Topic 14.1
The Structure & Growth of Flowering Plants
Biology 1001
November 9, 2005
II. Plant Growth and Organization of
Primary PLANT Tissues
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An Overview of Plant Growth
Plants exhibit indeterminate growth
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Growth continues throughout the plant’s life
Most plants grow continuously
A typical plant consists of embryonic, developing, and mature organs
Leaf growth is determinate
When do plants die?
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Annuals = (eg. Wildflowers and grains) complete a life cycle in a year
Biennials = (eg. Beets and carrots) live two years, usually with an
intervening cold period
Perennials = (eg. Trees, shrubs and some grasses) live many years
An Overview of Plant Growth
Primary and Secondary Growth
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Primary growth produces the primary
plant body – the whole herbaceous plant,
or the youngest parts of a woody plant
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Secondary growth produces the
secondary plant body – the “woody”
parts of the stems and roots of a woody
plant (leaves do not generally experience
secondary growth)
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Involves the apical meristems located at
the tips of roots and in the buds of shoots
and lengthens the roots and shoots
Involves the lateral meristems, the
vascular cambium and the cork cambium,
and adds girth to the plant
Primary & secondary growth occur at the
same time in different parts of the plant
Figure 35.10!!
Primary Growth of Roots
 Growth of the root occurs just behind
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the root cap, where new cells are
produced in the apical meristem
The root cap protects the root as it
pushes through the soil; it also
secretes a lubricating polysaccharide
slime
Growth occurs in three zones of cells
at successive stages of primary growth
The zone of cell division includes the
apical meristem and its derivatives
In the zone of elongation root cells
elongate up to 10X their length
In the zone of maturation cells
complete their differentiation and
become functionally mature
Figure 35.12!!
Organization of Primary Tissues in Young Roots
 Primary growth produces the
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epidermis, ground tissue & vascular
tissue of the young root
The vascular tissue (xylem &
phloem), collectively called the stele,
consists of a lobed core of xylem with
phloem between the lobes in dicots
In monocots the stele has a central
core of parenchyma cells and
alternating rings of xylem and phloem
The ground tissue is called cortex
The innermost layer of the cortex is
the endodermis
The outermost layer of the stele is the
pericycle, from which lateral roots
arise
Figure 35.13!!
Primary Growth of Shoots
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A shoot apical meristem is a
dome-shaped mass of dividing
cells at the tip of the terminal bud
Leaves arise as leaf primordia
from the sides of the apical
meristem
Axillary buds develop from
clumps of meristematic cells left
by the apical meristem at the
bases of the leaf primordia
Growth and differentiation occur
as cells divide & elongate at older
internodes below the shoot apex
Figure 35.15!!
Tissue Organization of Stems and Leaves
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Stems
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The epidermis covers the stem as part of the dermal tissue system
The vascular tissue runs the length of the stem in vascular bundles, arranged
in a ring in a dicot with xylem facing inward, phloem outward
The ground tissue is arranged as pith & cortex (internal and external to the
vascular tissue) in the dicot, and consists of mostly parenchyma cells, with
some collenchyma and/or sclerenchyma
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Leaves
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The epidermis is interrupted by stomata for CO2 and H2O exchange;
stomata are pores flanked by two guard cells, which regulate the opening
and closing of each stoma
Ground tissue in the leaf is called mesophyll (palisade & spongy) and
consists of photosynthetic parenchyma cells
Veins are the leaf’s vascular bundles; they are connected to the stem by leaf
traces, and each is enclosed by a bundle sheath. They network throughout
the leaf to bring the xylem & phloem into contact with all the ground tissue
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Primary Tissue Organization of Stems
Figure 35.16a!!
Tissue Organization of Leaves
Figure 35.17!!