Germinating seed. Image 3 of 4. Coloured scanning electron micrograph (SEM) of a late stage in the germination of a plant seed. The radicle (white), the embryonic root, is growing downwards in a response to gravity that is called geotropism. The root 'hairs' increase the ability of the root to obtain water and nutrients from its surroundings. The seed coat (testa, brown) is more fully split to reveal the embryonic shoot (plumule) and its seed leaves (cotyledons, green). Eventually the leaves will photosynthesise while the root gathers nutrients from the soil. This is a swede (Brassica napus) seed. For a sequence of seed germination, see images B787/394-397 and B787/398.