Pine cone science

Have you ever noticed that pine cones that start out closed and green on the tree, fall, dry out, and open?  Or that after they get wet, they close back up?  I have some dry old pine cones in my yard for the children to play with, so when I found a bunch of closed green pine cones while walking this morning, I gathered them and brought them home.  Instant science lesson!

 Here are two of the "new" pine cones - including one that has just started to open.

 Here's an "old" dry one, with all it's scales wide open.

 When we looked carefully, we could still see many of the seeds in the partly opened pine cone - the little papery looking "wings" laying inside each scale.

We gently pulled some of the seeds out, and after someone accidentally dropped one, and saw how it spiraled to the ground, several children enjoyed dropping the seeds.

Next, we set up our experiment.   We put the dry pine cone (shown in the second picture of this post) into a bucket of water.

Two children wanted to plant their pine cone seeds, one at home, but the other was ready to plant right away. I took her to a pot of soil, and she made a small hole for her seed...

 ...dropped it in, and covered it...

 ...carried over  a watering can...

 ... and got her seed started!  I labelled it, so we can see how long it takes to germinate.  She predicted that it will take "a long time," but then sat and watched it for a few moments before heading off to play.

About 30 minutes later we went back to the "dry" pine cone in the bucket of water.  Check it out!

So do you wonder why this happens?  Here's an excerpt from an online article from
http://www.utsandiego.com/news, written by staff writer Katie Burns:

"Q: Why do pine cones open when warm and dry and close when cold and wet?

A: "There are actually male and female pine cones," said Betsy Read, a biology professor at Cal State San Marcos. "The female pine cone is the one we are most familiar with that opens and closes. The opening and closing of the cone is part of the life cycle of the pine."

The male pine cone, which is small and bumpy, produces pollen. Wind-blown pollen falls on a female pine cone on either the same tree or another tree. Over the course of a few years, seeds develop under the scales of the female cone. The female pine cone opens when the seeds are mature and the conditions are right.

"The reason why the pine cones open when it's warm and dry is because that's a more favorable condition for the seed dispersal and germination," Read said.

Wet and cold weather would prevent the seeds, which are often winged, from spreading far enough from the tree to find a place to grow. Seedlings also wouldn't last long in winter rain or snow.

After a pine cone falls from the tree, it can still open and close. The scales open when dry because their outer halves shrink more than their inner halves, and they pull away from the cone. When wet, the scales swell shut."

We pulled our closed, wet pine cone out of the water, and admired it.  I asked the children what would happen to it now.  They all agreed it would probably dry out, and open again.  I wanted to put it somewhere that no-one would bother it, but we could all observe it, so I put it a few feet behind a fence, in the sun.

 Here it is six hours later...

It's now the following day, and it has hardly changed at all.  How long will it take to dry out completely?  I don't know - but I'll keep you posted!