Flowering Plant Organization

After completing this tutorial you should be able to:

• Identify the reproductive structures of the flower.
• Distinguish the characteristics of the Monocots versus the Dicots.
• Identify the morphological and anatomical features of Monocot versus Dicot seeds.

  Within the plant kingdom the angiosperms, or flowering  

  plants, constitute the largest and most conspicuous group
  
  of plants living today. They are characterized by the
  
  presence of flowers and the production of seeds enclosed
  
  in an ovary. These plants are thought to have been  most 
  
  important to the development of civilization. 
  
  The angiosperms are a very diverse group of economically
  
  important plants. There are more than 250,000 known 
  
  species of angiosperms, but only a small number have
  
  become the food staples of our civilizations. All 
  
  angiosperms are characterized by flowers and fruits. 
  
  A typical angiosperm flower consists of sepals, petals, 
  
  stamens and carpels. The fruits and seeds develop from
  
  the carpels. The flowering plants are divided into two 
  
  groups, the monocots and dicots. A few common dicots 
  
  are roses, tomatoes, potatoes, beans, and peas. The most
  
  common monocots are the grasses, lilies, palms, and
  
  orchids. Reproduction in these plants involves a double
  
  fertilization process. An embryonic plant is produced in 
  
  the seed as well as the cotyledons or endosperm which is
  
  rich in nutrients. This material is digested and used by 
  
  the developing embryonic plant. It is this material, in 
  
  many of the grasses, which has provided the  nutrients 
  
  which were prerequisite to the development of civilization. 
  
  The Division  Anthophyta is divided into two classes which 
  
  include the Monocotyledones and the Dicotyledones. 
     
   The characteristics of the Monocotyledones include:

• One cotyledon per embryo.
• Flower parts in sets of three.
• Parallel venation in leaves.
• Scattered rings of vascular bundles in stems.
• Lack of true vascular cambium.

  The characteristics of the Dicotyledones include:

• Two cotyledons per embryo.
• Flower parts in sets of four or five.
• Netted venation in leaves.
• A ring of vascular bundles or a cylinder of vascular tissue in the stem.
• Have true vascular cambium.

  A flower is a cluster of specialized leaves arranged on a

  stem of determinate growth. A typical complete flower will 
     
  demonstrate a number of reproductive and accessory parts.
     

  These flower parts include:

 
• Peduncle: flower stalk.
• Receptacle: the part of the flower stalk that bears the floral organs; located at the base of the flower.
• Sepals: the outermost leaflike structures which protect the flower. The sepals collectively constitute the calyx.
• Petals: usually inside the sepals. May be pigmented or absent. The petals constitute the corolla.
• Perianth: the combined calyx and corolla.
• Androecium: The male portion of the plant inside the petals. Consists of stamens, each of which consists of an anther. Inside the anthers are pollen grains, which produce the male gametes.
• Gynoecium: the female portion of the plant consists of one or more carpels; each made up of an ovary, style, and stigma= pistil. The ovary contains ovules that contain the female gametes. During pollination pollen grains are transferred to the stigma, where they germinate and grow a tube through the style to the ovary.

        Angiosperm Seeds  
       The seed may be defined as a mature fertilized ovule.

A seed consists essentially of a protective coat, some form of stored

food material, and an embryo. Differences in monocots and dicots 

are quite obvious in the seeds. Dicot seeds have two cotyledons that

are attached to the embryonic plant. These leaf-like structures

contain most of the nutrients from the endosperm. A dicot seed is

usually enclosed in a seed coat referred to as a testa. The 

hilum is a scar that is produced from the separation
 
of the seed from the ovary wall. The micropyle is a
 
small pore through which the pollen tube enters the ovule. 

When the seed coat is removed two large food-storing cotyledons 

may be found. The embryo, consisting of the epicotyl, hypocotyl, 

and the radical; is found between the cotyledons. The epicotyl

develops into the upper portion(stem and plumule) of the seedling.

The hypocotyl is the portion of the embryo located between the 

point of attachment of the cotyledons and the radicle. The radicle

is the embryonic root. Monocots have a single small cotyledon  
 
that functions to transfer nutrients from the endosperm

to the embryo. One major difference in monocot

seeds is that they usually have a great deal of endosperm that

occupies much of  of the volume of the seed. The small embryo of

the monocot has only a single cotyledon called a scutellum. Other

differences include the presence of a coleoptile (a protective

covering surrounding the epicotyl) and the coleorhiza (a protective

covering around the radicle).  

        Because of these stored food reserves many seeds, like many
 
fruits, are important food for humans and other animals.   

       A. Draw and label a typical complete flower.

      B. Draw and label typical monocot and dicot seeds.

                                
                                    
(Review Questions)

       Define the terms:
          

       1. anther:

       2. corolla:

       3. gynoecium:

       4. monocotyledon:

       5. Anthophyta:

       6. cotyledon:

       7. testa:

       8. radicle:

       9. coleoptile:

       10. coleorhiza: