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– **Eudicots**:
Plant embryo grows at germination
– Shoot called radicle becomes primary root
Hypocotyl emerges and lifts growing tip above ground
– Bears embryonic leaves (cotyledons) and plumule
Hypocotyl develops into stem

– **Monocots**:
Coleoptile protects young stem and plumule
– Mesocotyl extends shoot up to soil surface
– Secondary roots develop beneath plumule
– Primary root from radicle may not further develop
Onion develops similarly to grasses

– **Storage Organ**:
Hypocotyl enlarges as storage organ in some plants
– Examples: cyclamen, gloxinia, celeriac
– In cyclamen, storage organ is called tuber

– **Hypocotyl Elongation Assay**:
– Widely used in photobiology field
– Studies effects of light changes on hypocotyl elongation
– Investigates growth effects of plant hormones like ethylene
– Under normal light, growth controlled by photomorphogenesis
– Darkness-mediated skotomorphogenesis leads to highest growth rate

– **See Also**:

Hypocotyl (Wikipedia)

The hypocotyl (short for "hypocotyledonous stem", meaning "below seed leaf") is the stem of a germinating seedling, found below the cotyledons (seed leaves) and above the radicle (root).

Diagram of Scouler's willow (Salix scouleriana) seed, indicating position of hypocotyl.
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