Germinating wheat grain. Coloured scanning electron micrograph (SEM) of the root radicle of a germinating grain of wheat (Triticum sp.). The radicle is the first part of the seedling to emerge during germination. It emerges through the micropyle (not seen) and grows down into the soil. Roots exhibit positive gravitropism, under the influence of hormones they grow towards the pull of gravity. Germination may be triggered by humidity, temperature or other factors. Root hairs (bottom) have grown on the radicle. These tiny hairs greatly increase the surface area of the root for uptake of water and nutrients. Magnification: x150 when printed at 10 centimetres wide.