Germinating seed. Image 1 of 4. Coloured scanning electron micrograph (SEM) of one of the earliest stages of the germination of a plant seed. The radicle (white), the embryonic root, is beginning to emerge from the seed coat (testa, brown). This can be prompted by a number of things, including light, warmth and the presence of water. The rest of the embryonic plant is still inside the seed. Eventually, the embryonic shoot (plumule) will emerge and seed leaves (cotyledons) will begin to 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.