The Plant Body

Why are plants so vital?Because Plants are Producers.

Van Helmont - 1648

Commonly used and abused chemicals substances from plants

• 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 –VesselsandTracheids

Phloem – sieve elements

Garlic Roots

Fibrous Tap

Varieties of Root Systems

Lateral growth of a willow root