DESERT PLANTS 541 



The conclusions of DeVries and Pfeffer, impressive as to their in- 

 clusiveness 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 be- 

 coming an exact science. The water-relations of the organism have al- 

 ways stood out as a subject of great importance, and as the main as- 

 pects 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 re- 

 gret; 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 accumu- 

 lation 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 considera- 

 tion of the action of the epithelial cells and of other tissues which pre- 

 sented 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 appli- 

 cation. 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 morphol- 

 ogy of the chromosome, chlorophyll bodies and cell-organs in general, 



