Govt Exams
Hydrophytes living in aquatic environments have reduced xylem development as water provides mechanical support (buoyancy) to the plant body.
Xylem parenchyma cells remain alive at maturity and are involved in storage and lateral transport, unlike tracheids and vessels which are dead at maturity.
Pith consists of parenchyma cells that serve for storage and may become lignified with age; it is surrounded by the vascular cylinder.
Xerophytes have a thick, waxy cuticle that reduces water loss through transpiration, an important adaptation to arid environments.
Protoxylem forms first during primary development with narrow vessels and is often crushed, while metaxylem forms later with wider vessels and persists.
Companion cells are closely associated with sieve tube elements and help in loading and unloading of sucrose and control of sieve tube functioning.
Periderm (cork) is produced by cork cambium and replaces the epidermis in older roots and stems, providing protection.
Vascular cambium produces secondary xylem inward and secondary phloem outward, causing increase in diameter (secondary growth) of dicot stems.
Monocot stems have scattered vascular bundles distributed throughout the ground tissue (atactostele), unlike dicots where they form a ring.
Casparian strips are band-like thickening of suberin and lignin on radial and transverse walls of endodermis that regulate water and mineral movement into the stele.