Angiosperms IV
Primary Growth:
Roots and Stems
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
Functions of Root Systems
•
•
•
•
•
Anchorage
Storage
Absorption
Conduction
Reproduction (occasionally)
Typical
Eudicot Root
Young
Root (cont.)
• Above the
region of the
meristem are
the regions of
elongation
and region of
maturation
Meristem
Root
Hairs
Single epidermal
cells with a long
extension
Structure of an Older
Dicot Root (cont.)
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
Endodermis
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
• Storage tap roots (radish, jicama,
carrots)
Root Modifications (cont.)
• Fascicled storage roots (yams, sweet
potatoes, cassava)
Sweet Potatoes
Casava for sale
Sweet Potato vs.Yam
• Impomea batatas
(sweet potato)
• Diascorea batata
(yams)
Root Modifications (cont.)
• Prop roots
(corn)
Root
Modifications
(cont.)
• Aerial
roots
(Spanish
moss,
orchids)
Aerial roots on an orchid
Root
Modifications
(cont.)
• Pneumatophores for
gas exchange on white
mangrove plants
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
Older Eudicot Stem (xs)
• Epidermis
• Collenchyma
or fibers
• Cortex
• Vascular
bundles
• Pith
Eudicot Stem Vascular Bundle
• Bundle cap
(composed of
fibers)
• Phloem
• Fascicular
cambium
• Xylem
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)
Tendrils
• Leaf or stem modifications for
attachment
Rhizomes
• Underground,
horizontal stems
Stolon or Runner
• Above ground horizontal stems
– Seen in strawberry plants
Thorns
• Thorns are modified branch systems
Locust tree
Crategus
Spines
• Spines are modified leaves
Prickles
• Epidermal structures found in roses and other
plants
Tuber
• Underground, storage stem (a white
potato)