Bordered Pits in Pine (image) Virginia Tech Caption Three bordered pits are revealed in this 3-D microscopic cross-section of pine wood, with cellulose appearing in green and pectin in red. The image was taken with a specialized microscope that shows a never-before observed distribution of pectin in ring-like structures at the nanolevel, which helps explain how trees control sap flow and prevent air intrusion in their stems. Credit Virginia Tech Usage Restrictions None 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.