July 13, 1917] 



SCIENCE 



27 



tained in the vacuole at any moment is a 

 problem of some difficulty, to modify these 

 properties at will is in itself an undertaking 

 of no mean magnitude, while to investigate 

 with any degree of completeness the rela- 

 tions of the properties of the sap of the 

 vacuoles to the surrounding protoplasm 

 would seem to be a task of almost unsur- 

 mountable difficulties. 



Nevertheless, the time has come when an 

 investigation of the properties of the sap of 

 the vacuole in relation to the protoplast 

 and in relation to the factors of the envi- 

 ronment should be undertaken. It is in- 

 conceivable that the properties of the sap 

 should be uninfluenced by the forces which 

 ai-e acting upon and through the living 

 membrane surrounding the cell. It is diffi- 

 cult to think, for example, that the osmotic 

 pi-operties of the sap of the vacuoles should 

 be independent of the forces which are 

 tending to draw water from the cell in 

 transpiration and of the forces in the sub- 

 stratum which oppose water absorption. If 

 this be true, an investigation of the prop- 

 erties of the intracellular fluids of plants 

 in various environments, in which the 

 water-absorbing power of the air as well as 

 the water-yielding capacity of the soil vary 

 enormously, may throw much light upon 

 the basic physiological problems of ecology 

 and plant distribution. 



If progress is to be made, it is not merely 

 necessary that problems be clearly defined, 

 but that methods which are adequate and 

 practical for use under the conditions sur- 

 rounding the investigation shall be found. 

 The question of method becomes, therefore, 

 one of paramount importance. 



The phytogeographer must limit his 

 choice to those methods which can be used 

 under camp conditions. Otherwise he must 

 be willing to forego work on phytogeog- 

 raphy in the only regions in which it can 

 be satisfactorily investigated, that is, in 



those which have not been completely modi- 

 fied by the activities of man. Fortunately 

 the determination of the depression of the 

 freezing-point of a solution below that of 

 the pure solvent furnishes a relatively 

 simple method of calculating its osmotic 

 pressure or osmotic concentration. It is 

 quite possible to make cryoscopic determi- 

 nations sufficiently exact for phytogeo- 

 graphical problems in the field, and espe- 

 cially at the field laboratories which fortu- 

 nately are becoming more numerous. 



In addition to developing a simple tech- 

 nique for use in the field, one who hopes to 

 convince botanists that the investigation 

 of the physico-chemical properties of vege- 

 table saps should form an essential part of 

 a comprehensive ecological or phytogeo- 

 graphical study, must show that in any 

 region the sub-habitats, formations, asso- 

 ciations, plant societies or whatever the 

 nomenclatorial specialist may call them, are 

 measurably different in their sap prop- 

 erties, aJid that even more conspicuous dif- 

 ferentiation exists in the sap properties of 

 the larger phytogeographical regions. If 

 he can also show that such ecological groups 

 as the succulents, the epiphytes and the 

 parasites are differentiated in the physico- 

 chemical properties of their tissue fluids, 

 the necessity for the use of physico-chem- 

 ical methods in phytogeographical work 

 will be self-evident. 



The foregoing outline of the fundamental 

 conceptions underlying the studies which 

 my associates and I have carried out in 

 various regions has of necessity been so 

 detailed that it will be impossible at this 

 time to give any adequate summary of the 

 many hundreds of determinations of 

 osmotic concentration of tissue fluids of 

 plants growing in various environments 

 which are now at my disposal. 



The actual details, as far as published, 

 are available in a series of technical papers. 



