384 



O. LOEW. 



in English in Bulletin No. iS of the Division of Vegetable 

 Physiology and Pathology, U. S. Department of Agriculture 

 1899, under the title : The Physiological Role of Mineral 

 Nutrients. 1 From this a few lines containing the main points 

 may be extracted. The lime is according to this theory 

 necessary for the formation of certain calcium compounds of 

 nucleoproteids required in the organized structures of nuclei 

 and chlorophyllbodies, while the magnesia serves for the assimi- 

 lation of phosphoric acid, since magnesium phosphate can give 

 up its phosphoric acid more easily than any other phosphate 

 that occurs in plant juices. While calcium is fixed in the 

 organized structure, magnesium is movable, since one and the 

 same atom can in the form of secondary phosphate serve 

 repeatedly the same purpose as a carrier of assimilable phos- 

 phoric acid in the formation of nucleoproteids and lecithin. 



It follows therefore that in the case of an excess of lime 

 being absorbed, the assimilation of phosphoric acid will be 

 rendered more difficult, since this acid will then chiefly combine 

 with the lime whereby the chances for the formation of magne- 

 sium phosphate will be diminished. The effect will then be the 

 sane as if the amount of available phosphoric acid in the soil 

 were lessened, i. e., the growth of the plant will be retarded 

 and even starvation phenomena will set in. The effect of this 

 excess of lime will be still more marked with the decrease of 

 the phosphoric acid present. 



If on the other hand an excess of magnesia is entering the 

 cells, the calcium nuclein compounds of the organized structures 

 can not be formed or when previously formed, will be changed 

 into the respective magnesium compounds, which are not suited 

 for the same function, perhaps on account of a very different 

 capacity of imbibition. 



Hence nuclei and chlorophyllbodies will first suffer from the 

 excess of magnesia, and this can be traced under the microscope 

 on filaments of Spirogyra. Even in a 0,1 per cent, solution of 

 magnesium nitrate these cells will die within five days, while 

 on the addition of 0,3 per cent, calcium nitrate they will remain 

 alive for a number of weeks, although on account of the absence 



1 Comp. especially pp. 28 ; 37 ; 42 ; 47 ; 60. ami Bui. No. I. Bureau of Plant Industry. 

 That Bui. will be sent free of charge to any one who applies to the U. S. Dept. of 

 Agriculture, Washington, D. C. 



