SOILS — FERTILIZEES. 813 



plained on the ground that the roots of phmts and the humus material can 

 penetrate the rock crevices more easily. The depth of the humus layer seems 

 to be less for soils derived from limestones and crystalline rocks. 



The physical properties of a chernozem soil are determined largely by its 

 high content of fine particles and humus. In general the soils have a porosity 

 varying between 50 and 60 per cent, which decreases with the depth of soil, 

 a high water capacity and hygroscopicity, and conduct heat poorly. The specific 

 gravity varies between 2.5 and 2.6. 



The size of the soil particles is not determined by the parent rock alone, 

 but is the resultant of many genetic factors. The humus content in general 

 varies between 6 and 10 per cent, but in certain cases it has fallen as low as 4 

 per cent and exceeded 20 per cent. The humus is but slightly soluble in water, 

 the soluble amount varying between 0.02 and 0.05 per cent. 



The chernozem soils are rich in all the mineral elements of plant food. 

 The soils have a high zeolite content, which varies considerably (15 to 30 per 

 cent) for the different soils and is determined to a large extent by the character 

 of the parent rock. The zeolites contained about 50 per cent silicic acid. The 

 l)hosphoric acid content varies from 0.12 to 0.25 per cent and is much higher 

 for the surface than for the subsoil. It is believed that the total phosphoric 

 acid content is from 20 to 25 per cent higher than that soluble in hydrochloric 

 acid. • 



Eed boulder clay, J. Van Baren (Intemat. Mitt. Bodenk., 1 (1912), No. 3-1^, 

 pp. 855-366^ pi. 1). — In his studies of the glacial deposits of the Netherlands, 

 the author has encountered a red boulder clay, which occurs in a small area 

 near the coast of the Zuider Zee, between the Vecht and Yssel rivers. 



The soil is described as a very dry sandy clay, resembling in its typical state 

 the laterite of the Tropics. Analyses showed a low content of the mineral ele- 

 ments of plant food. The iron silicates were covered with a thin coating of 

 iron oxid, in which respect the soil differs from the overlying gray boulder clay 

 to the east. This led the author to believe that the red boulder clay is a dis- 

 tinct glacial formation, which owes its characteristic red color to the weather- 

 ing processes of the interglacial period. 



Reference is also made to the occurrence of soils similar in characterstics in 

 northern Germany, Russia, northern Italy, Great Britain, and the L'nited States. 



Soil acidity and its significance for soil cultivation, N. Solenow (Die 

 Bodenaciditdt und Hire Bedeutung fur den Kulturboden. Diss. Univ. Jena, 1909, 

 pp. 68; abs. in Chem. Al)s., 6 {1912), No. 2, p. 268).— The nature of the acids in 

 soils and their effect upon the germination of seed and the growth of plants are 

 discussed. 



It is shown that the number of bacteria in acid soils is small, while fungi are 

 numerous. It is stated that difficultly soluble acids in humus exert a harmful 

 effect by liberating toxic mineral acids. Methods of determining soil acidity 

 are discussed and an improvement of the method of Tacke and Siichting 

 (E. S. R., 19, p. 1009) is proposed. 



The fineness of the soil and the quality of wine, G. Chappaz (Proc. Agr. 

 et Vit., 28 (1911), No. U, pp. 509-51Jf; abs. in Rev. Sci: [Paris], 50 (1912), I, 

 No. 9, pp. 279, 280). — This article reports and discusses the proportion of coarse 

 material, rocks, and gravel in the soil of typical vine-growing regions in France 



Soils containing more than 50 per cent of rocks and gravel are considered 

 infertile. When present in smaller proportion rocks and gravel are considered 

 beneficial for grape growing by absorbing heat during the day and lessening 

 evaporation. It is a matter of common observation that the best wines are 

 obtained from vineyards on gravelly soils, although it is not maintained that 



