Secondary xylem and phloem in dicot stems are produced byA) PhellogenB) Apical meristemC) Axillary meristemD) Vascular cambium

Answer: D) Vascular cambium
In dicot stems, the secondary xylem and secondary phloem are produced by the vascular cambium.
1. Vascular Cambium:
o The vascular cambium is a type of lateral meristem that is responsible for the production of secondary tissues (xylem and phloem) in plants.
o It is located between the primary xylem and primary phloem and is responsible for secondary growth in dicots and gymnosperms.
o The vascular cambium produces secondary xylem (wood) towards the inside and secondary phloem towards the outside, contributing to the increase in the diameter of the stem or root.
2. Other options:
o A) Phellogen: Also known as the cork cambium, phellogen is responsible for the formation of cork (phellem) and phelloderm in the outer part of the stem, not secondary xylem or phloem.
o B) Apical meristem: The apical meristem is responsible for the primary growth of plants (lengthening of stems and roots), not for secondary growth (xylem and phloem).
o C) Axillary meristem: Axillary meristems are involved in the formation of lateral branches but do not directly produce secondary xylem or phloem.
Thus, the correct answer is D) Vascular cambium, as it is the meristem responsible for the production of secondary xylem and phloem in dicot stems.