Chapter 5 Secondary Growth Botany Chapter 5 Secondary Growth

Chapter 5 Objectives (Section 1) 1. Distinguish between primary and secondary growth 2. Describe the arrangement of tissues contributing to secondary growth and the mature tissues derived from each type • Vascular cambium • Cork cambium 3. Relate the growth of the vascular cambium to the formation of wood and bark in woody stems 4. Distinguish between inner bark and outer bark. Identify tissues associated with each.

Primary vs. Secondary Growth Primary growth is elongation Tissues for primary growth are derived from apical meristem Apical meristem is at the tip of shoots Lateral meristems will be derived from the peripheral zone of the apical meristem

Primary vs. Secondary Growth Secondary growth results in an increase in diameter Tissues for secondary growth are derived from lateral meristem (cambium)

Cambium Cambium is the main living tissue of woody stems Vascular cambium lies between the xylem and phloem, both of which are derived from it Cork cambium lies outside of the living phloem, and is derived from phloem and periderm

Cambium in Woody Stems Vascular cambium divides the wood from the bark Cork cambium divides the inner bark from the outer bark

Woody Stems: Wood vs. Bark Wood functions for conducting water and minerals and support Wood forms the bulk of the woody stem Wood is made of xylem (Remember, xylem is dead at maturity) Bark functions for conducting food and for protection of the wood and cambium Bark contains a variety of tissues: Living phloem Dead phloem Cork Epidermis

Section 1 Review Q’s (p. 106)

Chap 5 Objectives (Section 2&3) 5. Distinguish between “anticlinal” and “perclinal” cell divisions. Describe the growth resulting from each type. 6. Define “cavitation”. 7. Distinguish between “sapwood” and “heartwood” 8. Explain annual “growth rings” in wood from the context of secondary growth. 9. Define “suberin” and “lenticels” and discuss their functions 10. Discuss several commercial applications of wood and bark and their derivatives.

Patterns of cell division Anticlinal Periclinal

Cavitation Xylem tissue is dead, consisting of vessel elements and tracheids Transmission of water through xylem depends on cohesion through an unbroken column of water molecules. The water is pulled from above, not pushed from below Once an air bubble forms in the xylem (usually in the larger vessel elements), called “cavitation” the water below the bubble cannot be drawn up any longer

Sapwood vs. Heartwood Sapwood is xylem that is still functioning for transmission of water. It lies directly below the vascular cambium Heartwood is no longer conductive due to cavitation. It lies at the center of the woody stem

Growth rings The pattern of cell growth changes over the course of the growing season, resulting in a visible distinction between the secondary growth from one season compared to the next

Annual growth patterns The early growing season is generally warmer and moister with long days Cells formed in the spring tend to be larger, with thinner walls Cells formed late in the season are generally smaller.

One year old Basswood stem

Two year old Basswood stem

Three year old Basswood stem

Dendrochronology

Dendrochronology cores

Suberin

Lenticels

Section 2 Review Q’s (p. 112)