Epigeal and hypogeal germination are two types of seed germination processes that differ primarily in the behavior of the seed cotyledons (seed leaves) and the development of the seedling.
Epigeal Germination
- Definition: In epigeal germination, the cotyledons are lifted above the ground during the germination process.
- Process:
- The seed absorbs water and the embryo begins to grow.
- The hypocotyl (the stem beneath the cotyledons) elongates, pushing the cotyledons above the soil surface.
- The cotyledons unfold and may function to photosynthesize for a brief period until true leaves develop.
- Examples: Common plants exhibiting epigeal germination include beans (Phaseolus spp.) and sunflower (Helianthus annuus).
Hypogeal Germination
- Definition: In hypogeal germination, the cotyledons remain below the ground as the seed germinates.
- Process:
- The seed absorbs water, and the embryo begins to grow.
- The epicotyl (the stem above the cotyledons) elongates, pushing the shoot upward while the cotyledons stay buried in the soil.
- The cotyledons often serve primarily as a nutrient source and may not contribute to photosynthesis.
- Examples: Plants that undergo hypogeal germination include peas (Pisum sativum) and corn (Zea mays).
Summary
- Epigeal Germination: Cotyledons emerge above ground; associated with a longer hypocotyl.
- Hypogeal Germination: Cotyledons remain underground; associated with a longer epicotyl.
These different strategies can help plants adapt to their environments and optimize their chances of survival and growth.