320 EXPERIMENT STATION EECOED. [Vol. 36 



seed ; that is, about 1,000 atmospheres. As the moisture content of the soil in- 

 creased the surface force decreased rapidly. When about 3.5 per cent of water 

 was added to the air-dry soil, the force remaining was about 375 atmospheres. 

 When the moisture content reached 6 per cent above air-dry in this soil it was 

 held with a force of 130 or more atmospheres. At 11 per cent above air-dry 

 the holding power fell to 22.4 atmospheres. At the wilting coefficient of the 

 soil (13.3 per cent above air-dry in the silt loam subsoil) the "back pull" of 

 the soil particles amounted to not more than that of a 0.1 molecular volume 

 sodium chlorid solution ; that is, not more than about 4 atmospheres. This was 

 shown to hold true for a number of types of soil with widely varying wilting 

 coefficients. 



" The wilting of plants at the wilting coefficient of the soil can not be due to 

 lack of moisture in the soil, nor to lack of a gradient of forces tending to move 

 water toward the plant. The viev/ is held, therefore, that the wilting at this 

 critical soil moisture content must be due to the increasing slowness of water 

 movement from soil particle to soil particle, and from these to the root hairs, 

 the rate of movement falling below that necessary to maintain turgidity of the 

 cells of the aerial parts even under conditions of low transpiration." 



Thirty-six references to literature bearing on the subject are also cited. 



Use of two indirect methods for the determination of the hygroscopic 

 coefficients of soils, F. J. Alway and V. L. Clakk (C7. S. Dept. Agr., Jour. Agr. 

 Researrh, 7 {1916), No. 8, pp. 345-359, fig. 1). — Experiments conducted at the 

 Nebraska Experiment Station on the determination of the hygroscopic coeffi- 

 cients of a number of Nebraska soils from their maximum water capacities and 

 their contents of hygroscopic moisture are reported. ■ 



It was found that while the Briggs-Shantz formula, hygroscopic coefficient— 

 (maximum water capacity — 21)X0.234 (E. S. R., 26, p. 628), "with many 

 soils gives values fully in accord with those directly determined, with many 

 others it gives results .so widely divergent that it can not be regarded as suffi- 

 ciently reliable for studies of available soil moisture, or even for soil-survey 

 purposes." 



The studies of the relation between hygroscopic coefficient and hygroscopic 

 moisture showed " that the hygroscopic coefficient may be calculated from the 

 hygroscopic moisture found in a soil which has been allowed to come into equi- 

 librium with an only partially saturated atmosphere, and that this method will 

 require only simple equipment, a minimum of skill on the part of the operator, 

 and be so economical of time as to recommend it wherever a very large number 

 of samples have to be dealt with." 



Note on soil denudation by rainfall and drainage: Conservation of soil 

 moisture. G. D. Hope {Agr. ./our. India. 11 {1916). No. 2. pp. 134-Ul, pis. 4).— 

 Suggestions for the prevention of erosion of northeast Indian tea soils are 

 given, special reference being made to terracing and drainage as practiced on 

 Java tea soils. 



Soil aeration in agriculture, A. Howard {Agr. Research Inst. Pusa Bui. 61 

 (1916), pp. 22, pis. 2, figs. 3). — This is a lecture delivered at the meeting of the 

 Board of Agriculture at Pusa, India, on soil ventilation in its physiological 

 relation to crop production, including some practical applications of soil aera- 

 tion by means of drainage, irrigation, and manuring. 



The toxicity of bog water, G. B. Rigg {Amer. Jour. Bot., 3 {1916), No. 8, 

 pp. .'(36, 437). — Experiments made at the University of Washington with waters 

 drawn from sphagnum bogs of the Puget Sound region and Alaska are reported. 



It is reported that "(1) when they were filtered through filter paper, then 

 saturated with NaCl, MgSO«, NajHPO., or (NH^jSOi, and allowed to stand 



