Anatomical study on the shoot apex ofOsmunda japonica thunb

Abstract

The ontogenetic and seasonal variations in the organization of the shoot apical meristem ofOsmunda japonica Thunb. were investigated. The meristem is composed of an apical segmentation zone (SZ), a mother cell zone of the stele (MS) and a periphereal zone (PZ). A single apical cell is mostly discernible in all sesons throughout the whole process of ontogeny observed in the present study. The paical cell is usually four-sided, nearly triangular, with a regular segmentation pattern in transverse view. However, it is sometimes acccurately three-sided with a highly regular segmentation pattern in the active season, while it is often four-sided, nearly trapezoid or five-or six-sided, with a less regular segmentation pattern in the inactive season. The size of the apical cell represented by its free surface are increases with the increase in size of the plant body in the young plants. However, in the adult plants, the size of the apical cell is smaller in the active season and larger in the dormant season. The organization pattern of the shoot apical meristen ofO. japonica does not show an intermediate type between the eusporangiate and the leptosporangiate ferns, but the leptosporangiate fern type.