Germination

Diagrams and pictures


Fully imbibed grain just before the embryo emerges. After planting the grain quickly takes up water and the chemical processes of germination start.
Two days after imbibition and the embryonic axis has broken through the testa. The first structures to be seen are the coleoptile, which protects the shoot, and the root (radicle). The root has broken through its protective sheath, the coleorhiza.
The grain with the embryo dissected away from the endosperm. The structure between the endosperm and the embryo is the scutellum; it transfers nutrients from the endosperm to the embryo during germination. When millers separate the embryo from the endosperm they call it the wheat 'germ'. The embryo contains fats and proteins which may limit the keeping quality of the flour.
Simple diagram of the dry grain showing its principle parts; the endosperm, aleurone and seed coat, the scutellum and the embryo with its primordial shoot and root. During grain milling these tissues are crudely separated: the endosperm becomes the white flour, the embryo is the germ and the aleurone layer and the seed coat are the bran. The seed coat is a complex structure. The Cell Layers inside the Grain are described in detail in a separate section.
The imbibed grain, split open along its long axis, shows the embryo in close contact, via the scutellum, with the stored reserves of the endosperm. The internal processes of germination are well under way. Several hydrolytic enzymes are activated to perform specific tasks. The cell walls of the endosperm are broken down, the starch and storage proteins they contain are degraded and released, and the aleurone and embryo are activated ready for growth.
Germinating wheat grains at two, three and four days after imbibition. The coleoptile is adapted to thrust its way through the soil to find the surface. The seedling roots quickly anchor the grain in the soil. The fine root hairs absorb water and nutrients from the soil supplementing the stored reserves from the endosperm.