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Roots and Root Systems
• Root Systems are often classified as either:– TAP ROOT SYSTEMS
(found most commonly in eudicots)• have prominent tap root
and smaller branch roots
Root Systems
– FIBROUS ROOT SYSTEMS (common in monocots)• many similar sized roots
in an extensive network
YoungRoot (cont.)
• Above the region of the meristem are the regions of
elongation and region of
maturation
Meristem
Functions of Root Structures
• ENDODERMIS– innermost layer of the cortex – functions in water regulation– cells are “belted” with a suberized layer
called the Casparian strip– waterproofs the layer so water must
move through the cells (not the walls) into the stele
Functions of Root Structures (cont.)
• PERICYCLE– source of cells for
formation of branch (lateral) roots
– involved in formation of cambial layers in woody roots
– endogenous growth of branches
Functions of Root Structures (Cont.)
• PHLOEM– transport of nutrients
• XYLEM– protoxylem (first to mature
in the root)– metaxylem (last to mature)– water and mineral
conduction
• CAMBIUM (with pericycle cells will form vascular cambium in woody root)
Root Modifications (cont.)
• Fascicled storage roots (yams, sweet potatoes, cassava)
Casava for saleSweet Potatoes
Eudicot Stem Structure (cont.)
• Leaf primordia with trichomes
• Axillary (lateral) buds– give rise to
branches– exogenous
development
Structure of a Eudicot Stem• Apical Meristem
(shoot apex, shoot tip)
– composed of tunica and corpus layers
– tunica gives rise to protoderm
– corpus gives rise to procambium and ground meristem
Monocot Stem
• Scattered vascular bundles (atactostele)
• Surrounded by parenchyma cells (ground tissue)
Monocot Vascular Bundle
• Sheath of fiber cells
• Phloem with obvious companion cells
• Large metaxylem vessels
• Air space
Stem Modifications
• Tendril (may also be a leaf modification)
• Rhizome• Stolon or runner• Cladophyll
• Thorn• Prickle• Spine (leaf modification)• Tuber• Corm vs. bulb (leaf modification)