In studying the phylogeny of plants, there are certain general principles upon which all conclusions are based. One of these deals with the retention of ancestral-characteristics. A striking example of this is afforded by the anatomy of the cycads. The vegetative stem of these forms always has exclusively centrifugal metaxylem, but in the leaf petiole, the metaxylem is predominately centripetal, with only a slight development in a centrifugal direction. Centripetal wood structure is, of course, the more primitive, and its appearance in the leaf petiole of the Cycadales serves to relate them to their extinct Cycadofilicean ancestors, where centripetal wood was present in the stem. Similar bundles with centripetal wood are present also in the reproductive axes of certain Cycadales.2 Another well known seat of primitive conditions is the root, good examples of which are furnished by the Abietineae. The first and older subtribe, the Pineae, is characterized by the invariable presence of resin canals in the normal wood of both root and stem, while in the more modern subtribe, the Abietae, resin canals are generally absent in the normal wood of the stem. Resin canals do occur, in all four genera of the Abietae, in the center of the primary wood of the root.3 Recent investigations have shown that ancestral conditions may be recalled as a result of wounding. For example, these resin canals, present in the roots of the Abietae, are present invariably