Rainforest Canopy (image) Smithsonian Tropical Research Institute Caption Fossil evidence indicates that vein density increased in the leaves of flowering plants. Scientists suggest that this permitted the plants to transport more water and conduct more photosynthesis, leading to the evolution of giant, rainforest trees and productive, biodiverse forests. Credit STRI Archives Usage Restrictions Credit: STRI Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.