oring matter
with those of cyanine, we have found that the rose-red coloring matter
is the same as the blue, or at least results from a modification of the
same independent principle. It appears in the rose-red modification,
when the juice of the plant, with which it exists in contact, possesses
an acid reaction. We have always observed this acid reaction in the
juices of plants with red or rose-red coloration, while the blue juices
of plants have always exhibited an alkaline reaction.

We have exposed most of the rose-red or red-colored flowers which are
cultivated in the Paris Museum to the influence of alkalies, and have
seen that they first become blue and then green by their action.

It is often perceived that certain rose-red flowers, as those of the
_Mallow_, and in particular those of the _Hibiscus Syriacus_, acquire by
fading a blue and then a green coloration, which change, as we have
found, depends on the decomposition of an organic nitrogenous substance,
which is found very frequently in the petals. This body generates as it
decomposes ammonia, which communicates to the flowers the blue or green
color. By action of weak acids, the petals can be restored to their
rose-red color.

The alteration of color of certain rose-red flowers can also be
observed when the petals are very rapidly dried, for example, in
_vacuo_, by which it cannot be easily assumed that a nitrogenous body
has undergone decomposition to the evolution of ammonia. But, before all
things, it must be mentioned that in this case the modification of color
passes into violet, and never arrives at green; and, further, that it is
always accompanied with the evolution of carbonic acid, which we have
detected by a direct experiment. Petals which were before rose-red, and
have become violet by slight drying, evolve carbonic acid, and on that
account it may be assumed that the rose-red color is produced in the
petals by this carbonic acid, and that by its expulsion the petals
assume the blue color, by which the flowers with neutral juices are
characterized.

We believe that we are able to speak with certainty that flowers with a
rose-red, violet, or blue color, owe their coloration to one and the
same substance, but which is modified in various ways by the influence
of the juices of plants.

Scarlet-red flowers also contain cyanine reddened by an acid, but in
such cases this substance is mixed with a yellow coloring matter which
we will now descri