is, in which sugars are produced, and another, which
has no specific name, whereby proteins are elaborated. The translocation of
the synthetized material involves the change of insoluble compounds into
soluble ones, effected by the aid of enzymes. For storage purposes, the
soluble forms are usually, though not always, condensed again into more
complex forms, these latter changes requiring much less energy than do the
original syntheses from raw materials.

The destructive process, respiration, is characteristic of all living
matter, either plant or animal organisms. It takes place continuously
throughout the whole life of a plant. During rapid growth it is
overshadowed by the results of the synthetic process, but during the
ripening period in which the seed is matured, and during the germination of
the seed itself, growth is practically at a standstill and the respiratory,
destructive action predominates, so that the plant actually loses weight.

GROUPS OF ORGANIC COMPOUNDS FOUND IN PLANTS

As a result of their various synthetic and metabolic activities, a great
variety of organic compounds is produced by plants. Certain types of these
compounds, such as the carbohydrates and proteins, are necessary to all
plants and are elaborated by all species of autotrophic plants. Other types
of compounds are produced by many, but not all, species of plants; while
still others are found in only a few species. It is fairly easy to classify
all of these compounds into a few, well-defined groups, based upon
similarity of chemical composition. These groups are known, respectively,
as the carbohydrates and their derivatives, the glucosides and tannins; the
fats and waxes; the essential oils and resins; organic acids and their
salts; the proteins; the vegetable bases and alkaloids; and the pigments. A
consideration of these groups of compounds, as they are synthetized by
plants, constitutes the major portion of the study of the chemistry of
plant life as presented in this book. Following the discussion of the
compounds themselves, the chapters dealing with enzymes, with the colloidal
nature of protoplasm, and with the supposed accessory stimulating agencies,
aim to show how the manufacturing machine known as the plant cell
accomplishes its remarkable results, so far as the process is now
understood.

PHYSIOLOGICAL USES AND BIOLOGICAL SIGNIFICANCE

In connection with the discussion of each of the above