The next step in the process, the conversion of formaldehyde into sugars and starches, is not necessarily a photosynthetic one, as it can be brought about by protoplasm which contains no chlorophyll or other energy-absorbing pigment. It is, however, a characteristic synthetic activity of living protoplasm. There is little definite knowledge as to how the cell protoplasm accomplishes this important task. As has been pointed out, the polymerization of formaldehyde into a sugar-like hexose, known as "acrose," can be 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.