he reactions which go
to make up the vital activities of a living cell and those of the same
chemical substances when in inanimate form in the laboratory lies in the
presence in the colloidal mass of the accelerating catalysts known as
enzymes, which are produced by the protoplasm itself in some way which is
as yet wholly unknown; and which not only add to the possibilities of rapid
chemical change which are afforded by the colloidal nature of the material,
but also, because of their extreme sensitiveness to minute changes in
environmental conditions, serve to govern both the rate and the direction
of the individual chemical reactions which constitute the vital activities
of the protoplasmic mass. These enzymes are not distributed uniformly
through any given cell, or organism, but are localized in different parts
of the cell or tissue and so give to its different parts the ability to
perform their various different functions.

References

ATKINS, W. R. G.--"Some Recent Researches in Plant Physiology," 328 pages,
28 figs., London, 1916.

CZAPEK, F.--"Chemical Phenomena of Life," 152 pages, New York, 1911.

CZAPEK, F.--"Ueber eine Methode zur direkten Bestimmung der
Oberflaechenspannung der Plasmahaut von Pflanzen," 86 pages, 3 figs., Jena,
1912.

HOeBER, M. R.--"Physikalische Chemie der Zelle und der Gewebe," 671 pages,
55 figs., Leipzig, 1911.

LIVINGSTON, B. E.--"The Role of Diffusion and Osmotic Pressure in Plants,"
149 pages, Chicago, 1903.

MCCLENDON, J. F.--"Physical Chemistry of Vital Phenomena," 248 pages,
Princeton University Press, 1917.

MACDOUGAL, D. T.--"Hydration and Growth," Publication No. 297, Carnegie
Institution of Washington, 176 pages, 52 figs., Washington, D. C., 1920.

SPEIGEL, L., trans. by LUEDEKING, C. and BOYLSTON, A. C.--"Chemical
Constitution and Physiological Action," 155 pages, New York, 1915.

THOMPSON, D'A. W.--"On Growth and Form," 793 pages, 408 figs., Cambridge,
1917.

WILLOWS, R. S. and HATSCHEK, E.--"Surface Tension and Surface Energy and
their Influence on Chemical Phenomena," 116 pages, 21 figs., New York,
1919, (2d ed.).

CHAPTER XVII

HORMONES, AUXIMONES, VITAMINES, AND TOXINS

Reference has frequently been made, in preceding chapters, to the effect of
various stimulating or inhibiting agencies upon the physiological
activities of plant protoplasm. In the main, these agencies