Secondary Growth: Periderm and Cork Cambium

Question 1

2 types of dermal tissue in vascular plants

Answer 1

epidermis and periderm

Question 2

during secondary growth, ______ replaces epidermis, _____ replaces cortex

Answer 2

cork cambium (phellogen)
periderm (cork, cork cambium, phelloderm)

Question 3

periderm

Answer 3

cork (phellem) forms to outside of cork cambium; DEAD when mature

phelloderm forms to inside; thin layer of ALIVE parenchyma cells

-expansion of cortex causes cortex to break apart and fall of stem
-subsequent cork cambia arise from secondary phloem to inside

Question 4

periderm = _____

Answer 4

bark

Question 5

periderm

Answer 5

• consists of all tissues external to vascular cambium
• 2 distinct regions: inner and outer bark
• inner bark: LIVING secondary phloem, vascular cambium, innermost cork cambium and any remaining cortex; carries sugar and other organic molecules
• outer bark: DEAD tissue (incl dead secondary phloem, all layers of periderm outside of most recent cork cambium
• bark typically thinner than woody portion, essential for tree viability

Question 6

bark = protection

Answer 6

• cork cambium forms protective layers of tissues preventing water loss and infection by pathogenic organisms and predation
• cork cambium cannot grow in diameter and must reform inside the old one (toward a source of water and nutrients)
• cork cells enlarge and become impregnated with SUBERIN

Question 7

suberin

Answer 7

• complex polyester biopolymer (lipophilic)
• present in stems and roots, and functions as barrier of water and solutes
• cork cells are impregnated with suberin to make them “water proof”

Question 8

bark and gas exchange

Answer 8

bark needs to prevent water loss and allow gas exchange
- outer bark prevents water loss, infection by disease and predation
- inner bark carries sugar and other organic molecules (sap)
- LENTICELS

Question 9

lenticels

Answer 9

small openings in outer bark of stem and roots that allow gas exchange in tissue blocked by suberin coated cork cells

Question 10

antimicrobials: resin

Answer 10

pines and nonflowering plants produce resins that flow through resin canals in secondary xylem and phloem, periderm, and leaves

Question 11

antimicrobials: latex

Answer 11

• 10% of flowering plants produce latex, a milk substance that blocks entry of pathogens and contains compounds with growth inhibitory properties
• antimicrobial & deters insect and animal predators
• latex produced in vessels or special cells (LATICIFERS); network not as visible as resin canals
• latex produced close to surface, to be released upon injury

Question 12

secondary growth: monocot stems

Answer 12

monocots lack vascular cambium and thus true secondary growth
- increase in stem girth = anomalous thickening of ground tissue; no annual growth rings
- Arecaceae family, perennial trees, shrubs, including palms