Since it’s winter, and we’re all stuck looking at leafless plants outside, why not try growing some plants indoors? Better still, why not experiment with your plants to understand them better?
In this activity, you will confuse a bean sprout and train it to grow in any direction you want. Sound like fun?
You will need:
- a gallon-size zip-top bag
- paper towels, preferably 2-ply (if they are single-ply, double them)
- a pinto, lima, or kidney bean (try whatever you have) soaked in water overnight
- a stapler
Lay the paper towel flat inside the plastic bag. If it doesn’t fit exactly, fold the edge of the paper towel.
Put a staple in the middle of the bag, and place the bean just over the staple. Add two staples that are separated by more than the length of the bean.
The staples hold the bean in place, but should give enough room for the bean to grow between the staples. Watch to see how the bean grows and needs the space. Add just enough water to the bag to wet the paper towel. Take care not to have a pool of excess water in the bag.
Now tape the bag to a wall, or your refrigerator, or a window if it’s not cold. That’s right, put it right on a vertical surface. Don’t close the bag, because it’s good to allow water and air to move in and out. The picture shows you what it should look like. (Ignore the four staples, only put three on yours. I discovered that four staples trap the seed and ruin the activity.)
As soon as your plant has grown a root and a stem that is 1-2 inches long, turn the bag one quarter turn and put it back. You may have to wait a week – less if your bean is warm, more if your bean is in a cooler location, like my office.
This is what it may look like at this stage after I turned it.
Now wait. When the sprout has grown another inch or so, turn the bag again in the same direction. Since the opening of your bag will now be on the bottom, you should seal it. Then wait.
Yes, I know, you have to wait a while to get results. The timing will depend on the level of light and the temperature. That’s the way it goes with growing plants. Horticulturists – the people who grow plants – are some of the most patient people you will ever meet!
Here are the results of one bag I started in early January, about three weeks ago. Since I turned the bag clockwise, the roots and stem appear to be going around counter-clockwise.
From here on it’s up to you. Let the plant grow and turn the bag when you want to change the direction of growth, let it go for as long as you like. Can you make it grow in a full circle around the middle of the bag?
What is Going On Here?
Plants are affected by the gravitational pull of the earth. When you turn the bag, you change the direction of the force and the plant responds by changing direction of growth. This phenomenon is called geotropism. A tropism describes an organism’s response to a stimulus. In this case, the “geo” refers to the Earth, and it is the scientific way of saying that the earth makes leaves grow up and roots grow down. This phenomenon may also be called gravitropism.
The Garden’s horticulturists play with gravitropism. Look at this picture of the Visitor Center bridge in fall. Notice the gorgeous pink mums hanging from the trellis.
Left alone, the stems of these plants would naturally grow up like the mums planted on the sides of the bridge. Our horticulturists train the stems to grow down, cascading over the sides of their container, by tying small weights on the stems while the plants are growing in the greenhouses. They actually use metal nuts from a hardware store! The weights are removed before the planters go on display, and they look fabulous, thanks to the horticulturists’ success in playing with the plant’s response to gravity.