FINAL REMARKS. 69 



on the one hand, magnesium salts become poisonous in the absence of 

 calcium salts, and why, on the other hand, the absence of magnesium 

 salts in an otherwise complete culture solution leads to a gradual stop- 

 page of all further development and to final inanition. The formation 

 of the nuclei and plastids requires calcium as well as magnesium salts, 

 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 o-reat excess in a neutral medium, the formation of magnesium 

 phosphate, 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 fact 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 lime 

 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, 

 when it develops chlorophyll, however, requires more lime in propor- 

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



According to Wolff's calculations of the minima of lime and mag- 

 nesia for oats there is required 0.20 per cent of MgO and 0.25 per 

 cent of CaO 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 result- 

 ing crop than is generally supposed. The many contradictory state- 

 ments 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 large amount of magnesia, while a soil 

 very poor in magnesia may be benefited by it. In the application of 

 kainit and carnallit not only the chlorids but also the magnesia content 



«Bot. Jahresber. f. 1890, p. 75. 



