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WHERE DID ALL THOSE TISSUES COME FROM?
MERISTEM
This is undifferentiated, embryonic
tissue present throughout the life of the plant. The cells
are pluripotent and can differentiate/mature into any other type
of cell.
Primary meristems: located at the tips of roots
and shoots. Responsible for increase in length
- apical (at the tip of the plant)
- axillary (located in the leaf axils)
Secondary meristems: located in the margins of the
stem and root (vascular and cork cambium). Responsible for increase
in girth.
- vascular cambium
- cork cambium
And there's no way you'll get this without looking at a few pictures.
Note the locations of the apical and lateral meristems.
APICAL meristems (located at the tips of roots and shoots) give rise
to three PRIMARY MERISTEMS
- ground meristem - develops into ground tissues
- procambium - develops into vascular tissues and the vascular cambium
- protoderm - develops into the dermal system
LATERAL meristems are secondary meristems that form "tubes" within
the stem and root of the plant.
- vascular cambium - located between xylem and phloem
- cork cambium - located between phloem and bark
This rendering of a root tip shows the relative locations of the apical
and three primary meristems. The same growth is taking place in the
opposite direction in the shoot tip.
This sequence shows the progression of secondary growth in the two lateral
meristems.
determinate growth: growth occurs during a finite
juvenile phase, and then stops. (and it's all downhill from there...)
indeterminate growth: growth that occurs throughout
the life of the organism.
annual plant: lives for about a year, flowers and dies
perennial: lives for more than one season
PLANT ORGANS
STEM
This organ is responsible for the aboveground structure of the plant, and is
involved in both structural support and vascular transport.
Overview of external anatomy can be seen above. Internal anatomy:
Stems may be highly derived in form and function. Here are only a couple
of modified stems...
All plants begin their development as HERBACEOUS (i.e., non-woody)
organisms. Some species are perennial and woody, and these develop
WOODY stems.
Shown diagramatically, the tissue layers are arranged like so:
heartwood: dead center of the woody stem in which conducting elements
of xylem are clogged with tannins and resin, and no longer function to
conduct fluids.
sapwood: external ring of xylem still conducting fluids
springwood: large-lumen xylem formed in spring
summerwood: small-lumen xylem formed in summer/late autumn, just
before dormancy
(Be able to identify these, and know the differences between them!)
ROOT
This organ is responsible for the uptake of water and inorganic nutrients.
External anatomy can be seen above. Internal anatomy:
LEAF
This organ is the primary site of photosynthesis, though it may be
specialized to perform various other functions.
Overview of leaf anatomy:
Leaves may be simple, compound or doubly compound...
And leaves may be the most highly modified plant organs, and show a vast
diversity of form and function. Some of these include...
