Organize the structural and developmental events occurring during secondary growth in a woody dicotyledonous stem in their natural chronological sequence from initiation to protective outer bark formation.
- 1Meristematic activity in parenchyma cells between vascular bundles connects fascicular cambium with interfascicular cambium to form a continuous vascular cambial ring.
- 2Tangential cell divisions of the vascular cambium produce secondary xylem internally toward the pith and secondary phloem externally toward the cortex.
- 3Accumulation of secondary vascular tissues causes radial expansion that exerts pressure outward, leading to the cracking and rupture of the primary epidermis.
- 4Dendritic cells in the outer cortex differentiate into cork cambium (phellogen), which produces cork cells (phellem) externally to form a new protective barrier.
Answer
The correct developmental sequence begins with the formation of a continuous vascular cambium ring, followed by the tangential production of secondary vascular tissues, subsequent rupture of the primary epidermis due to radial growth, and finally the initiation of cork cambium to synthesize protective cork cells.
Secondary growth initiates when fascicular and interfascicular cambium merge to establish a continuous vascular cambial cylinder. As this cambium divides, secondary xylem accumulates internally while secondary phloem moves outward. The resulting increase in stem diameter ruptures the unyielding epidermis, necessitating the differentiation of cork cambium (phellogen) in the cortex to form suberized cork cells for protection.
Step-by-Step Solution
Key Concept
Secondary growth in dicotyledonous plants involves sequential lateral meristem activities: first, vascular cambium produces secondary xylem and phloem, and subsequently, cork cambium produces periderm to replace the ruptured epidermis.