From systematic to ecological wood anatomy and finally plant hydraulics: are we making progress in understanding xylem evolution?

Olson (2014; in this issue of New Phytologist, pp. 7–11) provides a valid criticism of our recent commentary (Nardini & Jansen, 2013).Although we see no controversy surrounding Bailey’s functional and evolutionary ideas, we would like to pay attention in this Letter to two related concerns: (1) the integration of experimental data from the field of plant hydraulics into traditional, comparative wood anatomy; and (2) the reversibility of evolutionary transitions between perforation plate types that form a continuum.