What is responsible for plants' branches having bends?

[animus]

Is it because of auxin? I was walking down the block before and wondering why, if plant growth is influenced by light, that the trees themselves (the trunk) weren't bent. Then I realized—duh, they kind of are; the branches are.

Is it auxin that causes the branches of trees to be bent and twisty? If so, why is the trunk (of most trees) perfectly straight?

[plasmodesmata11]

I would say yes, auxin is responsible for that. Furthermore, I would think that most tree trunks are straight because the sun is always moving, and therefore it isn't advantageous for what will later be the trunk to grow in any direction since the sun's location isn't fixed (and it wouldn't receive those signals if that were the case). Now if there are other large trees/ structures/formations around it that do make this the case, that is to say, they allow only a relatively small window of sunlight from one direction each day, then in that case a tree would probably grow towards it. Regulatory hormones besides auxins, like cytokinins and gibberellins, are also responsible, but for the purposes of this question I hope this answer shall suffice.

[JackBean]

They do not bend all over and over to the sun simply because they do not grow that quickly. But if you tried to grow something with artificial light on one side, you would see it's not growing straight up.

[animus]

Oooh. So the trunk is straight because the sun's movement doesn't really have enough of an impact to make it bend one way, but once the tree is large enough to have a network of branches, the whole shade thing comes into play and starts making them bend towards the source of sunlight?

Makes sense now; if I'm correct there. Hah. Thanks, both of you.