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?

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    $\begingroup$ I answered this in some detail in response to another question... biology.stackexchange.com/a/2646/430 $\endgroup$ – Rik Smith-Unna Aug 26 '12 at 22:55
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    $\begingroup$ Related topics: auxins, apical dominance. $\endgroup$ – Mechanical snail Sep 16 '12 at 4:04
  • $\begingroup$ Great answer Richard. Upvoted. You refer to a chaotic process that determines new areas of auxin concentration between meristems as the plant grows, so I guess the simplest answer to my question is "chance, within the confines of a system". There doesn't appear to be any DNA-style central planning at work. $\endgroup$ – mblackwell8 Sep 19 '12 at 0:23