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CHAPTER XII 
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 
