Microscopic Imaging of Shrub Stems (image) University of Minnesota Share Print E-Mail Caption Microscopic imaging reveals the pattern of annual rings in shrub stems, which the researchers used to determine that shrub growth is controlled by temperatures in June, the first month of the brief arctic growing season. Credit Daniel Ackerman Usage Restrictions With credit. Share Print E-Mail 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.