From the pumice tuff stratum of Yanagida Group(Miocene)of Uchiura-machi, Ishikawa Prefecture, a homoxylic fossil wood was discovered. Although minute and exact description of this fossil is not yet given, it is preliminarily identified as Tetracentron because of the typical anatomical features. The fossil has distinct growth rings with abrupt transition from the early-to latewood. Earlywood tracheids with typical scalariform bordered pits and latewood tracheids with sparse circular bordered pits on their radial walls and without pits on their tangential walls, occasional“ short tracheids” (Thompson& Bailey, 1916)or“ vascular tracheids”(McLaughlin, 1933), 1-to 5-seriate heterogeneous rays with high uniseriate wings. All of these characteristics agree well with those of one of the living vesselless dicotyledon, Tetracentron sinense Oliv., which is monotype of the Tetracentraceae and distributed from southern and central China to east of the Nepal Himalayas, through northern Burma, while Trochodendron is different from the present fossil for it has no short tracheids, but wider rays and shows more gradual transition from the earlywood to the latewood. Because the most of the previously reported homoxylic fossil woods from the Mesozoic and the Tertiary are regarded as lacking the short tracheids, it is considered that those may not have any relation with the living Tetracentron, and consequently it may be said that the present fossil is the only representative with direct affinity with it.

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Summary As an approach to the elucidation of the mechanism of gliding movement of blue-green algae, Spirulina, the structures of trichomes and individual cells were studied using light and electron microscopes. In the two Spirulina species, S. subsalsa of the tightly coiled trichome and S. platensis of the loosely coiled trichome, the spatial arrangement of thylakoids and the region of contact to the substrate were analyzed by comparison. A characteristic found common to both species was that the locus line of the point of contact to the substrate, which was drawn during the gliding movement, corresponded with the outer edge of thylakoid which was arranged along the long axis of trichome. It raises the possibility that the driving force is generated by proton motive force derived from photosynthesis.

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Studies were conducted on developmental anatomy in order to elucidate the differentiation pattern of vascular cambial initials in the first internode of Acer saccharinum. The procambium is transformed from an early homogeneous structure composed of short cells into a heterogeneous structure later having long and short cells. In the transformation process, some cells are elongating while the other cells form axial strands by repeated transverse divisions. The long cells with tapering ends differentiate into cambial fusiform initials and the short cells in axial strands into ray initials. The differentiation pattern of vascular cambium in the first internode of Acer sac charinum does not resemble that of Acer pseudoplatanus in the same genus because the ray initials originate from the segmentation of long cells in the later species.

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