ll, transfer to a
separatory funnel and allow the two layers to separate. The carotin will
now be in the upper layer of petroleum ether, and the xanthophyll in the
lower alcohol layer; these layers may be drained off separately and the
solvents evaporated in order to recover the pigments in dry form.

=Lycopersicin= (or lycopin) is a hydrocarbon pigment having the same
formula as carotin. It is, however, brilliantly red in color, and
crystallizes in a different form and has a different adsorption spectrum
from carotin. It is the characteristic pigment of red tomatoes, and is
found also in red peppers. Yellow tomatoes have only carotin as their
skin-pigment, while lycopersicin is usually present in the flesh of the
ripe fruits of all varieties and in the skin of red ones. It has been
shown, however, that if varieties of tomatoes which are normally red when
ripe, are ripened at high temperatures, 90 deg. F. or above, their skins
will be yellow instead of red when fully ripe. Hence, the occurrence of
carotin, or of lycopersicin, as the skin pigment is determined in part by
the varietal character (being different in different varieties when ripened
at normal temperatures) and in part by the temperature at which the fruit
ripens. The two pigments are, of course, isomers; but the difference in
their structural arrangement is not known.

=Fucoxanthin=, C_{40}H_{54}O_{6}, is a brownish-red pigment, found in fresh
brown algae, and in some brown sea-weeds. Its formula indicates that it is
an oxidized carotin. With iodine, it forms a compound having the formula
C_{40}H_{54}O_{6}I_{4}. It is unlike carotin and xanthophyll in that it has
basic properties, forming salts with acids, which are blue in color.

PHYCOERYTHRIN AND PHYCOPHAEIN

These are the principal pigments of red and brown seaweeds, respectively.
Their most characteristic difference from the pigments of non-aquatic
plants is that they are easily soluble in water, and insoluble in most
organic solvents, such as alcohol, ether, etc. At first thought, this would
appear to be impossible, since the plants grow in water and it would seem
that their water-soluble pigments would be continuously dissolved out of
the tissues. The reason why this does not occur lies in the fact that these
pigments exist in the cells of the seaweeds in colloidal form (see Chapter
XV), and, hence, cannot diffuse out through the cell-walls. The only way in
which they can be