<P> Plant defense against herbivory or host - plant resistance (HPR) describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores . Plants can sense being touched, and they can use several strategies to defend against damage caused by herbivores . Many plants produce secondary metabolites, known as allelochemicals, that influence the behavior, growth, or survival of herbivores . These chemical defenses can act as repellents or toxins to herbivores, or reduce plant digestibility . </P> <P> Other defensive strategies used by plants include escaping or avoiding herbivores in any time and / or any place, for example by growing in a location where plants are not easily found or accessed by herbivores, or by changing seasonal growth patterns . Another approach diverts herbivores toward eating non-essential parts, or enhances the ability of a plant to recover from the damage caused by herbivory . Some plants encourage the presence of natural enemies of herbivores, which in turn protect the plant . Each type of defense can be either constitutive (always present in the plant), or induced (produced in reaction to damage or stress caused by herbivores). </P>

How do some chemicals in plants protect them from their enemies