GaN nanowires with vastly different morphologies depending upon the growth direction are produced by direct nitridation and vapor transport of Gain disassociated ammonia. Nanowires grown homoepitaxially along the c-direction develop hexagonal-prism island morphologies (see Figure, left, and Cover), while wires grown along the a-direction form uniform, belt-shaped morphologies (Figure, right). A "ballistic" transport phenomenon for adatoms is proposed to explain the observed prismatic island morphologies.