2/17/2010 1 Secondary Body of the plant Secondary Body of the plant Tissues included • Vascular cambium • Secondary xylem • Secondary phloem • Secondary phloem • Periderm Vascular cambium (VC) • Type of meristem? • Which groups of plants have it? • Function? • Function? • Location? • Type of cells comprising it? General development Cell types • Fusiform initials • Ray initials
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2/17/2010
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Secondary Body of the plantSecondary Body of the plant
anticlinal divisions followed by intrusive growthanticlinal divisions followed by intrusive growth
Secondary xylem (2X) = wood
• Vertical system• Horizontal system
Origin?Cell components?
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Wood parenchyma• Axial parenchyma• Ray parenchyma– have secondary walls
OR1. Storage parenchyma2. Specialized vessel associated cells or contact cells
• Forms protuberances which penetrate through pits into the vessels after becoming inactive or vessels were injured—TYLOSIS or TYLOSES
Features of the rays
• Length, width, height• Length --XS• Width (no of cells in a horizontal direction) TS• Width (no. of cells in a horizontal direction)– TS• Height – TS; parallel to the longitudinal axis
(no. of cells or um)
Uniseriate– one cell wideBiseriate – 2 cell wideMultiseriate– more than 2
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• Sapwood/ alburnum--contains living cells and active in the transport of water
• Heartwood/duramen- dead cells and ceases to conduct water> disintegration of protoplasts> loss of cell sap> removal of reserve materials> formation of tyloses>oils, gums, resins, tannins, colored subs (oxidation; polymerization of phenols), aromatic cpds> gymnosperms-- aspirated
• Heartwood– more resistant to decay-- result of pathological conditions-- connected with ageing
2X of Gymnosperm
• Homogeneous• Small amount of
parenchyma
Vertical system
• Tracheids• Latewood ---f iber-tracheids• Absence of libriform fibers• Absence of libriform fibers• Tracheids overlap each other
>Pits are numerous at the ends of tracheids• Crassula– thickenings of the middle lamella and
primary walls• In Pinus, axial parenchyma--epithelium
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Horizontal system
• Ray parenchyma and Ray tracheids• How do you distinguish between the two?• Homocellular and heterocellular• Homocellular and heterocellular• Uniseriate ; more than one cell wide with resin
Origin?Cell components?• arrangement of tissue –determined by nature of
cambium (as in the xylem)• Function?
• Near the camibum –phloem rays and xylems rays are equal in size
• Mature outer portions – increase in width> lateral expansion of existing cells (radial cell division)—dilated
Conifer Secondary Phloem
• Relatively simple• VERTICAL SYSTEM
> sieve cells parenchyma cells including > sieve cells, parenchyma cells including albuminous cells and fibers
• HORIZONTAL SYSTEM> uniseriate; parenchyma cells only
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Sieve cells• Ends overlap one another• More sieve areas at point of overlap
Parenchyma cells (excluding albuminous cells)• (vertical) storage( ) g
Pinaceae- Secondary phloem contains NO FIBERS
Secondary phloem
• Resin ducts may be present• Narrow zone of phloem may be active• Collapse of sieve cells of nonconducting phloem• Collapse of sieve cells of nonconducting phloem