Vessels Per Square Millimetre or Vessel Groups Per Square Millimetre?

Descriptions of wood structure often include information on the number of vessels (pores) per sq.mm, and at times information on the percentage of solitary vessels and vessel multiples.Unfortunately, there is a problem in interpreting these data because there is more than one way to count vessels per unit area.Most of us have assumed that we have been doing our counts in the 'correct' way and that everyone else uses the same methodology.Consequently, most papers do not indicate what counting method was used.The purpose of this contribution to the IAWA Bulletin column on terminology is to I) call attention to the different methods and 2) suggest that materials and methods sections in descriptive anatomy papers indicate how pore density and percentages of solitary pores and pore multiples were determined.Dr. Baas, Dr. Regis Miller, and I discussed these topics at the IAWA meetings in Gainesville, Florida, August 1985.This note was written as a result of that discussion.