Epigeal

Epigeal (also spelled epigean, epigeic, or epigeous) refers to a type of seed germination in which the cotyledons (the first leaves of the seedling) are raised above the ground. This is in contrast to hypogeal germination, where the cotyledons remain below the ground. Epigeal germination is common in many plant species, including beans, sunflowers, and cucumbers.

Process of Epigeal Germination

During epigeal germination, the seed absorbs water and swells, causing the seed coat to break. The radicle (the embryonic root) emerges first and grows downward into the soil, anchoring the plant and absorbing water and nutrients. The hypocotyl (the stem-like part of the seedling below the cotyledons) elongates and pushes the cotyledons above the soil surface. Once above ground, the cotyledons open and begin photosynthesis, providing energy for the growing seedling until the true leaves develop.

Advantages and Disadvantages

Epigeal germination has several advantages:

• The cotyledons can perform photosynthesis, providing additional energy to the seedling.
• The seedling can grow more rapidly due to the additional energy from photosynthesis.

However, there are also disadvantages:

• The cotyledons are exposed to herbivores and environmental stressors, such as frost and drought.
• The seedling may be more vulnerable to damage if the hypocotyl is injured.

Examples of Epigeal Germination

Several plant species exhibit epigeal germination, including:

• Phaseolus vulgaris (common bean)
• Helianthus annuus (sunflower)
• Cucumis sativus (cucumber)

Comparison with Hypogeal Germination

In contrast to epigeal germination, hypogeal germination involves the cotyledons remaining below the soil surface. This type of germination is seen in plants such as peas and corn. Hypogeal germination provides some protection to the cotyledons but does not allow them to contribute to photosynthesis.

Related Pages

• Seed germination
• Cotyledon
• Hypogeal germination
• Photosynthesis
• Radicle
• Hypocotyl