e easily accomplished by ordinary laboratory reactions, and
acrose can be converted into glucose or fructose by a long and difficult
series of transformations. But such processes as are employed in the
laboratory to accomplish these artificial synthesis of optically-active
sugars from formaldehyde can have no relation whatever to the methods of
condensation which are used by cell protoplasm in its easy, almost
instantaneous, and nearly continuous accomplishment of this transformation.
Furthermore, these simple hexoses are by no means the final products of
cell synthesis, even of carbohydrates alone. In many plants, starch appears
as the final, if not the first, product of formaldehyde condensation. At
least, the transformation of the simple sugars, which may be supposed to be
the first products, into starch is effected so nearly instantaneously that
it is impossible to detect measurable quantities of these sugars in the
photosynthetically active cells of such plants. Other species of plants
always show considerable quantities of simple sugars in the vegetative
tissues, and some even store up their reserve carbohydrate food material in
the form of glucose or sucrose. Attempts have been made to associate the
type of carbohydrate formed in cell synthesis with the botanical families
to which the plants belong, but with no very great success. For each
individual species, however, the form of carbohydrate produced is always
the same, at least under normal conditions of growth. For example, the
sugar beet always stores up sucrose in its roots, although under abnormal
conditions considerable quantities of raffinose are developed. Similarly,
potatoes always store up starch, but with abnormally low temperatures
considerable quantities of this may be converted into sugar, which becomes
starch again with the return to normal conditions.

While it is impossible, with our present knowledge, to even guess at the
mechanism by which protoplasm condenses formaldehyde into sugars and these,
in turn, into more complex carbohydrates, the structure and relationships
to each other of the final products of photosynthesis are well known, and
are discussed at length in the following chapter.

References

BARNES, C. R.--"Physiology" (Part II of Coulter, Barnes and Cowles'
"Textbook of Botany"), 187 pages, 18 figs., Chicago, 1910.

GANONG, W. F.--"Plant Physiology," 265 pages, 65 figs., New York, 1908 (2d
ed.).