the Broad Bean and certain other Plants. 647 
13 . Comparison between the Effect of Boric Acid and Borax in the 
Nutrient Solution . 
Borax and boric acid were used in such quantities that an equivalent 
amount of boron was supplied in each case ; i. e. 1 grm. H 3 B 0 3 = i *54 grm. 
Na 2 B 4 0 7 .10 H 2 0 . It was uncertain whether boron in the form of the salt 
would prove more or less toxic than when presented as the acid. 
The range of concentrations in this case was from 1 :50,000 to 
1 : 100,000,000 H 3 B 0 3 , since any heavier dose was obviously toxic. Ten 
plants were taken as the unit. 
As might be expected from the results of the previous experiments, no 
very toxic action was noticeable with any of the concentrations of boric acid 
used, except in the 1 : 50,000 set. In this case, however, a distinct bushiness 
of the root resulting from an outgrowth of fine laterals from short and 
thickened roots was shown, and the leaves also were badly spotted. 
However, in the plants receiving an equivalent amount of boron in the form 
of borax no bushiness of the root was apparent, though the development 
was poor. This was the only definite indication that the action of borax 
was less toxic than that of boric acid, for in other respects the plants 
appeared similar, e. g. the leaves were affected in much the same degree, and 
even the dry weights of the roots were of the same order. All the remain¬ 
ing sets showed a gradual improvement corresponding to the reduction in 
the concentration of boric acid or borax. As in the previous experiment, 
the discoloration of the leaf was practically negligible at a concentration 
of 1 : 2,500,000 H 3 B 0 3 . The 1 : 12.500,000 H 3 B 0 3 and the corresponding 
borax set were decidedly the best of the whole series ; the controls, though 
perfectly normal and healthy, lacked the luxuriant growth and the dark colour 
of these plants (PI. XIII, Fig. 8). On the whole, the borax-treated plants 
seemed slightly superior to the corresponding sets supplied with boric acid, 
and, though no actual measurements were made, the transpiration rate was 
apparently greater in the former, which would support this view; however, 
a comparison of typical individuals showed that there was no appreciable 
difference (PI. XIII, Fig. 9). 
Discussion of dry weights. From a comparison of the dry weight figures 
(Tables IV and V and Text-fig. 4) it is evident that concentrations as low 
as 1 : 2,500,000 H 3 B 0 3 exerted a definitely toxic effect, which was more 
accentuated as the quantity of boric acid increased. Below 1 :2,500,000, 
however, no injurious action was apparent, and in one experiment there was 
some slight indication of stimulation in the dry weight, but this may 
possibly be rather attributed to individual variation. 
The absence of any increase over that of the controls in the dry weights 
of plants supplied with 1:12,500,000 H 3 B 0 3 was however unexpected, 
since to the eye the untreated plants were distinctly the smaller. In all 
probability these larger plants contained a higher percentage of water and 
