Govt Exams
The scattered distribution of vascular bundles in monocots (polystelic arrangement) means that damage to one bundle doesn't severely compromise the entire plant's transport system, unlike the concentric arrangement in dicots where the vascular cylinder is a continuous ring. This provides functional redundancy and allows monocots like grasses to survive grazing and mechanical damage.
Lenticels are porous structures in the periderm (cork) that allow gaseous exchange (respiration) to occur in woody stems where stomata are absent.
Mesophytes have higher stomatal density as water is readily available, while xerophytes have lower stomatal density as an adaptation to reduce water loss.
The pericycle is the outermost layer of the stele (inside endodermis) and gives rise to lateral roots and the vascular cambium during secondary growth.
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.