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Plant Form and Function
(Chapter 34)
In this lecture we will discuss the morphology and anatomy of plants as well as
some of their functional attributes.
And, because they comprise the bulk of the extant land plants, the lecture will
primarily focus on seed plants (i.e., gymnosperms and angiosperms).
Meristems
Meristem cells play an important role in the lives of plants.
Meristem cells are undifferentiated cells that can give rise to various specific
types of cells such that during development a complex plant can be produced from
a less complex plant embryo.
In many respects the meristem cells of plants are analogous to the stem cells of
animals.
When a meristem cell divides, one of the 2 resulting cells remains a meristem cell
while the other is free to differentiate into another type of cell.
Because of this, there is always a supply of meristem cells for future development.
The elongation of plant roots and shoots results from mitosis of what are called
apical meristems.
In addition, lateral meristems facilitate the increase in girth that accompanies
growth in some vascular plants such as trees and shrubs.
, 2
Apical meristems
Apical meristems are located at the tips of plant shoots and roots.
Apical meristems are responsible for primary growth in plants (i.e., growth that is
primarily associated with the process of plant elongation).
Primary growth produces primary tissue which in turn forms the primary plant
body.
The primary plant body comprises the young soft shoots and roots of a tree or
shrub, or the entire plant body in some herbaceous plants.
Apical meristems are delicate groups of cells that require protection.
The root apical meristem is protected by the root cap, which is derived from the
apical meristem itself.
The apical shoot meristem is often protected by young leaves.
An apical meristem gives rise to three types of embryonic tissue systems that are
together referred to as the primary meristems.
Cell division in and differentiation of primary meristem tissue results in the
development of the primary tissues of the plant body.
The three primary meristem tissues are:
1) protoderm— forms the epidermis
2) ground meristem— differentiates into “ground tissue” composed of
parenchyma cells
3) procambium— produces vascular tissue (1o xylem and 1o phloem)
, 3
Lateral meristems
While many soft herbaceous plants exhibit only primary growth (elongation mainly)
to achieve their adult forms, others (such as trees) undergo significant increases
in girth as well as elongation as they mature.
These increases in girth are referred to as secondary growth.
To accommodate secondary growth (again, resulting in an increase in plant
width/girth), trees and shrubs have an active lateral meristem.
A lateral meristem is a peripheral cylinder of meristematic tissue within the stems
and roots.
Woody plants can have 2 lateral meristems:
1) Cork cambium— located in the bark; produces cork cells for the outer bark of a
tree trunk or root. This replaces the epidermis, which is relatively thin and
inelastic in comparison to the bark tissue.
2) Vascular cambium— located just below the bark, produces 2o vascular tissue
(i.e., 2o xylem and 2o phloem) that is necessary for secondary growth.
Tissue formed from lateral meristems is known as secondary tissue and is
collectively referred to as the secondary plant body.
Secondary tissue can account for most of the trunk, branches, and older roots of
trees and shrubs.
Plant body organization
In a plant exhibiting both primary and secondary growth (such as a tree),
coordination of primary and secondary meristematic growth produces the body of
the adult sporophyte.
A vascular plant body has a root system and a shoot system.
The root system anchors the plant and facilitates water and ion absorption from
the soil for plant nutrition.
Plant Form and Function
(Chapter 34)
In this lecture we will discuss the morphology and anatomy of plants as well as
some of their functional attributes.
And, because they comprise the bulk of the extant land plants, the lecture will
primarily focus on seed plants (i.e., gymnosperms and angiosperms).
Meristems
Meristem cells play an important role in the lives of plants.
Meristem cells are undifferentiated cells that can give rise to various specific
types of cells such that during development a complex plant can be produced from
a less complex plant embryo.
In many respects the meristem cells of plants are analogous to the stem cells of
animals.
When a meristem cell divides, one of the 2 resulting cells remains a meristem cell
while the other is free to differentiate into another type of cell.
Because of this, there is always a supply of meristem cells for future development.
The elongation of plant roots and shoots results from mitosis of what are called
apical meristems.
In addition, lateral meristems facilitate the increase in girth that accompanies
growth in some vascular plants such as trees and shrubs.
, 2
Apical meristems
Apical meristems are located at the tips of plant shoots and roots.
Apical meristems are responsible for primary growth in plants (i.e., growth that is
primarily associated with the process of plant elongation).
Primary growth produces primary tissue which in turn forms the primary plant
body.
The primary plant body comprises the young soft shoots and roots of a tree or
shrub, or the entire plant body in some herbaceous plants.
Apical meristems are delicate groups of cells that require protection.
The root apical meristem is protected by the root cap, which is derived from the
apical meristem itself.
The apical shoot meristem is often protected by young leaves.
An apical meristem gives rise to three types of embryonic tissue systems that are
together referred to as the primary meristems.
Cell division in and differentiation of primary meristem tissue results in the
development of the primary tissues of the plant body.
The three primary meristem tissues are:
1) protoderm— forms the epidermis
2) ground meristem— differentiates into “ground tissue” composed of
parenchyma cells
3) procambium— produces vascular tissue (1o xylem and 1o phloem)
, 3
Lateral meristems
While many soft herbaceous plants exhibit only primary growth (elongation mainly)
to achieve their adult forms, others (such as trees) undergo significant increases
in girth as well as elongation as they mature.
These increases in girth are referred to as secondary growth.
To accommodate secondary growth (again, resulting in an increase in plant
width/girth), trees and shrubs have an active lateral meristem.
A lateral meristem is a peripheral cylinder of meristematic tissue within the stems
and roots.
Woody plants can have 2 lateral meristems:
1) Cork cambium— located in the bark; produces cork cells for the outer bark of a
tree trunk or root. This replaces the epidermis, which is relatively thin and
inelastic in comparison to the bark tissue.
2) Vascular cambium— located just below the bark, produces 2o vascular tissue
(i.e., 2o xylem and 2o phloem) that is necessary for secondary growth.
Tissue formed from lateral meristems is known as secondary tissue and is
collectively referred to as the secondary plant body.
Secondary tissue can account for most of the trunk, branches, and older roots of
trees and shrubs.
Plant body organization
In a plant exhibiting both primary and secondary growth (such as a tree),
coordination of primary and secondary meristematic growth produces the body of
the adult sporophyte.
A vascular plant body has a root system and a shoot system.
The root system anchors the plant and facilitates water and ion absorption from
the soil for plant nutrition.
