Hypocotyl

Hypocotyl

Seeds of Salix scouleriana showing the hypocotyl

The hypocotyl is a crucial part of a plant embryo, located between the cotyledons and the radicle. It plays a significant role during the early stages of plant development, particularly during germination.

Structure

The hypocotyl is the stem-like part of the seedling that emerges during germination. It is situated below the cotyledons, which are the first leaves of the plant, and above the radicle, which is the embryonic root. The hypocotyl is responsible for pushing the cotyledons above the soil surface in a process known as "epigeal germination."

Function

During germination, the hypocotyl elongates and lifts the cotyledons above the ground. This is essential for the young plant to begin photosynthesis, as the cotyledons often contain chlorophyll and can perform photosynthesis until the true leaves develop. The elongation of the hypocotyl is driven by cell division and expansion, influenced by environmental factors such as light and temperature.

Types of Germination

The role of the hypocotyl varies depending on the type of germination:

• Epigeal Germination: In this type, the hypocotyl elongates and raises the cotyledons above the soil. This is common in plants like beans and sunflowers.
• Hypogeal Germination: Here, the hypocotyl does not elongate significantly, and the cotyledons remain below the soil surface. This occurs in plants such as peas and corn.

Importance in Plant Development

The hypocotyl is vital for the initial establishment of the seedling. It not only aids in positioning the cotyledons for optimal light exposure but also serves as a storage organ for nutrients that support early growth. Additionally, the hypocotyl can become part of the mature stem in some plant species.

Related Pages

• Cotyledon
• Radicle
• Germination
• Seedling