From Seed to Seed:
Plant Science for K-8 Educators

Many tropical trees produce large amounts of latex in tubes called laticifers located in their bark. When the bark is damaged, the milky latex oozes out. This undoubtedly is a strong deterrent to the bark beetles and other insect pests that are plentiful in the rainforest. It is reasonable to speculate that the evolutionary "purpose" of this strange substance is deterring herbivores.

One of the interesting properties of latex is that it begins to congeal upon contact with air. Latex contains tiny globules; when isolated from the rest of the liquid, the globules form an elastic substance known as crude rubber. This crude rubber can then be refined into a number of rubber products. Although many plants produce latex, it is harvested on a commercial scale from Hevea brasiliensis, a tropical tree sometimes found growing in the wild but more commonly grown on plantations.

The history of rubber may go back as far as the 11th century, again providing you with ample opportunity to teach an interdisciplinary lesson. Evidence of its use has been found in the Mayan ruins of Central and South America. Many years later, in the 1400s, word spread to Europe of a strange, soft yet resilient substance used by native people of the tropics. By 1600, Spanish settlers were using rubber to waterproof clothing and shoes. But it wasn't until 1839 that Charles Goodyear discovered that by adding sulfur to rubber and applying heat and pressure, he could create a material that was more resilient and durable-and less sticky and foul-smelling. This process was named vulcanization, in honor of Vulcan, the Roman god of fire and craftsmanship. The invention of the pneumatic tire created a huge market for this unusual substance. Indeed, it could be said that the development of the pneumatic tire was entirely dependent upon the invention of vulcanized rubber, since no other substance available at the time would have worked for this purpose.