FLOWER AND FRUIT DEVELOPMENT

 

   THE FLOWER PARTS ARE BASICALLY    MODIFIED LEAVES

 

      1.   SEPALS

 

         a.   PROTECTION OF BUDS                FROM DESICCATION

 

         b.   ATTRACTS POLLINATORS

        

      2   PETALS

 

         a.   ATTRACT POLLINATORS

 

      3.   CARPEL (OVARY)

 

         a.   PRODUCE SEEDS

 

      4.   STAMENS

 

         a.   PRODUCE SPERM IN                   POLLEN GRAINS

 

 

MEIOSIS OCCURS AT TWO LOCATIONS:

 

   1.   WITHIN THE OVULE, WHICH IS

      WITHIN THE OVARY.

 

      a.   A MEGASPORE MOTHER CELL

         WITHIN THE OVULE                   UNDERGOES MEIOTIC                   DIVISIONS TO GENERATE A

         HAPLOID EGG NUCLEUS, TWO

         POLAR NUCLEI, AND 5                OTHER HAPLOID NUCLEI

         (THE FEMALE GAMETOPHYTE)

 

   2.   WITHIN THE ANTHERS

 

      a.   A MICROSPORE MOTHER CELL

         UNDERGOES MEIOTIC                   DIVISIONS TO PRODUCE                FOUR POLLEN GRAINS

 

   POLLINATION OCCURS WHEN A    POLLEN GRAIN LANDS ON A    STIGMATIC SURFACE

 

  

 

   1.   THE POLLEN GRAIN                   GERMINATES, PRODUCING A           POLLEN TUBE.

 

      a.   THE NUCLEUS OF THE

         GERMINATING POLLEN GRAIN

         DIVIDES TO PRODUCE A

         TUBE NUCLEUS AND A                   GENERATIVE NUCLEUS

         (THE MALE GAMETOPHYTE)

 

         -   THE POLLEN TUBE

            ELONGATES DOWN THE

            STYLE UNTIL IT                      REACHES THE OVULE

 

         -   WHEN THE POLLEN TUBE

            REACHES THE OVULE,                 THE GENERATIVE                      NUCLEUS HAS DIVIDED                AND GIVEN RISE TO TWO            SPERM CELLS

 

 

 

 

            1.   ONE FUSES WITH THE

               EGG TO FORM A 2N

               ZYGOTE

 

            2.   ONE FUSES WITH THE

               TWO POLAR NUCLEI TO

               FORM A 3N                            (TRIPLOID) ENDO-

               SPERM

 

FRUIT: THE FINAL STAGE OF GROWTH

 

A FRUIT IS A MATURE OR RIPENED OVARY.

 

FRUITS MAY BE:

 

   1.   SEEDS ENCLOSED IN AN                ENLARGED OVARY (PEAS,           BEANS, MESQUITE)

 

   2. MAY BE SEEDS IN A JUICY             OVARY (TOMATOES)

 

   3.   MAY BE SEEDS IN A DRY OVARY       (CORN AND OTHER CEREAL           GRAINS)

 

FRUITS DEVELOPE AND GROW AS A RESULT OF CELL GROWTH IN RESPONSE TO HORMONES

 

HOW DO CELLS GROW?

 

   GROWTH IS AN IRREVERSIBLE    INCREASE IN VOLUME

 

   A PLANT CELL GROWS IN VOLUME

   BY TAKING UP WATER.  WATER

   UPTAKE IS THE DRIVING FORCE    FOR CELL ENLARGMENT

 

   CELL WALLS HAVE TO BE RIGID

   BUT, THEY MUST ALSO BE ABLE TO

   STRETCH, FOR GROWTH TO OCCUR.

 

      TURGOR PRESSURE PRESSING

      AGAINST A CELL WALL WILL

      CAUSE IT TO STRETCH AND

      GROW

 

THE ROLE OF HORMONES IN PLANT DEVELOPMENT

 

   THE CONCEPT OF HORMONES IN

   PLANTS CAN BE TRACED BACK TO

   CHARLES DARWIN