Isn't everything in nature just amazing to look at? Take for example this jungle jalebi tree (Pithecellobium dulce) which I recently shaped a little. It had come all over the roof, so I cut a few branches to make a shaded sitting area under that tree (at the rooftop that is). Really a somewhat ugly and thorny tree (which also attracts ants because of it's sweet sap). But grows very fast, and requires zero maintenance. Sap from a tree. ( photo / image / picture from S-H's Garden ) Sap from a tree again. ( photo / image / picture from S-H's Garden ) Close up. ( photo / image / picture from S-H's Garden )
I think sap and/or resin makes an excellent glue (or is a key component of a glue at the very least). Other than that, I have no real idea.