Xylem specialization of Linum species is compared with that of their somewhat primitive relatives. Linum is more specialized in that axial parenchyma is greatly reduced or absent, rays are generally homogeneous and composed mostly of upright cells, vessel elements are short, and in some species there is a tendency toward vessel aggregation. Many Linum species retain primitive characteristics to a degree in reduced scalariform perforation plates and imperforate elements which have large bordered pit pairs Double vessel perforations common in many species of Linum are considered to represent reduced scalariform perforation plates Vessel-element length in herbaceous species was significantly greater in the stem base compared with the stem tip The basis for this variation must be understood if vessel-element length is to be used in comparative studies of herbaceous plants Anatomical findings are related to different systematic treatments of the family