Tissues
Chapter 4
Tissue
• a group of similar cells working together to
perform a set of functions
Plant Tissues
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Meristems
Simple (Ground) Tissue
Vascular Tissue
Dermal Tissue
Secretory Tissue
Meristems
• Apical Meristems – located at the ends of
shoots, roots and in buds; produce primary
growth – protoderm, ground meristem and
procambium
• Lateral Meristems – located around the
perimeter of shoots and roots; produce
secondary growth
Primary and Secondary Growth
Your growth, typical of animals
infant
child
You, today
Plant Growth
1st year – all primary growth
Primary growth – plant growth that
produces an increase in length and
new structures
Secondary growth – plant growth that
produces an increase in diameter in
existing plant parts in the second and any
subsequent growing seasons
2nd year – only secondary growth, in blue,
is shown below
2nd year primary (in green) and
secondary (in blue) growth
3rd year’s growth, showing
both primary (black) and
secondary (red) growth
Woody dicot stem cross section
showing growth rings
Apparent increase in limb height on
many trees is due to loss of lower limbs
Lateral Meristems (cont.)
• Vascular Cambium – produce vascular
tissue
• Cork Cambium – produces “bark”
Intercalary Meristems
• located near grass nodes
• produces an increase in stem and leaf
length
• contributes to the grazing and cutting
tolerance of grasses
Simple (Ground) Tissues
• Parenchyma
• Collenchyma
• Sclerenchyma
Parenchyma
• relatively spherical and thin walled
• alive at functional maturity
• perform a variety of functions
– photosynthesis (chlorenchyma)
– food and water storage
– pith
– wound healing
Collenchyma
• elongate with irregularly thickened cell
walls
• provide flexible support; celery strings
• alive at functional maturity
Sclerenchyma
• elongate (fibers) to irregular shape
(sclerids)
• very thick, lignified cell walls
• dead at functional maturity
Vascular Tissue
• Complex tissues since they include 2 or
more kinds of cells
• Xylem
• Phloem
Xylem
• similar to straws
• dead at functional maturity
• vessels – composed of vessel elements
(cells); uniform tubes, open at both ends,
relatively large diameter, may be relatively
short
• tracheids – tapered at both ends,
numerous pits rather than large openings
between adjacent cells
• conducts water and minerals upwards
Xylem
Phloem
• alive at functional maturity
• consist of sieve tube members and
companion cells
Sieve tube members – cylindrical,
conduct organic molecules up and
down through plant
Companion cells – regulate activity of
sieve tube members
Phloem
Phloem
Xylem
Dermal Tissue
• Epidermis – covers primary growth, single
layer of cells; often secretes cutin (lipid)
forming cuticle (reduces transpiration
and protection from pathogens)
• Periderm – covers secondary growth,
many cell layers; becomes
impregnated with lipids (suberin)
Epidermis (cont.)
• Root hairs - single cell extensions from the
epidermis near root tips
• greatly increase surface area in contact
with soil and thereby enhance water and
mineral absorption
Stomata
• openings in epidermis
• surrounded by Guard Cells that regulate
opening
Stomata from a epidermal peel of Commelina communis by Dr. J.
Weyers
Stomate
Guard Cells
Lenticels
• regions of loosely packed cells in the
periderm
• promote gas exchange with tissues below
Secretory Tissue
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produce a variety of products
nectar in flowers
oils in citrus and mints
latex
resins
opium
mucilage – e.g. for trapping insects