LABORATORY 2:  Flowers  This is the page for spring 2007.  It has been recently updated.  (If you are looking for the Fall 2006 page, please go to http://www.csdl.tamu.edu/FLORA/328Fall98/flowers2--fall.html )


INTRODUCTION

 The goal of this laboratory exercise is to familiarize you with flowers, their structure, variation, and importance to the flowering 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 covered and returned to the cabinet, 2) your bench space is clean and free of plant material (fresh material can go in the compost bucket), and 3) your table lamp, if separate from your scope, is OFF and put away.

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 hand-outs or textbook.  Become familiar with cross and long sections.

1.  Flowers are arranged in structures called inflorescences.  Inflorescences can be arranged in a variety of ways.  DRAW simple diagrams of the following inflorescences:  solitary, spike, raceme, panicle, umbel, catkin, and head.

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 longitudinal and transverse (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, if possible.

 C.  Is the ovary inferior or superior?

 D.  Is the flower from a monocotyledonous or dicotyledonous plant?


MATERIAL TO BE EXAMINED

1.  Ranunculus --Buttercup--Ranunculaceae (Ranunculus images)
These are very simple flowers that show a lot of primitive traits--they are actinomorphic (radially symmetrical), all the floral parts are unfused, there are many stamens and pistils, and the pistils have poorly-developed styles and stigmas.  Note that the gynoecium consists of many separate, simple pistils. The term for this is apocarpous.  Each pistil will mature into a one-seeded achene.

2.  Alstroemeria --cultivated Inca Lily--Liliaceae (Alstroemeria images)
These are slightly zygomorphic (bilaterally symmetrical)  flowers with 3  sepals and 3 petals.   Note that the sepals and petals and are similar in color and texture--i.e., there are no solid green sepals.  Alstroemeria has six stamens and an undivided style.  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.

3.  Capsella--Shepherd's Purse-- or Lobularia --Sweet Alyssum--Brassicaceae (Capsella images)
These actinomorphic flowers are very typical of the Brassicaceae, the family that includes cabbage, broccoli, turnips, mustard, and so on.  There are 4 sepals, 4 petals, and 6 stamens.  This is an unusual number for a dicot, and there are usually four long and two short stamens.  This arrangement is termed tetradynamous, and you can see another example here.   The ovary has two carpels and two locules, but notice that there is only one style.

4.  Pyrus--Pear--Rosaceae (Pyrus images)--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.

5.  Poa--Bluegrass--Poaceae (Poa images)--another grass may be substituted
Grass (Poaceae) are very different from the other flowers we are studying today.  The plants are wind-pollinated, so there are no showy sepals or petals for attracting pollinators.  Each flower has an ovary with two feathery stigmas and some stamens, but that's about it.  Each flower is enclosed by two glumes, the lemma and the palea to form what is called a floret.  Several florets are grouped together in a spikelet subtended by two sterile bracts called glumes.  For a nice drawing, select "spikelet" at this page. We will look at grass anatomy more closely in one of our Major Families labs.

"Vegetables" and spices of Floral origin
LOCAL NAME GENUS SPECIES FAMILY CLASS PART EATEN ORIGIN
Artichoke 







Broccoli 






Cauliflower 




                  

Cloves
 

                    
                      
                    



Saffron





                

                    


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?

8.  What is a gynoecium?  What is an androecium?

9.  What is a pollinium?  We saw pollinia in two different flowers, those of the Asclepiadaceae and Orchidaceae families.  What is the purpose of the pollinium in the life histories of these plants?

10.  A sunflower may look like a single flower, but it is definitely not.  Exactly what is a sunflower?

11.  What is a zygomorphic (irregular) flower?  What is an actinomorphic (regular) flower?

12.  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?

13.  Be able to name and count flower parts if given a fresh flower.

14.  What is a complete flower?  What is an incomplete flower?

15.  Where are pollen grains produced and from where are they released?

16.  Name the parts of a flower which make up the pistil.

17.  What is a compound pistil?  What is a simple pistil?

18.  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?

19.  Name the parts which make up a stamen.

20.  Know the difference between a longitudinal section and a transverse (cross) section;  for example, of an ovary.

21.  Know how to properly adjust a dissecting microscope.

22.  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.
(i.e., How can you differentiate between monocots and dicots using vegetative and floral characters?)

Last updated 1/29/2007

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