Botany - B.Ye. Yakubenko 2017

Part One. Plant Anatomy and Morphology
Chapter II. Histology
Laboratory Class Topic 4.7. Primary Dermal Tissue

General Remarks. When studying the primary dermal tissue, It is important to remember that There are two types: the epidermis and the epiblema (rhizodermis). They differ in their spatial arrangement, origin, and Functions. According to the histogen theory formulated by Schmidt, the SHOOT apex consists of the tunica and the corpus. The epidermis originates from the tunica of the shoot apical meristem and covers above-ground parts such as young shoots and leaves. Its Cells frequently contain METABOLISM/14.html">Chloroplasts, are covered externally by a cuticle, and in some plants, form various types of appendages in the form of hairs, scales, glands, and so on. The epidermis protects the plant from excessive Transpiration while not hindering The process of Photosynthesis. The epiblema is formed by the ROOT apical meristem, specifically the dermatogen. Epiblema cells lack chloroplasts; their Cell walls are not impregnated with a cuticle and form root hairs as outgrowths of the outer Cell wall, and they lack Stomata. The epiblema acts as an absorptive tissue due to the osmotic properties of its thin-walled cells and root hairs.

Objects of Study:

1. Leaf of zonal geranium (Pelargonium zonale (L.) Aït.)

2. Leaf of maize / corn (Zea mays L.)

Tasks:

1. Using a self-prepared slide of the geranium leaf epidermis, examine The Structure of the primary dermal tissue of a dicotyledonous plant. Under high microscopic magnification, draw a section of the epidermis with several stomata.

2. Using a self-prepared slide of a monocotyledonous plant epidermis from a corn leaf, observe, study, and draw the STRUCTURE OF THE epidermis under high microscopic magnification.

Equipment and Materials: MBR-1 or Biolam Microscope; fresh geranium leaves; fixed corn leaves; dissecting needles; Glass slides and cover slips; glass rods; filter paper; razor blades, charts; prepared slides, etc.

Procedure for preparing the geranium leaf epidermis slide. Place a glass slide transversely across a pencil case or stand, and apply a drop of Water onto it. Take a piece of a geranium leaf and peel off the epidermis from the lower side. To do this, tear the leaf from the edge to a depth of 0.5 cm away from the Veins, and by folding back one section of the leaf obliquely, strip off a piece of the epidermis measuring a few square millimeters. Place the stripped side down into the drop of water on the glass slide and cover it with a cover slip. Secure the slide with stage clips.

Microscopic examination of the slide. Under low magnification, locate a transparent area containing a glandular Hair (which is club-shaped with a brownish HEAD). Simple multicellular hairs are quite numerous and have pointed tips. Note that the guard Cells of the stomata are located at the junctions of 3–4 epidermal cells.

Under high magnification, study the structure of the epidermis and make a drawing showing: epidermal cells; glandular hairs; simple hairs; the substomatal air chamber; and the stoma (Fig. 27).

Procedure for preparing the corn leaf epidermis slide. Place a drop of water on a glass slide. Take a piece of a chopped corn leaf and bend it over the index finger of your left hand; very carefully make a shallow cut in the middle of the piece using a razor blade. With your right hand, take the incised piece of the epidermis and, pressing it against the main piece, tear it off. A thin, transparent area is clearly visible along the edges of the fragment. Place the stripped side down into the drop of water. Cut off the transparent area with a razor blade (about 1–2 mm wide) and cover it with a cover slip.

Microscopic examination of the slide. Under low magnification, find a thin area with a clear image, move it to the center of the field of view, and switch to high magnification.

The slide shows that the epidermal cells of the corn leaf have sinuous (wavy) walls. They can be elongated or shortened. The Cell walls, cytoplasm, nucleus in the shortened cells, and vacuoles occupying most of the cell are clearly visible. In some of them, separated by 2–3 rows of cells, regularly arranged rhomboid stomata of a unique structure characteristic of grasses can be seen.

Grass stomata possess two dumbbell-shaped guard cells. The thin-walled, vesicular-expanded ends contain chloroplasts. The guard cells are connected by their expanded parts, while the narrow part with a thick-walled, opaque middle region forms the stomatal pore. Two subsidiary triangular cells of the same length as the guard cells lie adjacent to them (Fig. 28).

Thoroughly study the structure of the corn epidermis. In your laboratory notebook, draw a section of the epidermal area and label the listed components.

Conclusions. 1. Two Types of primary living dermal tissue are known — the epidermis and the epiblema.

2. The primary dermal tissue covers the leaves and stems of monocotyledonous plants throughout their entire lifespan, whereas in dicotyledons it generally persists only during the growing season.

3. The leaf epidermis of monocots differs in structure from that of dicotyledonous plants.

4. The root tip in the root hair zone is covered by the epiblema.

Self-Assessment Questions

1. Why is the epidermis classified as a primary dermal tissue?

2. Why does the epidermis lack intercellular spaces?

3. How many cell layers does the epidermis consist of?

4. Which Organs are covered by the epidermis?

5. What parts make up a stomatal apparatus?

6. Name the Structural Features of guard cells in dicotyledonous plants.

7. How does the structure of stomata in monocotyledonous plants differ from that in dicots?

8. What additional structures enhance the protective function of the epidermis?

9. Could a stoma function if the epidermal cells lacked chloroplasts?

10. What are the epidermal derivatives?