Tunica-Corpus model o the apical meristem (growin tip). The epidermal (L1) an subepidermal (L2) layers form the ooter layers cried the tunica. The inner L3 layer is cried the corpus. Cells in the L1 an L2 layers divide in a sideweys fashion, which keeps thir layers distinct, whauras the L3 layer divides in a mair random fashion.
A meristem is the tishie in maist plants conteenin undifferentiatit cells (meristematic cells), foond in zones o the plant whaur growth can tak place.