No tunica-corpus in gymnosperms

Zone of thick-walled central mother cells

Gymnosperms do not usually show a tunica-corpus type of organization in their shoot apical meristem since the outer cells of the apical dome divide both anticlinally (i.e. perpendicular to the surface) and periclinally (parallel to the surface), thus contributing cells to the interior of the promeristem.

The more striking feature of gymnosperms is the presence of a distinct zone of central mother cells (C) in a median position below the surface layer. The central mother cells are irregularly arranged, and most of the growing season are relatively large and thick-walled as shown here from the apical meristem of eastern white pine (Pinus strobus).

Illustration from: Esau, 1977, Anatomy of Seed Plants, 2nd Ed., John Wiley & Sons, Inc.