Anatomy of Flowering Plants

K C Meena

PGT Biology

Tissues

• A group of similar cells performing same function.
• Types of plant tissues - Meristematic tissues and permanent tissues.

Meristematic tissues�

• Have power of cell division

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• Characteristics features
• Cells are thin walled
• No intercellular places
• Abundant cytoplasm
• Retains power of cell division

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• Classification based on position. Three types
• Apical meristem
• Lateral meristem
• Intercalary meristem

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• Based on the origin – three types
• Promeristem- embryo/ seedlings
• Primary meristem
• Secondary meristem

• Growth in plants is largely restricted to specialized regions of active cell division called meristem.
• Apical meristems are the meristems which occur at the tips of roots and shoots and produce primary tissues
• Intercalary meristem are the ones which occur between mature tissues
• Lateral meristem occurs in mature regions of roots and shoots and appear later than primary meristem

Permanent tissues:�

• The newly formed cells from primary and secondary meristems which become structurally and functionally specalised and lose the ability to divide are permanent tissues

Simple permanent tissues

• Parenchyma( storage)-living
• Collenchymas (support ) below epidermis, living
• Sclerenchyma – sclereids and fibres- dead

Compound permanent tissues

• Xylem- xylem vessels, xylem tracheids, xylem parenchyma, xylem fibres
• Phloem – sieve tubes, sieve cells, companion cells, phloem parenchyma

Simple tissues

Made up of only one type of cells

Parenchyma -

• Major component within organs Isodiametric,spherical, oval,round polygonal,elongated in shape.
• Thin cell walls made of cellulose.
• Closely packed or have intercellular spaces
• Function-Photosynthesis, storage, secretion.

Collenchymas –

• occurs in layers below epidermis, either in homogeneous layer or in patches
• Thickened at the corners due to pectin, cellulose, oval, spherical, polygonal
• Assimilate food when chloroplasts is present
• Intercellular spaces absent- function. Mechanical support

Sclerenchyma -

• long narrow cells, lignified walls, with pits
• Dead- fibers-thick walled, elongated, pointed
• Sclereids- spherical, dead, narrow cavity-lumen
• Found in – guava, pear, sapota
• Function. Mechanical support

Complex tissues

• More than one type of cells

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• Xylem.
• Conducting tissue for water and minerals

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• Tracheids. Elongated or tube like cells, dead, main water transporting element

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• Vessels. Long cylindrical, lignin in cell walls, large central cavity, devoid of protoplasm.

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• Xylem fibres- lumens present, septate/aseptate

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• Xylem parenchyma- living thin- walled, cell walls, cellulose, store food as starch or fat, tannins

Phloem - (transports food material)

• Sieve tubes- long, tube like, perforated, forms sieve plates
• Companion cells – pit is present , helps in maintenance of pressure gradient in the sieve tubes
• Phloem parenchyma – elongated, tapering, dense cytoplasm, cell wall, cellulose, pits
• Phloem fibres - unbranched, pointed, quite thick.

Tissue system :�

Epidermal tissue system

• Cuticle present- contains stomata ( guard cells, subsidiary cells, stomatal apparatus )
• Trichomes – (on stem) multicellular, secrete oils. Root hairs- single celled.

Ground tissues

• Tissues except epidermal and vascular tissues.
• Mesophyll. ( collenchymas, sclerenchyma, parenchyma )

Vascular tissue system

• Cambium. ( lateral meristem )
• Radial vascular bundle – in roots
• Conjoint open vascular bundle - in dicot stem and leaves
• Conjoint closed vascular bundle – in monocot stem and leaves

Anatomy of Dicotyledonous root �

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• Epidermis – root hair – cortex ( Parenchyma ) endodermis – suberin layer as casparian strips
• Pericycle (lateral roots) pith is small – conjuctive tissues ( between xylem and phloem )
• Cambium ring ( 2-4 xylem and phloem )
• Stele ( endodermis, pericycle, vascular bundle and pith )

Monocotyledonous root�

• No cambium in the vascular bundles. (6 vascular bundles and are scattered) called polyarch -
• pith is large – since no cambium, and no secondary growth

Dicotyledonous stem�

• Epidermis, cuticle, trichomes, hypodermis (collenchymas)
• Cortical layer ( parenchyma ) endodermis(starch sheath)
• Pericycle - vacular bundles – medullary rays
• Vascular bundles are in a ring ,Conjoint, open, and endarch protoxylem
• Pith is larger (parenchyma)

Monocotyledonous stem�

• Epidermis – hypodermis ( sclerenchyma ) scattered vascular bundles, sclerenchyma.
• Bundle sheath – vascular bundles are conjoint, closed, no cambium Peripheral vascular bundle are smaller than central
• No secondary growth- no trichomes
• Water containing cavities are present- no distinct pith

Dorsiventral leaf /dicot leaf:�

• Epidermis are adaxial epidermis (upper) and abaxial epidermis (lower)
• Cuticle – stomata is more on lower epidermis
• Mesophyll – it has two types of cells , palisade parenchyma and spongy parenchyma
• Vascular system vascular bundle are present in vein and midrib
• Reticulate venation –vascular bundle are surrounded by bundle sheath

Isobilateral / monocot leaf:�

• Same anatomy – but no spongy parenchyma and stomata on both side
• Bulliform cells – parallel venation

Secondary growth:�

• Primary growth- apical meristem ( grows length wise )
• Secondary growth –increase in girth
• It involves lateral meristem vascular cambium and cork cambium
• Vascular cambium
• Formation of cambial ring
• Intrafacicular cambium
• Interfascicular cambium
• Activity of cambial ring
• Formation of secondary xylem secondary phloem
• More active on the inner side so more xylem

• Spring early wood –more active and light coloured
• Autumn late wood – less active and dark coloured
• The two kinds of wood that appear as alternate concentric rings, constitute an annual ring
• Heart wood – dead, elements, highly lignified provides mechanical support
• Sap wood – peripheral region , secondary xylem, light in colour, conduction of water and minerals

Cork cambium:�

• Cortical and epidermis layer get broken
• Replaced to provide new protective cell layers
• Cork cambium/ phellogen –develop in cortex region and produce new cells towards both sides
• Outer cells form cork / phellum
• Inner cells form secondary cortex / phelloderm
• Bark - soft early bark – formed early in the season
• Late / hard bark – formed late in the season
• Lenticels. Lens shaped openings helps in exchange of gases

Secondary growth in roots:�

• Wavy ring – later becomes circular
• Secondary growth occurs in gymnosperms too (except in monocots) as monocot do not have cambium.