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Secondary Body of the plantSecondary 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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Identify immediate origin of the ff:

• Phloem ray• Tracheary elements• Fibers• Fibers• Phloem parenchyma• Xylem parenchyma• Ray parenchyma• Ray tracheid

General structure of VC

• Intense vacuolation• With primary pit fields

with plasmodesmatap• Radial walls thicker than

tangential walls(result of what type of direction?)

Procambium vs Vascular cambium

• Gabled endings• Stain deeply• Not differentiated into long

and short cells

• Flat endings• Protoplasts do not stain

strongly• With fusiform and ray initialsand short cells • With fusiform and ray initials

Cambial zone—but there’s only 1 layer of VC-- wide if cambium is active

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Ray initiation

• Single cell may be cut off the side of a fusiforminitial

• Cut off the end• Cut off the end• Reduction to a single ray• Segmentation by transverse divisions

Cambial activity• Tropical –active throughout the entire life of

plant• With definite seasonal climates—ceases with the

onset of unfavorable condition

Resumption of cambial activity usually consist of 2 stages

1. Cambial cells expand radially2. 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 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

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 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 libriform fibers, gelatinous fibers, wood 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 distributeddistributed

• Ring porous> of different diameters> more advanced> usually in xerophytes

Arrangement of axial wood parenchyma• Apotracheal

• Paratracheal• Paratracheal>scanty>unilateral> vasicentric

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Rays

• Parenchyma cells only• Procumbent and upright

cellscells• Homogeneous or

homocellular• Heterogeneous or

heterocellular

Secretory structures

• Laticifers• Ducts and cavities (traumatic)

Secondary PhloemSecondary Phloem

Two systems• Vertical

> sieve elements, phloem parenchyma, phloem fibers

• 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 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

>Rays become wavy

Dicot secondary phloem• VERTICAL

> sieve tube members, companion cells, parenchyma cells, fibersp y ,

• HORIZONTAL>variously sized rays; parenchyma only

Parenchyma—may contain crystalsFiber-sclereids—do not develop directly from

fusiform cambial initial; parenchyma cells of nonfunctioning phloem

Nonfunctioning or nonactive phloem• Presence of

definitive callose• Disintegration of the

t l tprotoplast• Collapse and

crushing of elements

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