扁圆封印木（相似种）茎干的解剖特征

贵州省水城矿区晚二叠世煤核中扁圆封印木（相似种Ｓｉｇｉｌｌａｒｉａ ｃｆ．ｂｒａｒｄｉｉＢｒｏｎｇｎ．）茎干的主要解剖特征如下：管状中柱，具多边形薄壁细胞组成的髓。初生木质部成环带状，外缘呈规则的齿槽状，向心式发育。次生木质部显束状特征，横切面管胞为方圆至长方形，纵切面为梯状壁增厚，并具流苏纹。射线１—２列细胞宽，数个至十余个细胞高。叶迹起源于初生木质部外缘的槽中，中始式，但以向心发育为主。

ANATOMICAL CHARACTERISTICS OF THE STEM OF SIGILLARIA CF.BRARDII FROM COAL BALLS IN GUIZHOU PROVINCE, CHINA

The stem specimens of Sigillaria cf.brardii were collected from the coal balls of Upper Permian in Shuicheng Coal Mines in Guizhou Province.The main anatomical characteristics of Sigillaria cf.brardii are described as follows: The stem is siphonostelic, with pith composed entirely of polygonal parenchyma cells, there are secondary walls in some pith cell cavities these secondary walls show the characters of cell division.Surrounding the pith is the continuous cylindrical primary xylem which consists entirely of tracheids.The outermost, and part are the protoxylem elements show spiral secondary thickenings.In cross section, the outer edge of exarch primary xylem appears regularly sinuous, with trace of mesarch leaf originating from the furrows.The centripetal metaxylem is characterized by scalariform wall thickenings on the tracheids, and delicated strands of secondary wall materials extending between abjacent bars, these structures are called fimbris, or williamson striations, and are characteristic in lepidodendrids.The secondary xylem consists of tracheids and vascular rays.The tracheids, too, have scalariform wall thickenings and fimbris.The rays are one to two cell width and several to more than ten cells in height.