Thorns are sharp, pointed structures that grow on the stems of certain plants, such as roses and blackberries. They serve as a defense mechanism, helping to protect the plant from herbivores and other threats. Thorns can vary in size and shape, and they are often made of hardened tissue. In addition to their protective role, thorns can also play a part in the plant's overall health by reducing water loss and providing support. Some plants, like cacti, have evolved to have thorns as a primary adaptation to survive in harsh environments, where water is scarce.