126 CHARLES B. LIPMAN 



ratio. It will be noted, moreover, in the table which is specially- 

 drawn up and presented herewith to compare the number of 

 positive and negative investigations, that in the latter case, the 

 experimenters are di-awn from a much wider range of territory 

 and must have worked under conditions which made them quite 

 independent of influencing one another. Not only their media, 

 but their plant materials, were of a large variety, giving but little 

 opportunity for a convergence of opinion, due to such causes, as 

 might operate in the case of the investigators supporting the 

 positive side of the question. The negative investigations fur- 

 ther insofar as they deal with many of the same plants and many 

 of the same chemical compounds that were included in the posi- 

 tive investigations, and yet resulted in negative results, would 

 seem to cast still further doubt on the validity of Loew's lime- 

 magnesia ratio hypothesis. 



The investigations placed under the head of indifferent in- 

 vestigations are such as to render perhaps more clear the function 

 of the specific elements, calcium and magnesium and to aid us 

 in forming a proper critical opinion, or in taking a properly criti- 

 cal al.titude with reference to the positive and the negative in- 

 vestigations. In showing the peculiarity of action of specific 

 elements they make very clear, for example, the great variation 

 in physiological action under different circumstances of mag- 

 nesium and calcium. This is nowhere better exemplified than 

 in Voelcker's experiments which show the beneficial effects of 

 lime and the harmlessness of lime in very large quantity, and on 

 the other hand, the distinctly harmful nature of magnesium to 

 plant growth. 



GENERAL CRITICAL REMARKS 



Many of the statements above reviewed as being unfavorable 

 to Loew's lime-magnesia ratio hypothesis have been answered 

 by Loew. For example, mention is made above of Loew's ob- 

 jection to Gossel's data because Gossel used secondary potas- 

 sium phosphate, while Loew used primary potassium phosphate. 

 Loew makes the claim that the former reduces the inj arious ef- 

 fects of an excess of magnesium. Admitting that it does, it is 



