A 50-50 blend of morning glory juice and latex created rubber with maximum bounciness, while a 75-25 mix of latex and morning glory made the most durable material.
It seems they were making bouncy balls for fun and sport. But, to be clear about the ingredients:
Morning glory plants tend to grow near rubber trees, and both plants were considered sacred in several Mesoamerican cultures. Morning glory, for example, was also used in religious ceremonies for its hallucinogenic properties.
From Rachel Kaufman’s reporting on rubber chemistry and industry in the prehistoric Americas.