seeds or other storage organs of plants. They are
practically indigestible by animals, as the proper enzymes to hydrolyze
them are not present in the digestive tract; hence, they are commonly
classed with the indigestible cellulose as the "crude fiber" of plants
which are to be used as food by animals.

PHYSIOLOGICAL USE AND BIOLOGICAL SIGNIFICANCE OF CARBOHYDRATES

If the organic compounds produced by plants be classified with reference to
their uses in metabolism into the three groups known, respectively, as
temporary foods, storage products, and permanent structures, it is clear
that the carbohydrates which have been discussed in this chapter may fall
into either one of the first two of these classes. There can be no doubt
that the first products of photosynthesis, whichever ones they may be in
different plants, may be directly used as temporary foods, to furnish the
energy and material for the building up of permanent structures. Also,
there can be no doubt that these same carbohydrates are translocated to
the storage organs and accumulated for later use by the same plant (as, for
example, in the case of the perennials), or by the next generation of the
plant (when the storage is in the endosperm adjoining the embryo of the
seed).

There is no known explanation as to why different species of plants make
use of different carbohydrates for these purposes; or why certain species
elaborate starch out of the same raw materials from which other species
produce sugars, inulin, or glycogen, etc.

In general, starch is the final product of photosynthesis in most green
plants; but there are many exceptions to this. The polysaccharides, which
are generally insoluble, must be broken down into the simpler soluble
sugars before they can be translocated to other organs of the plant for
immediate, or future, use. When they reach the storage organs, they may be
recondensed into insoluble polysaccharides, or stored as soluble sugars.
Examples of the latter type of storage are, sucrose in beet roots, glucose
in onion bulbs, etc. Sometimes, this habit of storage seems to be a species
characteristic; as potatoes store starch, while beets, growing in the same
soil and under exactly the same environment, store sugar. But in other
cases, the nature of the carbohydrate stored undoubtedly is correlated with
the external temperatures at the time of storage. It has been shown that
cold, which tends to physiological dryness, very fr