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And not just trees, but plants in general? What senses do they have? What kind of chemical things are going on?
Posts: 4953 | Registered: Jan 2004
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What senses do plants have? Well they can generally sense heat and light. Many, if not most, can sense gravity. Morning-glory and many other vining plants have a rudimentary sense of touch. If you are patient, you can literally watch a morning-glory reach out a tendril, sweep it out in an arc until it hits a fence rail or other support, then wrap itself around the support so it can climb as it grows.
As for spring, different plants know in different ways, but as KoM said, it's mostly due to changes in light and temperature. You can "force" spring bulbs into thinking it's spring by planting them in a pot and keeping it in the fridge for 6-8 weeks. If you do this in Oct-Nov, you can take the pot out of the fridge near the end of December and have tulips in January/Feb. When you take the pot out, keep in inside near a sunny window. The light and the warmth of the house will make the tulips think it is Springtime already.
On the other hand, many houseplants come from tropical regions where there aren't such clearly defined seasons. These will generally grow year round if given sufficient light and warmth because they haven't evolved to go dormant during cold weather or shorter days.
Posts: 6394 | Registered: Dec 1999
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In my high school AP Biology class, I did my research project on plant hormones. They're absolutely fascinating. Plants bend toward the light because there are hormones that are light-shy and induce growth; so they cluster on the side of the stem away from the sun and cause those cells to elongate, bending the stem towards the light.
There are hormones that sense gravity, and this is how roots know to grow down and shoots know to grow up. Round Up (the herbicide) works by interrupting these hormones. Watch a recently sprayed dandelion - its stems are twisting because it doesn't know which way to grow.
There are hormones that sense photoperiod and cause plants to bloom (as in the forced bulbs that Karl mentioned) or ripen or die (as in falling leaves). Poinsettias have to have twelve hours of light and twelve hours of dark for several months or else the bracts don't turn red.
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Telp, I was sure this was going to be some kind of "I'm happy and in love" post - I mean, our very own Silver Tree starts a thread asking how trees know it's spring, and it's a serious question? *shakes head*
Ah well, I sure hope you're enjoying spring, even if that's not why you posted. Posts: 3214 | Registered: Apr 2002
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adam613, are the other trees waking up and yours is just behind? If so you've probably discovered a "micro-climate". That's an area that is consistently a few weeks ahead or behind the general climate of you area. For instance, a tree planted close to the north side of a building might not bloom for a couple of weeks after the local trees have all bloomed.
I saw petunias blooming well after the first frost in Baltimore, but they were growing on the south side of an apartment building (full sun) and under the dryer exhaust vent for the complex (which was practically 24/7 in use).
We had snapdragons, which are treated as annuals, normally, over-winter in our front yard in Baltimore because they were on a southern exposure, next to a wall that got full sun all day and radiated the heat back out all night. The plant turned brown and the tops of the branches died, but in the spring it woke up and was blooming weeks ahead of schedule.
Posts: 6394 | Registered: Dec 1999
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