Root "sniffing" for the edge of a barrier in the soil - now with lateral roots and root hairs!

This nicely shows a primary root of Arabidopsis (mouse ear cress) encountering an obstacle to its growth (in this case a strategically placed glass slide. The root bends off sideways looking for the edge of the barrier. You can see root hairs forming as the root grows and then if you wait long enough, lateral roots emerge from the bends in the main root. One lateral root even starts its own journey to find the edge of the obstacle. Time lapsed over ~24h.

For research into this response see: Massa and Gilroy (2003) The Plant Journal 33: 345-445