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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 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 Leaves on the Outside • Parts: - Petiole - Midrib - Blade - Margin - Vein 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 selffruitful, 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