On the Foo(J of J*/aii/s. 
523 
T/ie Mineral Constituents of Plants. 
Every one is aware of the fact that when plants of any descrip- 
tion are burned, a quantity of whitish substance, or " ash," re- 
mains behind. Different plants, and different portions of the 
same plant, yield very variable quantities of this residue, but in 
no case is it absent altogether. Chemical analysis shows this ash 
to be a mixture of various saline bodies, some soluble in water, 
others not, siliceous matter, and unburned charcoal. Potash, 
soda, lime, and magnesia, in union with carbonic, sulphuric, and 
phosphoric acids ; certain portions of chlorides ; traces of iron 
and manganese ; silicates, soluble and insoluble, are the principal 
substances which thus remain after destruction by fire of the or- 
ganic tissues with which thev were associated. The relative pro- 
portions of the substances in the ashes of different plants vary 
exceedingly ; sometimes soluble carbonates are largely present, in 
other cases siliceous matter is the principal ingredient, while occa- 
sionally phosphates prevail. 
Now, if we take a plant whose ashes furnish a large quantity of 
carbonate of potash, for example, and examine its juice while 
living, we shall find this juice, instead of giving the well-known 
alkaline reaction proper to that salt, is strongly acid ; and a more 
extended investigation shows that this is due to the presence of a 
vegetable acid, generally tartaric, citric, or malic, so associated 
with the alkali in question as to constitute an acid salt. When 
this combination comes to be exposed to heat, the vegetable acid 
is destroyed, converted into carbonic acid and water, the first of 
which then unites itself to, and remains in union with, the alkali, 
such a compound not being further destructible by heat ; and so 
with the other bases when in combination Avith organic acids, 
they always remain after combustion as carbonates. 
An opinion has widely prevailed that these bodies were acci- 
dentally derived from the soil, and could not be considered essen- 
tial components of the plant, inasmuch as they were found to 
vary very considerably with the nature of the ground in which the 
plants grew. Professor Liebig has, in his excellent work so often 
referred to, devoted a considerable space to the refutation of this 
idea, and has endeavoured to show from analyses, which at first 
sight seem to point to the opposite conclusion, that a certain 
degree of constancy attends the quantity of bases in combination 
with organic acids present in the same plants grown in different 
situations, although the proportions of the bases themselves may 
be very different. He shows that in the ashes of two pine trees, 
grown under very different circumstances, and which on analysis 
gave different results, the quantity of oxygen present in the car- 
bonates was very nearly the same, showing that these bases were 
