68 Effect of Boron Compounds 



signs of poisoning in that, even with the weakest strengths, the lower 

 leaves were flecked with brown, especially at the edges, while with the 

 greater strengths the lower leaves were dead and the flecking had 

 extended to the upper leaves. In eleven days from the start the 

 plants with 1/1000 boric acid were completely dead, while the other 

 plants showed more or less signs of poisoning. The dry matter and 

 ash decreased steadily with the increase in the boric acid, while the 

 boric acid per 100,000 parts of dry matter increased steadily from 

 8 to 557 parts. Similar experiments were carried on with potassium 

 borate and with borax; the results showed that, weight for weight, 

 borax is less toxic than potassium borate, which in turn is less toxic 

 than boric acid, while at a strength of 1/100,000 there is little to choose 

 between the three poisons. Similar results were obtained with maize ; 

 plants treated with boric acid or potassium borate yielded about 2300 

 parts boric acid in 100,000 parts dry matter. The general conclusion 

 arrived at by Hotter was that the effect is not so much that of 

 a general poisoning as of a bleaching of parts of the leaf, mere traces 

 of boron being harmless. The cause of injury is local inhibition of 

 assimilation and killing of roots in stronger concentrations. Increase 

 of the strength of boron raises the toxicity until 1/1000 practically 

 inhibits increase in dry substance. The boron was found to be fairly 

 evenly distributed through sound and affected organs. 



Kahlenberg and True (1896) worked with seedlings of Lupinus 

 aUbus L., limiting their experiments to those of 15 24 hours in 

 duration. Various combinations of boron and other substances were 

 tested. With boric acid alone 2/25 gram molecule per litre killed the 

 plants, with 1/25 they were apparently just alive, while 1/100 and 

 less had no injurious effect. Boromannitic acid was possibly more 

 poisonous than the boric acid, while a combination of boric acid and 

 cane sugar proved slightly less toxic. The short duration of these 

 experiments limited their scope considerably, as with certain concen- 

 trations the toxic action would not become evident within the prescribed 

 limits of time. 



Agulhon (1910 a) worked with sterile nutrient solutions, and 

 found that the higher strengths of boric acid hindered growth, 

 200 mg. boric acid per litre rendering growth impossible. He sup- 

 ported Hotter's idea that the toxic action affects the roots and the 

 formation of chlorophyll, and he stated that the plants are less green 

 as the dose of boron increases, plants growing in doses of above 

 10 mg. per litre being yellowish. In other experiments he found that 



