discovered which determines the character of the
energy-storage compound which any given species of plant will elaborate.
The process of photosynthesis would seem to be identical in all cases, at
least up to the point of the production of the first hexose sugar; but the
transformation of glucose into other monosaccharides, disaccharides, and
polysaccharides seems to be a matter which obeys no rule or law.

Finally, there remains to be considered the occurrence and uses of sugars
in the fleshy tissues of fruits. These tissues have, of course, no direct
function in the life history of the plant. They surround the seed, but they
must decay or be destroyed before the seed can come into the proper
environment for germination and growth. In most fruits, starch is the form
in which the carbohydrate material is first deposited in the green tissue,
but as the fruit ripens the starch rapidly changes into sugars, with the
result that the fruit takes on a flavor which makes it much more attractive
as a food for men and animals. This purely biological significance of the
presence of sugars (and of the other substances which give desirable
flavors to fruits, vegetables, etc.), can have no possible relation to the
physiological needs of the individual plant, however.

It is apparent that the production of these immense stores of reserve food
by plants makes them useful as food for animals, and it is, of course, the
storage parts of the plants which are most useful for this purpose. This
biological relationship needs no further emphasis.

REFERENCES

ABDERHALDEN, E.--"Biochemisches Handlexikon, Band 2 ... Die Einfachen
Zuckerarten, Inuline, Cellulosen, ...," 729 pages, Berlin, 1911, and "Band
8--1 Ergaenzungsband (same title as Band 2)--" 507 pages; Berlin, 1914.

ARMSTRONG, E. F.--"The Simple Carbohydrates and Glucosides," 233 pages.
_Monographs_ on Biochemistry, London, 1919 (3d ed.).

FISCHER, E.--"Untersuchung ueber Kohlenhydrate und Fermente, 1884-1908,"
912 pages, Berlin, 1909.

MACKENSIE, J. E.--"The Sugars and their Simple Derivatives," 242 pages, 17
figs., London, 1913.

TOLLENS, B.--"Kurzes Handbuch der Kohlenhydrate," 816 pages, 29 figs.,
Leipzig, 1914 (3d ed.).

CHAPTER V

GUMS, PECTINS, AND CELLULOSES

These substances constitute a group of compounds which are very similar to
the polysaccharide carbohydrates in com