84 CHARLES B. LIPMAN 



the statement in public, and soon, of some definite information 

 free from all bias, with respect to the whole matter. 



The Ume-magnesia ratio hypothesis of Loew was an outgrowth 

 of studies made by Loew and by Bohm before him on the func- 

 tions of lime and magnesia in plant nutrition and growth. Loew 

 became so impressed ^dth the reversal of conditions among 

 other things, regarding the quantitative occurrence of lime and 

 magnesia in the seeds and in the straw of plants respectively that 

 he continued his experiments with a view to ascertaining if it 

 was necessary for lime and magnesia to bear a certain ratio to 

 each other in the medium of plant growth in order to insure nor- 

 mal development. As a result of these investigations Loew was 

 led to formulate^ what has since come to be the celebrated lime- 

 magnesia ratio hypothesis, which bears his name. According to 

 this hypothesis, either lime or magnesia is toxic to plants when 

 found in the medium of growth in large excess of the other; that 

 either of these substances wdll neutralize in part or in whole the 

 deleterious effects of the excess of the other; that different plants 

 require slightly different CaO : MgO ratios, and, to illustrate, 

 that such ratios should be 1 : 1 CaO : MgO for oats, 2 : 1 CaO : MgO 

 for barley and 3: 1 CaO: MgO for buckwheat. As subsidiary 

 to these important phases of the theory, Loew claims that both 

 lime and magnesia should be determined in soils by our regular 

 acid extraction methods of analysis in order that information 

 may be obtained with reference to the lime-magnesia ratio in 

 them, and, also, that the form in which lime and magnesia are 

 found in soils may affect to a considerable degree, the activity 

 of each, and hence the nature of the necessary ratio in every case. 

 Many of these additional observations of course resulted from 

 investigations of Loew and others carried out subsequently to 

 those above cited. In the latter there are pointed out the func- 

 tions of calcium and magnesium, showing that calcium cannot 

 replace magnesium in its work of carr^dng phosphoric acid to the 

 seed and that conversely magnesium cannot take the place of 

 calcium in the work of the latter as a "carbohydrate carrier" in 



i Flora, 1892, p. 368. 



