CHAPTER VIII 



SPECIAL FUNCTIONS AND RELATIONS OF 

 MINERAL NUTRIENTS 



THE ROLES OF MINERAL NUTRIENTS 



PLANT physiological literature contains many references 

 to the specific roles or effects of the various mineral nu- 

 trients. Some of the observations and results are of par- 

 ticular interest; but many of the suggestions are based 

 upon such slight evidence as to require no consideration 

 in this place. It is an interesting and important field of 

 work, but explanations of many of the effects which have 

 been noted are more easily formulated than proved, and 

 a satisfactory interpretation of the results is proving most 

 difficult. 



The method of inquiry involves, on the one hand, a 

 study of the effects produced upon the plant or cell when 

 an element is, as far as possible, eliminated; or, on the 

 other hand, observations upon the results of supplying the 

 particular nutrient element under study when it has been 

 deficient. These are practically the only methods which 

 can be employed; but it must be admitted that the 

 absence of any nutrient may lead to unbalanced conditions 

 which may induce general pathological effects, so that the 

 particular primary role may be obscured. An analogous 



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