Howard Penman: A Sower of Ideas.

Upon my first meeting with Penman in 1952 at North Carolina State, he explained his ideas and made me want to test them in field experiments. With help from several of my students and coworkers I realized my objective over the following fifty years, while improving measurement techniques and data interpretation. While establishing the essential accuracy and usefulness of the original equation, I resolved in 2001 a weakness that had also been noted by others. During that period I had several opportunities get to know Penman better and to appreciate his genuine interest in what I was discovering.