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Introduction to HorticultureImportance 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• Stems have 2 main 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• Palmate
Leaves on the Outside• Parts:
- Petiole - Blade - Vein
- Midrib - Margin
Tip
Midrib
Margin
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
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
PhotosynthesisLIGHT
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