Hypocotyl

hypocotyl
The part of a seedling stem that is between the soil line and the cotyledon leaves.
hypogeal ...

Hypocotyl- The part of an embryo or seedling below the cotyledon(s) and above the radicle (but sometimes including it).
Hypogeal- Describes seed germination in which the colytedons remain beneath the surface of the soil. (Cf Epigeal).

hypocotyl. The portion of an embryo or seedling between the cotyledons and the developing root tip.
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Index ...

hypocotyl The first leaf-like structure that appears on a germinating seed. Grows upward in response to light.
hypogeous germination Seed germination in which the cotyledons remain below the soil surface.

Hidden inside that coat is the radicle or beginning of a root, the hypocotyl or beginning of a shoot, either one or two seed leaves or cotyledons (the seed's food supply), and the epicotyl, which will become the first true leaves.

Plant tubers (actually enlarged hypocotyls) in late summer or early fall.
Germination temperature: 45 F to 55 F ...

See also: Flower, Plant, Bulb, Tuberous root, Tuberous