In contrast to animals are these not excreted by plants. Some secondary plant products can be reversibly degraded and are fed into the basic metabolism while others cannot. Although secondary plant products are very common does this not mean that every plant can produce every product. Some compounds are restricted to single species, others to related groups. Also are they often generated just during a specific developmental period of the plant.
Many secondary compounds have signalling functions.
Among them are plant hormones that will be dealt with elsewhere due to their importance. They influence the activities of other cells, control their metabolic activities and co-ordinate the development of the whole plant. Other substances like the just mentioned flower colours serve to communicate with pollinators or protect the plants from feeding by animals or infections. Some plants, for example, produce specific phytoalexines after fungi infection that inhibit the spreading of the fungi mycelia within the plant. A number of substances is secreted and influences the existence of other species.