124 CHARLES B. LIPMAN 



cal treatment of the medium in which the plant is produced. 

 To one who has given careful thought to the role of chemical 

 elements and compounds in plant growth, this kind of experi- 

 ment with the object in view adopted, together with the mode 

 of drawdng conclusions, appear, to put it mildly, to be somewhat 

 unusual in the realm of scientific work. Admitting, to begin 

 with, that magnesium is toxic to plants when found in the me- 

 dium of growth beyond a certain relatively small concentration 

 in soluble form (and no one will deny that who has ever made 

 experiments with magnesium salts) in plant growth, why should 

 it be assumed that when to such toxic quantities of magnesium 

 certain quantities of calcium are added and the toxic effect is 

 wholly or partly overcome, that it is because the lime-magnesia 

 ratio has been brought to the optimum in that particular medium? 

 Why may it not be assumed, for example, when soils are em- 

 ployed, that the addition of the calcium salt has influenced more 

 markedly the decomposition of the nitrogenous fraction of the 

 organic matter, and therefore placed at the disposal of the plant 

 more available nitrogen; or that through the whole principle of 

 the substitution of bases or exchange of bases, potassium in 

 necessary quantities, may have been set free from its insoluble 

 combinations by the calcium; or that phosphoric acid, which is 

 present in the soil in the more insoluble aluminum and iron phos- 

 phates, may have been rendered more soluble by its combina- 

 tion in part with the calcium? Or, if we may be allowed to sur- 

 mise still further, it is not at all improbable that the addition of 

 calcium which we know to be, among the alkalies and alkali 

 earths, the most active precipitant of clay and binding material 

 for sand, produces marked physical changes which would bring 

 about the improvement which is noted as the end result of the 

 application of calcium. Indeed it is evident at the present time 

 in plant physiological investigation that a certain beneficial ef- 

 fect induced by a certain kind of treatment may wholly mask, 

 through its marked good effects, the bad effects of say, a toxic 

 material, and it is not at all impossible that calcium may thus 

 bring about better conditions when added to a medium contain- 

 ing magnesium salts in toxic quantity. 



