What is tunica and corpus in plants?

In plants, the tunica and corpus are two layers of cells found in the meristematic tissue, particularly in the shoot apical meristem. The tunica is the outer layer, typically one or two cell layers thick, and is involved in producing new leaves and other structures. The corpus, located beneath the tunica, consists of several layers of cells that contribute to the growth and development of the plant by differentiating into various tissues. Together, these layers play a crucial role in the plant's growth and organization.