Effect of Boron Compounds 71 



(c) Toxic action of boron compounds in. soil experiments. 



Long before any experimental work was done with boron in water 

 cultures, the poisonous properties of the substance were recognised 

 with regard to plants growing in soil. Peligot (1876) grew haricots 

 in porous earthenware pots, the plants being watered by rain and by 

 solutions, each containing about 2 grams per litre of such substances 

 as borax, borate of potassium, and boric acid, other pots receiving various 

 fertilisers, as potassium nitrate, sodium nitrate, &c. This quantity 

 of boron completely killed off the plants receiving it, whether it was 

 applied as free or combined boric acid, while the fertilised plants com- 

 pleted their development well. On this account the deleterious action 

 was attributed to the boric acid and not to the sodium or potassium base 

 supplied. Peligot hinted at the improbability of a substance like boron, 

 which is so poisonous to plants, being really innocuous to human beings 

 when it is used as a preservative for foods. 



Nakamura (1903) also found that borax is harmful in pot cultures 

 if present in large quantities, 50 mg. borax per kgm. of soil exerting 

 a very injurious influence, while even 10 mg. per kgm. did some damage. 

 Agulhon (1910 c) found that the toxic doses of boric acid in soil cultures 

 approached those in nutritive solutions rather than in sand cultures, 

 a phenomenon that he attributed to the fact that the boric acid was 

 fixed by the soil, probably as insoluble borate of calcium, so that the 

 surface concentration obtained with sand cultures was avoided. He 

 found that the ash of plants grown with excess of boron contained 

 more than the normal amount of boron, while the weight of ash 

 per 100 dry matter was also increased. He concluded that the plant 

 thus suffers an over-mineralisation and in consequence an augmentation 

 of its hold on water, so that the fresh weight of the plant may indi- 

 cate a more favourable action of the boric acid than does the dry 

 weight. Other investigators (Fliche and Grandeau 1874) had found 

 the same increase in the proportion of ash in chestnut trees grown on 

 too calcareous soil, so Agulhon concluded that one is here dealing with 

 a general reaction of plants to an excess of a useful element. 



Other experiments were carried on in the open field, maize being 

 grown on control plots and on plots receiving 2 gm. boron per square 

 metre. At first the latter plants were behind, the dose being too 

 strong. Eventually, however, they pulled up level and the dry weights 

 from the two plots proved to be nearly the same, the fresh weights being 

 identical. Maize is evidently far less sensitive to boron poisoning than 



