Latex, as found in nature, is the milky sap of many plants that coagulates on exposure to air. It is a complex emulsion in which proteins, alkaloids, starches, sugars, oils, tannins, resins and gums are found. In most plants latex is white, but some have yellow, orange, or scarlet latex. Latex can also be made synthetically by polymerizing monomer that has been emulsified with surfactants.
The cells or vessels in which latex is found make up the laticiferous system, which forms in two very different ways. In many plants the laticiferous system is formed from rows of cells laid down in the meristem of the stem or root. The cell walls between these cells are dissolved so that continuous tubes, called latex vessels, are formed. This method of formation is found in the poppy family, in the rubber plant, and in the Cichorieae, a section of the Family Asteraceae distinguished by the presence of latex in its members. Dandelion, lettuce, hawkweed and salsify are members of the Cichorieae.
In the milkweed and spurge families, on the other hand, the laticiferous system is formed quite differently. Early in the development of the seedling latex cells differentiate, and as the plant grows these these latex cells grow into a branching system extending throughout the plant. In the mature plant, the entire laticiferous sytem is descended from a single cell or group of cells present in the embryo.
Latex has been attributed with many functions. Some regard it as a form of stored food, while others consider it an excretory product in which waste products of the plant are deposited. Still others believe it is primarily intended to protect the plant in case of injuries, drying to form a protective layer that prevents the entry of fungi and bacteria. Similarly, it may be a protection against browsing animals, since in some plants latex is very bitter or even poisonous. It may be that latex fulfils all of these functions to varying degrees in various different plant species.
Latex has many uses, but its first and foremost is rubber. Chicle, widely used as a base for chewing gum, is another latex product. Some paints (called latex paints) use latex as a binder. The latex used in these paints is typically made synthetically using emulsion polymerization. Finally, poppy latex is a source of opium and its many derivatives.