10/10/2011 1 Secondary + Arborescent Growth Ch 26 Annuals, biennials, and perennials • Plants often classified according to seasonal growth cycles – Annuals • Weeds wildflowers garden flowers vegetables • Weeds, wildflowers, garden flowers, vegetables • The entire cycle from seed to vegetative plant to flowering plant and to seed again within a single growing season. – Biennials • Two seasons are needed for the period from seed germination to seed formation. •1 st season is root production, short stem, and tt fl rosette of leaves •2 nd season is flowering, fruiting, seed formation, and death, completing the cycle.
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10/10/2011
1
Secondary + ArborescentGrowth
Ch 26
Annuals, biennials, and perennials
• Plants often classified according to seasonal growth cycles– Annuals
• Weeds wildflowers garden flowers vegetables• Weeds, wildflowers, garden flowers, vegetables• The entire cycle from seed to vegetative plant to
flowering plant and to seed again within a single growing season.
– Biennials• Two seasons are needed for the period from seed
germination to seed formation.• 1st season is root production, short stem, and
tt f lrosette of leaves• 2nd season is flowering, fruiting, seed formation,
and death, completing the cycle.
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– Perennials • Vegetative structures live year after year. • Herb perennials pass unfavorable seasons as
dormant roots, rhizomes, bulbs, or tubers.
• Woody perennials may delay flowering until adulthood is reached.
– Example: Aesculus hippocastanum
Precocious flowering: flowering before leaves emerge.
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The Vascular Cambium
• Meristematic cells of VC are highly vacuolated.– Vertically oriented fusiform initials (longer than
wide)wide)– Horizontally oriented ray initials (elongated or
squarish)
Malus domestica Robinia pseudoacacia
• Secondary xylem and phloem are produced through periclinal divisions of the fusiform and ray initials.
• IOW the cell plate that forms is parallel to• IOW the cell plate that forms is parallel to the surface of the root or stem.
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Periclinal divisions Anticlinal divisions
• Xylem & Phloem produced by fusiform initials known as– Axial system
Ray initials produce horizontally oriented• Ray initials produce horizontally oriented ray cells – Form vascular rays or radial system
Vascular cambium:Two cells- Fusiform and ray initials