I70 SOIL CONDITIONS AND PLANT GROWTH 



summary as yet : the student wishing full information may be 

 referred to the papers on the absorption of dye-stuffs by 

 Sjollema/ Endell,^ Ashley,^ Konig, Hasenbaumer and Hassler,* 

 Hanley,^ and Tadokoro,^ the last-named giving other references 

 also, and to Mitscherlich's papers on the absorption of water 

 vapour.'^ The general discussion of Leeden and Schneider* 

 may also be consulted. 



The Constitution of the Soil. 



The components of the soil do not form a mere casual 

 mixture. A much more intimate mingling prevails, amount- 

 ing almost to a loose state of combination, from which the 

 separate substances are only extracted by drastic mechanical 

 means, or gentle chemical treatment. The soil colloids and 

 the calcium carbonate appear to be responsible for the forma- 

 tion of the compound particles, and as soon as they are altered 

 by treatment, first with acid and then with alkali, the particles 

 fall to pieces and the silt, clay, etc., can be readily separated 

 by sedimentation processes. No method has been devised for 

 measuring the size of the compound particles. Their exist- 

 ence can be shown in a clay soil by making two analyses of 

 the same soil, one after the usual treatment with acid and alkali 

 to break up the compound particles completely, the other on 

 the untreated soil where the breaking up is only partial. The 

 demonstration, however, does not work so well for loams 

 (Table XLVL). 



The existence of these compound particles puts out of the 

 question any complete quantitative interpretation of a mechani- 

 cal analysis. The properties of a soil are not the sum of the 

 properties of the separate fractions — clay, fine silt, etc. — be- 



1 yourn.f, Landw., 1905, 53, 67. ^ Kolloid Zeitsch., 1909, 4, 246. 



^H. E, Ashley, The Colloidal Matter of Clay and its Measurement (U.S. 

 Geol. Sur. Bull., 388, 1909). 



*Landw. Verstcchs-Stat., 191 1, 75, 377. 



^J. A. Hanley, jfoum. Agric. Sci., 1914, 6, 58. 



" T. Tadokoro, yourn. Tohoku Imp. Univ. Sapporo (Japan), 1914, 6, 27. 



''These are summarised in Internat. Mitt./. Bodenkunde, 1912, i, 463-480. 



^ Ibid., 2, 81. 



