A stem internode (PO:0020142) that is the part of a plant embryo axis (PO:0019018) or a seedling stem (PO:0009047) above the scutellum (PO:0020110) and below the coleoptile (PO:0020033). [source: ISBN:0471244554, POC:Laurel_Cooper]
Comment
Occurs in grasses. In grasses, the hypocotyl and cotyledon may not be visible and may be represented by the scutellar node and scutellum, making the mesocotyl similar to the epicotyl in other taxa. Elongation of the mesocotyl during seedling growth pushes the coleoptile above the soil surface.