78 CARNEGIE INSTITUTION OF WASHINGTON. 



(including the porous cup atmometer, now in general use, the radio- 

 atmometer, and the standardized cobalt-chloride paper tests of foliar 

 transpiring power), and the main conditions affecting transpiration 

 composing the aerial environment complex in regard to water- 

 relations are now fairly susceptible of measurement. 



The second part of these studies involves much more difficult 

 problems. In the first place, comparatively little is known about 

 the subterranean surroundings of plants, this subject never having 

 received nearly as much attention as have the aerial surroundings. 

 In the second place, researches upon soil-water conditions involve 

 a much more difficult set of physical problems than do those of the 

 aerial- water environment. It has thus been necessary to attempt 

 the elaboration of new methods for measuring the water conditions 

 of the soil as these affect plants. While considerable progress has 

 been made in this direction, it is not yet possible to announce sat- 

 isfactory methods for determining the conditions controlling the 

 possible rate of water entrance from soil to roots. These are the main 

 environmental conditions that remain to be brought under quanti- 

 tative methods, and to them much attention is now being given. 



During the summer of 1912 Professor Livingston was assisted at 

 Tucson by Mr. E. M. Harvey, of the University of Chicago, who car- 

 ried out a series of measurements of the power of the soil to extract 

 water from a water-supplying surface, it being assumed that this 

 power is directly proportional to the resistance offered to water 

 absorption by roots. This procedure promises to be of value, but 

 possesses objectionable features, and more work will be necessary 

 before it can be stated within what limits and under what conditions 

 it may be available for the main problem in hand. 



Dr. Lon A. Hawkins, of the U. S. Department of Agriculture, 

 assisted Professor Livingston in the Laboratory of Plant Physiology 

 of the Johns Hopkins University during the period from October 1, 

 1912, to June 1, 1913, and carried out a somewhat elaborate series 

 of determinations of the moisture relations obtaining between soils 

 en masse and samples of the same or different soils separated from the 

 main soil by a porous clay wall. The results obtained remain mainly 

 to be subjected to calculation, but, while this will surely be useful 

 in some ways, it promises, as a method, little more than a new and 

 convenient means of soil sampling for water-content determinations. 



The abihty of soils to supply water to a standardized osmotic 

 cell or osmometer (considered preliminarily in Publication No. 50) 

 has also received considerable attention. Mr. H. E. Pulling, of the 

 University of Wisconsin, assisted Professor Livingston in this work 

 during the summer of 1913. After many failures it now appears at 

 least that a suitable osmotic membrane and mounting for this study 

 have been attained. This matter will be reported at a later date. 



