184 VEGETABLE PHYSIOLOGY 



CHAPTEE XIII 



THE CONSTITUENTS OF THE ASH OF PLANTS 



WE have seen in a previous chapter that when a plant is 

 carefully burned and the residue collected, the latter, which 

 is known as the ash, is found to contain a number of 

 elements which vary in different cases and which always 

 include certain metals, as well as some non-metallic 

 elements. The occurrence of this ash being universal, we 

 can conclude without any difficulty that some of its con- 

 stituents at least must be of importance to the organism, 

 though it cannot be denied that our information is exceed- 

 ingly incomplete. In the study of the nutritive processes 

 of animals we meet with similar phenomena. How far 

 any of the constituents of the ash can be regarded as 

 actual food is uncertain, nor can we solve this question 

 until we know something more about the composition of 

 living substance. Whether any of these bodies actually 

 enter into such composition is doubtful, but several of 

 them appear to be necessary for the assimilation of the 

 food which is either manufactured or supplied, as well in 

 the case of the vegetable as in that of the animal 

 organism. 



Many of them, again, while not serving as food or even 

 as materials for the formation of food, no doubt play 

 important parts in the general metabolism of the organ- 

 ism. At present we are not in a position to say definitely 

 how most of them are concerned in any or all of these 

 processes. 



From the nature of the plant-body and the absence of 



