There are three main factors that affect root and shoot growth, which are light (phototropism), gravity (geotropism) and water (hydrotropism).Both roots and shoots show positive tropism whereby growth is shown towards the stimulus whilst negative indicates growth away from the stimulus. Shoots grow upwards and therefore shows positive phototropism and negative geotropism. However, roots grow downwards and show negative phototropism, positive geotropism and positive hydrotropism.