180 PLANT SOCIOLOGY 



Stiles (1923). The absorption of nutritive matter from the soil 

 solution by roots calls for an electroequivalent exchange of ions or 

 molecules from the root to the soil solution. 



The dissolved mineral matter is, in part, indispensable to the plant 

 (as potassium, magnesium, sulphur, phosphorus, iron, and for higher 

 plants calcium) and, in part, exerts a favorable influence upon the 

 growth of the plant or, again, it may be of no effect at all or even be 

 harmful. Highly concentrated solutions are injurious to most plants. 

 The capacity to endure certain ions in large quantities is a specific 

 property of the species or genus (c/. also Iljin, 1925). 



Toxic Effects. — The farmer knows the harmful effect of large 

 quantities of fertilizer added to the soil. Analyses by Chauzit (see 

 Russell, 1921) showed that Vitis vinifera began to suffer seriously as 

 soon as 35 per cent or more lime was added. Calcium ions also have a 

 toxic effect upon fungi (e.g., Citromyces) under neutral and basic 

 conditions. In the grapevine, the chestnut tree, Calluna, and other 

 plants hme chlorosis occurs with excess of calcium. A small excess of 

 iron induces iron chlorosis in soy beans. The same metabolic disease, 

 however, is also caused by a shortage of iron (Marsh and Shive, 

 1925, p. 79). The poisonous nature of aluminum is affected by H ion 

 concentration, being intensified by an increasing H ion concentration 

 of the soil. Below pH 5 the solubility of AI2O3 rises rapidly. In 

 soils of more than pH 5, however, according to Magistad (1925, p. 20), 

 lucern, red clover, and oats suffered little from the poisonous effects of 

 aluminum. Kaho (1926) has discussed the harmful effect of soil 

 alkalies upon the protoplasm of plants. He was able to prove that 

 the toxic effect depends upon the penetrating power of the ions where 

 the anions enter the plant more abundantly than the cations. The 

 permeability of protoplasm seems to change under the influence of 

 different ions. 



Antagonistic Effect of the lons.^ — The classic investigations by Loeb 

 (1906) have shown that certain salts such as sodium chloride, when 

 alone, have a poisonous effect upon plants but that with the addition of 

 magnesium or calcium the poisonous nature of the sodium chloride 

 solution may be decreased or entirely neutralized.^ In this antagonis- 

 tic action the concentration of the solutions doubtless plays an impor- 

 tant role (see also p. 186). 



Law of Relativity.— According to Lundegardh (1931, pp. 204-209), 

 three phases of the action of nutritive salts may be distinguished: 



1 Instructive examples of the antagonistic action of different ions are also 

 cited by Iljin (1925). 



