Special Functions and Relations 191 



tion or absorptive action of the plants used as indicators. 

 Moreover there is diversity in the visible results of the 

 toxic action by the different nutrients ; thus salts of 

 ammonium kill the roots before the shoots are noticeably 

 affected, while sodium salts kill the shoot promptly. It 

 is important that there is toxic action, and that there may 

 be antagonistic or mutually antagonistic action. 



An entirely satisfactory explanation of these phenomena 

 is not at present available. Loew's views on the calcium- 

 magnesium relation are strengthened by the opinions of 

 Loeb and others who postulate in organisms a number of 

 metal proteins, so that any solution containing only one 

 class must be ultimately toxic. Even this view is not suffi- 

 ciently broad to account for all of the known facts ; for 

 example, the antagonism between inessential and essential 

 ions. 



LABORATORY WORK. - - SUGGESTED EXPERIMENTS 



Injurious action of single nutrients. - - After consulting the 

 literature of the subject determine the concentrations of MgCl 2 , 

 CaCL, KC1, and NH 4 C1, which when used separately will just 

 permit the growth of roots of wheat or peas. Employ ten 

 plants in tumblers or bottles, as in the nutrition studies. 



Balanced Solutions. - - Guided by the indications given under 

 nutrient solutions regarding manipulation, set up the experi- 

 ments outlined below, employing in each culture wheat or 



Canada field peas. Prepare stock cultures of ~Ca(NO 3 )o, 



oU 



N N N 



-Mg(NO 3 ) 2 , - -NaCl,- -CaCL, also double strength of nutri- 

 50 100 100 



ent solution ; from these prepare, by dilution, all the following 

 cultures, also employing distilled water as a check : 



