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Angiosperms are seed plants that bear flowers. “Angio” refers to “vessel”, and thus angiosperms are vascular plants that hold their seeds within specialized containers called pistils. Both male (pollen grains) and female parts are held within specialized and highly modified shoots called the flower. Seeds within the pistil are later dispersed in a modified and ripened pistil, dry or wet, termed the fruit. Flowers are typically not displayed singly, but rather arranged in groups we refer to as the inflorescence. This is the most important and diversified group of plants, numbering about 280,000 species, and represent the vast majority of plants in our flora.
Critical to understanding both how flowering plants are classified and using keys to identify them is a thorough familiarity with floral structure, the parts and how they are modified. We will assume (perhaps simplistically) that the flower is simply a modified shoot – with a modified stem and four kinds of modified leaves. This lab will provide you opportunity to dissect two quite different flowers with a microscope, identify the four main “leaves” of the flower and their individual parts, and begin to understand the incredible variation possible with the flower. As needed, review the lecture material (floral structure handout) and flower lecture powerpoint (pages 1-6).
In this and the next lab, a fruit display will be provided. As you have time, examine the various types of fruits – both fleshy and dry. You will learn the three basic types – simple, aggregate, and multiple fruits. Throughout the remainder of the course, you will learn specific fruit types from the attached list and on display as we examine specific flowering plant families.
Inflorescence type will not be examined today, but we will be learning specific types later in the course as we cover families with distinctive inflorescences useful in field identification. In the inflorescence powerpoint there is a review of inflorescences.
Flowers to dissect (and learn their parts):
1. Fuchsia (Onagraceae) 'fuchsia'
2. Lilium (Liliaceae) 'lily'
3. Antirrhinum (Scrophulariaceae) 'snapdragon'
Choose two of the three species and carefully examine the flowers. Using the floral diagram and provided lab handouts, identify the major floral parts.
1. Draw a longitudinal sketch of the flower next to the diagram and label visible parts
2. Indicate the number of sepals, petals, stamens (= merosity of flower)
3. Make a cross section of the ovary and view under the microscope
a. Determine the number of pistil(s) and carpel(s)
b. Is the flower hypogynous, perigynous, or epigynous?
b. Determine the type of placentation
4. Identify any kind of fusion occurring in the flower (connation, adnation)
5. Fill in the floral formula (see lecture handout for more information) – your lab instructor will review this with you at the end of lab