Why is there secondary growth in dicots and no such growth in monocots ?

Explanation

Secondary growth in dicots occur due to the activities of lateral meristem, i.e., the vascular cambium and cork cambium. Vascular cambium is formed during secondary growth. It is formed by the combination of interfascicular and intrafascicular cambium. Secondary growth increases the diameter of roots and stems in dicots. In monocots, the vascular cambium and cork cambium are not formed. So there is no secondary growth in monocots.