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Roots (Other Types of Roots and Root Modification (Aerial Roots of Orchids…
Roots
External Structure of Roots
Structure of Individual Roots
no leafs
no leaf scars
no leaf axils
no axillary buds
root cap
thick layer of cells
mucigel
dictyosomes secrete a polysaccaride
zone of elongation
few mm long
cells divide and expand
root hair zone
epidermal cells extend
root hair
forms only in part of root
Organization of Root Systems
radicle
embryonic root
adventitious roots
increase absorptive and transport capacities
Internal Structure of Roots
Zone of Elongation
where cells expand
some meristematic continues
cells are enlarging
similar to shoot's subapical meristem
cells differentiate
into visible pattern
no cells are mature
Zone of Masturation/Root Hair Zone
root hairs grow outward
increase absorption of water
and minerals
thin cuticle
could be layers of fats
cortex cells enlarge
transfer of minerals
from epidermis to vascular tissues
either by diffusion
or by absorption
Root Apical Meristem
cells originate
extend to root tissues
Root Cap
protection
apical meristem
cells are small
meristematic
Other Types of Roots and Root Modification
Contractile Roots
changes in shape
of cortex cells
Mycorrhize
ectomycorrhizal relationship
fungal hyphae
penetrate the outermost cortex cell root
never invade the cells
endomycorrhizal relationship
hyphae penetrate the root cortex
pass through wall of cortex
cannot pass casparian strip
Aerial Roots of Orchids
epiphytic
roots spread along the bark
live in rainforests
velamen
root epidermis
Prop Roots
after contact with soil
transport water and nutrients
to the stem
acting as stabilizers
secondary growth
strong supports
permitting a branch to extend
without bending/breaking
Storage Roots
store carbohydrates
accumulate during summer
photosynthesis
in biennial species
roots are the only permanent orans
carbohydrates stored
used to produce new shoot
in spring
