THE WATER-RELATION BETWEEN PLANT AND SOIL. 



INTRODUCTION. 



The work of Dixon^ and his colleagues, and that of Renner,^ of 

 Overton,^ and others have at length placed upon what appears to be a 

 rational physical basis the long-vexed question of the dynamics of the 

 ascent of water in plants, and recent studies of the relation of the 

 evaporating power of the air* and that of sunshine^ to plant transpi- 

 ration have made it possible at least to begin to consider the problems 

 of the aerial water relation of plants as involving measurable forces or 

 powers. Our knowledge of the subterranean water-relation of plants 

 remains, however, in an exceedingly primitive condition, although the 

 a priori analysis of the problem here involved may be carried forward 

 beyond the abihty of present methods to furnish experimental data. 



Livingston^ has insisted that the power of the soil to deliver water 

 to root surfaces is the prime external condition determining the moisture 

 supply to plants in non-saline and non-toxic soils, and the same writer 

 has emphasized the need of some adequate method for determining 

 this water-supplying power of the soil. Such a method is not yet at 

 hand, though encouraging progress toward its attainment has recently 



'Dixon, H. H., Transpiration and the ascent of sap. Prog. Rei Bot. 3: 1-66. 1909. 

 ^Renner, O., Beitrage zur Physik der Transpiration. Flora 100: 451-547. 1910. 



, Experimentelle Beitrage zur Kenntnis der Wasserbewegung. Flora 103; 171-247. 1911. 



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



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

 'Livingston, B. E., The relation of desert plants to soil moisture and to evaporation. Carnegie 

 Inst. Wash. Pub. 50. Washington. 1906. 



, Relative transpiration in cacti. Plant World 10: 110-14. 1907. 



, A rain-correcting atmometer for ecological instrumentation. Plant World 13: 79-82. 



1910. 



, The resistance offered by leaves to trauspirational water loss. Plant World 16: 1-35. 



1913. 

 Harvey, E. M., The action of the rain-correcting atmometer. Plant World 16: 89-93. 1913. 

 'Livingston, B. E., A radio-atmometer for measuring light intensity. Plant World 14: 96-9. 

 1911. 



, Light intensity and transpiration. Bot. Gaz. 52: 418-38. 1911. 



'Livingston, B. E., 1906, page 19 el seq. 



, Roles of the soil in limi ting plant activities. Plant World 12: 49-53. 1909. 



, The relation of the osmotic pressure of the cell sap in plants to arid habitats. Plant 



World 14: 153-64. 1911. 



, Present problems of physiological plant ecology. Amer. Nat. 43 : 369-77. 1909. [The 



essentials of this paper appeared also, with same title, in Plant World 12: 41-6. 1909.] 



, Present problems in soil physics as related to plant activities. Amer. Nat. 46 : 294-301 . 



1912. 



, Osmotic pressure and related forces as environmental factors. Plant World 16 : 165-76. 



1913. 

 Free, E. E., Studies in soil physics. Plant World 14: 29-39, 59-66, 110-19, 164-76, 186-90. 

 1911. Also reprinted, repaged. Tucson. 1912. 



