/ 
638 Waring ton.—The Effect of Boric Acid and Borax on 
controls occurs in all those concentrations of boric acid which are favourable 
to growth, viz. 1 : 12,500,000-1 : 25,000 approximately (Table I). A similar 
drop was found by Agulhon (1 (a)) in the case of wheat grown in water 
culture. When the concentration is sufficient to be toxic, the ratio rises, 
bringing the value up to much the same level as in the controls. Thus it 
would seem that it is primarily the root that is influenced by boric acid. 
In this connexion it is of particular interest that Agulhon (1 ( a )) and later 
Vinson and Catlin ( 35 ) have shown unquestionable stimulation of the root 
system of the radish with small applications of boric acid, since the root 
systems of the broad bean, radish, and wheat are so distinct from one 
another. 
[ 3 . The Effect of adding Boric Acid at Different Stages of Growth. 
A large number of broad bean plants were set up in the normal 
water-culture solution ; five additional plants received 1 : 50,000 and five 
1 : 2,500,000 H3BO3 respectively, besides the ordinary nutrient salts ; these 
concentrations of boric acid being chosen as they were both near the limits 
of its favourable action. 
The solutions were renewed every ten days, and at each change five 1 
more plants were supplied with the stronger dose of H 3 B 0 3 and five with 
the smaller quantity; but all plants, when once treated with boron, 
were kept continuously supplied with it throughout the experiment. 
Those which received boric acid from the start soon made more rapid 
growth than the untreated plants, all flowering well, and the set grown 
without H3BO3 for only ten days appeared very similar. However, twenty 
or thirty days’ growth in the absence of boron had a decidedly bad effect. 
Three of these plants showed the typical ‘ dying off’ of the main shoot, 
previously described as characteristic of broad beans grown without boron, 
and the remainder were poor and backward. In one case, ‘dying off’ 
occurred a few days after 1 : 2,500,000 H 3 B 0 3 had been supplied, which 
suggested that the physiological condition of the plant, of which this 
withering was the outward expression, had already set in before treat¬ 
ment. After forty days’ growth without boric acid, only three of the ten 
plants were still healthy, and after fifty days a single plant remained 
normal in appearance, while all those deprived of boron for sixty days were 
characteristically withered (PI. XIII, Fig. 6). 
It was noticeable that few plants flowered while still in the normal 
culture solution, and that though the ‘ dying off’ phenomenon was of general 
occurrence, the time of its appearance was quite irregular. In two plants, 
signs of withering set in within twenty-four days, while in others it did not 
appear until forty-six days’ growth. However, in all cases it occurred before 
the plants were harvested, unless boric acid was supplied in time. 
1 The unit was originally 10, but owing to the death of numerous seedlings in a spell of hot 
weather it had to be reduced to 5. 
