Fig.
7.4-3. Transverse section of fern rhizome. Most
ferns have xylem that consists of tracheids rather than vessels, and in general,
tracheids tend to be narrower than vessels.
Some plants do have narrow vessels, so to be absolutely certain, it is necessary
to see if perforations are present or not, and that is more easily done in
longitudinal section rather than a transverse section like this one.