THE LIME-MAGNESIA RATIO ' 129 



a longer time given to these experiments might show something 

 more, despite the fact that they are in accord with the negative 

 investigations above reviewed. It should be remarked here, 

 however, that in the citrus tree experiment which has now been 

 carried on for over three years, the only evidence that we could 

 obtain was that magnesium carbonate was extremely toxic to 

 citrus trees and that at a toxic quantity of magnesium carbo- 

 nate of 2% to begin with, additions of lime carbonate in all quan- 

 tities up to 10% with intervals of 1%, were powerless to mask 

 in anywise the toxicity of magnesium carbonate. Even 1% mag- 

 nesium carbonate was found to be distinctly toxic to the citrus 

 seedlings, whereas on the other hand calcium carbonate up to 

 10% of the dry weight of the soil, added to a lime content of 1.5% 

 already in the soil, had no detrimental effect whatsoever. There 

 was a difference in the shape of tree produced, as affected by lime 

 treatment, the soils with the highest hme content giving a shorter 

 tree growth, with more abundant foliage, and the soils ^vith the 

 sm.aller lime content, a taller tree growth with sparser foliage. 

 Throughout the three years, however, only a thrifty condition has 

 been observed in the trees treated with hme only, and nothing 

 more, as judged by the green color of the leaves and the generally 

 vigorous appearance of the plants. We have further found that 

 though we could not overcome the toxic effect of the very toxic 

 magnesium carbonate for the citrus trees, that when the mag- 

 nesium carbonate was allowed to remain in the soil for a year 

 and a half or two, and the soil remained uncropped, that after 

 that citrus trees could be grown, but the growth made is always 

 very slow and unsatisfactoiy. 



There should not be omitted from our consideration here the 

 work of Hansteen^"* on the relationships of certain salts of the 

 soil to plants grown in solution cultures. While Hansteen seems 

 to accept the general idea of Loew with reference to the lime- 

 magnesia ratio for purposes of farm practice, he nevertheless 

 points out certain objections to the theory even when regarded 

 from the viewpoint of the physiological action of calcium and 

 magnesium respectively which are above discussed. Thus, for ex- 



sUahrb. fur Wissen. Bot., vol. 47, 1909-10, p. 289. 



