Studies on the humus forms of forest soils

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Abstract
The results of microscopic observation and elementary analysis of each fraction separated physically from L, F, H-A, and A horizons of Higashiyama soil (yBB type) were described. Organic materials constituting each horizon were composed of various particles which differed in size, shape, color, extent of decay of tissues, and amount of adhering mineral particles, etc. In the Land F layers, plant remains became smaller In size, darker in color, and mineral particles adhering to them Increased with the progress of decomposition. Barks and twigs seemed to be more difficult to decompose compared with leaves. The same was true for the epidermilt of leaves, compared with their mesophylls. As for particles smaller than 60 mesh, tissues of plant remains were hardly recognizable, and there were abundant black globular particles, which might have been droppings of soil fauna. A large part of plant remains in the H-A and A horizons originated from roots at various stages of decay, and barks, twigs, and black globular particles were few. In sand fractions, small amounts of black particles were found. In silt fractions, particles recognizable as being of plant origin were few, and brown amorphous or black globular particlea predominated, most of which existed Independently apart from minerai particles. On the other hand, clay fractions were grayish brown in color, and a large part of organic matter presumably existed in combination with clay. Regular changes in elementary composition were observed with the gradation of horizons and with the decrease in particle size. Among them, the most remarkable changes were found in nitrogen content and C/N ratio; nitrogen content increased and C/N ratio decreased. with the exception of the unusual1y low C/N ratio for the sand fraction of the A horizon.

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