A skeptic’s guide to Sherwin Carlquist’s inferences of xylem function

Sherwin Carlquist’s work was filled with inferences of xylem function, and yet he did not carry out xylem physiological or biomechanical measurements. Moreover, his quantitative analyses were rudimentary and he disliked the standard scientific practice of quantifying uncertainty with statistical analyses. Also, took few pains to explain to other functional xylem biologists why his comparative approach was useful and appropriate. Here, I discuss why nevertheless his papers are extremely valuable contributions to inferences of xylem function. The most important insight is that Sherwin used a valid and essential approach for the inference of biological function, known as the comparative method. Together with optimality models, population biology (including xylem physiology), and studies of developmental potential, the comparative method is an indispensable part of a maximally supported inference of xylem structure–function relation. Detecting his insightful inferences of function often requires reading around his various idiosyncrasies, including the lack of statistics and instead his reliance on his extraordinary memory to detect patterns. With this guide to reading Carlquist’s work, I hope to give functional xylem physiologists better access to the richest and most wide-ranging body of functional hypotheses found in the xylem literature.