APICAL ORGANIZATION IN ROOTS OF THE CONVOLVULACEAE

Abstract

A sampling of radicles and germinated primary roots was obtained for several species of the Convolvulaceae in order to study ontogenetically the organization of the protomeristem. The findings differ from earlier studies in that only a few radicles and primary roots exhibited proto‐meristems with layered initials. Most radicles exhibited a pattern of layered initials in which the outer cell layers of cortex were not aligned with a layer of cortical initials but with cells at the base of the columella. In long primary roots the protomeristem, consisting of central cylinder initials, lateral rootcap‐epidermal initials, and common initials for the cortex and columella, was the general pattern for the members of the family. The reorganization of the protomeristem from a layered condition to common initials generally occurred upon germination. Different expressions of intermediate patterns indicated that periclinal divisions in the outer layers of cortex near the initials or in the immediate derivatives of the cortical initials were responsible for cellular displacements and new cell alignments. After reorganization, periclinal divisions in the peripheral portions of the common initials maintained the cellular continuity from the cortex into the columella. In addition, a few primary roots with a degenerated columella and a transversal meristem were observed.