Page:Popular Science Monthly Volume 79.djvu/545

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DESERT PLANTS

541

The conclusions of DeVries and Pfeffer, impressive as to their inclusiveness and with some of their applications ranging far ahead of the science of the time-yielded methods of practical calibration of a large number of biological processes and set physiology in the way of becoming an exact science. The water-relations of the organism have always stood out as a subject of great importance, and as the main aspects are presented with less complication in plants, where the essential features are not complicated by a circulatory system, it has naturally followed that the principal contributions have been made by workers who attacked the problems involved from a botanical point of view.

Osmotic action, being earliest and best known, has had thrown upon it the entire burden of the explanation of the water-relations, and all of the mechanical action of the organism which might in any manner be attributed to pressures originating by the action of electrolytes. One contemplates departures from it, as set out in text-books, with regret; but some very substantial modifications of our conceptions with regard to these matters are long overdue.

The simpler phenomena of swelling and of changes of form due to the imbibition action of wood, starch and other material in a colloidal condition found place even in my preliminary directions for work: it was well recognized, however, that secretion, excretion and the accumulation of water anywhere in an organism were not fully comprehensible on the theory of osmotic action, and I can still recall that while trying out the simple tests in plant physiology which had been outlined for me, and which were calculated to give an encouraging sense of sufficiency to the student, the professor of biology was leading us into a consideration of the action of the epithelial cells and of other tissues which presented many features not explainable by osmosis. However much this inadequacy may have impressed my teacher, candor compels me to say that it did not bear too poignantly upon me. and I was willing to leave these as well as many other troublesome things to such all-embracing causes as "special physiological action" or any other convenient bogie, as being entirely too mysterious for a beginner.

Osmosis has indeed brought us far, and the briefest review will demonstrate the tremendous strides that have been made by its application. Our conceptions of turgidity and of processes which depend directly upon cell-pressures are so well-established as to be subject to but slight possible modification. It is not so, however, with many other phases of the physiology of the cell. The greater mass of an organism is colloidal, complex as to constitution, diverse as to reaction to acids, alkalies and electrolytes in general, and lastly having highly specific inter-actions among its constituents. It is bodies or masses of this kind that are to be dealt with when considering the action and morphology of the chromosome, chlorophyll bodies and cell-organs in general,