erpene, Aetherische Oele, Harze,
Kautschuk," 822 pages, Berlin, 1912.

ALLEN'S Commercial Organic Analysis, Vol. 5, "Tannins, Dyes and Coloring
Matters, Inks," 704 pages, 6 figs., Philadelphia, 1911 (4th ed.).

COOK, M. T. and TAUBENHAUS, J. J.--"The Toxicity of Tannin," Delaware
College Agricultural Experiment Station _Bulletin_ No. 91, 77 pages, 43
figs., Newark, Del., 1911.

DEKKER, J.--"Die Gerbstoffe," 636 pages, 3 figs., Berlin, 1913.

GORE, H. C.--"Experiments on the Processing of Persimmons to Render them
Nonastringent," U. S. Department of Agriculture, Bureau of Chemistry
_Bulletin_ No. 141, 31 pages, 3 plates, 1911; and No. 155, 20 pages, 1912.

LLOYD, F. E.--"The Tannin-Colloid Complexes in the Fruit of the Persimmon,
_Diospyros_," in _Biochemical Bulletin_, Vol. 1, No. 1, pages 7 to 41, 34
figs., New York, 1911.

CHAPTER VIII

PIGMENTS

Practically all plant structures contain pigments. These may be considered
as of two types: (_a_) the vegetative pigments, which have a definite
energy-absorbing role in the metabolic processes of the tissues which
contain them, and (_b_) the ornamental pigments. It is probable that the
same chemical compound may serve in either one of these capacities under
different conditions, but, in general, it is possible to assign either a
definite vegetative, or physiological, use, or else a simple ornamental, or
biological, significance to each of the common pigments. The first type is
found widely distributed through the protoplasm, or cell-sap, of the plant
structures; while the ornamental pigments are located chiefly in the
epidermal cells, especially of flowers.

With respect to their colors, the plant pigments may be grouped as follows:

Green--the chlorophylls.
Yellow--the carotinoids, flavones, and xanthones.
Red--phycoerythrin, lycopersicin, anthocyanin.
Blue--anthocyan derivatives.
Brown--phycophaein, fucoxanthin.

Of these, the chlorophylls, the carotinoids, phycoerythrin (in red
sea-weeds) and phycophaein (in brown sea-weeds) are generally vegetative
pigments; while the others form the basis for most of the ornamental
pigments, although they may have a definite energy-absorbing effect, in
some cases.

THE CHLOROPHYLLS

The importance of the green coloring matter in plants has been understood
for more than a century, its connection with