Lecture 7 secondary growth

what do all plants in terms of growth? and what plant only have primary grwth?

Primary growth (herbaceous)

What kind of plants have primary and secondary growth?

woody plants

The secondary growth is produced by

• lateral meristems

  • Vascular cambium

    • Secondary xylem = wood

    • secondary phloem = part of bark

  • Cork cambium

    • periderm = most of bark

Mostly all woody plants are Eudicots

TRUE

cambium initial cell

stem cell

• with each division, one daughter cell remains an initial, the other will differentiate

Periclinal divisions

create a new layer of cells ( xylem or phloem)

anticlinal division

add cells to a layer ( more initials)

Fusiform initials (F)

• long

• vertical orientation

• Produce elongated cells of the xylem and phloem

Ray initials (R)

• short

• Horizontal orientation

• Produce parenchyma in “rays” that go across that xylem

Vascular rays

• parenchyma cells

• channels for movement

• starch storage, lipids, proteins

• production and storage of some secondary metabolites

Vascular cambium

• Arises from procambium b/n primary xylem and phloem

• Also arises in the spaces between vascular bundles

• forms a complete circle

• not found in monocots

Early Year 1 woody stem strcuture

• little secondary phloem and xylem

• No cork cambium

Woody stem structure, late year 1

• More secondary phloem and xylem

• Peridem developing

gymnosperm wood

• softwood

• Few fibers, little parenchyma, mostly tracheids, no vessel

• Ray parenchyma

Angiosperm (eudicot) wood

• “Hardwood”

• Fibers, parenchyma, tracheids, vessel elements

• Ray Parenchyma

Heartwood

• center of stem

• Darker, harder, drier

• No transport function

• Vessels get plugged up

• ALL cells are dead

• May accumulate secondary metabolites

Sapwood

• Outer (younger) parts of wood

• Lighter, softer, moister

• Water transport actively occurs

• Includes living cells (parenchyma)

How do hollow trees occur

Heartwood can eventually rot away

periderm

• dermal tissue system of the secondary plant body

• replaces the epidermis as the stem grows

cork cambium

meristem that produces the periderm

cork

protective tissue outside the cork cambium (contains suberin)

phelloderm

parenchyma formed to the inside of the cambium (similar to cortex)

Lenticels

allow gas exchange through the periderm