Plant Opal in Japanese soils

Several years ago the writers (6) found peculiar amorphous grains having a low refractive index (n = 1.45) in the tine sand fraction of Japanese volcanic-ash soils, especially in the A horizons of glassy-ash soils (Onji type). These grains have been considered PELE's tears (liquid lava drops) or bead-like glassy grains on the basis of their relative abundance in volcanic-ash soils. Their morphological, and chemical characteristics have been reported elsewhere by the authors (6). Furthermore, it has been noticed that many of red-yellow soils and paddy soils contain varying amounts of these grains. Some Japanese agronomists and phytopathologists have previously pointed out that silica cells in leaves of Oryza sativa have the effective power of resistance to blast (Imochi disease).