The shoots (stems) consist of \_\_\_\_\_ (where leaves and axillary buds are produced) separated by \_\_\_\_. Therefore they are \_\_\_\_.
Nodes
Internodes
Articulated
Shoot apex
- Devoid of:
- Produces:
- A cap
- Both stem and leaf simultaneously
Forms primary structure of stem (and roots)
Protoderm, ground meristem, procambium
What do leaves develop from
primordia
Intercalacary meristem
Cell division growth and regrowth at nodes
Primary structure stem epidermis always has
a cuticle
Primary structure stem cortex consists of
a chlorencyma or fibers along the stem ridge
Primary structure vascular cylinder
Vasuclar bundles embedded in a pith
Primary xylem and phloem are grouped together in units called
bundles
Collateral bundles
phloem oriented towards the exterior and xylem towards the interior.
primary xylem within the bundles in stems
is endarch, from the interior to the exterior
Monocot vs. eudicot vascular bundles
M: Scattered or pith parenchyma
E: Circle or ring
Monocots collateral bundle
Closed - intrafascicular vascular cambium does not differentiate b/w px and pp
Dicot collateral bundle
Open - between primary phloem and xylem
Intra vs. Inter f.v. cambium primary structure
- within the collateral bundles b/w phloem and xylem
- b/w vascular bundles
- connects to form a secondary meristimatic ring
Intra vs. Inter f.v. cambium secondary structure
- V.C. produces 2p to the exterior which crushes and overlaps 1p
- V.C. produces 2x towards interior which pushes the 1x inside
- much more xylem and phloem
Stems remain herbaceous because…
V.C. produces little 2x, no periderm, no C.C.
Remains herbaceous and destroyed during the winter
2nd structure in woody plants
- 2x =
- Bark develops from…
- Produce a lot of 2x and form annual rings
- 2x = wood
- Bark develops from C.C. but at the exterior so stems become woody and survive the winder
Bark:
- Outer side layer of cork cambium
- Inner?
- Periderm?
cork cells impregnated with suberin
phelloderm
Every year it develops on the interior of the previous one; outer periderm breaks and exfoliates (contains C.C., phelloderm, all its products)
Bark of the birch tree
Protects the inner tissues against cold and insects, filters UV radiation
Willow tree asprin
Willow bark contains tannins and salicin
Salicin hydrolyzed to salicyl alcohol, becomes salicylic acid
- Lasts longer than asprin
Precious bark
Quinine - treats malaria
Specialized stems - Rhizomes
- Underground stem - distinct internodes has leaves
Underground stems
ensure the survival of herbaceous perennial plants during the winter. They store food reserves and they have buds from which shoots/flowers will develop in next spring. Also, underground stems allow vegetative propagation.
