Plant Form & Function #2, Secondary Growth

Plant Form & Function #2, Primary growth increases length of stem axis: • new cells originate from meristems at tips of roots Secondary Growth & shoots

Secondary growth increases width of stem or Bio 1B trunk Instructor: Thomas Carlson • new cells originate from vascular cambium

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Monocot Stems & Trunks Eudicot Secondary Growth

• Majority of monocots do not have secondary growth • Large palm trees (e.g., coconut trees) do not have true secondary growth, but rather produce “woody” • The following slides on tissue from primary growth that make up the trunk secondary growth refer to • Certain monocots (e.g., Agavaceae family) have a specialized type of secondary growth that is different eudicots and not monocots than eudicot secondary growth • Monocot secondary growth information will NOT be required for the exam

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5 6 Meristems and Cell Production Annual vs Perennial Plants • Apical Meristem (Figs. 35.11, 35.12, 35.13, 35.16; Lab manual 4.1, 4.2, 4.3) • Annual: plant that goes through entire life – primary tissues cycle with ﬂowering, fruit production, and – increase length of shoot and root axis death within one year. Secondary growth does • Vascular Cambium Lateral Meristem (Figs. 35.11, 35.12, 35.19, not occur in annual plants 35.20, 35-21; Lab manual 4.6-4.11) – secondary tissues for wood production • Perennial: plant that lives multiple years and – increase in girth/width may have a below ground stem called a rhizome • Cork Cambium Lateral Meristem (Figs. 35.19, 35.22; Lab manual (e.g., goldenseal) or an above ground trunk and 4.5, 4.6, 4.9, 4.10, 4.11) – secondary tissues for cork & bark production branches (e.g., shrubs and trees) – increase in girth/width

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Secondary growth in young stems: tissues from outer to center (Fig 35-11) • Periderm • Cork cambium • Ground tissue (cortex) • Primary phloem • Secondary phloem • Vascular cambium • Secondary xylem • Primary xylem

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11 12 Secondary Growth in Eudicots (Figs. 35.11, 35.12, 35.19, 35.20, 35.22; Lab manual 4.6-4.11) • increases width/girth of stem/trunk

• feature of eudicots and gymnosperms

• occurs in both roots and stems

• new cells develop from vascular cambium

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Vascular Cambium Development (Figs. 35.11, 35.13, 35.17, 35.19-20, 35-22; Lab manual 4.6-4.11)

• cambium develops from cells between primary xylem and primary phloem within bundles • cambium also develops within parenchyma cells in regions between bundles • these regions merge to form a continuous ring of cells that is one layer thick

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17 18 Secondary Growth in Eudicots (Figs. 35.11, 35.12, 35.19, 35.20, 35.22; Lab manual 4.6-4.11) • Bark (Fig. 35.18, 35.21, 35.23) – tissue outside of vascular cambium – made up of secondary phloem & cork

• Vascular Cambium – single layer of cells in ring in stem/trunk • secondary xylem formed to inside of cambium to produce wood • secondary phloem forms to the outside of cambium • Wood – tissue inside of vascular cambium • all cells internal to the vascular cambium are secondary xylem except

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Secondary growth in tree trunks: tissues from outer to center (Fig 35-11, 35-19, 35-22)

• Periderm • Cork cambium • Secondary phloem • Vascular cambium • Secondary xylem (sapwood) • Secondary xylem (heartwood)

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23 24 Phloem Cell Types (Fig 35.10, 35.11, 35.14, 35.17-20, 35.22; Lab Man. Fig. 4.3– 4.11)

• Contains sieve cells, sieve tubes, and companion cells • Sieve tube member: elongated food-conducting plant cell with clusters of pores at both ends allowing sap to ﬂow to adjacent cells • Sieve tube members are stacked end-to-end to form sieve tubes • Companion cell: specialized cell found adjacent to sieve tube member

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Phloem Transports Sugars (Fig 35.10, 35.11, 35.14, 35.17-20, 35.22; Lab Man. Fig. 4.3–4.11) • Plant vascular tissue that transports sugars from the photosynthetic leaves DOWN to other parts of the plant including the roots where sugars are converted into starch for storage

• In the early Spring, in many tree species in northern latitudes, the starch in the roots is broken down into sugars which are transported UP the tree in the phloem to the small branches to provide nutrients for developing leaves & shoots

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Functions of Xylem Most Typical Function of Phloem • The main function of xylem is to transport water and minerals absorbed by the roots up the tree • Phloem cells transports photosynthate • Some tall tree species (e.g., redwoods & Douglas ﬁrs) are known to absorb water from fog through open in the form of sugar both up and down stomata in leaves. In these circumstances, the the tree movement of water in the xylem is downward in tree • There are also examples where the xylem ﬂuid transports sugars upward in the tree, e.g., in the Spring in sugar maples when the starches stored in the roots are converted to sugars which are transported up the tree by xylem to provide food and energy for the developing buds and leaves

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