The document discusses the vascular cambium and secondary growth in plants. It describes: 1. The tissues that make up secondary plant bodies including vascular cambium, secondary xylem, secondary phloem, and periderm. 2. The vascular cambium itself - it is a lateral meristem found in vascular plants that produces secondary xylem and phloem. It is composed of fusiform and ray initials. 3. The development and cell types of secondary xylem (wood) and phloem in both gymnosperms and angiosperms. Key cell types include tracheids, fibers, vessels, and parenchyma.

1. 2/17/2010
Tissues included
• Vascular cambium
• Secondary xylem
Secondary Body of the plant • Secondary phloem
• Periderm
General development
Vascular cambium (VC)
• Type of meristem?
• Which groups of plants have it?
• Function?
• Location?
• Type of cells comprising it?
Cell types
• Fusiform initials
• Ray initials
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General structure of VC
Identify immediate origin of the ff:
• Phloem ray • Intense vacuolation
• Tracheary elements • With primary pit fields
• Fibers with plasmodesmata
p
• Phloem parenchyma • Radial walls thicker than
tangential walls
• Xylem parenchyma
(result of what type of
• Ray parenchyma
direction?)
• Ray tracheid
Cambial zone—but there’s only 1 layer
Procambium vs Vascular cambium of VC
• Gabled endings • Flat endings
-- wide if cambium is active
• Stain deeply • Protoplasts do not stain
• Not differentiated into long strongly
and short cells • With fusiform and ray initials
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Ray initiation Cambial activity
• Single cell may be cut off the side of a fusiform • Tropical –active throughout the entire life of
initial plant
• Cut off the end • With definite seasonal climates—ceases with the
onset of unfavorable condition
• Reduction to a single ray
• Segmentation by transverse divisions Resumption of cambial activity usually consist of
2 stages
1. Cambial cells expand radially
2. Cells begin to divide
-- bark is easily peeled off
Types of cambium
Addition of new fusiform initials
• Storied – longitudinal anticlinal division
• Non-storied– oblique, pseudo-transverse,
anticlinal 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
OR
1. Storage parenchyma
2. 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
(no direction)
• Height – TS; parallel to the longitudinal axis
(no. of cells or um)
Uniseriate– one cell wide
Biseriate – 2 cell wide
Multiseriate– more than 2
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• Heartwood– more resistant to decay
• Sapwood/ alburnum--contains living cells and -- result of pathological conditions
active in the transport of water -- connected with ageing
• 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
2X of Gymnosperm Vertical system
• Tracheids
• Homogeneous
• Latewood ---f iber-tracheids
• Small amount of
• Absence of libriform fibers
parenchyma
• 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
• Uniseriate ; more than one cell wide with resin
duct
• Ray parenchyma + tracheids
> half bordered pit pairs (cross field)
• In Pinus, fenestriform pits
Resin ducts
• Vertical and horizontal system
• Schizogenous development
• Tylosoids – enlargement of
epithelial cells; blocks resin
ducts
• Usually produced as a result
of injury
2X of Dicotyledon (Angiosperm)
• More complex
• Vessel members, tracheids, fiber-tracheids,
libriform fibers gelatinous fibers, wood
fibers, fibers
parenchyma, rays
• Growth rings
> tropical origin—not distinguishable
> temperate – distinguishable
• Early wood and late wood
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Arrangement of vessels
• Diffuse porous
> vessels~ equal diameter and uniformly
distributed
• Ring porous
> of different diameters
> more advanced
> usually in xerophytes
Arrangement of axial wood
parenchyma
• Apotracheal
• Paratracheal
>scanty
>unilateral
> vasicentric
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Rays Secretory structures
• Parenchyma cells only • Laticifers
• Procumbent and upright • Ducts and cavities (traumatic)
cells
• Homogeneous or
homocellular
• Heterogeneous or
heterocellular
Two systems
• Vertical
> sieve elements, phloem parenchyma, phloem
fibers
Secondary Phloem • Horizontal
> phloem ray parenchyma
Origin?
Cell components?
• arrangement of tissue –determined by nature of
cambium (as in the xylem)
• Function?
• Near the camibum –
phloem rays and xylems Conifer Secondary Phloem
rays are equal in size
• Relatively simple
• Mature outer portions
– increase in width • VERTICAL SYSTEM
> lateral expansion of > sieve cells parenchyma cells including
cells,
existing cells (radial cell albuminous cells and fibers
division)—dilated • 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
>Rays become wavy
Dicot secondary phloem Nonfunctioning or nonactive phloem
• Presence of
• VERTICAL definitive callose
> sieve tube members, companion cells,
• Disintegration of the
p
parenchyma cells, fibers
y ,
protoplast
t l t
• HORIZONTAL
>variously sized rays; parenchyma only • Collapse and
crushing of
Parenchyma—may contain crystals elements
Fiber-sclereids—do not develop directly from
fusiform cambial initial; parenchyma cells of
nonfunctioning phloem
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