Question

Secondary xylem and phloem in dicot stems are produced by
A) Phellogen
B) Apical meristem
C) Axillary meristem
D) Vascular cambium

Answer 1

Hint: In dicot stem the vascular components are more complex than in the monocot stems.

Complete Answer:
- In dicot stem the tissue of xylem is formed inside the cambium,whereas the tissue of phloem grows outside the cambium. To say it in a simpler way,it means that xylem is at the center of the root and the phloem is outside the xylem.
- To complete the vascular cylinder around the plant, the secondary growth of dicots occurs by the growth of vascular cambium.
- In the dicot stem, the vascular bundle is in the form of rings. In each vascular bundle the xylem and phloem are separated by a substance called vascular cambium.
- Vascular cambium is produced by two types of meristem namely fascicular or intrafascicular and interfascicular cambium. Intrafascicular cambium is the primary meristem which occurs as strips in vascular bundles. Interfascicular cambium is a secondary growth from cells of medullary rays.
- In outer cortical cells of dicot stems phellogen or cork cambium is produced. It helps in increasing the girth. Apical meristems are formed at the tip of stem,root and their branches. - It is responsible for increasing the length of the plant.
- Axillary meristem is found behind the shoot of apical meristem during the formation of leaves and elongation of stems.

Note: Vascular system comprises xylem and phloem. They help in transporting water and other substances throughout the plant. Vascular plants grow higher than the other plants due to the rigidity of xylem cells which support the plant. Vascular tissues stop functioning when they get old. New vascular tissues replace the old ones. Vascular bundle is conjoint, collateral.