the _Mangostana Gambogia_, Gaertner, and the _Hypericum
bacciferum_ and _Cayanense_, yield similar yellow viscid exudation,
hardly distinguishable from gamboge and used for the same purpose by
painters. The _Garcinia elliptica_, Wallich, of Tavoy and Moulmein,
affords gamboge, and approaches very closely in its characters to
Graham's _Hebradendron_. In like manner the Mysore tree bears an
exceedingly close resemblance to that species. It is common in the
forests of Wynaad in the western part of Mysore, and has been named by
Dr. Christison _Hebradendron pictorium_. Another gamboge tree has
recently been found inhabiting the western Burmese territories. Both
these seem to furnish an equally fine pigment. As it can be obtained
in unlimited quantity, it might be introduced into European trade, if
the natives learn how to collect it in a state of purity, and make it
up in homogenous masses in imitation of pipe gamboge, the finest Siam
variety. It seems to possess more coloring matter, more resin and less
gum than the ordinary gamboge of commerce. Gamboge owes its color to
the fatty acid. The resin must be regarded as the chief constituent,
and is most abundant in that imported from Ceylon, which contains
about 76 per cent., and is therefore best adapted for painting.
Gamboge also has its medicinal uses.

Various species of _Lecanora_, particularly _L. tartarea_, known as
cudbear, are used in dyeing woollen yarn. The _Rocella tinctoria_ and
_fusiformis_ furnish the orchil, or orchilla weed of commerce, which
is sometimes sold as a moist pulp, but usually in the form of dry
cakes, known under the name of _litmus_; it produces a fine purple
color. Our imports, which have amounted to 6,000 or 7,000 cwts.
annually, are derived chiefly from the Canary, Azores, and Cape Verd
Islands. Rock orchilla was shown at the Exhibition, from the Berlingen
Isles, from Angola, Madeira and the Cape de Verds. Orchilla weed is
very plentiful about the shores of the islands of New Zealand, some
being sent from thence to the Exhibition; but from a want of knowledge
as to the time at which it should be gathered, and the mode of
preparing it for the market, it has not yet become a saleable
commodity there. The rich varieties of lichens on the rocks and plains
of Australia have not been tested, as they ought to be, with Helot's
lichen test. Various lichens, and _Rocella tinctoria_, from Tenasserim
and other parts of India, have been introduced by the