Abstract
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.
