Science - Biology - General Biology - 1 We study plants and
animals (P8010200)
1.3 Monoecious and dioecious flowers
Experiment by: Phywe
Printed: Oct 8, 2013 10:27:20 AM
interTESS (Version 13.06 B200, Export 2000)
Task
Task
What are the differences between monoecious and dioecious plants?
Examine the flowers of the willow.
Use the space below for your own notes.
Logged in as a teacher you will find a button below for additional information.
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Additional Information
Dioecy is a form of sex distribution in seed plants. The male and female reproductive
organs are sitting on different unisexual plants. Dioecy occurs in many plant families,
but only a few plant families are purely dioecious. To these belongs the willow family,
with willow, poplar and many others. As well the male as the female flowers of the
willow build spadices, which are called catkins.
Willows are often found on moist grounds. On slopes, stream and river banks willows
are often planted as they anchor the soil with their roots. Beekeepers plant willows
near their hives.
Early-flowering species such as the goat willow (salix caprea) are an important food
source for bees and butterflies, which appreciate the nectar of the willow flowers.
Even caterpillars, beetles and roe deer feed on the leaves of the willow.
But even as crop plant the willow plays an important role: The bark of the willow was
used early on as a natural medicine, it contains salicin, a compound that is metabolized
in the body to salicylic acid, the active ingredient of aspirin. In addition, the bark used
in tanning. Willow branches can be used to weave baskets and other wickerwork ,
earlier they were also an important element in the construction of timber-framed
houses.
Hints on Setup and Action
• Willows are protected, a full or large-scale tree cutting is prohibited in the spring
and summer months. Therefore only so many branches with the flowers should
be picked, as needed for the experiment.
• To show the students that the branches with the male catkins and the branches
with the female catkins are from different trees, a field trip to the sites with the
corresponding trees is recommended.
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Material
Material
Material from "TESS advanced Biology basic set General Biology, BIO" (Order
No. 15296-88)
Position No.
Material
Order No. Quantity
1
Tweezers, straight, pointed, 120 mm
64607-00
1
2
Dissecting needle, pointed
64620-00
1
3
Magnifier, plastic, 5x, d = 30 mm
88002-01
1
Additional Material
Razor blades
Twigs of a willow with catkins beginning to open
Material required for the experiment
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Setup and Action
Setup and Action
Have a look at the willow branches with the flowers. You can see two different types of catkins:
Some are oval shaped or round and, depending on how far they are opened they are, are pale
to bright yellow in colour (Fig. 1). The others are oblong, cylindrical and of a greenish colour
(Fig. 2).
Fig. 1
Fig. 2
Part 1
First examine an oval catkin, similiar to the one you can see in Figure 1.
Carefully cut one longitudinally with a razor blade. Look at the cross section using the
magnifying glass.
Write down your observations in the appropriate field on the Results page.
Part 2
Now examine the oblong, greenish catkins (Fig. 2) and also cut one of these longitudinally.
Look at the cross section using the magnifying glass.
Write down your observations in the appropriate field on the Results page.
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Results
Results
Part 1
What can you find in the cross section?
Which parts of the flower are these? Which parts of the flower are missing?
The catkins contain many stamens, which sit in pairs on a hairy leaf-scale (bract).
They form the male flower.
The catkins does not contain the female flower parts, like ovaries, styles and stigmas.
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Part 2
What can you find in the cross section?
Which parts of the flower are these? Which parts of the flower are missing?
In this catkin numerous, bottle-shaped greenish structures can be recognized. These
are the pistils, the female flower organs of the willow. Each pistil, in which ovary, style
and stigma can be distinguished, sits on a hairy leaf-scale (bract).
The oblong catkins do not contain male flower organs.
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Evaluation
Evaluation
Question 1
Compare the flowers of the willow to the flowers of the cherry tree and the flowers of the hazel.
Are the flowers of the willow hermaphrodites or are the separately sexed?
The willow has two types of flowers or catkins:
The male catkins are oval-shaped or round and of a bright golden yellow colour if
fully opened. They contain the stamens, which can be seen with the magnifying glass.
The female flowers or catkins are oblong and greenish and contain the pistil.
Therefore the willow has separately sexed flowers like the hazel. But in contrast to
the hazel, the male and female flowers are not on one plant, but on various. There
are male and female willow trees.
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Question 2
Sex-differentiated plants on which both male and female flowers are found on the same plant
are called monoecious; sex-differentiated plants in which the male and female flowers are
found in different plants are called dioecious plants.
To which group does the hazel belong?
To which group do willows belong?
The Hazel is monoecious.
Willows are dioecious.
Question 3
Some dioecious plants possess fruits which can be eaten, for example, the sea-buckthorn
(Hippophae rhamnosides). Its fruits are very rich in vitamin C and give a pleasant-tasting juice.
What should you be careful to do when planting dioecious bushes or trees if you aim to harvest
any fruits?
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In order to cultivate fruits, the flowers of the plants have to become pollinated. If you
want to reap the fruits of dioecious plants, one must remember, therefore, that you
plant female and male plants side by side, so that the pollen of the male plants can
get to the flowers of the female plants, which form the fruit.
Question 4
How occurs the pollination of the willows? Which role play insects?
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The pollination of the willows occurs with the aid of insects. This form of pollination
is also called Entomophily.
The flowers of the male willows form buds, these are the catkins. The single flower
is made up of two stamens, a small bract and a nectar gland. The scent of nectar
attracts the insects on their search for nectar, so carrying the pollen from one flower
to the next.
The female flowers or catkins, also produce nectar. Comes an insect that has previously
visited a male flower and pollen sticks to its body, then the female flowers will be
pollinated when pollen grains are transferred to the stigma.
The flowers of the willows provide the first nourishment of the year for many insects.
A lot of bees and butterflies, such as the Brimstone or the Little Fox feed on the nectar
of the Willows. Beekeepers plant therefore often willows near their hives.
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