As a plant grows, at some point the first branch forms. As it continues, branches grow new branches, and so on, in a seemingly random way. Is it random, or is it driven by the environment (heat or cold, sunshine, wind)? Or is it somehow defined in the plant's DNA, that each branch will grow at in such and such a direction, at such and such a time?
Does this generalize down to successively smaller branches, and eventually leaves?