Anatomy of flowering plants
Dr Gargi Singh
MSc (Botany) PhD (Mycology)
Panjab University, Chandigarh
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GARGI
Root apical
Apical meristem
Shoot apical
Intercalary
Meristematic meristem
Secondary (lateral)
meristem
Plant tissues Parenchyma
Simple Collenchyma
Sclerenchyma
Permanent
Xylem
Complex
Phloem
On the basis of its ability to divide, plant tissues are
grouped as
• Meristematic tissue
• Permanent tissue
Meristematic Tissue
• Living cells with ability to divide
• Polyhedral or isodiametric in shape intercellular spaces
• Cell wall is thin
• Protoplasm is dense with distinct nucleus
• Vacuoles if present, are very small
Intercalary meristematic
• Present in the top or base area of node
• Their activity is mainly seen in grasses (monocots)
• Regenerate parts removed by the grazing herbivores
• These are short lived
Lateral meristem
• Present along the sides of central axis of organs
• It takes part in increasing girth of stem or root. eg
intrafascicular cambium.
• It is found in vascular bundles of gymnosperms and dicot
angiosperms
Permanent Tissues
• The cells of the permanent tissues do not
generally divide further
• Simple tissues
• Complex tissues
Simple Tissues
• A simple tissue is made of only one type of cells
• The various simple tissues in plants are
parenchyma, collenchyma and sclerenchyma
Parenchyma Collenchyma Sclerenchyma
COMPLEX PERMANENT TISSUES
These are made of more than one type of cells and
they work together as a unit
• Xylem
• Phloem
Xylem is composed of 4 kinds of elements:
Primary xylem is 2 types:
Protoxylem: The first formed primary
xylem.
Metaxylem: The later formed primary
xylem.
PHLOEM (BAST)
• Sieve tube elements, companion cells, phloem
parenchyma & phloem fibres.
• Gymnosperms have albuminous cells & sieve cells.
They lack sieve tubes & companion cells.
Based on structure and location, tissue systems
are 3 types:
• They are present in the epidermis of leaves.
• They regulate transpiration & gaseous exchange.
• A stoma is made of two bean-shaped cells (guard cells).
• In grasses, the guard cells are dumbbell shaped.
• Based on the presence or absence of cambium,
vascular bundles are 2 types:
• Open
• closed
Dicotyledonous (Dicot) Root
Monocotyledonous (Monocot) Root
Dicotyledonous (Dorsiventral) Leaf- Epidermis
Monocotyledonous (Isobilateral) Leaf
SECONDARY GROWTH
• The growth of the roots and stems in length with the
help of apical meristem is called primary growth.
• Secondary growth is the increase in girth of dicot
plants.
• Tissues involved in secondary growth are the two
lateral meristems:
Ø Vascular cambium
Ø Cork cambium
Secondary growth in a dicot stem –
Stages in transverse views
Spring wood and Autumn wood
•Many physiological & environmental factors control the activity of cambium.
•In spring season, cambium is very active and produces many xylary elements
having vessels with wider cavities. This wood is called spring wood (early
wood).
•It is lighter in colour and has a lower density.
Spring wood and Autumn wood
• In winter, cambium is less active and forms fewer xylary
elements having narrow vessels. This wood is called autumn
wood (late wood).
• It is darker and has higher density.
• These two kinds of woods that appear as alternate concentric
rings constitute an annual ring. This is used to estimate the age
of tree (Dendrochronology).
Heart wood and Sap wood
• Heartwood is the hard, dead, dark brown-coloured, highly
lignified and non-functional central part of the secondary xylem
of old trees.
• The dark colour is due to deposition of organic compounds
(tannins, resins, oils, gums, aromatic substances, essential
oils etc). These substances make it hard, durable and
resistant to the attacks of microorganisms and insects.
• Function: Mechanical support to stem.
Heart wood and Sap wood
• Sapwood is the peripheral region of secondary xylem.
• It is living and lighter in colour.
• Function: It is involved in the conduction of water and
minerals from root to leaf.
Cork Cambium
• As the stem continues to increase in girth due to the
activity of vascular cambium, the outer cortical &
epidermis layers get broken.
• It is to be replaced to provide new protective cell
layers. Hence another meristematic tissue called cork
cambium (phellogen) develops, usually in the cortex.
Cork Cambium
Lenticels
• At certain regions, phellogen cuts off closely arranged
parenchymatous cells on outer side. These cells rupture
epidermis, forming a lens shaped openings called lenticels.
• They occur in most woody trees.
• Function: Lenticels permit gas exchange of between the outer
atmosphere and the internal tissue of the stem.
•Secondary growth also occurs in stems and roots of
gymnosperms.
•Secondary growth does not occur in monocotyledons.
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