TRACE ELEMENTS IN PLANTS 121 



induce boron deficiency in a number of crop plants such as beet 

 and swede. It will also be observed that if a soil contains 

 sufficient boron to induce toxicity symptoms, heavy liming 

 should reduce the severity of these. This was found to be so 

 with oats by Jones and Scarseth (1944). These workers grew 

 lucerne, oats and tobacco in pots of limed and unlimed soils 

 to which various quantities of borax were added. The calcium 

 and boron in the plants were determined. As a result the con- 

 clusion was drawn that a plant will only make normal growth 

 when there is a certain balance between the intake of calcium 

 and that of boron. From a consideration of their own data and 

 those obtained by Cook and Miller (1939) for sugar beet, Muhr 

 (1940) for soya bean and Drake, Sieling and Scarseth (1941) for 

 tobacco, they come to the conclusion that the ideal balance for 

 these various plants is attained when the ratios (in equivalents) 

 of calcium to boron in the respective plants are 100 for sugar 

 beet, 500 for soya bean and 1200 for tobacco. 



While, then, there is a quite considerable amount of evidence 

 of a relationship between boron and calcium, and also between 

 boron and potassium, in plant nutrition, the results obtained 

 with different species are so different that no generalization as 

 to the nature of this relationship appears possible at present. 



Microchemical tests made by Marsh and Shive on the apical 

 meristem of maize plants supplied with different quantities of 

 boron suggested a relation between boron and the pectin and 

 fat contents of these tissues. Thus with a supply of 170 p.p.m. 

 of calcium without boron tests for pectin in the cytoplasm were 

 positive and for fats negative, but with 5 p.p.m. of boron tests 

 for pectin in the cytoplasm were negative and for fats positive. 

 With an intermediate supply of boron (01 and 0-25 p.p.m.) 

 which was found optimal for growth (cf. Table XV) tests for 

 both pectin and fat were positive. It is suggested therefore that 

 boron plays some part in carbohydrate and fat metabolism. 



Swanback (1939), to whose work on absorption of cations by 

 tobacco reference has already been made, concluded from 

 analyses of tobacco plants supplied with calcium and potassium 

 at different levels with and without boron, that the latter 

 element aids the absorption and utilization of calcium. 



That boron is connected with carbohydrate metabolism was 



