A naturally occurring carboxylic acid, HOC6H4COOH, that acts as a plant hormone. Its production is induced by pathogen infection, and its methylated derivative, methyl salicyclate, moves through phloem to other parts of the plant. There it is reconverted to salicylic acid, which initiates the generalized state of heightened immunity known as systemic acquired resistance. Salicylic acid also plays a part in senescence and seed germination. When extracted from plants it is used in making aspirin and in the foodstuffs and dyestuffs industries.