coleoptilewhich grows beside it and forms a kind of sheath enclosing the shoot
apex (Fig. 2). A similar sheath appears over the root apex.
On germination, the cotyledons may remain in the seed and wither away as
the nutrients pass to the developing shoot, known as hypogealgermination, or
they may emerge as the first photosynthetic organs, known as epigeal(Fig. 3).
They normally have a simple form, quite different from the typical foliage leaf
and wither soon after the first foliage leaves have formed. In a few plants they
persist.D3 – The seed 51
Cotyledon ScutellumColeoptile
Shoot apexSuspensorNotch
(shoot apex)Suspensor(a) (b)Cotyledons
remain
in seedShootRootRootCotyledonYoung shoot1 cm 1 cm(a) (b)Fig. 3. Seed germination: (a) hypogeal in the bean, Fabasp.; (b) epigeal in Arabidopsis.
Fig. 2. Embryos of monocotyledons: (a) onion, Allium; (b) a grass.