chemical
re-agents, are colorless, but which, when the lichens are exposed to
the combined influence of atmospheric air, water, and ammonia, yield
colored substances. This series of colored products is usually
comprehended more for convenience sake than on account of chemical
identity, under the generic term orceine."

The whole subject of the chemistry of these bodies is at present in
a most unsatisfactory condition, demanding fresh investigation and
research, in illustration of which, the author exhibited tables of
the colorific and coloring principles, so far as they are at present
known, showing their chemical formulae and the authority therefor,
and various relative information. "It is highly probable that when
the chemistry of the lichens has been more fully studied, and the
whole subject of their color-educts and products better understood,
we shall begin to reduce the present confused mass of complex
substances, and find the same principles more extensively diffused
through different lichen species." Dr. L. entered somewhat minutely
on the chemical reactions of the better known colorific and coloring
principles, and their derivatives, so far at least as these throw
any light on the production and transmutation of the red or purple
colors extracted from what may be termed _par excellence_, the
_dye-lichens_. After a few remarks on the chemical constitution of
orchil and litmus, as given by Kane, Gelis, Pereira, and others, he
discussed the subject of decolorisation of weak infusions of orchil
and litmus by exclusion of atmospheric air, and by various
deoxidising agents, and the different theories as to the causation
of this phenomenon. "I have repeatedly had occasion to notice that,
when weak infusions of these substances are excluded for some time
from atmospheric air, in a bottle, with a tightly fitting cork, they
gradually lose color, but rapidly regain it on re-exposure. It is
curious that both orchil and litmus are what are called transient or
false colors, _i.e._, they slowly lose their bloom and tint by long
exposure to the atmosphere; the coloring matter, therefore, appears
to be decolorised both by exposure to, and exclusion from the air,
phenomena apparently of very opposite characters. The cause of the
latter phenomenon has never, so far as I am aware, been quite