Indoor plants tend to grow toward the light, so why do trees outdoors grow straight instead of leaning toward the equator?
—W. Anderson, Sacramento, Calif.
Edgar Spalding, a botany professor at the University of Wisconsin–Madison, sprouts off:
A plant on a windowsill experiences a stronger light gradient than does a tree outdoors, where gravitational cues can overpower more subtle light-direction cues. Indoor plants get a lot more light on one side than on the other, which activates photoreceptor molecules to a much greater extent on the lit side. This difference is biochemically translated as a growth response, known as phototropism, which makes the plant bend toward the light.
Trees growing at a latitude of, say, 60 degrees are also asymmetrically illuminated because of the slant of the noon sun—approximately 55 degrees at the beginning of the summer growth season—but the difference in light intensity there is smaller and more variable. The modest light gradient experienced by the tree is counteracted by a continuous gravitational influence, known as gravitropism, which guides plant growth upward. The strength of gravitropism trumps phototropism in the tree scenario but not on the windowsill.
The edge of forest gaps provides a good place to observe light-guided tree growth at any latitude. There the effect of a strong light gradient can be seen in the reaching of trees into the gap.
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8 Comments
Add CommentAlso, a tilted tree can't support itself very long.
Reply | Report Abuse | Link to thisAlso, a leaning tree can't support itself so even if it were advantageous to lean into the light, the tree would know better than to topple itself for a little extra light. Trees are so smart! Now, if we can only get them to stop making so many acorns and whirligigs ;)
Reply | Report Abuse | Link to thisI did a relevant experiment in High School biology class some time ago. I built a 12" diameter turntable that rotated continuously at I forget, 10 or 15 rpm. Atop that I placed a tray of soil planted with seeds. All the plants grew to bout 4" tall before we discontinued the experiment. Those near the perimeter leaned in dramatically (about 45 degrees, if I recall correctly) , while those further in leaned less, and at the center leaned not at all. This was a nice demonstration of the plants demonstrating accelerotropism in response to the centripetal acceleration of their environment.
Reply | Report Abuse | Link to thisThe relevance to the topic is that because the earth spins at a very high surface speed, one would think that at a mid-latitude of perhaps 45 degrees the centripetal acceleration would alter the direction of apparent gravity noticeably. It does not, however, because in reality the centripetal acceleration is miniscule compared with local gravity. So although plumb bobs there don't hang vertically, and trees there don't grow vertically, the effect is so small you cannot observe it.
And oh, by the way callejero, there are MANY trees that grow quite nicely for long periods of time at severe angles of lean - just take a look along undeveloped riverbanks. The water has often undermined the banks causing trees to lean dramatically. Quite a few do end up falling in, but a large percentage grow for decades in this fashion. You can verify this by looking at the growth after the initial lean - gravotropism causes new growth to follow the new vertical. These new stems can grow quite large while the original trunk remains severely tilted at angles of up to 75 degrees from vertical (and thus safely above the level of most flood waters).
I could see that it does not explain the question yet. Just look carefully at the growth of trees at the equator and compare with the growth at the pole. The direction is almost the same.
Reply | Report Abuse | Link to thisEverything grow accordingly and they are just nice to be seen on this world, including human and animal. Whether we could take it or not, God is the best creator. Nobody could challenge Him until now. Anybody out there dare to try?
what is he reasoning behind the theory that time changes when something nears the speed of light
Reply | Report Abuse | Link to thisi agree with you!
Reply | Report Abuse | Link to thisGod has nothing to do with this topic.
Reply | Report Abuse | Link to thisAnyway, to callejero, I live in a very windy town in the Central Valley due to the rain shadow effect (the Altamont Pass has lots of wind turbines there). Because of all this accelerated wind from the Bay Area, all the trees in our town point East. All the saplings have supports to help them grow straight, but they always get overcome by the wind after their removal.
Many scientists and their followers say that God has nothing to do with this topic.
Reply | Report Abuse | Link to thisBut after all these years, are there any scientists who could create new species of trees from pure soil or another medium?
May God bless science.