THE LIME-MAGNESIA RATIO 85 



the chlorophyll bearing parts of plants. Without going into 

 them here, it suffices to say that ample evidence is furnished as a 

 basis for such conclusions and explanations as are given for the 

 earlier observations of Bohm, Riiumer and Kellerman. 



With these ideas as a basis, Loew and his co-workers or pupils 

 in various parts of the world, proceed to gather experimental 

 data in support of the hypothesis thus indicated. It is a review 

 of these investigations as well as of those of other investigators 

 working entirely independently of Loew which I propose to give 

 here briefly. No attempt is made below to review all of the 

 investigations which have a bearing on the question of the lime- 

 magnesia ratio, but all important and typical investigations are 

 adverted to so far as the higher plants are concerned. The lower 

 organisms are merely mentioned when necessary for the elucida- 

 tion or emphasis of principles and facts appertaining, in the 

 main, to the higher plants. It is further to be noted that the in- 

 vestigations here considered are discussed in groups as follows: 

 I. Positive, or those supporting Loew's hypothesis; II. Nega- 

 tive, or those showing little or no support for its tenabiHty; and 

 III. Indifferent, or those which are related to the subject of the 

 functions of lime and magnesia in plant growth, but giving little 

 or no evidence either in support or contradiction of the hypothe- 

 sis in question. Obviously the lines in such classification must 

 at least in some instances, be arbitrarily drawn and particularly 

 as between the first two classes and the last, nevertheless, the 

 classification serves the purpose of bringing into sharp relief cer- 

 tain phases of the present status of the subject which can scarcely 

 be considered as being affected by the drawing of the lines as 

 indicated. 



THE POSITIVE INVESTIGATIONS, OR THOSE GIVING SUPPORT TO 

 THE LIME-MAGNESIA RATIO HYPOTHESIS 



The investigations to be referred to under this head represent 

 those undertaken by Loew and others to test the principle enun- 

 ciated by the former, not only in the paper above specifically 

 cited , but also in several others in which the function of the min- 

 eral nutrients and especially of calcium and magnesium in plant 



