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). The radicle (grey), the primary root, emerges through the micropyle (light yellow) and grows down into the soil. It is covered in tiny hairs that greatly increase the surface area of the root for uptake of water and nutrients. The leaf shoot (green), which is covered by a protective sheath (coleoptile), grows towards the surface. Germination may be triggered by humidity, temperature or other factors. Magnification: x15 at 10 centimetres wide.