Germinating pea (Pisum sativum) seed. The majority of the seed consists of a store of starch, which provides the embryo with energy. The radicle (cream), the primary root, has emerged and is growing downwards. It is covered in tiny hairs that greatly increase its surface area for the uptake of water and nutrients. The leaf shoot (green) grows towards the surface. Germination may be triggered by humidity, temperature or other factors.