Plant Cells and Tissues

Introduction

    Angiosperms (flowering Plants) and Gymnosperms (cone-bearing plants) arevfsdvxc ue. Discussing the arrangement and function of various cell types aids in the understanding of plant structure. This exercise is intense and you will have to keep up to do well. 

    Since your text is limited in the material on plant tissues, additional information is provided on the internet and on Darwin. A glossary, which should be extensively used during this exercise is included with this section. 

Objectives

      Be able to:

Grading color code.

A     B     C  

Stem  

  1. Herbaceous Dicotyledonous Stem with Primary Growth.

Primary growth in plants is a result of the activities of the apical meristem. It elongates the plant body, increasing its surface area and areas of contact with the air and soil. This growth occurs at the tips of the shoot (at the end of the branches) and at the end of the roots. Many herbaceous dicots and almost all monocots have only primary growth. 

Schematic Diagram of Development in Dicotyledon Stems

The following table includes a schematic diagram of primary growth showing tissue and cellular development. The stages of growth and development are given at the top of the table. It is obvious that this shows the sequence of development, differentiation, and maturation.

Tip of Shoot/Stem/Branch
Mitosis Cell Cycle		 Primary Meristems
Region of Elongation,
Cell Differentiation/Maturation 		Mature Tissues Mature Cells
Apical Meristem Protoderm Epidermis Epidermal Cells 1 
Ground Meristem Cortex Collenchyma 2
Parenchyma 3
Chlorenchyma 4
Fibers 5
Pith or Medulla Parenchyma 3
Pith Ray or Medullary Ray
Procambium Primary Phloem Fibers 5
Sieve Elements 6
Companion Cells  7
Parenchyma  3
Fascicular Cambium Meristematic Cells 8
Primary Xylem Vessel Elements 9
Tracheids 10
Fibers 5
Parenchyma 3

 Features of Cells in Above Table

Cell Living or Dead 1 Primary Function Other Function Unique Feature(s) Basic Shape
1) Epidermal  Living Prevent desiccation and protection   Cuticle in cell wall Tile shaped
2) Collenchyma Living Mechanical support in young tissue   Walls have uneven thickness round to rectangular
3) Parenchyma Living Center for metabolism & storage totipotent Non-descript; varying in size round....almost
4) Chlorenchyma Living Photosynthesis   Chloroplasts round
5) Fibers Dead Mechanical Support   Thick secondary cell wall with lignin long and narrow
6) Sieve Living Transport "Organics Sieve Plate, no nucleus when mature  long and narrow
7) Companion Living Control Sieve Cells   Accompany sieve cells small and long
8) Meristematic Living Divide     small and rectangular
9) Vessel Dead Translocate water and minerals & mechanical support Store wastes open ends; lignin in wall long and narrow
10) Tracheid Dead Translocate water and minerals and mechanical support Store wastes closed ends; lignin in wall long and narrow

The information in the above table is often a beginning point for discussion in class or lab. For example, chlorenchyma are not always round. We will discuss shape when studying microscope slides. 
1. When mature

  1. Shoot apical Meristem Longitudinal Median Section

     

    1. Get slide 3  of a longitudinal section through the terminal bud of Syringa from the slide box. 
      1. Study this section using the dissecting microscope and the various powers using the compound microscope. Identify the following tissues or regions.
meristematic region leaf primordium apical meristem
region of elongation lateral bud primordium region of differentiation
protoderm

ground meristem
  1. Draw the shoot apex. Outline the primary meristems. Follow the drawing instructions given by the instructor. 
  2. Draw and label two or three enlarged cells of each primary meristem . These drawings should be used in review, as you will not have time to look at each slide before the practicum.
  3. Questions: Answer beneath the drawings.
    1. Which cells were the longest? Be able to describe what tissues are derived from the procambium, protoderm, and ground meristem.
    2. What process provides the cells for the primary growth?
    3. Are internodes visible in the apex?
    4. What provides the information to form these three primary meristems?
    5. What do we call the process the apical meristem cells growing into the three primary meristems.
  1. Herbaceous stem showing differentiated Tissues and Cells (Cross Section)
    1. Get a Medicago  stem x.s. section from the provided slides.
      1. Study this section using the dissecting microscope and the various powers using the compound microscope. Identify the following tissues or regions.
pith   (medulla) epidermis xylem
pith ray   (medullary ray) phloem cortex
vascular bundles
  1. Make an outline drawing of the entire cross section of the stem. Delineate  and label the different tissues. 
  2. Study the cellular structure in each tissue. Identify the following cells.
parenchyma sieve tube elements companion cells
collenchyma vessel elements tracheids
chlorenchyma epidermal cells interfascicular cambium
fibers
  1. Make a drawing of a stem sector showing cellular detail beginning in the pith, passing through a vascular bundle and cortex, to the epidermis. Include each cell type in the drawing. 
  2. Be able to describe the origin and function of each cell and tissue.
  1. Remove slide 10 of Cucurbita stem section from your slide box.
    1. Study this slide, identifying the various tissues and cells. Note that there are two "ranks" of vascular bundles, large and small. Note the position of the phloem. Compare the orientation of the cells and tissues in this slide to those of Medicago.
    2. Be able to describe the origin and function of each cell and tissue.
  2. Remove slide 48 from your slide box of Cucurbita stem l.x.
    1. Study this slide, identifying the following tissues and cells. Note the size and length of each cell.
epidermis companion cells chlorenchyma
fascicular cambium collenchyma fibers
parenchyma tracheids sieve tube cells
fibers.
  1. Questions:  Answer at the bottom of the drawings.                        
    1. Is any secondary growth present in the stems?
    2. What cell types are present in these stems which function as strengthening tissue?
    3. By what means other than strengthening tissue are herbaceous stems held erect?
    4. If the center of the stem section is hollow, explain the origin of this space.
    5. What tissue gave rise to the xylem, phloem, pith, epidermis, pith ray cortex, chlorenchyma, sieve elements, companion cells, parenchyma (consider all locations, fibers, collenchyma, and vascular cambium?
    6. Which cells are the longest?
    7. Could you identify the sieve plants?
    8. What is the difference between a sieve tube element and a sieve tube?
    9. What was the origin of the space in the center of the stem?
    10. Which cells are the shortest?
    11. Were end walls visible in the vessels?
  1. Herbaceous Monocot Stem With Primary Growth

The development in monocot  stems is similar to that of dicot stems. However, the vascular bundles are scattered throughout the monocot stem (in contrast to having a ring of vascular bundles as in dicots). Thus, numerous procambial strands would be seen in a longitudinal section of the apical meristem. Many monocots do not produce tissue by secondary growth. 

Schematic Diagram of Development in Monocotyledon Stems

The following table includes a schematic diagram of primary growth showing tissue and cellular development. The stages of growth and development are given at the top of the table. It is obvious that this shows the sequence of development, differentiation, and maturation.

Tip of Shoot/Stem/Branch
Mitosis Cell Cycle		 Primary Meristems
Region of Elongation,
Cell Differentiation/Maturation 		Mature Tissues Mature Cells
Apical Meristem Protoderm Epidermis Epidermal
Ground Meristem Pith and Cortex Fibers
Parenchyma
Bundle Sheath
Procambium  

Primary Phloem

 

 Sieve 
Companion 
Parenchyma
Primary Xylem Lacuna (air space and not cell)
Vessels
Parenchyma
Tracheids

 

  1. Remove slide 11 which is a Zea mays stem x.s. from the slide box.
    1.  Study the stem with the dissection and compound microscopes. Identify the following tissues.
pith xylem phloem
vascular bundle epidermis cortex
  1. Study the cellular detail of the stem. Identify the following cells.
epidermal fibers vessels tracheids
parenchyma chlorenchyma sieve elements companion
  1. Make a cellular drawing of one vascular bundle located near the epidermis and extend the drawing to the epidermis. Label each cell.
  2. Be able to describe the origin and function of each cell and tissue.
  3. Questions:   Answer below drawings.
    1. How are the vascular bundles oriented in respect to the center of the stem?
    2. What is the origin of the large intercellular passage in the xylem?
    3. Compare the differentiation of procambial strands in monocotyledonous stems.
    4. How do monocot stems differ from dicot stems?
    5. What cells are found in monocot stems that are not found in dicot stems?
  1. Secondary Growth in Dicotyledon Stems

    Secondary growth increases the girth of the plant and adds to its supporting and conducting tissue. Its occurs as a result of activities of the vascular cambium and the cork cambium. Primary growth does not cease once secondary growth begins but continues near the tips of the shoot and root throughout he life of the plant.

    1. Early Stage of Secondary Growth
      1. Remove slide 4 of Sambucus stem x.s. from the slide box.
        1. Study the slide carefully. Note the development of the interfascicular cambium between the vascular bundles. Also a small amount of secondary xylem and secondary phloem may be present. You should recognize all tissues and cells.
        2. Make an outline drawing of the stem. Delineate the different tissues and label. Be certain to show secondary growth. State on your drawing what cells are in these tissues. Do not draw these cells.
      2. Get the demo Sambucus stem CS one year old stem.
        1. Study the slide carefully. You should recognize the tissue and cell types. Note the increase of secondary xylem and phloem. A cork cambium called the phellogen is now present. This meristem produces cells towards the stem interior that are called phelloderm and towards the exterior called phellem (cork).
        2. Make an outline drawing of this stem section. Delineate different tissue areas and label. State in your drawing what cells are in these tissues. Draw a few enlarged phellem, phellogen, and phelloderm cells.
      3. Remove slide 40, Magnolia young stem X.S. Study the slide carefully. Be able to identify the following when present.
pith tracheids phloem xylem
cortex epidermis parenchyma collenchyma
fibers chlorenchyma phellem phelloderm
sieve elements phellogen companion cells vessel
primary phloem secondary phloem primary xylem lenticels
secondary xylem vessel elements cork cells primary xylem
  1. Make an outline drawing of this stem section. Label the tissues or regions.
  2. Draw and label two cells from each tissue or region. Make certain to show variations with these two cells.
  3. Be able to describe the origin and function of each cell and tissue of the above slides.
  4. Questions: Answer under drawings or on back of page.
    1. The secondary xylem is produced by which meristem?
    2. What tissue is found in the center of the young Sambucus stem?
    3. What tissue is found in the center of the one year old Sambucus stem?
    4. The primary xylem develops from what primary meristem?
    5. The fascicular cambium develops from what primary meristem?
    6. What is the function of the epidermis?
    7. What cells are found in the cortex?
    8. Does secondary growth increase the height or diameter of the stem?
    9. What is the function of the interfascicular cambium?
    10. Is primary or secondary xylem located next to the pith?
    11. Is Primary phloem or primary xylem located next to the pith?
    12. Where is the cuticle located?
    13. What cells contain lignin?
    14. What is the function of the cuticle?
    15. What cells contain suberin?
    16. What cells are dead at maturity?
    17. What is the function of the secondary phloem?
    18. What is the function of the secondary xylem?
  1. Later stages of secondary growth
    1. Remove slide 5, Tilia one year old stem from the slide box.
      1. Locate the various tissues and cells. Note the development of secondary xylem, secondary phloem, xylem rays and phloem rays. Be able to reconstruct this stem from the apical bud. Review the function of the various tissues and cells.
    2. Remove slide 6, Tilia three year old stem from the slide box.
      1. Note the increase in secondary growth with time. Each year's growth of secondary xylem begins with the production of large cells called spring xylem or spring wood. The cells are large in the spring because of optimum growth conditions. In the later part of the year's growth, the secondary xylem cells are small. The cells are smaller because of the poor growing conditions that exist later in the summer. In our climate, the summer xylem develops during the hot dry summers when growing conditions are not optimum. The pith often contains dark stained mucilage cells. Xylem and phloem rays are well developed for lateral transport of materials.

  2. Cell Orientation in Cross and Longitudinal Sections of Secondary Xylem

    1. Remove slides 7, Pinus , c.s., r.s., and t.s. and slide 8, Tilia c.s., r.s., and t.s.

      1. Each of the above slides has a cross section (s.c.) radial section (r.s.) and tangential section (t.s.). If you do not understand the meaning of these sections, see the glossary. First, look at these slides without a microscope. Then study with the dissecting and compound scopes. Identify the following cells and tissues. Remember or review the origin and function for each cell. Be able to recognize each section, as well as the tissue and cells of each section for the practicum quiz.

        spring wood summer wood pith parenchyma
        tracheids vessel elements cork xylem rays
        phloem rays sieve elements fibers companion cells
        pits resin ducts

      2. Make a drawing of a radial, tangential and cross section. Do not draw more cells than are necessary to accurately show the structure of these sections.

    2. Remove slides 1 and 2 of Pinus and Fraxinus macerated wood.

      1. Study under the compound microscope. In preparing the macerated wood, the cementing substance of the middle lamella has been dissolved and the individual cells of the xylem separated. Identify the individual cells.

      2. Questions and Observations
        1) List the differences between the Pinus and Fraxinus wood.
        2) What types of cells give strength to both woods?
        3) What types of cells conduct water and minerals in both woods?
        4) Compare a vessel element to a tracheid.
        5) Where are parenchyma cells located in Fraxinus
        6) What is the function of resin ducts?

    3. Wood Blocks and Sections

      1. Study the grain in the blocks and sections of wood that are on demonstration. Relate the grain to cell structure. Identify the following:

      spring wood summerwood xylem bark
      heartwood sapwood soft wood xylem rays
      pith radial section tangential section cross section
      hard wood vascular cambium fascicular cambium

 ROOTS

  1. Herbaceous Dicotyledonous Roots with Primary Growth.

Primary growth in dicot roots is a result of the activities of the apical meristem. It elongates the plant root, increasing its surface area and areas of contact with the soil. This growth occurs at the tips of the shoot (at the end of the branch roots).  Many herbaceous dicots and almost all monocots have only primary growth. 

  1. Types of Roots

    The three basic types of roots are tap, fibrous (diffuse) and adventitious. These   are described in the texts and atlas.

    1. Examine the Riker mounts and other examples that are provided and identify the roots types exhibited.

  2. Primary Root Structure

    Schematic Diagram of Development in Dicotyledon Roots

    The following table includes a schematic diagram of primary growth showing tissue and cellular development. The stages of growth and development are given at the top of the table. It is obvious that this shows the sequence of development, differentiation, and maturation. The following table was constructed with the assumption that the root was grown in the dark as they are in the soil.

    Tip of Shoot/Stem/Branch
    Mitosis Cell Cycle    		 Primary Meristems
    Region of Elongation,
    Cell Differentiation/Maturation         		Mature Tissues Mature Cells
    Apical Meristem   Root Cap Root Cap
    Protoderm Epidermis Epidermal and Epidermal Hairs
    Ground Meristem Cortex
    Parenchyma
    Endodermis
    Endodermal
    Procambium Pericycle Pericycle
     

    Primary Phloem

     

    		 Sieve 
    Companion 
    Parenchyma
    Vascular Cambium Meristematic
    Primary Xylem Vessels
    Parenchyma
    Tracheids

    Remember that roots grown in the dark do not have chloroplasts and are supported by the soil, so they have few or no cells that provide mechanical support. Many roots also store large amounts in leucoplasts. The starch takes on a blue stain in most staining mixtures. 

     Features of Cells in Above Table

    Cell Living or Dead   Primary Function Other Function Unique Feature(s) Basic Shape
    1) Epidermal  Living Prevent desiccation and protection   Cuticle in cell wall Tile shaped
    2) Parenchyma Living Center for metabolism & storage totipotent Non-descript; varying in size round....almost
    3) Sieve Living Transport "Organics   Sieve Plate long and narrow
    4) Companion Living Control Sieve Cells   Accompany sieve cells small and long
    5) Meristematic Living Divide     small and rectangular
    6) Vessel Dead Translocate water and minerals & mechanical support Store wastes open ends; lignin in wall long and narrow
    7) Tracheid Dead Translocate water and minerals and mechanical support Store wastes closed ends; lignin in wall long and narrow
    8) Root Hair Living Increases area for absorption of water and minerals Extention of epidermal cell hair on tile shape cell
    9) Endodermis Living Controls  water and mineral entrance into the stele Casperian strip small and rectangular
    10) Pericycle living Origin of cork cambium, branch roots, & vascular cambium at end of xylem. small and rectangular

     

     

     

    1. Epidermis: For a study of root hairs, obtain a germinating seed of radish in which an extensive growth of root hairs have developed on the young primary root. Place he seedling in water in a watch glass. Be careful not to let the root hairs dry out.

      1. Observe the seedlings under a dissecting microscope. Note the root cap as well as the root hairs.

      2. Draw the radish seedling, labeling the regions of the root.

      3. Grasp the radish root with forceps above the region of root hairs and break off a portion of the root. Carefully place this in a drop of water on a slide. Care with a cover slip and observe under low power. Locate an area in the zone of root hairs where the root hairs are uninjured and can be easily examined. Study a single root hair.

      4. Draw one root hair.

      5. Questions: Answer under drawing.

        1. What is the origin of a root hair.

        2. Compare the epidermis of the root with that of a stem and show how each is adapted to carrying out it's particular function.

        3. What is the difference between a root hair and a hair-like (very small) root?

        4. How many cells are involved in a root hair?

        5. How many cells are in a hair-like root?

        6. Does every epidermal cell have a root hair?

    2. Primary meristems, regions, and tissues of the root?

      1. Remove slide 12 of the Allium root tip l.s. Locate the following and study under  the compound microscope.

      root cap apical meristem protoderm
      procambium ground meristem
      1. Diagram the Allium root tip. Label the tissues. Draw a few cells of each primary meristems showing the relative size.

      2. Questions

        1. What is the function of the apical meristem?

        2. What is the function of the root cap?

        3. How does the root apex differ from teh shoot apex?

    3. Remove the slide 13 of the Ranuniculus root c.s. from the slide box.

      1. Study under the compound microscope and identify the following tissues and cells.

        epidermis fibers cortex endodermis
        pericycle phloem xylem parenchyma
        starch grains sieve elements companion cell vascular cambium
        vessels tracheids
  1. Make an outline drawing of the root and label the various tissues. 
  2. Draw and label a narrow strip of enlarged cells extending from the outside of the root to the center. A break in the cortex is permissible for condensation.
  3. Questions
    1. Compare the structure of the cortex in the root with that in the stem.
    2. What function does a young stem perform that young roots do not?
    3. Name the tissues through which water  pass from the epidermis to the xylem in the root.
    4. How do branch roots develop?
    5. What supports the roots which have little mechanical tissue such as schlerenchyma?
    6. What is the position of the oldest primary xylem in the root?
    7. In the root, what is the function of the following :  epidermis, cortex, endodermis, pericycle, phloem, and xylem?
    8. Contrast the relative position of primary xylem and phloem in the root and stem.

LEAVES

Leaves vary considerably in form, margin shapes, venation, and in many other ways. Close observation r4veals that the leaves of plants are quit individualistic and are good to use in identifying plants. These variations influence their function. The blade provides an absorbing surface, both for gases and sunlight. The epidermis provides protection and inhibits water loss. The stomates can be opened or closed to facilitate gas exchange and prevent water loss. The same type of conducting tissues provide the translocation of materials in, through, and out of the leaf.

  1. External Leaf Morphology of Angiosperms

    1. Angiosperm leaves

      1. Dicot leaves
        The leaves of dicotyledons show a large range of external characteristics. These variation exists in the venation, margin, shape degree of lobing, tip of blade, base of blade, size, etc. Study the leaf examples that are on demonstration and learn their components.

        1. Simple leaves  -   blad is one uit

          1. petiole

          2. blade

          3. pinnately netted veined

          4. palmately netted veined

        2. Compound leaves - blade difided to the midrib into several units.

          1. petiole

          2. rachis

          3. pinna

          4. pinnule (if bipinnately compound)

        3. Leaf variations - Some of the following leaf variations may not be on demonstration.

          1. Sessile leaves - no petiole is present

          2. Peltate leaves - have a roundish blade with the petiole attached at the middle of the underside. Natturtium is an example.

          3. Perfoliate leaves - The stem appears to have grown upward through the blade. Miners lettuce is an example of Stipulate leaf - Stipules are usually small, green, leaf-like appendages that occur at the base of the petiole on some leaves, with one on either side. Peas have stipules.

        4. Leaf Margins

          1. Entire

          2. Serrate

          3. Dendate 

          4. Lobed

        5. Venation of Leaves - These terms usually apply to the major veins unless specifically stated that the term also applies to the minor veins. 

          1. Pinnate

          2. Palmate

          3. Netted  - The ends of the minor veins are jointed together. 

    2. Monocot Leaves
    1. Many monocots may be seen in our area, such as alms, banana, New Zealand flax, etc. You have already observed a common monocot leaf when you observe your corn plant. Know the following about grass (corn) leaves.
      1. blade with parallel veins
      2. sheath
      3. auricle: ear-like structure; in grasses, small projections that grow out
      4. ligule: in grass leaves, an outgrowth from the upper and inner side of the leaf blade where it joins the sheath.

3. Modifications of Leaves

  1. Tendrils, spines, suction cups, etc., may be modified leaves.

  2. Juvenile leaves, grow from young shoots, differ in shape from those produced on older branches.

  3. Isobilateral leaves, hang edgewise on the stem, are the same on both surfaces.

  4. Phylloid, a flattened petiole which appears as a blade.

  5. Other modifications, insectivorous leaves, storage leaves, etc.

B. Gymnosperm Leaves

1.   The leaves of all gymnosperms native to the U.S. and Europe, are needle like, or scale-like. In pines, the leaves are needle-like, two or more growing together in a group called a fascicle which is sheathed at the base.  In other native gymnosperms the leaves may be arranged singly.  The shape of the leaf, such as flat, angular, etc.,aids in identifying the species. In junipers, the leaves are of two pressed to the twig. Some gymnosperms that are native to other countries have fan-shaped leaves, i.e. Ginkgo Biloba.

  1. Study the gymnosperm leaves that are provided in the laboratory.  Be able to identify the leaves, fascicles (if they exist) on each specimen.

  1. Leaf Structure
    1. Epidermis:
      1. Obtain a Valerian sp. From the front table. Tear off a small segment of epidermis and place it on a clean microscope slide in DEIONIZED water.  Cover with a cover slip and study with the compound microscope.
      2. DRAW at least two cells of each type. Identify the guard cells and stomates.
      3. Obtain a leaf from the monocot provided. Remove the epidermis as described by the instructor. Place the epidermis in deionized water on a clean microscope slide. Cover with a cover slip and study with the compound microscope.
      4. Draw the guard cells and surrounding epidermal cells.
      5. Questions:
        1. Were the stomates on the monocots and dicots the same?
        2. Which epidermal cells contained chloroplasts?
        3. What is the function of the guard cells?
1) In palisade parenchyma located above the midvein?
2) What is the position of the xylem in relation to the phloem?
3) Are there as many stomates in the upper epidermis as in the lower?
  1. Cleared Leaf
Place a small portion of the cleared leaf on the microscope slide. Ocver and observe under low power. Select a region between the midrib and margin an # examine it for veins and vein endings. 
  1. VII. Observation of Fresh Material

Obtain one or more leaves that are provided on the front table. Make cross sections through the blade and petioles of each leaf.  Make a wet mount and study with the compound microscope. Determine if all leaves have the same anatomical structural:

Glossary

Angiosperm:  (Gr, Angion, a vessel+sperma: seed) [angi o sperm]:
A plant that produces flowers and fruits 
Apical Meristem: 
group of meristematic cells at the very tip of a shoot or root.
Bark: 
A nontechnical term applied to all tissues outside the vascular cambium.
Bordered Pit:
A pit in which the secondary cell wall overarches the pit membrane (primary cell wall).
Callose (L. callosus , callous) [kal’os]: 
A complex branched carbohydrate, which is a common wall constituent associated with sieve plates )see below). This may primarily develop in  response to injury.
Chlorenchyma (Gr. Chloros, green + enchyma, a suffix meaning tissue) [klo-reng-ki-ma] 
This term may be used to describe both a simple tissue and the cells in that tissue. This tissue consists of cells with chloroplasts. The cells in this tissue appear as parenchyma cells that contain chloroplasts. The cells are living at maturity and are physiologically adapted for photosynthesis.
Companion Cells: 
A specialized cell that is associated with sieve tube elements. There cells have the general appearance of parenchyma. The cells are living at maturity and are physiologically adapted for controlling sieve element function.
Cork:
A secondary tissue produced by the cork cambium (phellogen). This tissue is composed of phellem cells that are dead at maturity. The cork cell walls are infiltrated with suberin, a waxy or fatty material resistant to the passage of gases and water vapor.  The cork is the outer part of the periderm. Cork is equivalent to phellem.
Cork Cambium:
The lateral meristem that forms the periderm, producing cork (phellem) towards  the surface of the plant and phelloderm towards the inside. This cambium is found in both roots and stems. Cork cambium is often called the phellogen.
Cortex: L. cortex, bark)
The primary tissue of a stem or root bounded externally by the epidermis and internallly in the stem by the phloem and in the root by the pericycle.
Dicotyledon [di kot I le dun]
One of the two classes of Angiosperms, often abbreviated as dicots. Dicots have an embryo with two cotyledons.
Epidermis (Gr. Epi, upon + derma, skin) : 
The outermost layer of cells of leaves, young stems, and young roots.  The epidermis is absent from the root cap and is not differentiated on the apical meristem. These cells are living at  maturity and provided protection and prevent gas exchange.
Facicular Cambium
The cambium within the vascular bundles. These cells are meristemic, producing cells that differentiate into secondary phloem and secondary xylem.
Fiber (L. fibra, a filament or fiber)
An elongated, tapering think-walled schlerechyma cell occurring in various parts of the plant. The secondary cell wall generally contains lignin and is thicked to provide mechanical support. The cells are generally dead at maturity.
Ground Meristem (Gr. Meristas, divisible) :
A primary meristem which gives rise to cortex, pith and pith rays.
Ground tissue: 
All tissues other than the epidermis (or periderm) and the vascular tissues. This is also called fundamental tissue.
Growth Ring: 
A growth layer in secondary xylem formed by alternating spring and summer wood.
Gymnosperm (Gr. Gymno, naked +sperma, seed) [jim no soerm] : 
A plant that produces seeds in cones. The seeds are not surrounded by a fruit; thus, they are naked
Heartwood:  
Non-living, darl-colored wood that is used for storage commonly found in the center of roots and stems. (see sapwood)
Intercalary Meristem (L. intercalare, to insert) [in tur-kaler I]
A meristem that is found in the nodes of certain planats, such as grass. This is a primary meristem that increases shoot length
Interfascular Region:
This is also called the pith ray or medullary ray.
Lateral Meristems:
The meristems that provide the cells for secondary growth. These are the vascular cambium and cork cambium (phllem). Lateral meristems are also called secondary meristems.
Medulla: 
The ground tissue located in the center of stems.
Medullary Ray:
See definition of Interfascicular region
Meristenatic Region: 
Region of apex where cells are undergoing mitosis and cytokinesis.
Monocotyledon [mon o kot I ledon] 
A member of one of the two classes of Angiosperms often abbreviated as monocots. Monocots have an embrto with one cotyledon.
Parenchyma (Gr. Paren , beside, +en. In+chein, to pour) [pa-reng ‘k ma]
A simple tissue composed of parenchyma cells. The parenchyma cells are living at maturity, have thin walls ans often fit loosely together, leaving intercellular spaces. These cells come in various sizes and forms and carry out many physiological activities.
Peri.derm
Outer tissue that replaces epidermis when it is destroyed in secondary growth. This tissie provides protection when epidermis is no longer functional. It included the cork (phellem), cork cambium (phellogen), and the phelloderm.
Phellem :
See cork
Phelloderm (Gr. Phellos, cork + derma, skin) [fel’o derm]
A tissue formed inwardly by the cork cambium. This tissue makes up the inner part of the periderm.
Phellogen (Gr. Phellos, cork + genesis, birth) [fel-lo-gen] :
See cork cambium
Phloem Ray:
Parenchyma cells running across the phloem with the long axis of each cell oriented from vascular cambium to outer edge of stem.  These cells are adapted for lateral transport across the phloem.
Pith:
See medulla.
Pith Ray:
See medulla ray.
Pits
A recess or cavity in a cell wall where the secondary wall does not develop
Plasmodesmata (Gr. Plasma, something formed + desmos, a bond, a band) [plas mo des ma-ta]
The tiny cytoplasmic threads that extend through openings in cell walls and connect the protoplasts of adjacent cells.
Primary growth: 
The growth in plants that occurs in the apical meristems of roots and shoots, as contrasted with cambiums. This growth increases the length of the plant in the vertical axis.
Primary Meristem or Meristamatic Tissue [mer I-ste-mat-ik]
A tissue derived from the apical meristem which consists of three types; 1) protoderm, 2) procambium, and 3) ground meristem.
Primary Phloem (Gr. Phloos, bark) [flo em] :
A tissue that conducts organic substances (food) consisting of sieve tubes with companion cells (companion cells may be lacking as in Gymnosperms), parenchyma, and fibers.  This tissue develops from the procambium.
Primary Plant Body:
The part of the plant that develops from the apical meristems and is composed entirely of primary tissues. Non-woody plants are usually composed of primary tissue
Primary Tissues: 
Cells derived from the apical and primary meristems of root and shoot.
Primary xylem (Gr. Xylon, wood) [zi’lem]: 
A plant tissue that conducts water and minerals, consisting of vessels (vessels may be lacking as in Gymnosperms), tracheids, fibers, and parenchyma.
Procambium (L.pro, before + cambium one of the alimentary meristem body fluids supposed to nourish the body organs) [pro kami um]: 
A primary meristem that differentiates into the primary vascular tissues (primary phloem and primary xylem) and into the fascicular cambium.
Protoderm (Gr. Protos , first + derma, skin)
A primary meristem that gives rise to the epidermis
Radical Section:
A longitudinal section cut parallel with the radius of a stem or root.  This cut is parallel with the xylem rays and passes through the pith.