No one knows exactly why plants make these crystals and the crystals could serve multiple functions. Some of the sharp, needle-like, crystals might help defend plants from being eaten. Some crystals might bind heavy metals or harmful substances and keep them in kind of a molecular toxic waste containment center.
The best feature of this story, though, is the gallery of photos. The Botanic Crystal Fashion Show is composed of excellent pictures, all taken by Harry T. (Jack) Horner at Iowa State University. It's well worth taking a look.
Subject: Web resources, Plants