Hygroscopic Pinecones

December 08, 2020

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Photographer: Menashe Davidson
Summary Author: Menashe Davidson

Recently, my curiosity was triggered when I read about the ability of a pinecone to open its woody scales in a dry environment and close them again when the humidity in the air is high. Luckily, Yaar HaMeginim (Defender's Forest) is only a 20-minute drive from my home and is filled with Jerusalem pines. There were plenty of cones (top) scattered about after a long dry summer so I gathered up several dozen and took them home for an experiment. The open, dry cones were dipped in water (bottom photo, left). After an hour, (bottom, right) they’d closed.

As the cones aren’t alive, this movement doesn’t use any internal energy. The trick lies in the nature of the cone’s scales, which consist of two different microscopic tissues that have different affinities for water (they’re hygroscopic). This allows the cones to close when atmospheric conditions become humid and to open up when conditions are arid.