60 



the former for the production of calcium nucleo-proteids and the latter 

 for making possible the assimilation of phosphoric acid. If lime salts are 

 in great excess in a neutral medium, the formation of magnesium phos 

 phate and consequently the assimilation of phosphoric acid will be 

 retarded, since the lime as the stronger base will withhold phosphoric 

 acid when soluble phosphates come in contact with lime salts. Many 

 plants, therefore, which have absorbed too much lime and relatively 

 too little magnesia from the soil precipitate a part of the lime in the 

 form of oxalate. Indeed Monteverde' observed that the amount of 

 oxalic acid increases with the amount of lime absorbed. 



The excess of lime is in reality the cause of an increased production 

 of oxalic acid — a facb best explained by the assumption that before car- 

 bonic acid is finally produced by the combustion of carbohydrates, a 

 series of organic acids, of which oxalic acid is one stage, is rapidly 

 passed, this stage being fixed by the presence of lime. Similar obser- 

 vations were also made by Wehmer with fungi in culture solutions to 

 which lime salts were added. In the presence of lime salts there was 

 more oxalic acid formed than in its absence, or, more correctly expressed, 

 more was preserved from being again destroyed by further oxidation. 



The fact that seeds generally contain much more magnesia than liine 

 may be considered an interesting case of adaptation. A rapid develop 

 ment by an easy assimilation of the reserve phosphoric acid is thus 

 assured — a favorable circumstance, as it lessens the danger of the mold- 

 ing and putrefying of the seeds sown in moist ground. The same plant 

 after it develops chlorophyll, however, requires more lime in proportion 

 to magnesia than does the seedling in its early stages. According to 

 Wolff's calculations of the minima of lime and magnesia for oats there 

 is required 0.2 per cent of each for the dry matter, but for plants with 

 more abundant foliage the minimum of lime would be larger. 



The proportion of these two constituents in the soils is a more potent 

 factor in the resulting crop than is generally supposed. The many 

 contradictory statements in regard to the influence of magnesia in the 

 soils are easily explained by the aid of the above theory. A soil rich 

 in magnesia will be damaged by liming with magnesian limestone, 

 since this would increase still more the already l^rge amount of magne- 

 sia, while a soil very x)oor in magnesia may be benefited by it. In the 

 application of kainit and carnallit also the magnesia content of these 

 potassa fertilizers has to be considered and eventually liming has to be 

 carried on in conjunction with it. 



» Bot. Jahresb. f. 1890, p. 75. 



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