120 THE FUNCTIONS OF 



This explains the accentuation at the high boron level of 

 the symptoms of boron toxicity with increasing potassium 

 concentration, but does not explain why the boron deficiency 

 symptoms at the low boron level should be accentuated with 

 increase in the potassium supply. 



In their experiments on the relation of calcium to boron thirty 

 cultures were used in which six levels of calcium supply (5, 10, 

 50, 100, 250 and 500 p.p.m.) and five of boron (0-001, 0-01, 0-5, 

 5-0 and 10-0 p.p.m.) were employed. The results show that 

 calcium acts similarly to potassium in that with the lowest 

 boron concentration (0-001 p.p.m.) the severity of the symptoms 

 of boron deficiency increases with increase of the supply of 

 calcium, the effect of the latter in this respect being, indeed, 

 greater than that of potassium. In its influence on boron toxi- 

 city produced by the highest boron concentration (10 p.p.m.), 

 however, calcium acts in exactly the opposite way to potassium, 

 for with progressively increasing calcium supply the severity of 

 the symptoms of boron toxicity becomes less. Chemical analyses 

 of the plants show that with the lower concentrations of boron 

 in the nutrient solution (0-001, 0-01 and 0-5 p.p.m.) the boron 

 content (both total and soluble) is independent of the calcium 

 concentration of the nutrient solution, but with the higher con- 

 centrations of boron in the nutrient solution (5-0 and 10-0 p.p.m.) 

 increase in the concentration of calcium brought about a decrease 

 of both total and soluble boron in the plants. This accounts 

 for the effect of increasing concentration of calcium in reducing 

 the toxicity of boron when supplied in high concentration. It 

 may be noted that, in contrast to the earlier findings of Miss 

 Warington with broad bean and of Minarik and Shive with soya 

 bean, boron appears to have no effect on the absorption of 

 calcium by tomato, and there does not appear to be any relation 

 even between soluble boron and soluble calcium such as Marsh 

 and Shive found in maize. However, the ratio of calcium to 

 boron in the plant is influenced by the supply of potassium, 

 increase of this cation in the nutrient solution bringing about a 

 lowering of the calcium/boron ratio. Calcium appears to have 

 no significant influence on the potassium/boron ratio. 



The results obtained by Reeve and Shive are in harmony with 

 the well-known fact that heavy liming of certain soils will 



