The Study on Phytogenic Particles, Especially, on Plant Opals, in Humic Horizons of Present and Buried Volcanic Ash Soils (Part I)

The Problem on the Source of Plant Opals

Abstract

The morphology of plant opals in the humic horizons of present and buried volcanic ash soils distributed in Tohoku, northern Kanto, eastern Tokai and Kyushu districts were investigated. Plant opals in leaves of some grasses were also examined. The results obtained were summarized as follows;
1) The morphology of plant opals in leaves of Graminaceous grasses is closely related to taxomic groups of grasses, which well confirms that of the previous reports. Dumbbel shaped plant opals, Panicoids, are characterized by subfamily Panicoideae and saddle shaped plant opals, Chloridoids, are contained specifically by Eragrostoideae.
2) The sizes of Sasaoid type plant opals vary with taxomic groups within subfamily Bambusoides Their median of size distribution is 24μ in genus Sasa and is 18μ in genus Pleioblastus.
3) The plant opals separated from the leaves of Miscanthus sinensis (Susuki in Japanese) are more soluble than those of Pleioblastus sp. (Nezasa in Japanese) when treated with 1%-Na₂CO₃ solution for an hour at 60°C. Microscopic observation of the insoluble residues confirms the above fact.
4) The geographical distributions and mutual relations in the various types of plant opals in the humic horizons of volcanic ash soils are as follows.
Sasaoid types are recognized commonly in all sites studied, while Panicoid types are found mainly in samples from Tohoku, northern Kanto and a part of Kyushu districts. Festucoid and Point shape types show high frequency in samples from Hokkaido. Fan shape and Elongate shape types as well as Sasaoid types are recognized extensively. Chloridoid are not common types. The amounts of Point shape types and the ratios of Fan shape types vs. Elongate shape types are closely related to the amounts of Festucoid types.