Chapter 33: Stems
varied
- support the leaves
- internal transport
- make new living tissue(buds-meristematic):branch, new leaves, flowers
- reproduction-asexual fashion
- photosynthesis(if green)
- storage(CHO)
Woody Stems-have secondary growth
Vascular cambium produces: 1)secondary phloem to its exterior 2)secondary xylem to its interior
Year one: herbaceous stem(dicot)
Year two: begin secondary growth
- vascular cambium becomes continuous
- divide(vascular cambium)
- new secondary phloem pushes out the old primary phloem; new secondary xylem pushes and crushes the pith and primary xylem
- cortex, epidermis sloughed off
cork parenchyma and cork cambium:
came from de-differentiated parenchyma>>>cork cambium>>>periderm
cork cells dead at maturity, have suberin (water-proofing, reduces water loss and soaking in)
Types of Wood-
- sapwood-young wood, close to bark, functional
- heartwood-older wood, close to center, non-functional, denser, better support
- hardwood-wood of angiosperms
- softwood-wood of gymnosperms
- annual rings-rings of growth in spring and summer (spring-few fibers, thick layer; summer- more fibers, thin layer) (1632 B.C. Mt. Thera erupted on Crete, layer of ash in rings of old trees)
- knot- dead branch surrounded by growing wood
- transport of stems-one way (water up, sugar down)
Back