The growth of water trees that lead to breakdown in polyethylene insulation of underground power cables is studied in real time, using a special observation cell for polyethylene that can be placed on the stage of a conventional microscope. The growth of the water tree was followed by time-lapse photography. Sample results are given. The water tree is shown to grow from a single streamer to a bushlike structure. This structure acts as an electrode, and the cycle repeats, with another streamer being sent out. >