Lab - Flower Dissection
Botany/Reynolds
NAME: _____________________________
Objectives:
1) To identify various kinds of flowers and inflorescences
2) To learn how to identify the reproductive parts of several angiosperm flowers
3) To be able to explain how the evolution of flowers has increased angiosperm diversity
Background:
Angiosperms have several special adaptations that have allowed them to inhabit a variety of
habitats and become the most successful plant species on earth. These adaptations include:
1) production of gamete and seed bearing structures, such as flowers or cones
2) specialized male gametophyte structures called pollen
3) protective coverings for the embryo, known as seeds
Angiosperm flowers are often attractive, with bright colors and fragrances, as well as food rewards
such as nectar and protein packed pseudopollen. As a result of these rewards, animals are attracted
to flowers and spread their pollen from flower to flower of the same species. This process is called
pollination. Other angiosperms, including many grasses and trees, and all gymnosperms (conifers)
do not produce showy flowers and rely on wind for pollination. This method is less efficient, but
still effective due to the massive amounts of pollen produced.
Most angiosperm flowers are specially adapted to attracting animal pollinators, usually insects, in
order to carry their pollen to the female parts of another flower. Others, such as wind-pollinated
flowers, are missing entire whorls because the petals are unnecessary. Flowers that contain both
the male and female reproductive organs are called ‘perfect flowers’. A stylized ‘perfect’ flower is
shown in Figure 1 below.
Figure 1: Diagram of a simple flower. You should be able to identify all the major parts.
The major reproductive organs of a flower are:
1) Sepals: the outermost layer of a flower. Sepals enclose the flower bud before it opens and
protects the flower while it is developing
2) Petals: the next layer of a flower. Petals are often brightly colored in order to attract pollinators.
Together with the sepals, these are called ‘sterile leaves’ because they are not directly
involved with the production of reproductive cells.
3) Stamens: the male sexual parts of a flower. Stamens have anthers and filaments. The filament
is the long, thin stalk that supports the anther. The anther is where the male
reproductive gametophytes, or pollen grains, are formed.
4) Pistils: the female sexual parts of a flower. Pistils have an ovary at their base, which contains
the ovules. The female gametophytes, or egg cells, are formed in the ovules. The ovary
narrows into a thin stalk called the style, which connects to the sticky stigma at the top.
The stigma is responsible for catching the pollen grains that land on the carpel.
Flowers are often found in clusters called inflorescences. These arrangements of multiple
flowers make them more visible and attractive to pollinators. Inflorescences are either
determinate or indeterminate. Determinate inflorescences bloom from the top down (the ones
on the end are the first to open) and indeterminate inflorescences bloom from the bottom up.
This allows the inflorescence to continue growing after flowering.
Several common inflorescence types are shown in Figure 2 below
Catkin – hanging, with reduced or no
petals; flowers are unisexual & usually
wind pollinated
Composite Head– A collection of two or
more simple flowers in a disk
(characteristic of Asteraceae)
Panicle – Branched with secondary
branches (pedicellate)
Umbel – Branched where pedicels are the
same length and arise from a single point
(characteristic of Apiaceae)
Raceme – unbranched with pedicellate
flowers
Spike – unbranched with sessile flowers
Whorls – arranged with multiple flowers
along same point
Figure 2. Common types of inflorescences. (adapted from www.answers.com)
In this lab, one of the species we will be dissecting (the daisy) is a composite head. This
inflorescence type is characteristic of the Asteraceae (Sunflower Family). There are 2 types of
flowers are called disk flowers and ray flowers. The disk flowers produce the seeds, like in a
sunflower. Figure 3 shows the general shape of this inflorescence type.
Ray Floret
Disc Floret
Composite Head
Figure 3. Diagram of a composite flower cross-section with ray and disc florets.
Flower Dissection Exercise:
NOTE – BE VERY CAREFUL with the scalpels, they are sharp for a reason!
1) Pick two of the flower species provided. Draw a sketch (on back of this page) of each flower.
Label it with the species name.
2) Observe the exterior parts of the flower. Label the sepals and petals.
3) Using the scalpel provided, VERY GENTLY cut the exterior of the flower lengthwise (from top
to bottom).
4) Peel back the sepals and petals to reveal the interior reproductive structures. If you have
dissecting pins available, pin them back away from the interior reproductive structures. Draw a
detailed sketch of your observations for each flower. Label the stamens and pistils.
5) Use a microscope to examine an anther from the lily under the dissecting scope and put some
pollen grains onto a microscope slide and observe them under magnification. Sketch the anther.
6) Using the scalpel provided, gently cut open the ovary lengthwise to see the ovules inside. Use a
dissecting microscope to observe the number of ovules more clearly. Sketch what you see.
7) If available, make a cross section of another ovary. How are the flowers different?
Discussion Questions: (answer on back below sketches)
1. Why are wind-pollinated flowers less common than animal-pollinated flowers? How has this
type of pollination helped angiosperms become so successful?
2. What is the difference between inflorescences and simple flowers? Why is the daisy considered an
inflorescence? What are the pros and cons of producing inflorescences?
3. Based on your dissections, how are monocot flowers different from dicot flowers? Give at least 2
examples (HINT: count each of the flower parts)
4. Visit the following websites: http://waynesword.palomar.edu/terminf1.htm &
http://waynesword.palomar.edu/terminf2.htm. Name and describe the characteristic inflorescence
types for: 1) Family Araceae; 2) the Common Fig; and 3) the Coconut.
BONUS: What is the world’s largest individual flower? What is its nickname & why?
Lab Flower Dissection
Botany/Reynolds
NAME: _____________________________
FLOWER SKETCHES (BEFORE DISSECTION): Be sure to label the major parts:
Alstroemeria:
Daisy:
DISSECTION SKETCHES – CROSS SECTION (after the 1st cut). Be sure to label parts.
Alstroemeria:
Daisy:
PRIVATE PARTS (ALSTROEMERIA ONLY) – USE THE DISSECTING MICROSCOPE
ANTHER/POLLEN
OVARY:
USE THE BACK OF THIS PAGE TO ANSWER THE DISCUSSION QUESTIONS