Why does it grow in the observed way ?

Crystal growth has been all the time an intriguing but complicated problem. The macroscopic shape depends in a subtle way on several factors, such as the properties of the surroundings. Indebted to the increasing power of computers, physicists are enabled to simulate a real growth. On the other hand, experiments also provide important insights. "Despite the many parameters involved, theorists have predicted that icicles, as well as other natural features like stalactites, should all converge to the same shape as they grow. In a paper appearing in Physical Review E, Antony Chen and Stephen Morris at the University of Toronto, Canada, describe an experimental setup that allows them to image icicles as they grow under controlled conditions, and test these predictions. They mounted a camera through a slot in the side of a refrigerator, within which icicles formed as water dripped from a nozzle and onto a rotating wooden support. Rotating the support helps even out the effects of drafts and temperature gradients." [http://physics.aps.org/synopsis-for/10.1103/PhysRevE.83.026307]