Botany 2104.  Plant Form and Function

ROOTS

Root Functions
anchorage:  deep roots or spreading roots
absorption of water and minerals
storage (food or water)
conduction

Eudicots:  taproot system
the radicle grows into a single primary root; additional roots branch off of the primary root
can grow very deep into soils
can enlarge radially for storage

Monocots:  fibrous root system
after the radicle begins to grow, additional roots grow from the stem (adventitious roots) that are uniform in diameter with the radicle; still have extensive branch root
tend to be shallower than taproots
very good at anchorage and preventing soil erosion

Root Tip
region of cell maturation:  cells become specialized; has root hairs
region of cell elongation:  cells enlarge
region of cell division:  location of the apical and primary meristems
root cap

Root Cap
protects the meristems as expendable cells face the ripping action of the soil
senses gravity
secretes mucigel
prevents dessication
better contact with soil for water and mineral absorption
lubricates the soil for easier root passage
provides a specific microhabitat (rhizosphere) for beneficial soil microorganisms

Root Hairs
extensions of epidermal cells
greatly increase the root surface area for absorption

Eudicot Root
Monocot Root
Branch Roots
Adventitious Roots
Modified Roots: Food Storage
Modified Roots: Propagation; adventitious buds of aspen, apple, redwood
Modified Roots: Aerial Roots of Epiphytic Orchids
Beneficial Root/Microbe Interactions: Mycorrhizae (fungi); Rhizobial Bacteria

STEMS

Stem Functions
support and display leaves (for photosynthesis), flowers (for pollination), fruits (for seed dispersal)
conduction between the leaves and roots via xylem and phloem
photosynthesis
storage (food, water)
with leaves, form the shoot system

External features of stems
nodes vs. internodes
phyllotaxy: alternate, opposite, whorled

Internal features of stems
In most eudicots, the vascular bundles are arranged in a ring and divide the ground tissue into pith and cortex regions.
In most monocots, the vascular bundles are found throughout the ground tissue.

Modified Stems
runners = horizontal, above ground stems; adventitious roots form at nodes. 
rhizome = horizontal, underground stem; adventitious roots form at nodes. 
cladophylls
thorns

Thorns, Spines, and Prickles
A. Thorn = modified stem
B. Spine = modified leaf

12 September 2013