176 VEGETABLE PHYSIOLOGY 
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 constituents at least 
must be of importance to the organism, though it cannot 
be denied that our information is exceedingly incomplete. 
It is certainly possible, if not actually probable, 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 association has not been found. Hach 
element plays more than one part, and not improbably the 
role it plays at any moment depends to a very large extent 
on the condition of the organism. We may well conclude 
that in the organisation of the plant also there is no definite 
devolution of a particular function to a single constituent 
of its composition. It is probable that the well-being of 
any organism depends on the interaction of many elements 
with the protoplasm—interaction which may vary from 
time to time and from place to place, according to the 
changes of the environment or the automatic readjustments 
going on in the living substance. The influence of varying 
quantities of the mixture of elements may be considerable. 
Correlations of the functions of the plant, or the abnormal 
