of those proximate principles of
plants which are mere combinations of water with carbon
(hydro-carbonates or hydrates of carbon) has been already given, but
must here be repeated:--

100 parts consist of
| Water. | Carbon.
Gum (pure gum-arabic) | 58.6 | 41.4
Sugar (pure crystallized) | 57.15 | 42.85
Starch | 56.00 | 44.00
Lignin | 50.00 | 50.00

These are so many mutually convertible products, of which gum may be
looked upon as the basis; indeed gum is that organizable product which
exists most universally in the proper juices of plants. "There are
some instances in which sugar appears to be the first organic compound
formed by the combination of the external elements, as when abundantly
existing in the ascending sap of trees--the maple, for example. Starch
may be considered as little else than gum divided into minute
portions, each of which is enclosed in a membraneous cell (and
containing some incidental particles, which, when starch is burnt,
leave about .23 per cent. of residuum, consisting entirely of
phosphates); and, in this state, it appears to answer very important
ends in the vegetable economy. It is remarked by Decandolle, that,
'while gum itself may be considered the nutrient principle of
vegetation, diffused freely through the structure of the plant, and
constantly in action, starch is apparently the same substance, stored
up in such a manner as not to be readily soluble in the circulating
fluids,' thus forming a reservoir of nutritious matter, which is to be
consumed, like the fat of animals (which it closely resembles in
structure), in supporting the plant at particular periods[H]."

This view explains the fact of starch being found accumulated in
amazing quantity in some plants, more particularly at certain periods
of their existence, as in the cases I am now to cite. The fertility of
some palm-trees is very great, and to furnish nutriment to the
flowers, fruit, and seeds, an enormous supply of starch is needed;
accordingly, in these we find the stem a complete storehouse of this
essential principle. Thus the several palms and palm-like plants,
which yield sago, such as the _sagus Rumphii_, _cycas circinalis_, _C.
revoluta_, _corypha umbraculifera_, _caryota urens_, and _phoenix
farinifera_--trees which are mostly confined within the tropics, at
the mome