Lecture 15 - Secondary Growth

Secondary growth

• From secondary meristems

• Increase in girth

Plant types that secondary growth occurs in

Woody plants

No monocots / herbaceous eudicots

What plant parts does secondary growth occur in?

Primarily stems and roots, rarely leaves

Girth growth in palms / woody monocots

Occurs due to adding more parenchyma and vascular bundles

NO secondary meristem

Banana tree pseudostem

Sheath of leaves

Two types of secondary meristem

Vascular cambium

Cork cambium

Vascular cambium

Forms secondary vascular tissue, major girth expansion

Cork cambium

Forms new dermal protective layer / periderm

When is the vascular cambium formed?

During primary growth

Label

Label

Vascular cambium initial types

Fusiform

Ray

Label

Ray initials

Produces radial or lateral transport system cells, isodiametric in spokes

Fusiform initials

Produces axial or vertical vascular transport cells

Flat, elongated, highly vacuolar

Label

Label

Two regions that form vascular cambium

Fascicular cambium

Interfascicular cambium

Fascicular cambium

Meristem cells within vascular bundle

Interfascicular cambium

Meristem cells between vascular bundles

How does vascular cambium form?

Joining of fascicular and interfascicular cambia

Vascular cambium division directions

Inwards - Secondary xylem

Outwards - Secondary phloem

Label

Label annual growth rings

When is the vascular cambium active?

Spring to fall, larger xylem

Label Gymnosperm vs. Angiosperm wood

Annual ring paleobiology significance

Used to determine ancient climate conditions

Oldest living tree?

Debated, but most evidence points to around ~5,000 years old

(Methuselah)

What does cork cambium produce

Cork to the outside

Phelloderm to the inside

What does the cork cambium give rise to

Periderm

Periderm

Consists of cork cambium plus the layers of cells it produces

Bark

Consists of all tissues external to the vascular cambium including 2P and periderm

What is cork lined with

Suberin + wax

prevents water/gas exchange

Lenticel

Eruptions/gaps in parenchyma for diffusion

Bark

All tissues outside of vascular cambium

Where is (wine) cork from?

Cork oak

Primary & secondary growth occurs…

Simultaneously in different locations

Where does primary growth occur

Apical tips, produces buds and leaves

Secondary growth occurs where?

Internally, expands growth

Heartwood

Older, non-functioning xylem

Dark in appearance due to mineral accumulation

Sapwood

Younger, functioning xylem, exteriorly

Secondary growth in root

similar to stem

Lacking in most herbaceous eudicots and all monocots

Secondary growth in root special event

epidermis and cortex are shed

Anatomy difference in root secondary growth

Formation of vascular cambium that encircles the root