Introduction to
Horticulture
Importance of Plants
Plant Parts & Their Functions
The Importance of Plants
• Without plants, life on earth could not exist
• Plants are the primary source of food for
humans and animals
The Importance of Plants cont.
• Plants also:
– Provide oxygen
– Provide shade
– Supply us with medicines
– Renew the air
– Slow down the wind
– Hold soil in place
– Are a home for wildlife
– Furnish building materials and fuel
Parts of the Plant
• Most plants are made
up of four basic parts:
– Leaves
– Stems
– Roots
– Flowers (these later
become fruit or seeds)
Roots
• Usually underground – not visible
• Functions:
– Anchor the plant and hold it upright*
– Absorb water and minerals from the soil &
conduct them to the stem*
– Store large quantities of plant food*
– Propagate or reproduce in some plants
* = essential to all plants
Roots on the Inside
• Very similar to a stem
• Older roots of shrubs
& trees have:
– Phloem on the outside
(old phloem is bark)
– Cambium layer
– Xylem (wood) on the
inside
• Phloem
– Carries manufactured food down to the root for food
storage
• Xylem
– Carries water and minerals up to the stem
Roots on the Outside
• Different from a stem
• On a stem, the
terminal bud
initiates growth
• On a root,
the root cap
initiates growth
• Root cap continuously
makes new cells that
protect the root as it
pushes into the soil
Root External Structure
• Behind the root cap
are root hairs
• Root hairs become
side roots that branch
out as the root grows
older
• Absorb moisture and
minerals which are
conducted up to the
larger roots and the
stem
Roots as Crops
• Cash crops
– Carrots
– Beets
– Radishes
– Sweet Potatoes
Root Propagation
• Plants with tuberous
roots:
– Dahlia
– Peony
– Sweet Potato
• Are propagated by
separating the root
clump or by rooting
spouts from the root
Types of Root Systems
Fibrous Root System vs. Tap Root System
• Stems have 2 main
Stems
functions:
– The movement of
materials
• Movement of water and
minerals from roots up
towards the leaves
• Movement of
manufactured food from
the leaves down to the
roots
– Support of the leaves
and reproductive
structures
• Flowers and fruit or
seeds
Stems cont.
• Stems are also used
for:
• Food storage
– Irish Potato
• Reproductive
methods
– Stem cuttings or
grafting
• Green stems
manufacture food just
like leaves
Stems on the Outside
• Lenticels
– Breathing pores
Stems on the Outside cont.
• Bud scale scars
– Indicate where a
terminal bud has been
located
– The distance between
two scars represents
one year of growth
• Leaf scars
– Show where leaves
were attached
Unique Stems
• Irish Potato & Gladiolus
– Very different stems
– Stems are used for food storage and plant
reproduction
Stems on the Inside
• In all stems:
– Water and
minerals travel
up the XYLEM
– Manufactured
food travels
down the
PHLOEM
Dicots
– Dicots (2 cotyledons - seed leafs) the xylem
and phloem are separated by the cambium
– The cambium produces new cells
– Grow continually because the cambium builds
new xylem and phloem cells
– Trees are a perfect example!
• Sap = new xylem
• Heartwood = old, inactive xylem
• Tree bark = old, inactive phloem
Monocots
• One cotyledon (seed leaf)
• Grasses, corn
• No outside cambium
• Vascular bundles that contain xylem &
phloem
• Cells don’t increase in number, they grow
in size (won’t keep growing like a tree)
Monocots vs. Dicots
What do we do with Stems?
• Food
– Asparagus
– Irish Potato
– Celery
• Building Materials
– Wood
• Which root system is
easier to transplant?
Fibrous roots or tap
roots?
• Answer: Fibrous
roots
• Why? Because when
plants are dug up out
of the ground, a
greater % of the
fibrous roots system
is saved.
• If a root loses to
many root hairs
while being
transplanted, the
plant will die.
• Larger roots only
conduct & store
water, nutrients,
and food
• Root hairs absorb
moisture from the
ground
Leaves
• Are the food factory of
the plant
• They produce all of
the food that is used
by the plant and
stored for later use by
the plant or by
animals
Leaves Come in All
Shapes and Sizes!
• Needles are actually very narrow leaves
• The thorns on a cactus are leaves
• Some leaves are flat
• Other leaves, like onion leaves, are cylindrical
• The shape and size of leaves helps to identify
plants
Leaf Arrangement
• Leaves are arranged
in many different
patterns and
positions:
– Alternate
– Opposite
– Whorled
– Compound
• Leaf Composition
– Simple
– Compound
• Pinnate
• Bi-Pinnate
Leaves on the Outside
• Parts:
- Petiole - Blade - Vein
- Midrib - Margin
Tip
Margin
Midrib
Leaf Parts cont.
• Petiole - leaf stalk
• Blade - the larger, usually flat part of the
leaf
• Midrib - large central vein from which all
other leaf veins extend
• Veins - form the structural framework
• Margins - edges of plant leaves
Leaves on the Inside
• Leaves have specialized cells that perform
very important, very specific tasks.
Leaf Cells
• Epidermis - skin of the
leaf
– Single layer of cells
– Chief function: protect the
leaf from loosing too much
moisture
– Guard Cells - open and
close a small space or pore
on the underside of a leaf
called a stoma to allow the
leaf to breathe (exchange
O2 for CO2) and transpire
(or give off moisture)
Leaf Cells cont.
• Chloroplasts
– Food making cells
– Chlorophyll - green color
• Photosynthesis
– Process by which chloroplasts make food
– The oxygen created is used directly by people
and animals
– Without oxygen there would be no burning,
rusting, or rotting
Photosynthesis
LIGHT
6H2O + 6CO2 ----------> C6H12O6+ 6O2
Six molecules of water
plus six molecules of
carbon dioxide in the
presence of light produce
one molecule of sugar
plus six molecules of
oxygen
Plant Food
• Food made in the leaves moves down the
stem to the roots
• It is then used by the plant or stored in the
roots or stem as sugar, starch, or protein
• The plant is also used as food for people
and animals
• The leaves are usually the most nutritious
part
Respiration
• Plants always breathe
• They consume oxygen
and release carbon
dioxide
• Roots, stems, and leaves
all need oxygen to grow
• Plants produce more
oxygen during
photosynthesis than they
consume while breathing
Flowers, Fruits, & Seeds
• Flowers are pretty & contain nectar in
order to attract insects
• These insects fertilize the flower by
pollination
• Pollination begins fruit and seed formation
Fruits & Seeds
• Fruits and seeds are eaten, collected, and
spread out by animals and people
• This reproduces the plant
Seeds
• Seeds have special devices to ensure
propagation
• Some seeds are sticky (thistles), some
float in the wind (dandelions), others can
survive stomach acid (cherry pits)
Flower Parts
• Flowers differ in shape, size, and color,
but all have relatively the same parts
Flower Parts cont.
• Seeds are the most common way plants
reproduce in nature
– Sexual process involving male and female
parents
• A complete flower has both male and
female parts
• Only one parent is needed if a plant is self-
fruitful, or can pollinate itself
Flower Parts cont.
• 4 main parts
– Sepals
– Petals
– Stamens
– Pistil
The Sepals
• Green, leaf
like parts of
the flower
that cover
and protect
the flower
bud before it
is open
Petals
• Are actually leaves
• Generally the most striking part of the
flower
• Bright colors are used to attract insects for
pollination
The Stamens
• Male reproductive part
• Each stamen consists of:
– Filament
– Anther – contains the pollen (male sex cell)
The Pistil
• Located in the center
of the flower
• Female part
• Produces female sex
cells (eggs or ovules)
• If fertilized, the eggs
become seeds
Parts of the Pistil
• 3 main parts:
– Stigma – sticky,
catches the pollen
– Style – tube that leads
to the ovary
– Ovary – eggs develop
here, after fertilization
the ovary grows to
become a fruit or seed
coat
Flower Construction
• Insects looking for nectar have to climb
over the anther and brush pollen on their
legs
• As they climb towards the center looking
for food, they deposit pollen on the stigma
Fertilization
• After an insect deposits pollen, fertilization
begins!
• The pollen grain
sprouts and sends
a long stalk (pollen
tube) down
the style to the
ovary
Fertilization cont.
• The pollen sperm cell can then fertilize the
female egg cells and seeds begin to
develop
• The ovary enlarges into a seed coat or
fruit
Pollen
Incomplete Flower
• Has ONLY male parts or female parts
• Male flower – sepals, petals & stamens
but no pistil
• Female flower – sepals, petals, & pistil, but
no stamens
• Examples: Kiwi, Ginkgo
Flowers are Important!
• Many plants are grown only for their
flowers
• Floriculture industry in a multimillion dollar
business!!!
What is the major
function of flowers?
What is a fruit?
• A ripened flower ovary
• Botanically, fruits = vegetables
& vegetables = fruits
• In most plants, a fruit is
formed following fertilization of
the ovules
• They contain seeds
What about seedless fruit?
• Seedless fruit -- fruit that form
without pollination or fertilization
• These fruit are called
PARTHENOCARPIC
• Examples: Banana, navel
orange
• When the fruit ripens, the ovary
wall thickens.
• This is called the pericarp
• The pericarp has three
sections:
• The endocarp
• The mesocarp
• The exocarp
Types of Fruits
• Aggregate fruits
• Multiple fruits
• Simple fruits