l. This is the first internode above the cotyledonary
node (Fig. 1). In monocots, this internode is mostly very
short, so that the first plumular leaf is basally embraced
by the cotyledonary sheath or coleoptile.
hypocotyl. The hypocotyl is the shoot axis segment below
the cotyledonary node (Fig. 1). Usually, it is inconspicuous
except for the collar region. There is often an abrupt change
in diameter between the hypocotyl base and the slender
primary root, then the collar covers the flat base of the
hypocotyl. Seedlings occasionally have a well elongated
hypocotyl, even while growing in permanent light, e.g.
Tacca and some Juncaceae (Fig. 7H and L). In many aquatic
Alismatales the hypocotyl is the storage organ of the embryo
and therefore it is much enlarged, the ‘m