The Plant Body

Why are plants so vital? Because Plants are Producers. Van Helmont

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 – Vessels and Tracheids

Phloem – sieve elements

Garlic Roots

FibrousTap

Varieties of Root Systems

Lateral growth of a willow root