Nocturnal and diurnal root velocity. (a) Average root velocity over the nocturnal and diurnal period. (b) Normalised root velocity in the nocturnal and diurnal period. The velocity was normalised to the daily total (nocturnal + diurnal = 100%). n = 3 for the control treatment, n = 4 for the root cooling and illumination treatments. Error bars are S.E.