Germinating wheat grain. Coloured scanning electron micrograph (SEM) of a germinating grain of wheat (Triticum sp.). The majority of the seed consists of a store of starch, which provides the embryo with energy, surrounded by a seed coat (yellow). At centre is the micropyle (grey). The radicle, the primary root, will emerge from the micropyle first and grow down into the soil. The leaf shoot, which is covered by a protective sheath (coleoptile, green), will then grow towards the surface. Germination may be triggered by humidity, temperature or other factors. Magnification: x27 at 10 centimetres wide.