'Tis the season for nanometer-scale Christmas trees. Researchers from the University of Wisconsin–Madison stumbled onto these pine tree structures by accident as they were trying to shape lead sulfide into slender wires measuring about 100 nanometers (millionths of a millimeter) in thickness. Instead they discovered many nanowires branching from a central trunk like a spiral staircase. The nano–wise men say the structures must have arisen from a slight irregularity in the crystal structure of the growing trunks. The screwy finding, published online May 1 in Science, might offer a new route to complex nanostructures for prototype solar cells, biosensors, light-emitting diodes and lasers.