Module 5 stems.pptx

MODULE 5: VEGETATIVE STRUCTURES Stems, primary growth, and secondary growth Stems • Structural support • Occasional • Conduction site of photosynthesis of fluids between roots and leaves Primary growth • Growth in LENGTH A plant growing taller, a branch growing longer, etc. • Occurs at the...

MODULE 5: VEGETATIVE STRUCTURES Stems, primary growth, and secondary growth Stems • Structural support • Occasional • Conduction site of photosynthesis of fluids between roots and leaves Primary growth • Growth in LENGTH A plant growing taller, a branch growing longer, etc. • Occurs at the apical meristem • • Tunica-corpus • Two layered tunica cells divide “anticlinally” • • model Side-to-side divisions to maintain surface area Multiple layers in corpus divide “periclinally” • “Up and down” divisions to maintain volume of cells internally. Primary growth • Cells are added at the meristem and specialize as they grow away from it. • Tunica generates Epidermis • Surface internal tissues (axillary buds, etc.) • • Corpus generates Vascular tissue • Internal parenchyma, • Primary growth • Putting • You can see the sequence of alternating structures that form nodes, axillary buds, etc. • Ground • it together. meristem Origin of most of the pith and cortex Vascular bundles regularly arranged in a ring Dicot stem - herbaceous Woody stems • SECONDARY • Found growth – yearly or seasonal growth in width in woody dicots and gymnosperms (especially conifers) • Cylindrical vascular cambium Xylem inside • Phloem outside • From fusion of fascicular and interfascicular cambiums • Rings due to contrast between earlywood (spring) and latewood (summer) • Dicot stems - woody Woody stems heartwood and sapwood Wood figure Wood figure and tree anatomy Dendrochronology • Individual trees can be aged by their rings • As well as local conditions at the time • You can also age a forest (or an ancient forest, if you have fossil trunks) by the overlap of the ring patterns of different aged trees. • Using tree cores • No need to cut the tree down Woody stems - bark Woody stems - bark Lenticels Wood types and evolution • Cycads wood • have early type of “manoxylic” – Alternating bands of xylem and parenchyma • Well-formed cortex and pith • All other woody gymnosperms and angiosperms have “pycnoxylic” wood Cortex and pith are highly reduced • Xylem is dominant – tightly packed rings • Monocot stems No true wood production Monocot stems • Screaming monkey faces! (or mildly surprised, in this case) Stem modifications - xerophytes Stem modifications - rhizomes Stem modifications - stolon Stem modifications - tubers Stem modifications - corms Stem modifications - bulbs Stem modifications - tendrils Stem modifications - thorns