52 PHYSIOLOGICAL ROLE OF MINERAL NUTRIENTS. 



The extraordinary effects of lime salts on the development 01 root 

 hairs is of special interest, as it furnishes the key to the observation of 

 Wolff that the potassium and ammonium salts of the soil are absorbed 

 in increased quantities by plants after manuring with lime salts. 



Magnesium salts do not, of course, rank with mercuric cMorid and 

 other violent metallic poisons as to the degree of toxicity. Their 

 injurious action, moreover, decreases in the same measure as the 

 amount of calcium salts in the cells to be tested increases ; it further 

 depends upon the degree of protection of the nucleus against the 

 entering salts, upon the thickness of cellular membranes, and, last but 

 not least, upon the degree of acidity of the cell sap. Such differences 

 will account for the observation of Kearney, that magnesium sulphate 

 proves much more poisonous for seedlings of lupin and alfalfa than for 

 those of maize, and for the recent observation of Duggar of the excep- 

 tionally low toxicity of magnesium salts for marine algsB. Wherever, 

 further, the entering magnesium salt can be transformed in the cells 

 into the secondary phosphate, there the toxic action becomes exceed- 

 ingly weak, as the writer has himself proved (see above the experi- 

 ment with Spirogyra made in presence of monopotassium and of dipo- 

 tassium phosphate). The primary question is, Which magnesium salts 

 react easily upon the calcium compounds of the nucleus? 



LIFE WITHOUT LIME SALTS. 



While lime salts are indispensable for animals, Phanerogams, and 

 higher algss, they are not so in the case of bacteria, fungi, and lower alga?. 

 Thus far no investigations relating to the higher fungi have been made 

 in this regard. The occurrence of lime in the ash of yeast and of 

 tubercle bacilli' 8 must be regarded as merely accidental. It was first 

 observed by Adolph Mayer that for yeast magnesia is of greater impor- 

 tance than is lime. Later the writer proved that yeast and bacteria can 

 do without lime entirely, 6 and Molisch has observed that this is also true 

 of mold fungi. c It has been observed, on the other hand, that in cer- 

 tain cases the presence of lime promotes the action of fungi, but this is 

 very probably due only to a secondary effect. Thus, the nitrification 

 in soils is enhanced by calcium carbonate, and, according to Thaxter 

 and Wheeler, a the scab of potatoes and of sugar beets is increased by 

 liming the soil. Recently Laurent e reported that certain bacteria, 

 Bacillus coli communis and B. fluoresceins putidus, can attack potatoes 



a According to de Schweinitz and Dorsett (Centralbl. f. Bakt., No. 23, 1898), the 

 phosphates of sodium, calcium, and magnesium predominate in this ash over that 

 of potassium, while the reverse is true in the ash of yeast. 



b Flora, 1892, pp. 374 and 390. 



cBer. Wien. Akad., 1894, Vol. CI1I. 



^ Storer, Relation of Agriculture, Vol. II, p. 546. 



< Ann. de l'Institut Pasteur, 1899, Vol. XIII, p. 1. 



