LABORATORY 2: Flowers

Transcription

1 LABORATORY 2: Flowers INTRODUCTION The goal of this laboratory exercise is to familiarize you with flowers, their structure, variation, and importance to the plant. By the end of today s laboratory exercise you should be able to recognize and identify the parts of a flower and to briefly describe their importance to the life of a flowering plant. Through the study of flower morphology, you will also become accustomed to the correct use of a dissecting microscope. THE MICROSCOPE Becoming familiar with its use will make the whole experience much more pleasant--you will see more and you won't become fatigued doing it. 1. Eye-strain can be avoided by insuring that your microscope is properly adjusted for YOUR eyes. Set up your scope so that it receives bright light from the lamp. Focus, at highest magnification, on the end of your teasing needle. Shut your left eye and focus with the main focus adjustment; then shut your right eye and focus with the adjustment on the left objective. Do this every time you use the scope. Use the zoom ring or dial to increase or decrease the magnification. 2. You are responsible for your immediate working area! At the end of each lab period, be certain that: 1) your scope is clean and covered, 2) your bench space is clean and free of plant material (fresh material can go in the compost bucket), and 3) your table lamp is OFF. ACTIVITY Carefully EXAMINE all floral material provided using the following exercise and questions as a guideline. To gain an ultimate familiarity with floral morphology, compare the material against descriptions and definitions in your lecture notes or textbook. Become familiar with cross and long sections. 1. Flowers are arranged in groups called inflorescences. We will examine some inflorescences particular to certain families later in the semester. For now, know what an inflorescence is and which one we looked at today. 2. DRAW a longitudinal section of a typical flower labeling the following parts: receptacle, calyx, sepals, corolla, petals, perianth, pedicel, ovary, ovule, style, stigma, pistil, gynoecium, anther, filament, stamen, and androecium. 3. EXAMINE by dissection the floral material provided making long and cross sections of the flower and its parts. On a separate sheet of paper, SKETCH the flowers and label the parts. Then, FOR EACH FLOWER, answer the following questions: A. Is the flower actinomorphic (regular) or zygomorphic (irregular)? B. How many sepals are present? Petals? Stamens? Carpels? To count carpels, count the style branches and/or count the zones of placentation by cross- sectioning the ovary. C. Is the ovary inferior or superior? D. Is the flower from a monocotyledonous or dicotyledonous plant? E. Is the flower perfect (both sexes present) or imperfect? Complete (all four floral whorls) or incomplete?

2 MATERIAL TO BE EXAMINED (You can refer to the web page for additional images. You should draw the flowers and their parts for your own reference. 1. Gladiolus- cultivated- Iridaceae - Gladiola or Alstroemeria - cultivated - Liliaceae In Gladiolus, each flower is subtended by 2 green bracts. These are not the sepals. The sepals and petals and are similar in color and texture--i.e., there are no solid green sepals. These are slightly zygomorphic flowers with 3 sepals and 3 petals. The sepals are free (not united), and so are the petals, but there may be some fusion of petals to sepals. Gladiolus has 3 stamens adnate to the corolla and one style with 3 branches. Alstroemeria has 6 stamens. The ovary is inferior, with 3 carpels. Placentation is axile and the fruit will be a capsule. Note the monocot plan of having floral parts in 3's. 2. Sesbania Fabaceae--Rattlebush These zygomorphic flowers are borne on slender pedicels. The calyx is briefly united below into a small cup with 5 teeth representing the 5 sepals. The petals are not all alike--there is one large petal (the banner), two smaller side petals (the wings), and two small, fused petals which together form the keel. This arrangement is termed papilionaceous and is typical of the bean family. There are 10 stamens, 9 united briefly basally and a 10th which is free. This condition is called diadelphous. The ovary is superior and consists of one slim carpel. The fruit will be a legume. This flower shape is typical of most of the important crop plants in the Fabaceae. 3. Lobularia --Sweet Alyssum or Capsella Shepherd s Purse Brassicaceae These flowers are regular and have 4 sepals and 4 petals arranged in a cross shape. (This accounts for the alternate name for this family, the Cruciferae. There are 6 stamens, 4 long and 2 short. This arrangement is called tetradynamous. The ovary consists of two carpels. It has two locules, which may be observable in the fruit. The fruit is a silicle the two halves will fall away from the central septum (in this case called a replum.)

3 4. Helianthus annuus - wild type (Asteraceae) - Sunflower Note that what appears to be a single flower is actually an inflorescence consisting of many small flowers. This type of inflorescence is called a HEAD or CAPITULUM. This feature is diagnostic of the Asteraceae, the largest of dicot families. Heads take several forms, although all types are usually subtended by a cluster of bracts known as phyllaries. This type - the radiate head - features fertile flowers (disc florets) with actinomorphic (radially symmetrical) corollas in the center and zygomorphic flowers (ray florets) that are non-functional reproductively around the margin. Floral structure - disc floret : The calyx is represented by two awns placed on top of the ovary near the point of attachment to the corolla tube. The calyx is highly specialized and variable in this family (sometimes absent), and the term 'calyx' is replaced by the term PAPPUS for this family. The tubular, sympetalous corolla has 5 lobes (5 petals involved), 5 stamens are attached to the corolla (epipetalous) and fused by their anthers (synantherous). The single style with two style branches comes up through the middle of the anther tube. While there is only a single locule and seed in the ovary, the two stigma lobes indicate a syncarpous gynoecium made up of two carpels. These flowers are fertile and will set fruit. Floral structure - ray floret: The corolla here is also sympetalous (5 petals fused), but the product of this fusion is a zygomorphic (bilaterally symmetrical), straplike ligule structure that serves to attract pollinators. A close examination of a ray floret shows no androecium or style and a reduced ovary that will not set fruit. 5. Pyrus--Pear--Rosaceae--We will do this if we can get flowers Pear flowers are typical of many species in the Rosaceae (rose family.) They are regular. There are 5 sepals, 5 petals, and many stamens. The ovary is inferior and is composed of 2 to 5 fused carpels. This ovary will form the "core" of the pear, while the fleshy part of the pear that we eat develops from the receptacle and the hypanthium, a floral cup made up of the bases of the sepals, petals, and stamens. The hypanthium encloses the ovary and is fused to it. 6. Poa-- Poaceae Bluegrass or other grass. Grass family flowers (florets) are very reduced. There is no calyx and no proper corolla. Instead, each floret is subtended by two bracts, the lemma (outer) and palea (inner.) There are 2 or 3 stamens, and 2 or 3 feathery style branches. The basic unit of the grass inflorescence is the spikelet, which consists of one or more florets with their lemmas and paleas, and two sterile bracts called glumes. The florets and spikelets are modified for wind pollination. The fruit is a caryopsis or grain. We will study grasses in more detail at a later date.

4 "Vegetables" and spices of Floral origin--complete the chart Common name Genus Specific Epithet Family Class (monocot or dicot) Artichoke Part Eaten Inflorescence- - fruit will be achenes at maturity Origin Broccoli Immature Flower Buds Cauliflower Immature Inflorescence Capers Pickled Flower buds

5 Cloves Pickled Flower bud Hops Female Inflorescence Saffron Stigma QUESTIONS FOR REVIEW-- Refer to lecture notes, handouts, and the laboratory activity. 1. What purposes do flowers serve? 2. What is the difference between a monoecious and a dioecious plant in terms of their flowers? 3. What is a fruit? What is a mature ovary? 4. What is a seed? What is a mature ovule? 5. What is the difference between an ovule and a seed? 6. What are two ways to count the number of carpels present in a pistil? What is a carpel? 7. What is the difference between a perfect and a imperfect flower?

6 8. What is a gynoecium? What is an androecium? A hypanthium? 9. A sunflower may look like a single flower, but it is definitely not. Exactly what is a sunflower? 10. What is a zygomorphic (irregular) flower? What is an actinomorphic (regular) flower? 11. A Gladiolus flower is quite large and showy. A grass flower is small, inconspicuous, and non-showy. Based on this information, what can you say about the pollination of each of these? 12. Be able to name and count flower parts if given a fresh flower. 13. What is a complete flower? What is an incomplete flower? 14. Where are pollen grains produced and from where are they released? 15. Name the parts of a flower which make up the pistil. 16. What is a compound pistil? What is a simple pistil? 17. Why do you think a sunflower inflorescence so strongly resembles a flower? What purpose, in terms of the evolution of such a structure, might this type of inflorescence serve? 18. Name the parts which make up a stamen. 19. Know the difference between a longitudinal section and a transverse (cross) section; for example, of an ovary. 20. Know how to properly adjust a dissecting microscope. 21. We have now covered the vegetative and floral parts of the typical flowering plant. Make a table which contrasts the vegetative and floral characters of monocots and dicots.