Secondary Growth Flashcards
Secondary growth
Activity of the two lateral meristems: vascular cambium and cork cambium
Increase in thickness of girth of a plant
Annuals
Entire life from seed to vegetative plant to flowering plants to see occurs in a single growing season
-seeds connect generations
-semelparous: single reproductive event
Biennials
Winter Annuals with life cycles
Live for 2 growing seasons
-semelparous
Perennials
Plants that live year and year (more than 2 seasons
-Iteroparous
Cork
One of 3 parts of the periderm: it is a secondary tissue that replaces the epidermis in most woody roots and stems.
Bark
All tissues outside the vascular cambium including the periderm when present
And the end of first years growth, the bark includes any primary tissues still present, the secondary phloem, the periderm and any dead tissues remaining outside the periderm
Hardwood vs softwood
Angiosperm woods
-structure more complex
-vessel elements, tracheids, fibres and parenchyma cells
-large rays
Conifer woods
-simpler structure
-lack of vessels
-less parenchyma (only parenchymous cells are associated with resin ducts)
-tracheids make up most
Bark consists of all tissues outside the _____
Vascular cambium
Wood is _____
Secondary xylem
Growth rings result from the periodic activity of the _____
Vascular cambium
Herbaceous plants
Undergo little or no secondary growth
-temperate regions
-either entire plant or part of the shoot lives 1 season
Woody plants
Plants whose shoot undergo secondary growth
-shrubs and trees
-love more than 1 year
Which plants have secondary growth
Perennials-Woody
Very few herbaceous from annuals and biennials
Vascular cambium
Meristematic cells
-highly vacuolated
-two initial forms: fusiform and ray
Fusiform initials
Vertically oriented
More long than wide
Appear flattened or brick shaped in transverse sections
Ray initials
Horizontally oriented
Slightly elongated
Effect of secondary growth on stem
Formation of cylinder of secondary vascular tissues
-included rays: extend radially
-more secondary xylem than phloem produced
-primary phloem pushed outward: thin walled cells destroyed; phloem fibers persist
Closer to vascular cambium means
More alive
When are xylem larger, and when are they smaller
Larger at beginning of next years growth, smaller as year goes on
Periderm
Replaces epidermis - protective
Consists of 3 parts:
-Phellem or cork
-phellogen
-phelloderm
Phellem
Or cork
Outer protective tissue
Phellogen
Cork cambium
Lateral meristem
Phelloderm
Similar to cortical parenchyma, formed towards inside of stem
Lenticels
Portions of the periderm with numerous intercellular spaces
-allow for gas exchange through periderm
-present on fruits
What type of division occurs in cork, xylem and phloem
Periclinal
-parallel to old cell walls
Bark
All tissues outside the vascular cambium
Outer bark
Everything outside the innermost phellogen (Cork cambium)
Inner bark
The tissues between the vascular cambium and the innermost phellogen (cork cambium)
-includes conducting phloem: living sieve tube elements, active in transport And non-conducting phloem: dead sieve tube elements, live parenchyma cells (rays and axial parenchyma)
Study of tree rings
Dendrochronology
Wood
Accumulated secondary xylem
Hardwoods vs. Softwoods
Hardwoods-angiosperms
Softwoods-conifers: lack vessels
Growth rings
Periodic activity of vascular cambium
Annual rings
If growth coincides with one year
-false:due to environmental conditions that alter growth rates
Early woods vs. Late woods
Less dense (wider cells, thinner walls)
More dense
Heartwood
-as wood dries, oils, gums, resins, tannins infiltrate it
-add colour and smell
-non conducting
Sapwood
Live conducting xylem
