ON THE STEM APEX, LEAF INITIATION AND EARLY LEAF ONTOGENY IN FILICALEAN FERNS

A general account of the stem apex organization in ferns is presented in support of the classical single apical cell concept. The range in variation of apical cells and of their modes of division are described. Evidence is brought out to indicate probable directing effects of the apical cell on modes of division of surrounding cells and on the leaf mother cell. Initiation of and eventual establishment of a stabilized apex in fern leaves is described. Of the more than 50 genera studied, the leaves of all are traceable to a single mother cell from which the leaf apical cell is cut out. Apical dichotomies are described in a number of genera as well as their effect on early leaf development. Results are discussed in a phylogenetic and morphogenetic context of leaf appendicularization.