342 University of California Vablications in Agricultural Sciences [Vol. 1 



largely discarded in view of the recent investigations, which 

 have shown that plant growth is not a simple function of any 

 any particular element, but is to a very large extent influenced 

 by the combinations of elements in the solution from which 

 the plant derives its nourishment. Thus while calcium may 

 in certain cases act as a neutralizer of oxalic acid,' it exhibits 

 a more general function of antagonism for salts of potassium, 

 sodium, magnesium, and other salts which would be toxic if 

 calcium were not present.- While this antagonistic function 

 may be characteristic, it would seem from the experiments of 

 Tottingham^ that either this antagonistic action of calcium or 

 the toxic effects of magnesium are influenced by the total con- 

 centration of the solution. Tottingham, therefore, concludes that 

 the injurious effects of magnesium depend not onlj^ on the amount 

 of calcium present but also upon the complex balance between 

 all the salts in the solution. It follows tliat while the later in- 

 vestigations have undoubtedly given a wider conception of the 

 role of the various nutrient elements, the exact relation which 

 exists between the recognized nutrient function of these elements 

 and the balancing function in the solution is not definitely known. 

 Tlie part which the total concentration of the solution takes 

 in the complicated problem of plant nutrition is by no means 

 clear. On the one hand, the experimental evidence of Cameron* 

 and his co-workers shows that the plant growing in water culture 

 is not influenced to any extent by wide variations in the total 

 concentration of the solution, a view which is further supported 

 by the researches of Tottingham,^' who concludes that nutrient 

 solutions ranging from 0.01 per cent to 0.14 per cent do not affect 

 the dry weight in the case of wheat grown in these solutions. 

 A similar view is taken by Stiles,'"' who thinks that the individual 

 variation of plants gi'own in water cultures is as large or larger 

 than that which is often accredited to a variation in the compo- 



1 Sobimper, Flora, vol. 73, pp. 207-261, 1890. 



2Loew, Flora, vol. 75, pp. 368-.394, 1892; and U. S. Dept. Agrie. Bur. 

 riant Ind. Bull. 45, 1903; Osterhout, Bet. Gaz., vol. 42, pp. 127-134, 1906, 

 and vol. 44, pp. 259-272, 1907. 



3 Tottingham, Physiol. Ties., vol. 1, pp. 133-245, 1914. 



4 Cameron, Jour. Phys. Chein., vol. 14, p. 320, 1910. 



5 Loc. cit. 



fi Stiles, Ann. Bot., vol. 29, pp. 89-96, 1915. 



