Lecture 14: Seeds and Fruit

• Seeds

• Fruits

• Fruit types

• Seed dispersal

• Video: seed dispersal

• Real fruit samples

What is a seed?

• A matured ovule, containing:

• 1. a plant __________

• 2. a food supply

• 3. covered by a _____________

Embryo• The seed contains a well-formed

multicellular young plant embryo (germ)

• Embryo is _________ (2n)

• It will become a whole plant

Nutritive tissue• Seed contains a food supply

• Stored food contains enough energy for the embryo to grow through the soil, when seedling is unable to photosynthesize.

• Food source can be the _________, which is ______ (_n) – as a result of double fertilization

Seed coat• A thick protective coat – outer layer of the seed

• Formed from the _______________

Seed coat

Gymnosperm seed

• Single fertilization produces the diploid embryo (2n)

• Food source is the haploid megagametophyte

Flowering plant seed

• In angiosperms (flowering plants) there is

• DOUBLE _______________

• Which produces a diploid ________(2n) and,

• A triploid (3n) __________

• Endosperm is the food source

Dicot vs. monocot seed

• Dicot has two cotyledons (like bean)

• Endosperm (food) is kept in the _________

• Monocot has one __________ which absorbs the endosperm tissue during germination (corn)

Fruit• In flowering plants – Fruit is a mature,

ripened o_____ that contains the seeds

• Pericarp – the ovary wall ovary

Fruit types• A. Simple• B. Aggregate• C. Multiple

A. Simple fruit• A. Simple fruit – develops from a ______

ovary of a single flower.• Simple fruits can be either fleshy or dry when

mature• Simple fleshy fruit• 1. __________• 2. Hesperidium• 3. __________• 4. Pepo• 5. _________

Simple fleshy fruit• 1. Berry – entire fruit wall is soft

and fleshy at maturity. Inside is slimy.

• For example, grapes, tomato, etc.

• 2. _______________ is a berry with tough, leathery rind (peel)

• Examples: oranges, lemons, other citrus.

Simple fleshy fruit: drupe

• 3. _______ type – outer part of fruit wall is soft and fleshy, inner part is hard and stony

• For example: ______________________

Simple fleshy fruit: pepo

• 4. ________ – also a fleshy fruit with a tougher outer rind

• All member of the squash family: pumpkin, melons, cucumbers

Simple fleshy fruit: pome

• 5. Pomes: most of the fleshy part of pomes develops from the enlarged base of the perianth (corolla and calyx) that has fused with the ovary wall

• Pomes include ___________________

Simple dry fruit: capsule

• Simple dry fruits are dry (not fleshy) at maturity. Simple dry fruits that open at maturity include: capsules and legumes

• Capsule – fruit is dry at maturity and splits open along several seams

• Example: Cotton

Simple dry fruit: Legumes• Legumes are dry at maturity and split open

along _______ seams

• Examples: pea pods, bean pods, peanut

Simple dry fruits

• Simple dry fruits that do NOT open at maturity include

• Caryopsis: seed coat is fused to the ovary wall (cereal grains like ____________________)

• Nuts: single-ovary wall and seed coat remain separate, ovary wall is very hard(acorns)

B. _____________• __________ fruit develops from one flower

with many separate pistils/carpels, all ripening simultaneously

• Examples: strawberry, raspberries, blackberries

C. Multiple fruit• Multiple fruit develops from ovaries of

several flowers borne/fused together on the same stalk

• For example: ____________

What is the purpose of the fruit?• The main function of the fruit is to disperse the seeds• Dispersal is important because • 1. It spreads the progeny in order to colonize new

environments• 2. Reduces ______________ for resources with parents• 3. Reduces the chances of predators destroying all of the

plant’s yearly seed production• Four types of seed dispersal:• A. Self dispersal• B. ______ dispersal• C. Water dispersal• D. _______ dispersal

A. Self dispersal

• Plants disperse their seeds by forceful ejection – explosive fruits!

• Witch hazel, squirting cucumber (jet propulsion)

Self dispersal• The peanut plant sows

(buries) its own seeds!

• Geocarpic: carpel grows inside the earth (soil)

B. Wind dispersal• Fruit and seeds may have special devices for

wind dispersal

• Plumes catch wind currents: Dandelion

• Trees take advantage of their great heights for wind dispersal. Fruits with wings are used to slow the descent to land: maple, ash fruit

C. ___________ Dispersal• Fruits and/or seeds use flotation devices to

travel by water (in rivers, oceans, etc.)

• Fruit may have air spaces and corky floats: for example ________________

D. Animal dispersal• Plants have _____________ with animals to

accomplish seed 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)

Video on seed dispersal• Watch the video, take notes, answer these questions:• What carries the dandelion seeds for miles?• What feature of trees gives them a particular advantage

when dispersing seeds by air?• How does the squirting cucumber disperse its seeds?• Although plants use wind and water, what do most plants

use as carriers for their seeds?• Blackberries on a tree do not ripen simultaneously, why?• What plant do elephants help to disperse? How do they

do it? What percentage of these seeds germinate in elephant dung? Why?