A sticky, milky fluid of mixed composition produced by about 10% of flowering plants. It has no known metabolic function and is thought to serve as a defence against insects and other herbivores that feed on the plant. Latex is produced in specialized cells called lactifers and accumulates at the point of damage on the leaf or stem. Insects may become trapped in the sticky exudate or succumb to one of the many bioactive substances that can be found in latex, including alkaloids, cardiac glycosides, phenolics, and terpenes. The latex of some species, notably rubber trees, is collected for commercial purposes.