Biological Foundations 112, Lecture 1


Growth and Differentiation of the Young Stem

Chapter 31, pages 668-691
Plant Anatomy-1 9:59-19:05


I.   Development of the Young Stem from the Seed

     A.   Seed Structure

            1.   Embryonic shoot

            2.   Embryonic root

            3.   Cotyledons

            4.   Seed Coat

     B.   Seed hydrates, which begins the process of seed germination

            1.   Absorbs water

            2.   Metabolism begins in the seed

            3.   Radicle breaks through seed coat and pushes down into the soil

            4.   Shoot and cotyledons push up through the soil to the sunlight

            5.   Plumule fans out

            6.   Cotyledons shrivel as they release their food stores

            7.    Photosynthesis begins

            8.    Plant is on its own

      C.   Stem begins to differentiate

II.  Morphology of the Stem

     A.   Definition of Terms

           1.   Anatomy - internal structure of the stem

           2.   Morphology - external structure and form of the stem

     B.   Functions of the Stem

           1.   Support

           2.   Conduction

           3.   Storage

     C.   General Structure of the Stem

           1.   Node

           2.   Internode

           3.   Leaf Scars

           4.   Bundle Scars

           5.   Lenticels

           6.   Buds

                 a.   Type

                       (1)  Apical or Terminal buds

                       (2)  Lateral buds

                       (3)  Leaf buds

                       (4)  Flower buds

                       (5)  Adventitious buds

                 b.   Arrangement on the stem

                       (1)  Alternate

                       (2)  Opposite

                       (3)  Whorled

                 c.   Bud Scale Scars

                       (1)  Bud scales - structures that cover the terminal buds during winter dormancy

                       (2)  The bud scales fall off in the spring when the terminal buds begins to grow

                       (3)  The bud scales leave scars on the stem where they fall off

                       (4)  The bud scale scars on the stem tell when the stem begins to grow each
                              spring.  Thus the bud scale scars can be used to determine the age of the
                              stem.

III. Monocots, Dicots, and Gymnosperms

     A.   Monocots ------ one seed leaf per seed

     B.   Dicots ---------- two seed leaves per seed

     C.   Gymnosperms -- many seed leaves per seed

IV. Differentiation in Stems

     A.   Two types of growth in stems

           1.   Primary Growth

                 a.   Is growth in length of the stem

                 b.   Caused by the activity of the apical meristem in the terminal bud

                 c.   Produces herbaceous stems

           2.   Secondary Growth

                a.   Is growth in girth of the stem

                b.   Caused by the activity of the vascular cambium

                c.   Produces woody stems

     B.   Regions of the growing shoot tip

               a.   Apical Meristem

                     (1)  Produces leaf primordia on its flanks

                     (2)  Produces lateral buds on its flanks

                     (3)  Produces flower buds on its flanks

                     (4)  Produces cells that will differentiate into stem tissues in the center

               b.   Stems cells are laid down like a brick-layer lays bricks, on top of another

               c.   Cells that differentiate into stem tissues do so as they get older

     C.   Differentiation of Apical Meristem cells into Mature Stem cells

            1.   Apical Meristem cells differentiate into Primary Meristem Tissues

            2.   Primary Meristem Tissues are:

                  a.   Protoderm - differentiates into the epidermis of the stem

                  b.   Ground Meristem - differentiates into the cortex, pith rays, and pith

                  c.   Procambium - differentiates into the vascular tissue of the stem

            3.   Each Primary Meristem Tissue differentiates into a Primary Tissue

            4.   THUS:   Apical Meristem -> Primary Meristem Tissues -> Primary Tissues


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