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