MERISTEMS TISSUE AND ITS CLASSIFICATION.pdf

Meristems and Its Classification
Basic concept of meristem
For B.S level
For presentation

1. Meristematic Tissues
Introduction of Meristematic
Tissue
Structure of Meristematic Cells
Classification of Meristems:
1.On the Base of Position
2.On the Base of Function
3.On the Base of Origin and
Development
4.On the Base of Growth Pattern
and Planes of Division
(KASHIF RAZA)

2. Meristematic Tissues
ThetermMeristemisderivedfroma
GreekwordMeristos=Divisible
Itisatissuecomposedofimmaturenot
welldifferentiatedcellswhichhasthe
capacityofdivisioniscalled
meristematictissue.
ItisalsocalledFormativetissues.
Loaction:
Theapicesofroots,shootsand
theirlateralbrancheshavemeristemat
theirtips.
Itincreaseslengthofrespectiveaxis.

3. Structure of Meristematic Cell
The cells in the meristem are thin walled.
Meristematiccellsarespherical,polygonal,oval
andisodiametricinshape.
Richinprotoplastwithoutreservematerial.
Thevacuolesaresmallandarescattered
throughouttheprotoplast.
Thickwalledmeristematiccellsarefoundinthe
apicalmeristems.
Types:
1.Initiatingcells:Thesecellsretainthe
meristematicactivitythroughoutthegrowthof
theplant.
2.Derivativecells:Thesecellsderivefrommeristem
intovarioustissueelement
3.Differentiationcells:Thederivativesundergo
morho-physiologychangesandthisprocessis
calleddifferentiation.

4. Classification of Meristems
OnTheBaseOfPositionOfMeristem:
1.Apicalmeristem:
Themeristemspresentatthetipofrootsandshootarecalled
apicalmeristems.
Theyplayimportantroleinprimarygrowth.
2.Intercalarymeristem:
Themeristemsituatedatthebasesofinternodesiscalled
intercalarymeristem.
Theyimportantroleintheintheproductionofleavesand
flower.
3.Lateralmeristem:
Thelongitudinalaxisofdividingcellspresentinthevascular
andcorktissueoftheplantsarecalledlateralmeristem.
Theyplayanimportantroleinthediameterofstemand
root.
Theyareinvolvedinsecondarygrowth.

5. On The Base Of Origin and Development of Meristem
1.PrimaryMeristem:
Themeristemdevelopingfromdirectlyfromthe
embryoniccellsarecalledprimarymeristem.
Fundamentalbodypartsaredevelopedsuchas
epidermis,cortexandmesophyllandprimary
vasculartissues.
b.SecondaryMeristems:
Themeristemdevelopedfromdifferentiatedand
maturetissuebyresumingthemeristematicactivityis
calledsecondarymeristem.
Secondaryvasculartissueandprotectivetissue
developfromsecondarymeristem.
Itsexamplearephellogenandcorkcambium.
Terms:
Meristematiccellslayerthatareresponsibleforthe
developmentoftheperidermiscalledphellogen.
Cellsthatgrowinwardsfromtherearetermed
Phelloderm.
CellsthatdevelopoutwardaretermedPhellem.

6. On the Basis of Function
a.Protoderm:
Itistheouterlayerofmeristem
whichwillbecomeepidermal
meristem.
b.Procambium:
Thisisresponsibleforthe
developmentoftheprimary
vascularwhichwillbecomethe
vasculartissue.
c.Groundmeristem:
Whichwillformtheground
tissue.(parenchyma,collenchyma,scl
erenchymatissue).

7. On The Basis of Growth Pattern and Planes of Division
a)Mass Meristem:
A meristem in which cell division in all planes results in
increase in mass.
For example: growth resulting in the formation of
endospermand takes place in young embryos of some
plant.
b) Rib Meristem:
A meristem in which cell division occur anticlinal (t right
angles to the longitudinal axis) in one plane and give rise
to vertical rows and column.
This type of growth occurs during the development of
cortex of root and pith and the cortex of stem.
c) Plate Meristem:
A meristem in which cell divides by anticlinal divisions
with the result that number of layers do not increase and
a platelike structure formed.
Growth shown byflat blades of angiosperm leaves.