High in the treetops of a Chinese rainforest, Ming Guo began to explore the influence of a single cell. A student in China’s Tsinghua University, Guo was studying the mechanical properties of plant cells. As part of his master’s thesis he took on an intriguing question: Does a cell’s physical integrity — its size, shape, squishiness, or stiffness--have anything to do with how tall a tree grows? In search of an answer, Guo visited forests across the Yunnan province, collecting leaves from the tallest trees, some towering over 200 feet--too high for Guo himself to climb. So, he enlisted the help of a student in the university’s rock-climbing club, who scaled the trees and retrieved leaves at various heights along their length. After analyzing the individual plant cells within each leaf, Guo observed a pattern: The higher the leaves, the smaller the cells. And, more interesting still, the size of a single cell could more or less predict how tall a tree can grow.