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- #National Eligilibility Cum Entrance Test
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Which of the following is made up of dead cells?
Option: 1
Xylem parenchyma
Option: 2
Collenchyma
Option: 3
Phellem
Option: 4
Phelloderm
Answers (1)
Secondary Growth in Extra Stelar Region
- The continuous secondary growth in the intrastelar region adds more and more secondary xylem and secondary phloem.
- This exerts pressure on the tissues lying towards the outer side, that is, cortex and epidermis.
- The epidermis ruptures due to the exertion of the pressure and the underlying tissues are exposed to the environment.
- At this stage, a secondary tissue called periderm develops.
- Periderm develops through the activity of cork cambium or phellogen.
- Cork cambium or phellogen is the secondary meristem that develops generally from the collenchymatous cells of hypodermis, sometimes from the cells of the epidermis (apple), pericycle (Cimatis), phloem (vitis).
- Phellogen gives rise to cork or phellem on the outer side and secondary cortex of phelloderm on the inner side.
- Phellem or cork is the dead tissue with suberised cell walls. It is impermeable to water and is used commercially.
- Quercus suber is commercial cork.
- Secondary cortex or phelloderm is living tissue. It stores food and replaces the damaged primary cortex.
- Phellem, phellogen and phelloderm are called periderm.
- Periderm and fragments of epidermis form the protective tissues in an old dicot stem.
- Phellem or cork is the dead tissue with suberised cell walls. It is impermeable to water and is used commercially.
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