1. Soil Microbiology;Alexander,1961
2. Vernaldas Ultveckling. Stockholm. Quoted by I. Oparin in Genesis and Evolutionary Development of Life;Arrhenius,1908
3. The Origin of the Comets;Bailey,1990
4. Methods for Chemical Soil Analysis;Blakemore,1987
5. Trace Elements in Biochemistry;Bowen,1966