Transcript Chapter 6
Chapter 6 Lecture Outline Flowers, Fruits, and Seeds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outline Introduction Differences Between Dicots and Monocots Structure of Flowers Fruits Fruit and Seed Dispersal Seeds Introduction Annual plants - Cycle completed in single season. • Cycle = from seed germination to mature plant producing seeds Biennial plants - Cycle completed in two growing seasons. Perennial plants - Cycle takes several to many growing seasons or plant produces flowers on new growth, while other plant parts persist indefinitely. Differences Between Dicots and Monocots Two major classes of flowering plants: • Magnoliopsida (dicots) and Liliopsida (monocots) Dicots Monocots Two cotyledons One cotyledon Flower parts in multiples of four or five Flower parts in multiples of three Leaves with distinct network of veins Leaves with parallel primary veins Vascular cambium and cork cambium present Vascular cambium and cork cambium absent Vascular bundles of stem in ring Vascular bundles of stem scattered Pollen grains with three apertures Pollen grains with one aperture Structure of Flowers Flowers begin as embryonic primordium that develops into a bud. Flowers occur as specialized branches at tips of peduncles. • May have branchlets of pedicels (stalk of single flower) Receptacle - Swollen end of peduncle or pedicel • Other parts of flower attached to receptacle in whorls: sepals, petals, stamens, and pistil. Structure of Flowers Sepals - Outermost whorl • Collectively referred to as calyx • Protects flower while in bud Petals - Next whorl inside sepals • Collectively referred to as corolla – Showy corollas attract pollinators. – Inconspicuous or missing corollas in many trees, weeds, grasses, and wind-pollinated plants • Calyx and corolla form perianth in monocots Structure of Flowers Stamens attached around base of pistil. • Each stamen consists of filament with anther at top. – Pollen grains developed in anthers. Pistil consists of stigma, style, and ovary. • Ovary develops into fruit. Structure of Flowers Ovaries evolved from carpels with margins rolled inward. • Carpel - Leaf with ovules on margins – Carpels may be fused together into compound ovary. – Pistil can consist of one to several carpels. Superior Ovary - Calyx and corolla attached to receptacle at base of ovary. Inferior Ovary - Receptacle grows up and around the ovary. • Calyx and corolla appear attached at top of ovary. Ovary contains ovules. • Ovules develop into seeds after fertilization. Structure of Flowers Flowers can be produced singly or in inflorescences. • Inflorescence - Group of flowers Fruits Fruit - Matured ovary and its accessory parts • Contains seeds • All fruits develop from flower ovaries and accordingly are found exclusively in flowering plants. Tomato fruit Fruits Fruit Regions • Exocarp - Skin • Endocarp - Inner boundary around seed(s) • Mesocarp Tissue between exocarp and endocarp – Peach fruit Three regions collectively called pericarp. Fruits Variability of fruits • Can consist of only ovary and seeds • Can include adjacent flower parts • May be fleshy or dry at maturity • May split or not split • May be derived from a one or more ovaries Fruits Fleshy Fruits - Mesocarp at least partly fleshy at maturity. Simple fleshy fruits develop from flower with single pistil. • Drupe - Simple fleshy fruit with single seed enclosed by hard, stony endocarp (pit) Drupes: peaches, almonds, olives Fruits Simple fleshy fruits • Berry – From compound ovary, with more than one seed, and with fleshy pericarp – True berry - With thin skin and relatively soft pericarp o – Tomatoes, grapes, peppers, blueberries, bananas Pepo - Relatively thick rind o Pumpkins, cucumbers Grape berries Fruits • Berry – Hesperidium - Leathery skin containing oils o Citrus – Pome - Flesh comes from enlarged floral tube or receptacle that grows up around ovary. o Endocarp papery or leathery o Apples, pears - Core and a little of adjacent tissue is from ovary; remainder is from floral tube and receptacle Apple pomes Fruits Dry Fruits - Mesocarp dry at maturity • Dehisicent or indehiscent Dehiscent fruits - Split at Maturity • Follicle - Splits along one side – Larkspur, milkweed, peony • Legume - Splits along two sides – Legume family: peas, beans, lentils, peanuts Milkweed follicle Legumes Fruits Dehiscent fruits • Siliques and silicles - Split along two sides, but seeds on central partition, which is exposed when two halves separate. – Silique - More than three times longer than wide – Silicle - Less than three times longer than wide – Mustard family: broccoli, cabbage Silicle Silique Fruits Dehiscent fruits • Capsules - Consist of at least two carpels, and split in a variety of ways – Irises, poppies, violets, snapdragons Capsules Fruits Dry Fruits Indehiscent Fruits - Do Not Split at Maturity • Single seed united with pericarp – – Achene - Base of seed attached to pericarp. o Sunflower seed, buttercup, buckwheat Nut - Similar to achene, but larger, with harder and thicker pericarp, and a cluster of bracts at base o Acorns, hazelnuts, hickory nuts Inside of sunflower achene Acorn Fruits Indehiscent Fruits • Grain (Caryopsis) - Pericarp tightly united with seed – Grasses: corn, wheat, rice, oats, barley • Samara - Pericarp extends Corn section as wings for dispersal. – Maples, ashes, elms • Schizocarp - Twin Samaras fruit that breaks into one-seeded segments called mericarps – Schizocarp of mericarps Parsley family: carrots, anise, dill Fruits Aggregate Fruits • Derived from single flower with several to many pistils – Individual pistils mature as clustered unit on single receptacle. o Raspberries, blackberries, strawberries Blackberry aggregate fruits Multiple Fruits • Derived from several to many individual flowers in single inflorescence – Mulberries, Osage orange, pineapples, figs Osage orange multiple fruit Fruit and Seed Dispersal Dispersal by Wind • Fruits: Samaras, plumes or hairs on fruit • Seeds: Small and lightweight, or with wings Fruit and Seed Dispersal Dispersal by Animals • Seeds pass through digestive tract. • Fruits and seeds adhere to fur or feathers. • Oils attract ants. – Elaiosomes on bleeding hearts used as food by ants. Seeds from bleeding hearts. Elaiosome is white. Water Dispersal • Some fruits contain trapped air for floatation. Seeds Structure • Ovules develop into seeds. – Cotyledons - Food storage organs that function as “seed leaves” – Embryo = cotyledons and plantlet – Plumule - Embryo shoot – Epicotyl - Stem above cotyledon attachment – Hypocotyl - Stem below cotyledon attachment – Radicle - Tip of embryo that develops into root Bean seed Seeds Epigeous germination • Hypocotyl lengthens, bends and becomes hook-shaped. • Top of hook emerges from ground, pulling cotyledons above ground. Epigeous germination Hypogeous germination • Hypocotyl remains short and cotyledons do not emerge above surface. Germination Germination is beginning or resumption of seed growth. • Some require period of dormancy. – Brought about by mechanical or physiological factors, including growth-inhibiting substances present in seed coat or fruit – Break dormancy by mechanical abrasion, thawing and freezing, bacterial action, or soaking rains. o Scarification - Artificially breaking dormancy • After ripening - Embryo composed of only of few cells when fruit ripens; seeds will not germinate until embryo develops. Germination Favorable environmental factors needed for germination. • Water and oxygen • Light or its absence • Proper temperature range Enzymes in cytoplasm begin to function after water is imbibed. Longevity Seed viability varies, depending on species and storage conditions. • Viability extended: – At low temperatures – When kept dry Vivipary - No period of dormancy; embryo continues to grow while fruit is still on parent. Vivipary in red mangrove Review Introduction Differences Between Dicots and Monocots Structure of Flowers Fruits Fruit and Seed Dispersal Seeds