General Question

NaturalMineralWater's avatar

What causes a branch to form in one spot instead of another on the trunk of a tree? (Or any plant for that matter)

Asked by NaturalMineralWater (11257 points ) August 29th, 2009

I was just looking at a plant outside that has massive, torso sized leaves on it and began to wonder.

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15 Answers

XOIIO's avatar

I think it’s whatever direction it’s get the most sunlight from. A plant needs light to make sugars, which help it to grow. damn I can’t remember what the process is called

La_chica_gomela's avatar

@XOIIO: photosynthesis?

NaturalMineralWater's avatar

Well i understand the photosynthesis but what I’m wondering is what makes the plant decide.. ok .. here is gonna be a branch.. and this part is just gonna be trunk.. lol

What is it? Plant genetics? XD

XOIIO's avatar

@la chica, thank you.

@naturalnineralwater I don’t think it “decides”, I think it’s just that where there us more photosynthesis happening a growth starts there, and continues so that it can get more light. Plants don’t think, they just do.

NaturalMineralWater's avatar

@XOIIO Obviously they aren’t conscious beings, but if it were only photosynthesis than plants would never form branches on the other side.. the shady side would they? If that’s all it is than wouldn’t trees have longer branches east to west from the rise and set of the sun?

I’m curious as to the makeup of the matter in that spot at the branches “conception”.

dpworkin's avatar

It depends upon the genetics of the plant, just the way your genes determine your morphology. Some plants seem to branch according to the Fibonacci series (qv).

NaturalMineralWater's avatar

@pdworkin I could have as easily asked why our arms and legs are formed where they are I suppose. I’m still waiting for someone to say “because God told it to do that”, or “that’s how God designed it”.

dpworkin's avatar

I’m sorry. There is no God or any other designer. It is all random, contingent, adventitious and Darwinian. Does that help? I know, it’s hard to stare into the void, but some people find it liberating.

Harp's avatar

Branching is determined by a complex interplay between genetics and the environment. The plant is genetically programmed to produce periodic nodes along its stem as it grows upward. In most plants, these are spaced according to a specific pattern encoded in the DNA.

These nodes are potential branches, but not all of them will necessarily develop, and here is where the environment plays a role. Growth requires precious energy, and the hormonal system of the plant will adjust to environmental factors to allocate that growth energy in a way that will maximize its future ability to gather light.

If there is not much light in the environment, the tip of the plant’s stem releases a hormone called auxin which inhibits the growth of the branch buds further down on the stem. This causes the plant’s growth to be concentrated up at the top of the stem, so that it goes upward instead of branching out laterally. This sustained upward growth may allow the plant to reach up above whatever has been shading it.

If there is an abundance of light in the environment, there’s plenty of energy to apply to growth in all directions. In this case, less auxin is produced by the tip so that more branches can deploy out laterally to grab that light.

Also, if the tip is damaged (as often occurs) it can no longer produce auxin, so the buds further down the stem are no longer inhibited and will be prompted to grow. This is why pruning shrubs encourages bushier growth.

NaturalMineralWater's avatar

@Harp Very interesting indeed. I could say something prosaic about light and life being linked in a religious sense, but that doesn’t coincide with the fact that cave crickets and lizards don’t seem to mind the dark one bit. That is unless we make some mundane comparison via yin and yang. (or simply mention pruning again)

There is something to be said for all this genetic programming. Who is the programmer? What is the programmer? We speak of programming (something which screams structure and design) as if all the ducks are in a row but then in the same breath claim it’s all “random” or “perchance”. I find that fascinating.

Harp's avatar

Well, I’d say there’s a difference between a program and a design. A program is a structure that determines a future sequence of events. There doesn’t have to be purpose, or a programmer, behind programming.

In terms of genetics, the structure of the DNA molecule is the program, but there’s no guarantee at all that the end result of that program will have the ability to survive in its environment. If a particular program survives, it replicates; if it doesn’t survive, then it simply disappears. What’s left after millions of years of running these programs are a few examples of programs that replicated well. We’ll never know about the many more programs that didn’t replicate well.

Our tendency to think of this process in terms of “success” and “failure” is unfounded. The process itself is indifferent to its results.

NaturalMineralWater's avatar

@Harp Well, I don’t personally buy it… but perhaps I was programmed not to.xD

Even in mathematics and programming languages things that are “random” tend to still have some sort of algorithm suggesting an inherent coding “scheme”. Granted this is coming from a far larger observation than just plant life.

XOIIO's avatar

You wouldn’t be programmed not to get it, that would imy that once you would have been programmed to get it. It would be easier to not give you any information on the subject.

NaturalMineralWater's avatar

@XOIIO Not sure I understand that statement. I definitely don’t know what a “imy” is. Oh.. I guess it’s “mean”.

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