantity of boric acid as 
1 : 100,000,000 does not exert any 
appreciable influence on growth, but 
from 1 : 12,500,000 up to 1 : 25,000 
a considerable increase over the 
figures for the control plants is seen. 
m 
£ 
1 
o 
< 
•4 
•3 
•1 
Text-fig. 2. Broad beans grown in water 
culture solution containing different quantities of 
boric acid. March 10-May 17, 1921 (average of Above I : 25,000 a toxic effect is ap- 
five plants) : -Dry Weight; —. — . — per 
cent. Nitrogen ;-- - Actual N. 
parent in the case of the preliminary 
experiment carried out in the spring, 
though in the two remaining series the same quantity of boric acid appears 
to have been beneficial. This varying effect of a similar amount of the 
poison has already been shown to be dependent on seasonal conditions. 
It is evident that though on the whole the addition of I : 50,000 
boric acid yielded the best results, such widely varying quantities as 
1 : 12,500,000 or 1 : 25,000 were able to exert a beneficial effect of much the 
same order. 
(d) —— ratio . A decided drop in the —°° —ratio below that of the 
v 1 Root 1 root 
