have been found to obey the ordinary laws of chemical
reactions. Thus, the effect of the variations in intensity of light upon
photosynthesis causes increase in the rate of this activity which may be
represented by the ordinary responses of reaction velocities to external
stimuli. Similarly, the effect of rises in temperature upon the rate of
assimilation and upon respiration are precisely the same as their effect
upon the velocity of any ordinary chemical reaction. Within certain
definite ranges of temperature, the same statement holds true with
reference to the rate of growth of the plant, although the range of
temperature within which protoplasm lives and maintains its delicate
adjustment to the four vital processes of life is limited; beyond a certain
point, further rise in temperature does not produce more growth but rather
throws the protoplasmic adjustment out of balance and growth either slows
up markedly or stops altogether.

Hence, we may say that the methods by which the plant machine (protoplasm)
accomplishes its results are essentially and definitely chemical in
character and may be studied purely from the standpoint of chemical
reactions, but the maintenance of the machine itself in proper working
order is a vital phenomenon which is largely dependent upon the external
environmental conditions under which the plant exists. A study of the
phenomena resulting from the colloidal condition of matter is throwing a
flood of light upon the mechanism by which protoplasm accomplishes its
control of vital activities. But we are, as yet, a long way from a complete
understanding of how colloidal protoplasm acquires and maintains its unique
ability of self-regulation of the conditions necessary to preserve its
colloidal properties and of how it elaborates the enzymes which control the
velocity of the chemical reactions which take place within the protoplasm
itself and which constitute the various processes of vital activity.

The object of this study of the chemistry of plant growth is to acquire a
knowledge of the constitution of the compounds involved and of the
conditions under which they will undergo the chemical changes which, taken
all together, constitute the vital processes of cell protoplasm.

CHEMISTRY OF PLANT LIFE

CHAPTER I

PLANT NUTRIENTS

There is some confusion in the use of the terms "nutrient," "plant