Prof. Krasnov states that the decomposition of the roots of plants gives rise to the humus, but attaches much more importance to the effect of climatic conditions. Thus, he remarks, “that it is impossible not to note that the Tchernozem occupies a band stretching from S.W. to N.E., that is, the position where the influence of a temperate and moist climate ends, and the region of dry S.E. winds begins. In the N. and N.W. of Russia the woods predominate, unless destroyed by man, or prevented by the marshy nature of the country.