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I checked up on branching last night and here's what I took away from
it:
Shoot growth occurs in the apical meristem and this tissue is flanked by
microscopic leaf primordia. One or both of the primordia will become a
leaf at a node while the meristem continues to grow away from the node.
The leaf branching pattern is species specific - the leaves at
successive nodes will be in planes that are at a predictable angle to
each other. Auxiliary buds form in the leaf axils, but will not
necessarily begin to grow into a branch due to apical dominance - their
growth is inhibited by the hormonal influence of the apical meristem.
The shoot apex is a source of the plant hormone auxin. Auxin has been
shown to inhibit the growth of the auxiliary buds in shoots where the
apical meristem has been removed, when applied exogenously. According
to the plant physiology text I have, just how the auxilliary buds are
released from apical dominance is not clear. Cytocynin, another plant
hormone, and auxin are mutual antagonists - they exert an inhibitory
effect on each other. It's thought that cytocynin might have something
to do with inhibiting apical dominance. It was also mentioned that both
ethylene and absisic acid, other important plant hormones, may play a
role in various ways.
That's my basic understanding of it though there is much, much more to
it. Maybe Tom Kimmerer could shed some light on this.
CF
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