Lecture 25 - Plant Growth & Development (part 2) Flashcards
What does secondary growth do?
increases the diameter of a plant
Secondary growth
increases the plants girth (diameter) through the activity of lateral meristems
Where does secondary growth occur in?
- Occurs in all Gymnosperms, most Eudicots and a select few Monocot species
- Occurs in roots and shoots, never leaves
Secondary growth occurs simultaneously with…
primary growth in woody plants
What does primary growth & secondary growth do?
• Primary growth adds leaves, increases height
• Secondary growth increases girth in the older regions
- increases the diameter of a plant
Primary Growth (process)
- Apical cells in the root/shoot tips are undifferentiated
- When they divide, some daughter cells will remain in the meristematic region
- Other daughter cells become partially differentiated into primary meristem cells (protoderm, ground, procambium)
- Daughter cells from those will differentiate into cells in mature tissues
What is the direction of primary growth?
vertical, downward
What is the direction of vascular cambium secondary growth?
both directions
What are the 2 lateral meristems of secondary growth?
- vascular cambium
- cork cambium
What happens at the very beginning of secondary growth?
Primary growth from the activity of the apical meristem is nearing completion and the vascular cambium has just formed
Where does primary growth continue?
in the apical bud
Where does secondary growth occur?
along the vascular cambium
What do some of the initials of the vascular cambium give rise to?
vascular rays
What are vascular rays?
files of parenchyma cells that CONNECT secondary xylem and phloem & TRANSPORTS water B/T them
- aids in wound repair, and stores carbohydrates
What do vascular rays aid in?
aids in wound repair, and stores carbohydrates
What happens when girth increases the first time?
secondary phloem can’t keep up with filling in the gaps
- Eventually the epidermis ruptures and falls off
- A cork cambium develops from the cortex parenchyma cells, producing cork cells
• Cork will replace the epidermis
Where does the cork cambium develop from?
develops from the cortex parenchyma cells
What does the cork cambium produce?
cork cells
What does cork replace?
the epidermis
What happens in year 2 of secondary growth?
the vascular cambium produces more secondary xylem and phloem
- The cork cambium produces more cork cells
What happens when girth increases the second time?
the outermost cork cells get sloughed off (just like the epidermis did)
What happens if cork cambium is lost during secondary growth?
another one will form deeper in the cortex tissue to make more cork cells
What happens if the cortex is eventually sloughed off?
the cork cambium will arise from the secondary phloem tissue
What forms a layer of periderm?
Each cork cambium and the tissues is produces (cork)
