I realize this may be a completely stupid question, but I think my husband, who is an engineer, is playing a joke on me. He says that the magnetic field from power lines will prevent a tree from growing into power lines, and that the branches will actually grow around and away from the lines, avoiding them all together. I say this is not true, because I've seen work crews out cutting branches around power lines. Is he playing a joke on me, or is this a true phenomenon, and if so, can you please provide scientific basis for your explanation?