The part surrounded by vascular bundles located in the center of root and stem is called marrow. It is composed of parenchyma or sclerenchyma cells. The cells are spherical, thin-walled, and capsuled. It originates from the ground tissue. The medulla is absent in the roots of dicotyledonous plants. Many times the medulla is destroyed in the center of the root and stem and creates voids. It is called lysigenous cavity. Stems of pumpkin, papaya, bamboo, cucumber etc. contain lysigenous.
Function of medulla: It stores food. Sclerenchymaske¬renchyma gives the plant strength.