Any of the tissue or tissue systems of plants can contain idioblasts.^[1] They are isolated cells which differ from neighboring plant tissues and contain non-living substances. They have various functions such as storage of reserves, excretory materials, pigments and minerals. They could contain oil, latex, gum, resin, tannin or pigments etc. Some can contain mineral crystals such as acrid tasting and poisonous calcium oxalate or carbonate or silica. Idioblasts are divided into three main categories: excretory, tracheoid and sclerenchymatous.

Idioblasts can contain biforine cells that form crystals. The chemicals are excreted by the plant and stored in liquid or as crystals. In bundles they are known as (druse form) and as crystals they can be (raphide [needle] form). When the end of the idioblast is broken the crystals or other substance is ejected by internal water pressure. The chemical packets of calcium oxalate appear to have no function other than a poisonous deterrent to herbivores.^[2]

• Plant defense against herbivory
• Phytolith