The sunflower is a special type of flower because it is considered compound. That means that what we consider a single flower is actually more than a thousand small flowers called "florets." Because sunflowers are large and easy to grow, they are a perfect flower to study close-up without a microscope. Children enjoy growing these cheerful flowers and can learn from cutting the flower open so the parts can be identified and named. Being able to describe the parts of a sunflower is an excellent demonstration of botanical skill.
- Skill level:
Things you need
- Live sunflower that has bloomed
- Sharp knife
- Magnifying glass (optional)
Carefully cut your sunflower so that about 10 inches of stalk remains below the flower head. Cut your sunflower in half so that you can see the inside of the stalk below the flower head. Keep the other half of the sunflower head.
Identify the stalk of the plant and refer to it as a "peduncle." Call the whole flower head an "inflorescence" and explain that an inflorescence is a group of flowers in this case, and that the sunflower head is composed of many smaller flowers. Point to the white interior of the peduncle and observe the pith, as well as the domed receptacle that forms the top of the inflorescence stalk.
Observe the green leaflike formations on the outside of the flower head; they are the "bract." The bract appears between the stalk and the inflorescence.
Pluck one of the soft, yellow, orange or white petal-shaped forms above the bract and identify it as a "ray floret." Ray florets are sterile and attract pollinating insects, and surround the head of the sunflower plant.
Place the two halves of the sunflower together again. Notice the outer ray florets and how they are different from the "disk florets," which form the interior flowers of the plant. Study one cross section again, perhaps with a magnifying glass, and observe the differences between the disk florets in the centre of the head, and those on the exterior of the head near the ray florets. The florets closest to the centre are the youngest florets and may be immature. The immature florets have a long pod-like structure.
Move your magnifying glass toward the edge of the disk florets and observe the flowers in varying stages of fertilisation. Florets that have begun to open send forth "anthers" that carry pollen, so you can track the development of a sunflower by the percentage of disk flowers that have produced anthers and have been fertilised.
Point out the fertilised florets closest to the ray florets. Once the florets are fertilised they appear as soft colourful tubes with tops that resemble a crown. As the living sunflowers mature you can continue to observe the pollination of the flower heads as the disk florets all gradually open.
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