Origin and Development of Tissues in Stem of Selaginella wildenovii

Abstract

1. The stem of Selaginella wildenovii grows by means of a tetrahedral apical cell. 2. The endodermis, pericycle, and vascular strand have a common origin and are all stelar. The endodermis forms the outermost layer of the stele. 3. The endodermis and pericycle arise from a common initial. 4. Elongation of the endodermal cells and formation of air spaces are explained by the mechanics of differential cell growth. 5. The protoxylem differentiates first in the leaf traces and later in the stem. The protophloem differentiates slightly later than the protoxylem.