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This is the third volume in a series describing and illustrating the venation patterns of the genera of select families of flowering plants. As these studies progress, new interpretations are being made and old ones modified. In the first volume dealing with the Annonaceae, the venation patterns were relatively easy to interpret since the secondary venation was usually pinnate and seemed to have been formed during the stage of lateral leaf expansion. In the second volume on the Lauraceae, the basic secondary venation pattern was acrodromal rather than pinnate. Acrodromal venation is oriented more longitudinally than laterally. Since growth in leaf length preceeds and usually overlaps growth in leaf width during the development of a leaf, acrodromal venation was considered to have been formed during the early part of the stage of lateral expansion.
In the Myrtaceae, the main secondary venation pattern is also acrodromal but, in addition, the pattern also has pinnate secondary-like veins connecting the acrodromal veins and the midvein. This pattern is interpreted as having been formed during the stage of leaf elongation for reasons which will be explained in the text of this volume. All this means is that the interpretations of the leaf venation patterns are apt to change or be modified with the appearance of each new volume in the series.