THE ABSORPTION OF MINERAL ELEMENTS 



75 



of solutions containing only one of the salts used in the complete 

 nutrient medium. If the roots of a plant are divided into four 

 parts and each of them placed in a separate medium of the four 

 salts that enter into the composition of Knop's solution, then, 

 instead of developing normally, the roots would be poisoned. The 

 same would happen if, in turn each of the salts was supplied; for 

 instance, during the first week one of the salts, the next week 

 another, and so on. 



This poisonous effect of single salts was first observed on 

 mussels (Ringer, 1883), and on sea animals (Loeb, 1898). Solu- 

 tions of sodium chloride, corresponding in concentration to sea 

 water, were found to have a 

 pronounced toxicity, if very 

 pure salts were used. But very 

 small quantities of calcium and 

 magnesium checked this toxic 

 effect. In a pure solution of 

 sodium chloride, for instance, 

 not a single embryo developed 

 from the fertilized eggs of the 

 sea urchin. But the addi- 

 tion of 1 cc. of a very dilute 

 solution of CaS0 4 caused the 



development of 3 per Cent Of roots of wheat : (1) in a balanced solution 



emhrvos- 2 cc 20 ner cent- of NaC1 + KC1 + CaCl2: (2) in a partly 

 embryos, z cc, zu per cent, balanced so i ution of NaCl + CaCl 2 ; 



and 4 CC, 75 per Cent. Pure (3) in a pure solution of CaCl 2 ; (4) in a 



solutions of calcium salts also pure solution ^J^g. {redravm a/ter 

 are toxic, although this can be 



counteracted by the addition of sodium salts. Thus different salts 

 destroy the toxic effect of each other. This phenomenon has 

 been termed "antagonism of ions." 



Ion antagonism can be easily observed on the development of 

 roots of plants in water cultures. It has been studied in detail 

 by Osterhout. Figure 29 shows the results of one of his experi- 

 ments. In pure solutions of CaCk and of NaCl the roots have 

 developed very poorly. Much better growth was secured in solu- 

 tions where Na was balanced by Ca, but the best development was 

 obtained when a third cation was added, namely K. The greatest 

 antagonism is usually observed between univalent and bivalent 

 cations, but ions of the same valence may be antagonistic In 



