[paul.fr]

Notch another one in the "silly topics by paul column". When i was a kid, i remember having a pinecone and being told that if it was going to rain it would close, and if it was going to be sunny it would open up.

Now is that true?

[kdlynn]

i don't know about pine cones but i know that the leaves on the trees turn upside down when it's going to rain... so why not pine cones?

[kdlynn]

nobody knows a real answer to this? lol. i'm usually proven wrong pretty quickly when i just guess like that...

[WylieE]

Not a silly topic at all!

Some pine cones open and close based on humidity.
 
In these species when the weather is wet and humid the scales swell and the pine cones close.  There is an advantage here to the seeds- pine cone seeds are spread by the wind and on a rainy day they may not go as far.  When it is dryer out the outside of the scale shrinks more than the inside and the scales open up- allowing the seeds to get out.

So in this case the pinecones act as a hygrometer- an instrument to measure the humidity.  Since they can identify changes in the humidity that we might not be able to perceive we can use them as tools to make predictions.  So if the pine cone scales are open the air is dry and probably a lower chance of rain.

The cones don't have to be on the tree to do this.
In fact it is annoying to people who use them for crafts because when they get wet they close back up.  To avoid this they dry them out completely by putting them in the oven at 200 (F) for a couple of hours.  Once the water has been completely removed they will stay open. 

Not all species open and close with humidity some open in response to fire. 

Colleen

[paul.fr]

Thank you, Colleen.