Definition - What does Hypocotyl mean?
A hypocotyl is a germinating seedling’s stem, normally found underneath the seed leaves but above the root. This leaf-like structure tends to grow in response to light stimulation. Because the hypocotyl is the main extension organ, it gradually develops into the stem as the plant continues to grow.
MaximumYield explains Hypocotyl
Plant embryos push up a radicle during germination and this becomes the main root soon after. The hypocotyl only emerges after the radicle appears and encourages the seedling to lift its growing tip out of the soil and above the ground, consequently marking the appearance of the very first leaves.
The rate at which the hypocotyl grows is controlled by photomorphogenesis.
In plants such as Gloxinia and Cyclamen, the hypocotyl swells up to accommodate food and nutrients. In some plant species such as sunflowers and beans, the hypocotyl can grow for several inches above ground level.