GFP labelled B. subtilis 3610 (NRS1473, green) exhibiting crowd movement around a timothy grass root (Phleum pratense, red) growing in transparent soil saturated with water (1 mPa s-1). Filamentous flocks show the persistent, diffuse and less branched morphology associated with non-viscous solutions. Images were collected at 30-minute intervals using a 2X objective. Time lapse covers a 10 hour period.