By Barb Williams
You may have noticed that here in the Pacific Northwest it rains often, which is one reason we have such a variety of healthy plants in the Bellevue Botanical Garden. When it rains, or when watery dew drops collect on the leaves, you may notice the sparkle of water droplets shimmering like diamonds on surfaces. Or they may be precariously hanging from “drip tips” at the leaf’s end. Many leaves end in a sharp point. The points are called “drip tips.” They, along with the central vein, enable the water to run off the leaf blade (surface). This is important because standing water on some leaf blades can promote disease.
On the leaves of the Snowberry bush, water “beads up” and looks like little diamonds. These beads or droplets form because the hydrogen and oxygen molecules that make up the chemical equation for Water (H2O), want to hold onto one another. This is called “surface tension.” If you
poke one of these water droplets, you may be able to break the surface tension. Putting soap on the water droplet will also break the surface
tension because it inhibits the strong bond between the hydrogen and oxygen molecules. Some leaf blades, like new Geranium leaves, have little bristles that hold the water droplets in place.
Go outside after a rainstorm or in the early morning when the dew has collected on the leaves. Notice the “Leaf Diamonds” on different leaves. Use a hand lens or magnifying glass to look at them closely. How high are the droplets? Is all the water on the leaf surfaces in droplet form? Why do you think this is so? Have fun!
Surface Tension Experiment:
You will need:
- 1 eye dropper with water in it
- 1 penny
Place the penny on a flat surface. Fill the eyedropper with water by sucking water into the dropper. Drop one small drop of water onto the penny, one drop at a time. Notice how many drops it takes before the water spills over the sides of the penny. Use a hand lens to observe how high the drop gets after each drop is added to the first drop.