Page:Popular Science Monthly Volume 79.djvu/544

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540
THE POPULAR SCIENCE MONTHLY

THE WATER RELATIONS OF DESERT PLANTS
By Dr. D. T. MacDOUGAL

DESERT BOTANICAL LABORATORY, TUCSON, ARIZ.

WHILE working as a student in the laboratory of Professor 0. P. Jenkins at DePauw University twenty-three years ago, a typewritten schedule of experiments in plant physiology by Professor J. C. Arthur was placed in my hands as a guide in some practical work that was to extend throughout the collegiate year. The program in question probably constituted the first attempt of its kind in an American school, and its series of demonstrations may be taken to represent with fair accuracy the concepts and assumptions which might be safely presented to a student at that time.

Sachs and his students had made contributions of immense importance in growth, organogeny, irritability and tropisms in general, but the first serious efforts at analysis of the physical phenomena underlying the action of organisms may be assigned to Pfeffer and DeVries. Pfeffer established the principles of osmosis by a study of the behavior of crystalloidal substances toward membranes, the results of which were published in 1877, and in the same year DeVries brought out his contributions on turgidity. To the latter we owe the first systematic analysis of turgor, and of the mechanism by which the rigidity and firmness of soft-bodied organisms are maintained and by which movements are executed. The plasmolytic method for the detection of the differential action of substances and membranes, and the establishment of the principle of isotonic coefficients were also the work of DeVries. Both of these authors were intent on finding the solution of problems in plant physiology, in which they were notably successful, but their results form the basis of the dissociation theory of Arrhenius, and theory of pressure in solutions of van't Hoff, which together may be regarded as the basis of modern physics and chemistry.

It seems highly characteristic of research in plant physiology that devotion to many of its problems may lead the student far afield from botany, or the stricter domain of biology. The worker in this subject frequently finds it necessary to build cantilever bridges across chasms which yawn in front of him to find that the farther ends of his spans comes down to the solid ground of chemistry, physics, climatology or geology. At present, however, he has come upon rifts which he can not cross without aid from the farther side.