Solution:

Palm is a monocotyledonous plant, yet it increases in girth slowly due to secondary growth. It is due to parenchymatous cell division and enlargement in the ground tissue. Thus, repeated divisions cause an increase in girth of the stem. Palms have a thickening meristem below their leaf primordia. It adds ground parenchyma and vascular bundles continuously. The ground parenchyma may also further divide even after the completion of elongation. This leads to increase in girth like dicot plants.