2a Fruit and dispersal of seed
Fruit Overview
Definition:
A fruit is a mature ovary of a flowering plant.
Functions:
Aid in seed dispersal.
Protect seeds.
Control seed germination.
Evolution:
Many types of fruits have evolved.
Fruit Development Process
The fertilization of the egg cell in the ovule occurs.
Fertilized egg divides to produce an embryo plantlet.
The ovule containing the plantlet matures into a seed.
The ovary matures into a fruit, defined as a ripened ovary.
Fruit Classification
Based on Structure:
Dry vs. Fleshy: Fruits are classified as either dry or fleshy.
Type of Formation:
Simple Fruit: Formed from one pistil of a flower.
Aggregate Fruit: Formed from several pistils in a single flower.
Multiple Fruit: Formed from several flowers growing together.
Misnomers in Fruit Terminology
Common misunderstandings about fruits:
Gymnosperms such as juniper berries are not true fruits.
The peanut is a legume, not a true nut.
Types of Simple Fruits
Dry at Maturity:
Legume: Splits along two sides to form two halves (e.g., pea, peanut).
Follicle: Splits along one side (e.g., milkweed).
Capsule: Splits in various ways (e.g., poppy, tulip).
Fleshy at Maturity:
Drupe: Contains a stony inner layer (e.g., cherry, coconut).
Pome: Has a core with seeds surrounded by papery ovary walls (e.g., apple, pear).
Berry: Thin skin, usually many seeds (e.g., tomato, banana).
Pepo: Berry with thick rind (e.g., watermelon, cucumber).
Hesperidium: Berry with leathery skin (e.g., orange, lemon).
Aggregate Fruits
Formed from several carpels in a single flower.
Examples: Raspberry, Strawberry.
Multiple Fruits
Formed from an entire inflorescence of flowers (e.g., pineapple, fig).
Accessory Fruits
Fruits consisting of parts that are not derived solely from the ovary (e.g., pomes, pepos).
Example of Accessory Tissue: The hypanthium in apples.
Pericarp Structure
The pericarp develops into three layers:
Exocarp: Outermost layer, often the epidermis.
Mesocarp: Middle layer, varies in thickness.
Endocarp: Inner layer, shows considerable variation.
Specific Types of Berries
Berry: Fleshy with thin skin (e.g., kiwi).
Pepo: Thick rinds (e.g., pumpkins).
Hesperidium: Leathery skins (e.g., citrus fruits).
Pomes: Majority of flesh from floral tube (e.g., apples).
Aggregate drupe: Cluster of drupes from a single flower (e.g., raspberry).
Dry Dehiscent Fruits
Legumes: Derived from a single carpel, splits open (e.g., peanuts).
Silique: Splits along two sides, seeds on a central partition (e.g., radish).
Follicles: Splits along one side, revealing seeds (e.g., milkweed).
Capsules: Common fruit type, splits to release seeds (e.g., cotton).
Dry Indehiscent Fruits
Achene: Single-seeded, small, dry fruit (e.g., sunflower).
Nuts: Large single hardened achenes (e.g., acorns).
Caryopsis: Pericarp tightly united with seed (e.g., corn).
Samara: Dry indehiscent fruit with wing (e.g., maple).
Fruit Dispersal Methods
Seed Dispersal
Plants produce many seeds; survival depends on appropriate conditions.
Mechanisms of Dispersal:
Autochory: Self-dispersal (e.g., flinging seeds).
Allochory: Dispersal aided by external factors (e.g., wind, water, animals).
Wind Dispersal
Anemochory: Light seeds capable of flight (e.g., dandelions).
Water Dispersal
Hydrochory: Fruits float due to air-filled cavities (e.g., coconuts).
Animal Dispersal
Zoochory: Fruits dispersed by animals (e.g., berries).
Types:
Endozoochoric: Seeds eaten and excreted.
Epizoochoric: Seeds stick to animals.
Myrmecochory: Ant-assisted dispersal (e.g., violets).
False Fruits
Fruits that are not derived solely from ovary (e.g., figs, gymnosperms).
Parthenocarpy
Development of fruit without fertilization, resulting in seedless fruit.
Plant Identification
Dichotomous Keys: Tool for identifying plants by branching choices (e.g., leaf arrangement).
Fruit Classification Keys
Simple vs. Compound Fruits: Basic branching for classification.
Categorization steps leading to specific fruit types.