Plant Structure and Function Stem

Support leaves Transport materials Provide storage

Types of Stems

Types of Stems Woody or nonwoody (herbaceous) Stolons Tuber Cacti Grow along soil surface Produce new plants Tuber Store energy Cacti Green fleshy stems Store water and photosynthesis Modified for protection

Stem Structures Did you know that a sign nailed 2m (7ft) high on a tree will remain at that height, even though the tree may grow much taller?

Stem Structure Grow in length only at tip Apical meristems Primary tissues Lateral meristems Secondary growth (diameter)

Stem Features Node Internode Bud Leaf attaches to stem Space between nodes Lateral bud Bud Stem or leaf Apical meristem enclosed by bud scales

Winter Identification of Trees

Primary Growth in Stems Apical meristem Dermal, protect plant Ground, cortex and pith Pith located at center of stem Vascular tissue, occurs in bundles Xylem (inside) and phloem (outside) Monocots v.b. scattered Dicots v.b. rings

Monocot and Dicot Vascular Bundles

Secondary Growth in Stems Stems increase in thickness Cell division in vascular cambium Dicot and gymnosperms Stem forms b/w xylem and phloem in vascular bundle Vascular cambium produces 20 xylem (inside) and phloem (outside) 20 xylem represents the wood of the plant New cambium cells increases stems diameter

Stem Growth pg581 http://academic.kellogg.edu/herbrandsonc/bio111/stems.htm

Older xylem stop producing water Darken wood called heartwood Will increase in diameter Lighter – colored wood called sapwood Stays about the same Phloem near outside of stem Bark Cork, cork cambium, and phloem Protective layer Cork cells die at maturaty Cannot elongate and will rupture as stem increases in diameter Bark pattern (maples and oaks)

Cross Section of Woody Stem

Annual Rings Springwood Summerwood Water plentiful Vas. Cambium form new xylem cells Wide and thin cell walls Summerwood Water scarce Vas. Cambium forms smaller thicker cells Difference causes a change in appearance One ring each year used to determine age

Stem Functions Transport nutrients and water Store these nutrients Support leaves

Translocation Movement of carbohydrates through a plant Source to sink Source (storage) Sink (usage) Pressure – flow hypothesis Actively transported into sieve tubes Water transported by osmosis

Pressure – Flow Hypothesis

Transport of Water Water and mineral nutrients occur in xylem Water is constantly evaporating from plant Stomata Transpiration

Cohesion – tension theory Water is pulled up the stem xylem by the strong attraction of water molecules to each other and the wall of the xylem Cohesion and adhesion properties Tug – n – pull, from roots up the xylem

Cohesion – Tension Theory