Pollen Tubes (image) University of Tennessee at Knoxville Caption This image shows pollen tubes extending from grains of pollen in the rare vine Austrobaileya. University of Tennessee, Knoxville, researcher Joe Williams found that the tubes' ability to grow quickly played a major role in the evolution of the large variety of flowering plants. Credit Joe Williams/University of Tennessee, Knoxville. Usage Restrictions Only with appropriate caption or credit. 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.