CHAPTER IV 



THE PROGRESS OF OUR KNOWLEDGE OF THE 

 ROLE OF THE CONSTITUENTS OF THE ASH 

 OF PLANTS 



PERHAPS there is no department of vegetable physiology 

 in which so little progress has been made as this one, 

 none in which the results of investigation have been so 

 unsatisfactory. It has been found possible to determine 

 what elements can be detected in greater or less quantity 

 in plants ; which of them are of widespread occurrence ; 

 which only appear occasionally or in special individuals. 

 Within certain limits their distribution in the plant-body 

 has been ascertained, but nearly all attempts to associate 

 particular elements with definite functions have resulted 

 in more or less complete failure to gain any accurate 

 information. 



Before discussing these researches and the results to 

 which they have led, we may well remind ourselves of the 

 difficulty of the problem and of the possibility, or even 

 the probability, that a definite association of any of the 

 elements with a particular function does not and cannot 

 exist. Even in the animal body, the study of which is 

 far more complete than that of the plant, such associations 

 have not been found. Each element plays more than one 

 part, and not improbably the part it plays at any moment 

 depends to a very large extent on the condition of the 

 organism. We may well conclude that in the organization 

 of the plant also there is no definite devolution of a par- 

 ticular function to a single constituent of its composition. 

 It is probable that the well-being of any organism depends 



