Our knowledge of how plant roots respond to stress is based largely on indirect data. Scientists didn’t have a good way to see through soil. A team overcame that problem. They used neutron imaging. They measured water moving through the soil and being taken up by individual poplar seedling roots after a drought. Smaller diameter roots took up more water (per unit surface area) than bigger roots. Neutron imaging is used to measure soil water movement and water uptake by individual roots in situ.