angiosperms vi
DESCRIPTION
Angiosperms VI. Secondary Growth In Stems. What is secondary growth?. Growth in “girth” of woody plants Tissues derived from cambial layers VASCULAR CAMBIUM produces secondary xylem and secondary phloem CORK CAMBIUM (phellogen) produces cork (phellem) and phelloderm tissues. - PowerPoint PPT PresentationTRANSCRIPT
Angiosperms VISecondary Growth
In Stems
What is secondary growth?
• Growth in “girth” of woody plants• Tissues derived from cambial layers
–VASCULAR CAMBIUM• produces secondary xylem and secondary
phloem–CORK CAMBIUM (phellogen)
• produces cork (phellem) and phelloderm tissues
Typical Woody Eudicot Stem (overview)
• Periderm or “bark”
• Vascular cambium
• Secondary xylem
• Pith
Woody Eudicot
Stem
Typical Woody Eudicot Stem(detail)
• Secondary xylem• Vascular
cambium• Rays• Secondary
phloem (including phloem fibers)
• Cortex
Secondary Xylem (angiosperms)
• Vessels• Fibers and
tracheids• Wood rays• Growth rings
(annual rings)
Secondary Xylem (“up close and personal”)
• Fibers• Tracheids• Vessels• Ray
parenchyma
“Growth Rings”• Spring (Early) Wood
– first cells produced by the vascular cambium– large cells (good growing conditions)
• Summer (Late) Wood– smaller cells produced toward the end of the
growing season– poor conditions (cooler, drier)
• Radical change in cell size allows for recognition of annual “growth rings”
Bristlecone Pine
(oldest of tree species in
North America)
4900 + years old
Oak Wood in Section
Note: thick, multiseriatewood rays
Other Variations• Heartwood
– darker in color– occupies center of the stem, more dense
(stronger)– deposit of waste products such as resins, gums,
oils, and tannins• Sapwood
– lighter in color– outer layers, less dense (weaker)– contains the sap (dissolved nutrients and water)
Woody Stem and Periderm
sapwood
heartwood
Woody Twigs
• Terminal bud with bud scales
• Axillary buds• Lenticels• Leaf scar
Twig Structures
Lenticels• Pores in the
cork layers which allow for gas exchange in the periderm
Uses of Secondary Growth• Wood Products
– Various uses based on the density of the wood (often in lbs./cubic foot)
– Furniture, baseball bats, plywood, pulp products, musical instruments, particle board, artistic pieces, fuel
• Other Products– rope, cinnamon, dyes, drugs (quinine),
charcoal, cork, maple syrup
CorkHarvesting
Making MapleSyrup
30-50 gallons of sap to make 1
gallon of syrup