Dubrovsky J. G., North G. B., Nobel P. S., Root growth, developmental changes in the apex, and hydraulic conductivity for Opuntia ficus-indica during drought, New Phytologist, 1998, 138(1):75-82, doi: 10.1046/j.1469-8137.1998.00884.x
The experiment compares root responses to rapid and gradual vermiculite drying. It also covers changes after rehydration.