Botany - B.Ye. Yakubenko 2017

Part Three. The Plant Kingdom (Plantae)
Chapter IX. Division Angiosperms, or Flowering Plants (Angiospermae, Magnoliophyta)
Laboratory Class. Topic 14.41. Structure of Dicotyledonous Seeds

General Remarks. Seeds of dicotyledonous plants possess specific structural features. In dicots, nutrient reserves are stored in the embryonic cotyledons, endosperm, or perisperm. Typically, the seed coat is free and does not fuse with the pericarp.

Objects:

1. Common bean seed (Phaseolus vulgaris L.)

2. Pedunculate oak acorn (Quercus robur L.)

Tasks:

1. Examine and study The Structure of the non-endospermic seed in the common bean.

2. Examine and study the STRUCTURE OF THE non-endospermic seed in the pedunculate oak.

3. Make a drawing of the non-endospermic seed and label its component parts.

Equipment and Materials: MBR-1 or Biolam microscopes, magnifying glasses, scalpels, razor blades, forceps, fresh or fixed material of bean seeds or oak acorns, and other accessories.

Macroscopic study of a non-endospermic seed in an herbaceous plant. We will study the structure of a non-endospermic seed in herbaceous plants using the bean seed as an example. First, examine and study the general appearance of the bean seed. Unlike the cereal seeds considered previously, the structure of a dicot seed clearly reveals two main structural parts: the seed coat and the embryo. Upon close observation, a small bump can be seen at the upper end of the seed. Pressing on it causes a droplet of liquid to exude (in fixed seeds). This feature represents the micropyle. Just below it, a broader white hilum is visible—the scar where the seed was attached to the pod Valves.

To observe and study the embryo, cut and peel off the seed coat, or tear it and gently fold it away from the embryo. Open the embryo along the cleft between the two cotyledons and draw it in detail at a larger scale. As you can see, the embryo consists of two Kidney-shaped cotyledons (Fig. 109).

On one of them, near the upper end, a well-developed seedling is clearly visible. It features a differentiated radicle, hypocotyl, and embryonic leaves that shield the apical bud. In your lab notebook, draw the general view of the seed and a separate drawing of the embryo, labeling all the named components.

Macroscopic study of a non-endospermic seed in a woody plant. We will study the structure of a non-endospermic seed in woody plants using the pedunculate oak acorn as an example. First, examine and sketch the external appearance of the acorn. To inspect the structure of the oak seed, remove the cupule using a scalpel. Make a surface cut on the fruit and remove the pericarp; the seed lies directly beneath it. It consists of a seed coat and an embryo. Just like in the bean, the embryo possesses two massive nutrient-storing cotyledons, among other parts. One of them bears a young seedling structurally similar to that of the bean.

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Fig. 109. Structure of a non-endospermic seed:

a — general view of a bean seed; b — embryo of a non-endospermic seed:

1 — bud; 2 — embryonic leaves; 3 — hypocotyl; 4 — radicle; 5 — cotyledons

Draw a germinated oak seed and label: the seed coat, cotyledons, hypocotyl, bud, radicle, lateral roots, and hypocotyl axis.

Conclusion. A non-endospermic seed consists of the embryo and the seed coat. Nutrients are stored directly within the embryo, specifically in the cotyledons.

Self-Check Questions

1. From which part of the Ovary does the seed develop?

2. In which part of the bean seed are nutrients stored?

3. From which part of the ovary does the pericarp form?

4. From which part of the ovule does the seed coat develop?

5. What is the chromosome set of the embryo Cells?

6. Does the oak seedling push its cotyledons above the soil surface?

7. Does the common bean seedling push its cotyledons above the soil surface?