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The Plant Body
Why are plants so vital?
Because Plants are Producers.
Van Helmont - 1648
Commonly used and abused
chemicals substances from plants
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caffeine in coffee
theophylline in tea
theobromine in chocolate
nicotine in tobacco
cocaine from coca plant leaves
THC in Cannabis
and many other narcotic and psychoactive
substances
Cooksonia – 408 MYA
Plant Tissue Types
• Meristematic tissue - site of growth in plant;
origin of the other tissue types
• apical meristems - site of primary growth; lateral
meristems - site of secondary growth
• Dermal tissue system - the outer protective
covering of the plant
• Vascular tissue system - comprises the xylem and
phloem - it is embedded within the ground tissue
system – xylem forms wood in woody plants
• Ground tissue system - the inner supportive
tissues of the plant – pith in herbaceous plants
Primary Plant Growth
• Primary growth originates in the apical
meristems and results in increases in length
- tissues originating from primary growth
make up the primary plant body (primary
xylem, primary phloem, etc) - many
vascular plants consist entirely of primary
tissues
Secondary Plant Growth
• Secondary growth originates in the lateral
meristems and results in increases in width - there
are two lateral meristems
• Vascular cambium which produces secondary
vascular tissues - secondary xylem to the inside
and secondary phloem to the outside
• Cork cambium is outside the vascular cambium it forms periderm, which is made of cork tissue the periderm replaces the epidermis as the dermal
tissue system of the plant
Xylem tissues
• Secondary xylem is dead at maturity and transports water
essentially through a hollow tube - angiosperms have
tracheary cells are called vessels and tend to have flattened
ends, as well as tracheids
• in gymnosperms the tracheary cells are called tracheids
and usually sharply tapered
• eventually the xylem becomes full of sap and is no longer
used for water transport, then functions in support and
forms wood
• Phloem cells are called sieve tube elements because of the
sieve like plates at the end of the cells - they are alive at
maturity but are crushed as the plant grows in diameter and
must be continually replaced
• Some sieve cells have companion cells which govern
transport of material through the sieve
Xylem –
Vessels
and
Tracheids
Phloem – sieve elements
Garlic Roots
Fibrous
Tap
Varieties of Root Systems
Lateral growth of a willow root