School of Sciences, Lautoka Campus BIO509 Lecture 22: Fruit and Seed dispersal

The main function of the fruit is to disperse the seeds. Why is dispersal necessary? It spreads the offspring in order to colonize new environments. Reduces competition for resources with parent plants. Reduces the chances of predators destroying all of the plant’s yearly seed production.

Seed dispersal agents Wind Animals Water Self dispersal

Dispersal by wind Seeds are very light. Shaped so they are easily carried by the wind. - Winged fruit - Winged seeds - Inflated sacs - Small size - Plumes - cottony or woolly hairs

What feature of trees gives them a particular advantage when dispersing seeds by air?

Animal dispersal Many plants depend on animals for seed dispersal; they may offer a nutritional reward Animals learn to recognize ripened fruit colors Fleshy fruits eaten and dispersed with feces.

Animal dispersal Some dry fruit attach and cling to animals (they hitchhike on the animals). Some have Velcro-like hooks that cling to animal fur (burdock, cockleburs) Others have sticky substances that stick to host (mistletoe)

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Dispersal by Water Buoyant seeds (air sacs) Waxy material on outside of seed/fruit. Stream water current (flash floods; seeds must be scarified by rock abrasion to germinate)

Self dispersal / mechanical dispersal Ejection (mistletoe) Explosive. - squirting cucumber (jet propulsion) Gravity Mimicry (some parasitic plants mimic host plants)

Did you know ? The peanut plant sows (buries) its own seeds. After fertilization, the flower stalk (pedicel) of the peanut curves downward, and the developing fruit (legume) is forced into the ground.

Humans as transporters of seeds. Far most important transporters of seeds especially for crop plants. Carried many food plants, noxious weeds and plant diseases and medicinal plants around the world. Most countries have strict regulation regarding the importation of plant materials.

Seeds and Germination

Parts of a seed External seed coat or testa Developing plant embryo. Stored food called endosperm. Seeds may be in one part (monocot) or two parts (dicots).

The Embryo Plumule – Tip of embryo shoot Epicotyle – Shoot above point of attachment of cotyledons Hypocotyle – Shoot below point of attachment of cotyledons Radicle – Bottom of embryo that develops into root

Monocots have single cotyledon (called scutellum). Dicot cotyledons store endosperm, but moncots store endosperm outside cotyledons. Plumule and radicle are enclosed in sheath-like coleoptile and coleorhiza, respectively. Coleoptile and coleorhiza protect the embryo at germination, but soon drop off.

Factors affecting seed germination Water Oxygen Light Certain temperature ranges.

Questions??