LAUSR

In plants, xylem vessel length is important for long-distance water transport; however, the currently used methods for vessel length measurement are inconvenient and time-consuming. The semi-automated Pneumatron device is based on the pneumatic theory, is similar to the air injection method, and can rapidly estimate vessel length. Mean vessel length was compared between the newly-developed Pneumatron device and air injection method in seven species with different vessel lengths (2.3 to 78.7 cm). The results were consistent between two methods, regardless of whether the same or different samples were used. The theory underlying the gas flow in vessels was improved and expanded, and compared to that underlying the water flow to better understand the pneumatic processes within a stem sample. Moreover, a new and simple equation for gas flow in vessels was derived based on the molar gas flow (mol·s -1) rather than volume flow, because the former remains constant with distance throughout the stem axis. We strongly recommend using the Pneumatron device in future studies owing to its low cost, convenience, rapidity, and simple operation. Nonetheless, several cautions are warranted to avoid artifacts during measurements.