ic adaptations; morphological adaptations; accommodations;
concluding statements 249-258

INDEX 259-268

INTRODUCTION

The history of biological science shows that the conceptions which men have
held concerning the nature of plant and animal growth have undergone a
series of revolutionary changes as the technique of, and facilities for,
scientific study have developed and improved. For a long time, it was
thought that life processes were essentially different in character than
those which take place in inanimate matter, and that the physical sciences
had nothing to do with living changes. Then, too, earlier students had only
vague notions of the actual structure of a living organism. Beginning with
the earliest idea that a plant or an animal exists as a unit organism, to
be studied as such, biological science progressed, first to the recognition
and study of the individual organs which are contained within the organism;
then to the tissues which make up these organs; then (with the coming into
use of the microscope as an aid to these investigations) to the cells of
which the tissues are composed; then to the protoplasm which constitutes
the cell contents; and finally to the doctrine of organic evolution as the
explanation of the genealogy of plants and animals, and the study of the
relation of the principles of the physical sciences to the evolutionary
process. The ultimate material into which organisms are resolved by this
process of biological analysis is the cell protoplasm. But protoplasm is
itself made up of a complex system of definite chemical compounds, which
react and interact according to the laws of physical science. Hence, any
study of the chemistry of plant growth is essentially a study of the
chemical and physical changes which take place in the cell protoplasm.

Protoplasm differs from non-living matter in three respects. These are (1)
its chemical composition; (2) its power of waste and repair and of growth;
and (3) its reproductive power. From the standpoint of chemical
composition, protoplasm is the most complex material in the universe. It
not only contains a greater variety of chemical elements, united into
molecules of enormous size and complexity, but also a greater variety of
definite chemical compounds than exist in any other known mixture, either
m