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