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Hypocotyl of a Jeffrey jaw

Hypocotyl ( Greek hypo "below" and kotyle "cavity"; English hypocotyl ), also germ stalk or germ axis , is a technical term in botany and describes the lowest section of the stem axis of a seed plant from the root neck (this is the border zone between root and stem axis) up to the cotyledons (germ layers).

The next higher section of the stem axis between the cotyledons and the primary leaf or the primary leaves is the epicotyledon .

Thickening of the hypocotyl

A thickened hypocotyl is called a hypocotyl tuber , which, like other tubers, is used to store reserve substances. Examples of species are radishes or beetroot .

Storage organ

In a few plant species, nutrients or reserve substances are stored in the hypocotyl, in the embryo . This thickened storage hypocotyl then serves as a nutrient reserve for the seed during germination , as in the case of the Brazil nut .