no use of it;[3] and the
chlorophyll[4] is the apparatus by which the carbon is extracted from the
atmospheric carbonic acid--the leaves being the chief laboratories in
which this operation is effected.

[Footnote 3: I purposely assume that the air with which the bean is
supplied in the case stated contains no ammoniacal salts.]

[Footnote 4: The recent researches of Pringsheim have raised a host of
questions as to the exact share taken by chlorophyll in the chemical
operations which are effected by the green parts of plants. It may be
that the chlorophyll is only a constant concomitant of the actual
deoxidising apparatus.]

The great majority of conspicuous plants are, as everybody knows, green;
and this arises from the abundance of their chlorophyll. The few which
contain no chlorophyll and are colourless, are unable to extract the
carbon which they require from atmospheric carbonic acid, and lead a
parasitic existence upon other plants; but it by no means follows, often
as the statement has been repeated, that the manufacturing power of
plants depends on their chlorophyll, and its interaction with the rays of
the sun. On the contrary, it is easily demonstrated, as Pasteur first
proved, that the lowest fungi, devoid of chlorophyll, or of any
substitute for it, as they are, nevertheless possess the characteristic
manufacturing powers of plants in a very high degree. Only it is
necessary that they should be supplied with a different kind of raw
material; as they cannot extract carbon from carbonic acid, they must be
furnished with something else that contains carbon. Tartaric acid is such
a substance; and if a single spore of the commonest and most troublesome
of moulds--_Penicillium_--be sown in a saucerful of water, in which
tartrate of ammonia, with a small percentage of phosphates and sulphates
is contained, and kept warm, whether in the dark or exposed to light, it
will, in a short time, give rise to a thick crust of mould, which
contains many million times the weight of the original spore, in protein
compounds and cellulose. Thus we have a very wide basis of fact for the
generalisation that plants are essentially characterised by their
manufacturing capacity--by their power of working up mere mineral matters
into complex organic compounds.

Contrariwise, there is a no less wide foundation for the generalisation
that animals, as Cuvier puts it, depend directly or indirectly upon
plants for the materials of thei