Chapter 2
Lecture Outline
Tissues
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Outline

Organs and Tissues

Meristematic Tissues
• Apical Meristems
• Lateral Meristems
• Intercalary Meristems

Tissues Produced by Meristems
• Simple Tissues
• Complex Tissues
Organs and Tissues

Plants have three or four major groups of
organs:
• Roots
• Stems
• Leaves
• Flowers

Each organ is composed of tissues.
• A tissue is a group of cells performing a similar
function.
• There may be more than one tissue per organ.
Meristematic Tissues
Apical Meristems

Meristems - Permanent regions of growth
and active cell division

Apical Meristems - Found at the tips of roots
and shoots
• Roots and shoots increase in length as the apical
meristems produce new cells (= primary growth).
Meristematic Tissues
Apical Meristems
• Primary meristems
develop from apical
meristems.
–
Protoderm
–
Ground Meristem
–
Procambium
• Primary meristems
produce primary tissues.
Meristematic Tissues
Lateral Meristems

Lateral Meristems - Produce secondary
tissues that increase the girth of roots and
stems (= secondary growth)
• Vascular Cambium - Produces tissues that
function primarily in support and conduction.
–
Composed of a thin cylinder of brick-shaped cells that
extends the length of stems and roots
• Cork Cambium - Lies outside vascular cambium
just inside the outer bark
–
Produces bark
Meristematic Tissues
Intercalary Meristems

Grasses and related plants do not have
vascular cambium nor cork cambium.
• They have intercalary meristems.
• Intercalary Meristems
–
In vicinity of nodes (leaf attachment area)
–
Add to stem length
Tissues Produced By Meristems
Simple Tissues


Simple Tissues - Consist of only one kind
of cell
Parenchyma - Composed
of parenchyma cells
• Parenchyma cells:
–
Thin, pliable walls
–
Usually 14-sided at maturity
–
Living cytoplasm, often
containing large vacuoles and
various secretions
–
May remain alive a long time
–
Have spaces between them
Parenchyma cells
Tissues Produced By Meristems
Simple Tissues
• Types of parenchyma tissue and cells:
–
Aerenchyma - Parenchyma tissue with extensive
connected air spaces, usually in aquatic plants
–
Chlorenchyma - Parenchyma cells containing
chloroplasts that function in photosynthesis
–
Transfer cells - Develop irregular extensions of inner wall
that greatly increase surface area of plasma membrane
o
Nectaries of flowers
Tissues Produced By Meristems
Simple Tissues

Collenchyma tissue Contains collenchyma
cells
• Collenchyma cells:
–
Living cytoplasm
–
May remain alive a long time
–
Cell walls thick, with uneven
thickness
–
Pliable and strong, thus
providing flexible support
Collenchyma cells
Tissues Produced By Meristems
Simple Tissues

Sclerenchyma tissue Contains sclerenchyma cells
• Sclerenchyma cells:
–
Thick, tough, secondary walls,
normally impregnated with lignin
–
Dead at maturity
–
Function in support
–
Two types:
o
sclereids
o
fibers
Tissues Produced By Meristems
Simple Tissues
o Sclereids
–
Stone Cells
–
Scattered in tissue
–
Cells as long as wide
Tissues Produced By Meristems
Simple Tissues
o
Fibers
o
Much longer that wide and contain lumen (tiny cavity)
Fibers in cross section and longitudinal section
Tissues Produced By Meristems
Complex Tissues

Complex tissues - Composed of two or more
kinds of cells
• Vascular tissues include xylem and phloem.

Xylem - Chief conducting tissue for water
and minerals that are absorbed by the roots
• Composed of parenchyma cells, fibers, vessels,
tracheids and ray cells
Tissues Produced By Meristems
Complex Tissues
• Vessels – Long
tubes made of
vessel elements
–
Vessel elements:
o
Thick secondary
cell walls
o
Open at both ends
o
Secondary walls
develop irregularly
o
Perforation plate
between end walls
Vessels
elements
Spiral
thickenings
on vessel
walls
Tissues Produced By Meristems
Complex Tissues
• Tracheids
–
Tapered at the ends with pairs
of pits that allow water to pass
from cell to cell
o Pits - Areas without
secondary cell
–
Dead at maturity
–
Thick secondary cell walls
–
May have spiral thickenings on
cell walls
Tracheids
• Rays - Function in lateral conduction
and food storage
–
Composed of long-lived parenchyma cells
Tissues Produced By Meristems
Complex Tissues

Phloem - Conducts dissolved food materials
produced by photosynthesis throughout plant
• Composed of sieve tube members, companion
cells, fibers, parenchyma cells and ray cells
Tissues Produced By Meristems
Complex Tissues
• Sieve Tube Members:
–
–
–
–
Lack secondary cell walls and nuclei
Lay end to end to form sieve tubes
Walls have sieve plates with small
pores
Callose forms callus plug - Prevents
leaking of sieve tube contents when
cell injured
Phloem
• Companion cells - Aid in conduction of food
Tissues Produced By Meristems
Complex Tissues

Epidermis- Protective layer that is one celllayer thick covering all plant organs
• Composed mostly of parenchyma cells, guard
cells of stomata, secretory glands and hairs
Leaf cross section
Tissues Produced By Meristems
Complex Tissues
• Cutin - Fatty substance on the surface of outer walls
of epidermis that forms cuticle
–
Wax secreted on cuticle
–
Cuticle and wax prevent water loss by evaporation
o
Resistant to bacteria and other disease organisms
• Root epidermal cells produce root hairs.
–
Increase absorptive area of root surface
• Leaves have stomata bordered by pairs of guard
cells.
Tissues Produced By Meristems
Complex Tissues

Periderm - Replaces epidermis when cork
cambium begins producing new tissue
• Constitutes outer bark
• Primarily composed of cork cells
–
Dead at maturity
–
While still alive, cytoplasm secretes
suberin (fatty substance) into walls.
o
–
Makes cork cells waterproof and
helps protect phloem
Lenticels - Loosely arranged pockets of parenchyma
cells formed by cork cambium that protrude through the
surface of periderm. Allows for gaseous exchange.
Tissues Produced By Meristems
Complex Tissues

Secretory Cells and Tissue
• Secretory cells may function individually or as
part of a secretory tissue.
–
Flower nectar
–
Citrus oils
–
Glandular hair mucilage
–
Latex
–
Resins
Review

Organs and Tissues

Meristematic Tissues
• Apical Meristems
• Lateral Meristems
• Intercalary Meristems

Tissues Produced by Meristems
• Simple Tissues
• Complex Tissues