26 



SCIENCE 



[N. S. Vol. XLVI. No. 1176 



Phytogeography has two main phases, 

 the historical and the physiological. 



In the investigation of the historical fac- 

 tors involved in the geographical distribu- 

 tion of plants, the methods of physical 

 chemistry can be of little service. 



The physiological problems of ecology 

 and phytogeography are essentially those 

 of the relation of the organism to its envi- 

 ronment. It is here that physical chem- 

 istry, along with other quantitative and 

 experimental methods of research may be 

 profitably applied. 



It is a truism to say that the relations of 

 the living protoplasm to its inert environ- 

 ment constitutes one of the most funda- 

 mental groups of biological problems. To 

 cooperate in the solution of these problems 

 is the greatest opportunity of ecologists. 

 That the contribution of ecology has not al- 

 ready been greater is largely attributable to 

 the non-quantitative character of most of 

 the work hitherto done. 



In the closer analysis of the relationship 

 of the organism to its surroundings it is 

 apparent that there are two planes of con- 

 tact of protoplast and environment: that 

 which lies between the protoplast and sepa- 

 rates it from the outside world, and that 

 which lines the vacuoles of the cell and 

 separates the deeper-lying protoplasm from 

 the internal environment of the vacuolar 

 solution, just as the plasma membrane sepa- 

 rates it from the external world. 



The processes which are taking place in 

 these two planes are presumably physico- 

 chemical processes. Certainly, physico- 

 chemical methods of investigation are those 

 which may be applied wdth the greatest 

 hope of advance in the solution of the prob- 

 lems presented by those planes of contact 

 of organism and environment. 



That these processes are of fundamental 

 significance to the student of the complex 

 problems of ecology and phytogeography 



of the higher plants should be evident from 

 the fact that the differentiation of tissues 

 in the vast majority of flowering plants, 

 with which alone I am concerned in this 

 paper, is such that the cell membrane comes 

 into contact with two quite distinct phases 

 of the environment. In water absorption, 

 it separates the fluids of the cell from a soil 

 solution of quite different properties. In 

 water loss, it separates the fluids of an- 

 other set of cells from an atmosphere vary- 

 ing enormously in its water absorbing 

 capacity. 



These two environmental factors, which 

 stated in physiological terms may be re- 

 ferred to as the force with which the sub- 

 stratum withholds water from the plant 

 and the force with which the atmosphere 

 tends to withdraw water from the plant, 

 have by common consent been given the 

 place of first importance in the environ- 

 mental complex. 



The importance of a thoroughgoing in- 

 vestigation of the relationship of the plasma 

 membrane to the concentration and the 

 composition of the intracellular and the 

 extracellular solution has long been recog- 

 nized. Nor have physiologists interested in 

 the problem of transpiration failed to recog- 

 nize the fundamental significance of the 

 membrane which separates the fluid con- 

 tents of the cell from its gaseous environ- 

 ment. 



It is quite natural that the problem of 

 the permeability of the cell membrane 

 should have been far more extensively in- 

 vestigated than that of the relationship of 

 the protoplast to the cell sap. Experi- 

 mental modification of the solution sur- 

 rounding the cell is subject to only the 

 limitations imposed by the solubilities and 

 other properties of chemical reagents and 

 the viability under the influence of these 

 reagents of the cells or tissues employed. 

 To determine the properties of the sap eon- 



