tunica

The tunica-corpus theory is a concept in plant morphology that describes the structure of the apical meristem, which is the growing tip of a plant shoot. This meristem is divided into two distinct regions: the tunica and the corpus.1

The tunica is the outer layer or layers of cells, while the corpus is the inner core of cells. The tunica typically contributes to the surface layers of the plant, and the corpus forms the deeper tissues. Cells in the tunica often divide in a way that contributes to the surface, while the corpus provides the internal growth. This theory helps explain how plant shoots develop and form new tissues and organs, such as leaves, which originate from the flanks of the shoot apex.23