Tunica-corpus organization
Outer tunica gives rise to epidermis
Inner tunica & corpus generate all other shoot tissues
Median longitudinal section of the dome-shaped apical meristem in maple (Acer sp.) showing a tunica-corpus organization in this angiosperm. The tunica comprises two outer layers of the dome in this apex which are designated L1 and L2. Its cells divide only anticlinally (i.e. in a plane perpendicular to the surface).
The inner cells divide in various planes (periclinally and anticlinally) and comprise the corpus (C). The outer cell layer of the tunica (L1) gives rise to protoderm which in turn will form the epidermis of the shoot. The second tunica layer (L2) and the corpus initiate all other tissues of the leaves and the primary stem. Below the corpus is a rib meristem (Rm) that gives rise to columns of cells that will eventually comprise the pith. Two leaf primordia arise simultaneously on the flanks of the apical meristem in plants like maples that have opposite leaves.
