Watch how plant cells eject raphides (needle-shaped oxalate crystals) under microscope

https://youtu.be/s8FdV20BkiY?t=74Raphides are needle-shaped crystals of calcium oxalate, found in more than 200 families of plants. Both ends are needle-like, but raphides tend to be blunt at one end and sharp at the other.Little is known about the mechanisms of sequestration or indeed the reason for accumulation of raphides but it is most likely a defense mechanism against herbivory. It has also been suggested that in some cases raphides may help form plant skeletal structure. Raphides typically occur in parenchyma cells in aerial organs especially the leaves, and are generally confined to the mesophyll. As the leaf area increases, so does the number of raphides, the process starting in even young leaves. The first indications that the cell will contain crystals is shown when the cells enlarge with a larger nucleus.Raphides can produce severe toxic reactions by facilitating the passage of toxin through the herbivore’s skin when the tissue containing the raphides also contains toxins. The lethal dose to mice is around 15 mg/kg. Raphides seem to be a defense mechanism against plant predators, as they are likely to tear and harm the soft tissues of the throat or esophagus of a plant predator chewing on the plant’s leaves. The venomous process is in two stages: mechanical pricking and injection of harmful protease. Typically ingestion of plants containing raphides, like those common in certain houseplants, can cause immediate numbing followed shortly by painful edema, vesicle formation and dysphagia accompanied by painful stinging and burning to the mouth and throat with symptoms occurring for up to two weeks. Airway assessment and management are of the highest priority, as are extensive irrigation and analgesics in eye exposure.Raphides cannot normally be destroyed by boiling; that requires an acidic environment or chemical solvents like ether, but heating raphide containing plant materials (like tubers) can fix the raphides into a dried starchy matrix so they are no longer mobile and thus less harmful. Some other plants store raphides in mucilaginous environments and also do not taste acrid.

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