Pine cones respond to humidity. The scales open when the pine cone is dry because the outer half of the scale shrinks more than the inner half. This causes the scales to pull away from the cone. When the pine cone is wet, the scales swell shut.
In dry air, pinecones open their scales and disperse the seeds inside. When it’s warm and dry, the conditions are favourable for seeds to scatter away and grow.
If it is damp or rainy, pine cones will close their scales and protect the seeds. Wet and cold weather prevents seeds from going far and any seeds that start growing would not last long in winter weather.
In this experiment you have made a hygrometer from the pine cone. A hygrometer is an instrument used to measure humidity.
Humidity is the amount of water vapour in the air. You’ll probably see it listed in the newspaper or on TV as ‘relative humidity’. When there is a relative humidity of 100 per cent, the air is holding as much water vapour as it can at a particular temperature. This is when mists or fog forms.
Humidity is monitored because it can affect how comfortable people feel. For example, if it is hot and the humidity is high, perspiration on your skin does not evaporate quickly making it hard to cool down. Not a good day to run a marathon!
Warning: This experiment requires the use of an oven. Younger scientists should ask for an adult’s help.
You will need
- dry pine cone with open scales (rather than a heavy, closed, woody cone)
- permanent marker
- spray bottle
What to do
- Place your pine cone in the oven at 150 degrees Celsius for 10 minutes.
- Remove the pine cone from the oven carefully as it may be hot. As soon as it is cool enough to handle, use a lump of Blu-Tack to fix your pine cone to the bottom of the jar.
- Use the marker to colour in one of the scales on the pinecone. This will be the scale you use for your measurements.
- Mark the level of the scale using the marker on the outside of the jar. Mark this point as dry.
- Fill the spray bottle with water and spray your pinecone with a fine mist until it is damp. Seal the jar.
- Observe the pine cone over the next few hours. Mark the highest point that the scale reaches as wet.
- Now you can leave the lid off your pine cone jar. After a few days, your pine cone will give you an indication of how humid it is where you keep the jar.
Dry your pine cone, then colour a scale with a marker. On the outside of the jar, mark the level of the scale as the dry point. Wet the pine cone and leave it for a few hours. Mark the level of the scale again as the wet point.