1. Seeds & Fruits

2. A Seed is a mature ovule, which contains the embryo plant for the next generation.
A Fruit is a mature or ripened ovary. A fruit is the packaging structure around the seed.

3. Seeds
Seed- A matured ovule without accessory parts. Remember, the ovule surrounds the female gametophyte.
Onion Seeds

4. A) The zygote (2n) becomes the embryo (2n).
Remember from the flower chapter that double fertilization occurs.
A) The zygote (2n) becomes the embryo (2n).
B) The primary endosperm becomes the endosperm.
Remember that the endosperm is the nutrient rich storage tissue that will feed the seed when it germinates. Endosperm is common in monocots and remains in the seed as a food reserve. This food is absorbed through epidermal cells for food for the embryo. Endosperm is not common in dicots. In dicots, the endosperm’s energy is transferred to cotyledons (seed leaves) as the seed forms (matures).

5. Cotyledons
Cotyledon – seed leaf; there are two in the embryo/seedling of dicotyledonous plants (dicots) they generally store food and can expand and become photosynthetic; in monocotyledonous plants (monocots), only one cotyledon is present, generally a digestive organ.
Dicots have 2 seed leaves emerge from the embryo. Dicots include the eudicots, magnoliids, and a few basal angiosperms.
Monocots have 1 leaf emerge from the embryo. This is the coleoptile. Monocots, later, often have parallel venation on leaves, sheaths instead of petioles and usually no secondary growth. Examples: Lily, Corn, Onion, Grasses

6. Embryo & Seed Development in Cotton
The zygote goes through mitosis to form the proembryo and suspensor (supports embryo in endosperm).
The cotton seed has a seed coat and contains the mature ovule (mature embryo within).
The Embryo Develops.
The Cotyledons Form. These are seed leaves that store food. After germination, cotyledons expand and become photosynthetic.
In the seed, the radicle (embryonic root) is at one end and the shoot tip is at the other end.

7. Onion Seed (A Monocot)

8. Note: Seed structures do vary.
Raphe – ridge on seeds, formed by the stalk of the ovule.
Hilum – Large scar left when the seed breaks away from its placental connections (the seed’s belly button).
Micropyle – This is where the pollen tube entered the ovule.
Notice that this dicot does not have endosperm, which is typical for the majority of dicots.
Radicle – embryonic root (1st Root to emerge & first structure to emerge from seed as well).
Epicotyl – after seed germination, this is the portion of the embryonic shoot that will be above cotyledons.
Hypocotyl – after seed germination, portion of the embryonic shoot below the cotyledons but above the radicle.
Common Bean

9. Castor Bean (A Dicot with Endosperm)
Caruncle – A spongy outgrowth of the seed coat that absorbs water, which is necessary for germination.

10. Yellow Foxtail Grass (A Monocot)
Coleoptile – the first leaf in germination of monocots that sheaths the succeeding leaves; ensheathes the shoot apex.
Yellow Foxtail Grass (A Monocot)
The seed of grasses is joined to its fruit. This is called the grain or caryopsis.
Food is transferred from the endosperm to the scutellum to the growing embryo.

11. Germination
Germination is the beginning or resumption of growth of a seed, spore, bud, or other resting structure. Germination starts the metabolism of stored food (endosperm or cotyledons) in the seed.
1) The first step of germination is imbibition (the uptake of water). Seeds by themselves are very dry (only 5-10% water).
2) After imbibition, the swelling of the radicle (embryonic root) starts first and bursts the seed coat.

12. The Germination Process Differs Among Plants
Epigeal Germination – The hypocotyl raises the cotyledons and shoot apex towards the light. The cotyledons emerge from the soil and become leaf-like photosynthetic structures.
Stages in the Epigeal Germination of a Bean Seed (Dicot).
Note: The Hypocotyl (below cotyledons) elongates first.

13. Stages in the Hypogeal Germination of a Pea Seed (Dicot).
Hypogeal Germination – The epicotyl straightens, the cotyledons remain below ground and only the apex and first leaf are raised upward.
Note: The Epicotyl (above cotyledons) elongates & hypocotyl (below cotyledons) remains below ground.

14. Stages in the Germination of an Onion Seed (Monocot). Note:
From a previous slide during this chapter, we saw an onion seed diagram. Onion seeds have a single coiled cotyledon.
Note:
The first leaves will start at the base of the cotyledon.

15. Stages in the Germination of a Corn Seed (Monocot).
After the primary root emerges, it branches to form the root system. Adventitious roots emerge from the lower stem and prop roots form to hold the stem upright. The emerging young leaves are protected by a sheathing-like coleoptile.
Note: The Coleoptile is the emerging sheath that protects the shoots. The Coleorhiza is an emerging sheath, which protects the roots. The primary root rapidly pushes through the coleorhiza.

16. Germination May Be Delayed By Dormancy
Dormancy - Growth and Development are temporarily suspended. During dormancy, seeds have reduced physiological activity.
Some seeds remain dormant and can later be viable for long periods of time (Some up to 100 years). The Oriental Lotus seeds have been known to last 1000 years in a dormant state and then be viable.
Different Items Can Break Dormancy
Some simply need just a little water. Lettuce needs light. Some legumes, locust for example, need heavy scaring of their seed coats. Some need moisture and freezing temperatures at correct levels and times. Certain pines will not germinate unless they have been subjected to the rather high heat of a fire.

17. BIO 141 Botany with Laboratory
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