This book examines the sophisticated mechanisms that plants use to defend themselves against attack by insects and pathogens, focusing on the networks of plant signalling pathways that underlie these defences. In response to herbivory, plants release a complex blend of as many as 100 volatile chemicals, known as semiochemicals ('sign chemicals'). These act as an airborne SOS signal, revealing the presence of the herbivore to the predators and parasitoids that are its natural enemies. Plants also...