How do trees decide when and where their branches grow?
In: Biology
Plants are not actually inanimate objects, they just move very slowly and don’t have the kind of brain that can make particularly complicated decisions.
Plants are able to communicate with each other. There’s a variety of acacia tree that can produce poison (tannins), but it’s expensive to make, so it doesn’t normally create much of it. But if an enemy starts to prey on one, the tree will release a smell that makes the rest of the acacia trees around know that shit just got real and they’ll all arm themselves with tannin for the entire area, a pretty good way to get animals to eat something else. It’s even more interesting because a human can break a branch off the tree without causing the “we’re being eaten” alert to go out like it does when an animal starts munching its leaves. The poison isn’t just a blind response to any and all damage, but only to things that seem like an animal eating the tree. And communicating saves the trees from all having to produce the poison constantly which would cost them energy.
There are other plants that have teamed up with parasitic wasps. When a caterpillar (the wasp’s food) starts to eat the plant, the plant releases a special smell that shouts “wasp dinner time” and the wasp comes over and ganks the caterpillars for it.
Even mushrooms are in on the intelligence and communication, Leafcutter ants actually communicate with their mushroom farm partners. If the ants bring back a poisonous plant the fungus can’t tolerate, the fungus tells the ants to toss that crap away and the ants will get rid of the poisonous plant for them. Win-win for everybody.
There’s a plant called a *touch-me-not* that curls up the leaves when bothered. People guessed it was just an automatic thoughtless reaction. An experimenter dropped 56 of them from a certain height and they all curled up. After a few more drops, less of them bothered curling up. After a while doing these safe drops, they all stopped curling up for the drop completely. But they still would curl up if poked with a stick or something other than dropping them, so they’d learned that specific thing (dropping) could be ignored. The plants remembered this info for a full month from when taught (some insects like bees forget info after only a few days)
As for deciding where branches would be placed best, plants use different tools to decide the right conditions than we would. Plants have as many as 11 different photoreceptors (light sensors), while the human eye has only 4 kinds of them, so plants can actually analyze sunlight in more complexity than we can. It’s like our astronomers use different telescopes to look at things in space in ultraviolet or infrared or other kinds of light we can’t see with the naked eye, plants do the same thing in a way. It might be useful for moving their growing branches to the optimal spot for their green food-factories to get the ideal amount of the right colors of light they need to eat (even something like light that’s the wrong color can mean worse eating for a plant. Humans care less about color because we don’t eat it with photosynthesis. The reason brown algae and a lot of aquatic plants are brown instead of green is because they use a brown dye to eat better underwater because light bends different down there, so being pure green like a tree would actually produce less food)
The mechanism for plant limbs to go to their best spots is also interesting. There are climbing vines that as they spread, they basically rub their fingertips along the walls and feel different features, then they do things like coil around supports, find certain plants they like to stay tied to and wrap around those plants, move towards the best light sources, etc. Researchers cut the fingertips off of those vines, and after that the vines still grew, but they did it in a much more stupid way, just moving in basically straight lines and not finding the good climb holds and not placing themselves well. It was like the “brains” in charge of the movement activity were in the plant’s fingertips and not the the rest of the vine’s body. I don’t know if ordinary tree branches have the same branch-intelligence in their fingertips, it wouldn’t surprise me if they did, they’d have millions of years to work on it.
Latest Answers