The most common inorganic salts found in the cells are the phosphates, sulphates, nitrates, chlorides of calcium, magnesium, potassium, sodium, zinc, Iron etc. Some of these salts are metabolic waste products.

Crystals of calcium carbonate, calcium oxalate and silica are common waste products found in the cells of different parts of the plants.

A. Calcium carbonate: Numerous small calcium carbonate (CaCO3) crystals, accumulated to form the appearance of a bunch of grapes, are suspended from a stalk in the epidermal cells of leaves of banyan (Ficus benghalensis), Indian rubber plant (Ficus elastica), or plants of Cucurbitaceae and Acanthascae family.

These are called cystoliths. In cucurbitaceous (Ex-Momordica) these are seen as double cystolith and in Acanthaceae as elongated cystolith.

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B. Calcium oxalate : The needle like or acicular crystals of calcium oxalate are called raphides, found in the storage organs, pith or cortical cells of aroids (Colocasia, Amorphophallus etc.) and in many aquatic plants (Pistia, Eichhornia).

This crystal may occur as solitary, needle like structures as in the petiole of Bougainvillea or in the form of bundles of needle like crystals as in Pistia. Sometimes, these crystals may also be grouped into star-like aggregates called sphaeraphides or druses as seen in Pistia, Opuntia, Colocasia, Papaya etc. Mass of solitary crystals, deposited in the vacuoles is called crystal sand (Ex-Atropa).

C. Silica: Deposition of crystals of silica is found either on the wall of the cell or may be embedded inside the cell lumen of many grasses wheat, rice, oat etc.