Organization of tissue of Primary Dicot root :
Secondary Growth
Growth in plants is caused by the activity of the apical meristems present in the apices of stems, branches and roots. The primary structure of the plant is given by apical meristem. Apart from the linear growth, there is a corresponding enhancement in the thickness of the stems and roots to bear the demands of the increasing height and weight of the stem and its branches. This increase in thickness is called ‘Secondary growth’. It is very common in Gymnosperms and Dicotyledonous plants, but is normally absent in Monocotyledonous plants. However, in some exceptional plants of Monocoty-ledons such as Dracaena and Yucca, anomalous secondary growth can be observed.
The increase in the thickness of Dicot stem occurs in two stages. They are:
(i) Stelar secondary growth and
(ii) Extra-stelar secondary growth or Cortical secondary growth.
