Germinating wheat grain. Coloured scanning electron micrograph (SEM) of a germinating grain of wheat (Triticum sp.). The majority of the seed comprises a store of starch surrounded by a seed coat (yellow). This starch provides the embryo plant with the necessary energy for germination. Germination may be triggered by humidity, temperature or other factors. A root radicle (lower left) emerges from the seed coat and begins to grow down into the soil. The leaf shoot (green) that grows to the surface is surrounded by a protective sheath called the coleoptile. Wheat is an important food crop. Magnification: x17 when printed 10cm wide.