THE WATER-SUPPLYING POAYER OF THE SOIL AS 

 INDICATED BY OSMOMETERS. 



INTRODUCTION. 



From a review of the literature of the water-relation between ordinary- 

 plants and the soil in which they are rooted it appears that researches 

 in this field of plant physiology have thus far been few, and that present 

 knowledge in this regard is very meager. The importance of the 

 water-relations of plants, both in themselves and as a basis for the 

 dynamic study of other plant relations, is not likely to be overestimated. 

 The water-relation appears to play a prime role in the influence of most 

 environmental complexes met with in nature and in agriculture, and 

 among the numerous phases of this general relation the particular phase 

 which has to do with the passage of water from soil to roots is not by 

 any means the least worthy of careful study. 



It is somewhat surprising to note with what thoroughness the 

 dynamics of root absorption has been overlooked in plant physiology; 

 only very recently has the physiological ecology of roots begun to 

 receive attention, and the soil has been studied mainly as such rather 

 than as a portion of plant environment. Physiological writers appear 

 usually to suppose that vacuolar osmotic pressure in peripheral cells 

 of roots is in some way directly accountable for the continuous supply of 

 moisture to growing and transpiring parts situated higher up, and the 

 exceedingly complex set of conditions controlling water movement 

 through the root periphery is frequently dismissed with brief and vague 

 reference to osmotic phenomena. With the development of our knowl- 

 edge following Dixon's^ admirable researches on the conditions deter- 

 mining the rate of the rise of water in plant stems it became more and 

 more clear that the moisture condition of the transpiring and otherwise 

 water-consuming parts of the plant body probably exercise the funda- 

 mental controlling influence upon the ascent of water. It also became 

 more and more apparent that this influence was exerted through a 

 comparatively simple physical connection between the various portions 

 of the plant. Various vague theories of complex and unanalyzed "vital" 

 pumping action in living cells died very hard and their shadows still 

 frequent the literature, but most students familiar with the older 

 contributions referred to by Dixon and with the rather rigorous and 

 very convincing work of Dixon, of Overton,^ and of Renner^ have 

 apparently laid "vitalism" aside in this connection. 



^Dixon, H. H., Transpiration and the ascent of sap. Prog. Rei Bot. 3: 1-66. 1909. [This is 

 a summary of the whole problem and is accompanied by many references to the literature.] 



^Overton, J. B., Studies on the relation of the living cells to the transpiration and sap-flow in 

 Cyperus. Bot. Gaz. 51 : 28-63, 102-20. 1911. 



^Renner, O., Experimentelle Beitrage zur Kenntnis der Wasserbewegung. Flora 103: 171-247. 

 1911. 



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