FACTORS INFLUENCING REPRODUCTION 841 



coefficient of 12 per cent on the basis of air-dry weight. Calculations 

 from the moisture-holding capacity at saturation, which are probably 

 unreliable for these soils, gave, on the basis of volume, wilting co- 

 efficients of 21 per cent for the decomposed humus, 15 per cent for the 

 raw humus, and 12 per cent for the mineral soil.^° The most reliable 

 physical property which could be determined with the apparatus at hand 

 is the moisture-holding capacity, saturated.^ ^ The mild humus had a 

 moisture-holding capacity, saturated, of 138.5 per cent of its air-dry 

 weight, or 82.6 per cent of its volume. It absorbed water rather rap- 

 idly. The raw humus, on the other hand, took up water with extreme 

 slowness, the cylinder, only a centimenter thick, requiring 48 hours or 

 more to become saturated. The capacity of this soil is 504.6 per cent 

 of its air-dry weight, but only 65.1 per cent of its volume. The high 

 percentage of water on the basis of weight gives an idea of the extreme 

 lightness of this raw humus. The mineral soil takes up water with 

 great rapidity and holds, when saturated, 66.8 per cent of its air-dry 

 weight and 56.9 per cent of its volume. This soil looks rather clayey 

 and sticky when wet, but leaves practically nothing in suspension in 

 water after an hour and a half. 



Chemical Properties of Soils 



The only chemical property determined in this investigation was the 

 acidity. The determinations were made in such a way as to secure 

 quantitative results comparable with those of other workers. Two 

 methods of testing acidity were employed: First, the method given by 

 Coville in his "Experiments in Blueberry Culture" (pp. 26-28) ;^^ and, 

 second, the new Truog method.^' The results should be comparable with 

 those of other workers using either of these methods. But the meth- 

 ods are not comparable with each other. The method used by Coville 

 measures the acid which can be extracted by a given quantity of hot 

 distilled water, expressing the results in decimals of normal acidity. 

 Ten grams of soil are shaken up with 200 cc. of hot distilled water and 

 left to stand over night. A measured quantity of the filtered extract, 

 boiled to drive ofif the CO,, is then titrated with an .05 normal solution 



'" Briggs, L. J., and Shantz. H. L- : "The wilting coefficient for plants and its 

 indirect determination." U. S. Dept. Agr., Bureau of Plant Industry, Bull. 230, 

 1912, pp. 66-68. Hilgard's method of determining the moisture-holding capacity 

 at saturation calls for using vokime instead of weight, but the Briggs and vShant'z 

 formula is based on dry weight. See Hilgard, E. W. : "Soils." New York, IQ12, 

 p. 209. 



" Hilgard, E. W. : "Soils." New York, 1912, p. 209. 



" See note 4 for citation. 



"Truog, E. : "A new test for soil acidity." Agr. Expt. Sta. Univ. Wis. Bull. 

 249. 1915- 



