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Zinnias: Flower Cycles and Parts

If you have been following Growing With Science, you know that we have been closely observing the insects on a small planting of zinnias for the last few weeks (posts about zinnia insects 1, 2, and 3).

mix-of-zinnias-87

The variety of zinnias we have been observing are Profusion® Fire, which are hybrids between regular zinnias (Zinnia elegans), and the Mexican or narrowleaf zinnias (Zinnia angustifolia).

While initially observing the insects on the plants, we also noticed something about the plants themselves, specifically the flowers. Do you notice anything about the flowers in the photograph above?

As it turns out, the flowers change as they become older.

tightly-closed-zinnia-bud-63The zinnia flower head starts out as a tightly closed bud.

young-red-zinnia-flower-19

When the flower head first opens, it is deep, bright orange, almost scarlet.

medium-orange-zinnia-22

As the flower head matures, it becomes a medium orange. Do you see any other changes?

old-yellowed-zinnia-11

The oldest flower heads have faded to almost yellow. They look a bit worse for wear.

There have been some changes to the flowers within the flower head as well, but we need to learn some vocabulary before we can investigate it.

Flower Parts

 

Mature_flower_diagram.svg

(“Mature flower diagram” by Mariana Ruiz LadyofHats. Public Domain image at Wikimedia Commons.)

You may have seen a diagram like this one describing the various parts of a hypothetical flower. Basically, the ovary, style and stigma form the female part of the flower that receives the pollen. The stamens, made up of filaments and anthers, are the male parts of the flower that produce pollen.

Very few flowers actually conform to this simple diagram, and the zinnias are certainly much more complex. Rather than a single flower, what we see is actually a cluster of minute flowers called disk and ray florets.

 

young-floret-parts

You may have to scroll back up to the bigger photographs above to see the parts clearly, but in the young flower head the ray florets around the outside are flowering, which is evident by the yellow stigmas. Only a few disk florets in the center have begun to open.

 

medium-floret-parts

In the middle-aged flower head, most of the ray florets have finished flowering and many of the disk florets around the outside have begun to flower.

older-floret-parts

In the older flower heads, the outer florets have finished flowering and are developing the all-important seeds. Only the disk florets at the very center are still flowering.

Flower Part Dissection Activity for Children

Note: check whether the children have severe pollen allergies before starting this activity.

Gather:

  • Living flowers of different types (see flower notes)
  • Safety scissors and other dissecting equipment (age appropriate)
  • Diagrams/illustrations of flower part with labels
  • Dissecting microscope (optional)
  • Paper (optional)
  • Pens or markers (optional)
  • Tape (optional)

Flower notes:  Tiger lilies or other lilies are excellent examples of simple flowers as seen in the diagram. Daisies and sunflowers are good examples of the complex flowers. Working with a large group? You might want to ask your local grocery store or florist if they would be willing to donate flowers that have passed their freshness date. Keep the flowers alive in a vase of water.

Have the children observe the different types of flowers closely. Provide diagrams or illustrations naming the flower parts. Once everyone has had a chance to observe the flowers, allow the children to dissect the flowers to examine the parts more fully. Very young children can simply pull them apart. Older children might use safety scissors. Still older children can use dissecting pins and a dissecting microscope, if available.

Remove the petals or pull off the ray florets. Can you find the stigma? What about the stamens? Is the stamen releasing pollen? What color is the pollen? What is inside a disk floret?

Older children might want to spread the parts onto a piece of paper or card stock and tape them down. Label the parts.

Extension:  If the flower parts aren't damaged too badly, allow the children resemble the parts to make their own mix of "Franken-flowers."

Resources:
The Clover & the Bee; A Book of Pollination by Anne Ophelia Dowden

This image does not do this beautiful book justice. It includes many highly-detailed, scientifically-accurate diagrams of different types of flowers with their parts labelled. It also discusses pollinators and how they use differently-shaped flowers in different ways. Super scientific reference for educators and older children.

Age Range: 10 and up
Hardcover: 90 pages
Publisher: HarperCollins; 1st edition (May 1, 1990)
ISBN-10: 0690046774
ISBN-13: 978-0690046779

This is an older book by the same author which covers similar material.

Publisher: Ty Crowell Co (June 1963)
Language: English
ISBN-10: 0690506562
ISBN-13: 978-0690506563

 

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4 thoughts on “Zinnias: Flower Cycles and Parts

  1. Penny

    When I do this activity with my sixth grade Junior Plant Scientist class, I buy the deep picture frames available in dollar stores so the kids can create their own botanical art by pinning the pieces and labeling them.

  2. Zya

    My 5th grade class are doing plants for there science fair I am so glad that I found a website on my project

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