t least a part of the seasonal
changes in color of plants is either the cause of, or the effect of,
variations in sugar content of the tissues of the plants, accompanying the
changes in external temperatures.

Oftentimes, the anthocyanin pigments seem to be associated with sugar
production, as contrasted with the chlorophylls, which seem to be more
favorable to the production of starch. But in this case also, it is
impossible to say whether the pigment is the direct causative agent in the
type of carbohydrate production or whether it is the effect of the same
external factors which determine, or modify, the character of the
carbohydrate condensation.

BIOLOGICAL SIGNIFICANCE OF ORNAMENTAL PIGMENTS

The ornamental pigments undoubtedly have definite biological significance.
When present in the storage roots, such as beet-roots, carrots, etc., or in
the above-ground parts of plants, they may have served to protect these
organs against herbivorous animals which were accustomed to consume green
foods.

In flowers, the brilliant ornamental pigments undoubtedly serve to attract
the insects which visit these blossoms in search of nectar, and in so doing
promote cross-fertilization. Recent experiments have demonstrated that
colors are much more efficient than odors in attracting insects.

Taken altogether, it is apparent that the pigments may have a variety of
important roles in plants. At the same time, some of them may be waste
products, with no definite use in the plant economy.

REFERENCES

ABDERHALDEN, E.--"Biochemisches Handlexikon, Band 6, Farbstoffe der
Pflanzen- und der Tierwelt," 390 pages, Berlin, 1911.

PERKIN, A. G. AND EVEREST, A. E.--"The Natural Organic Colouring Matters,"
655 pages, London, 1918.

WAKEMEN, NELLIE A.--"Pigments of Flowering Plants," in _Transactions_ of
the Wisconsin Academy of Sciences, Arts, and Letters, Vol. XIX, Part II,
pages 767-906, Madison, Wisc., 1919.

WATSON, E. R.--"Colour in Relation to Chemical Constitution," 197 pages, 65
figs., 4 plates, London, 1918.

WHELDALE, M.--"The Anthocyan Pigments of Plants," 304 pages, Cambridge,
1916.

WILLSTAeTTER, R. AND STOLL, A.--"Untersuchung ueber Chlorophyllen, Methoden
und Ergebnisse," 432 pages, 16 figs., Berlin, 1913.

CHAPTER IX

ORGANIC ACIDS, ACID SALTS, AND ESTERS

Organic acids, either in free form, or partially neu