The Primary and Secondary Growth of Plant

Overview
 Definations of the terms, growth,

development, primary growth, and
finally growth.
 Meristems ( apical and lateral
meristems)
 Primary growth in details.

 Secondary growth in details
 Annual rings
Defination of terms..
 Growth simply refers to the

permanent increase in size of an
organism.
 Development is the increase in
complexity of an organism.
 Primary growth is the increase in
length of a plant.
 Secondary growth is the increase in
girth of a plant.
Meristems
 Meristematic tissues are clumps of

small cells with dense cytoplasm
and proportionately large nuclei.
 Meristem is a type of plant tissue
consisting of undifferentiated cells
that can continue to divide and
differentiate.
Meristems
 Apical meristems
 located at tip of stems and roots
 Plant tissues that result from
primary growth are called primary
tissues.
 make up primary plant body
 root apical meristem protected by
root cap
Meristems
Lateral meristems
 Most trees, shrubs, and some herbs

have active lateral meristems.
 increases girth in nonwoody plants -
secondary growth
 Woody stems
cork cambium
 produces cork cells
 vascular cambium
 produces secondary vascular tissue
Meristems
Primary and secondary growth
 Primary growth results from cell

division at the apical meristem at
the plant tip.
 Secondary growth results from cell
division at the lateral meristem,
increasing the shoot’s girth.
Primary growth in plants
 Primary growth is the upward

growth of the stem and the
downward growth of the roots. It is
the type of growth that makes a
plant longer.
Primary growth
 Most primary growth occurs at the

apices, or tips, of stems and roots.
Primary growth is a result of rapidly-
dividing cells in the apical
meristems at the shoot tip and root
tip.
Primary growth
 Subsequent cell elongation also

contributes to primary growth. The
growth of shoots and roots during
primary growth enables plants to
continuously seek water (roots) or
sunlight (shoots).
Primary growth
 Zone of cell division

 cells divide every 12 to 36 hours
toward the edges of the concave
dome
 Apical meristem daughter cells
divide into protoderm, procambium,
and ground meristem tissues.
 Zone of elongation
 roots lengthen because cells
produced by primary meristems
grow longer than wide
Primary growth
 Zone of maturation
 cells differentiate into specific cell
types
 root surface cells mature into
epidermal hairs, each with root hair
 cortex produced by parenchyma
cells
 inner boundary differentiates into
endodermis
 surrounded by Casparian strips
Primary growth
Secondary growth
 The increase in stem thickness that

results from secondary growth is
due to the activity of the lateral
meristems, which are lacking in
herbaceous plants. Lateral
meristems include the vascular
cambium and, in woody plants, the
cork cambium .
Secondary growth
 The vascular cambium is located just

outside the primary xylem and to the
interior of the primary phloem.
Secondary growth
The cells of the vascular cambium
divide and form secondary xylem
(tracheids and vessel elements) to
the inside and secondary phloem
(sieve elements and companion
cells) to the outside
Secondary growth
 The thickening of the stem that
occurs in secondary growth is due
to the formation of secondary
phloem and secondary xylem by the
vascular cambium, plus the action of
cork cambium, which forms the
tough outermost layer of the stem.
The cells of the secondary xylem
contain lignin, which provides
hardiness and strength.
Secondary growth
 In woody plants, cork cambium is

the outermost lateral meristem. It
produces cork cells (bark)
containing a waxy substance known
as suberin that can repel water. The
bark protects the plant against
physical damage and helps reduce
water loss.
Secondary growth
 The cork cambium also produces a

layer of cells known as phelloderm,
which grows inward from the
cambium. The cork cambium, cork
cells, and phelloderm are
collectively termed the periderm.
Secondary growth
 The periderm substitutes for the

epidermis in mature plants. In some
plants, the periderm has many
openings, known as lenticels, which
allow the interior cells to exchange
gases with the outside atmosphere .
This supplies oxygen to the living-
and metabolically-active cells of the
cortex, xylem, and phloem.
Secondary growth
 After a long period of secondary

growth, two types of woods appear
in the stem such as, sapwood,
heartwood. Sapwood is recently
formed wood and heartwood is
earlier formed wood.
Secondary growth
 In woody stems the stomata are

blocked by the presence of cork
cells
 The epidermis of woody stems
breaks up to form tiny pores called
lenticels which allow gaseous
exchange.
Annual rings
 The activity of the vascular

cambium gives rise to annual growth
rings. During the spring growing
season, cells of the secondary
xylem have a large internal
diameter; their primary cell walls
are not extensively thickened.
 This is known as early wood, or
spring wood.
Annual rings
 During the fall season, the

secondary xylem develops
thickened cell walls, forming late
wood, or autumn wood, which is
denser than early wood.
Annual rings
 This alternation of early and late

wood is due largely to a seasonal
decrease in the number of vessel
elements and a seasonal increase in
the number of tracheids. It results in
the formation of an annual ring,
which can be seen as a circular ring
in the cross section of the stem .
Annual rings
 An examination of the number of

annual rings and their nature (such
as their size and cell wall thickness)
can reveal the age of the tree and
the prevailing climatic conditions
during each season.
Topic one summary
 So my fellow students we’ve looked

at:
 What growth and development mean

 Meristems
 Primary growth
 Secondary growth, and finally
 Annuall rings
Thank you for your kind
attention
 +256 773165393 / +256 750089250

 francyorache@gmail.com
 FACEBOOK: Orache Francis
 Twitter: @Francis Orache
Your classmate,
Before a bye-bye…….

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Overview

 Definations of the terms, growth,

 Primary growth in details.

 Growth simply refers to the

 Meristematic tissues are clumps of

 Most trees, shrubs, and some herbs

 Primary growth results from cell

 Primary growth is the upward

 Most primary growth occurs at the

 Subsequent cell elongation also

 Zone of cell division

 The increase in stem thickness that

 The vascular cambium is located just

 In woody plants, cork cambium is

 The cork cambium also produces a

 The periderm substitutes for the

 After a long period of secondary

 In woody stems the stomata are

 The activity of the vascular

 During the fall season, the

 This alternation of early and late

 An examination of the number of

 So my fellow students we’ve looked

 What growth and development mean

 +256 773165393 / +256 750089250

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