Question

With the help of diagram, explain secondary growth in dicot roots.

Answer 1

Secondary growth in a dicot root-

1. Vascular cambium is formed secondarily from conjunctive parenchyma cells lying just below each phloem strand.
2. The number of cambium rings forms is equal to the number of phloem present.
3. The cells of pericycle lying outside the protoxylem also become meristematic to form part of strips of cambium.
4. These strips join with the former cambium to form a wavy ring of vascular cambium.
5. This cambium ring produces secondary xylem on the inner side and secondary phloem on the outer side.
6. In roots, growth rings are not distinct because there is no seasonal variation under the soil.
7. From the outer region of pericycle arises the phellogen which cuts phellem (cork) on the outer side and secondary cortex or phelloderm toward the inner side.