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Plants grow UP

No matter which way you plant them, seeds grow with leaves up and roots underground.  Climbers like ivy, always reach for the top of a tree. Green beans always climb up their support, never down.  This one in my garden was heading down a support but changed direction and is now growing right back up on top of itself.

bean growing UP

It's an effect called gravitropism, or tropism.

The plant hormone auxin causes plants to repspond to gravity by always sending roots in the direction of gravitational pull and stems against the direction of gravitational pull.

Try this to observe gravitropism with your kids:

1) Prepare three growing environments by inserting a folded paper towel in a ziploc bag.

2) Put a bean seed in the middle of the paper towel and wet it. Partially seal the bag.

3) Tape them to a sunny window.

4) After the bean has sprouted (note the sprout going UP), turn two of the bags a quarter turn. Leave the third one in place as a constant.

5) Keep the paper towel moist but not soaked.

6) Let the plants grow another inch or so and turn again.

What happens?  Do the plants get confused?

PS.  I am on vacation and the house we're at has a  slow internet connection.  I am reducing pictures because they take too long to load.  Sorry!