is of secondary importance, particularly as exarchy is represented within the genus _Medullosa_. The extrafascicular strands of xylem and phloem and the accessory strands are points in which _Sutcliffia_ and _Medullosa anglica_ agree and, as Miss de Fraine[426] adds, the meristeles of _Sutcliffia_ may be homologous with the leaf-trace strands of _Medullosa_. Scott[427] gave expression to the characters shared by these two types by describing _Sutcliffia_ as the most primitive of the Medulloseae. It is suggested that the protostelic axis of _Sutcliffia_ may be regarded as the starting-point of the monostelic Cycads, the central mass of tracheal tissue being replaced by a parenchymatous pith, while the extrafascicular and accessory strands arose independently of the central stele in response to increased physiological demands consequent on the increase in size of the stem. From the same starting-point evolution may have progressed along another line through such a type as _Medullosa anglica_ leading to the more complex Permian species of _Medullosa_. Chodat’s view[428] that the Medulloseae are Protocycadaceae, if we include _Sutcliffia_ as well as _Medullosa_ in the Medulloseae, is probably correct. There is clear evidence of a close bond of union between recent Cycads and the Medulloseae, and _Sutcliffia_ offers a possible means of deriving complex polystelic types from a monostelic ancestor. Worsdell’s opinion[429] that the stele of _Lyginopteris_ affords evidence of derivation from a polystelic ancestor and is not homologous with the true monostele of _Heterangium_ is opposed to the undoubted signs of intimate connexion exhibited by these genera. The Lyginopterideae are, as Scott[430] says, a less advanced group than the Medulloseae and, it may be added, they are more remote from the modern representatives of the Cycadales. The Lyginopterideae and the Medulloseae are probably offshoots of a common stock, but the Medulloseae occupy a position farther removed from the filicinean ancestry than _Heterangium_ and _Lyginopteris_[431]. The relative meagreness of our knowledge of the reproductive organs of the Medulloseae gives precedence to anatomical data in phylogenetic considerations, but the evidence furnished by _Trigonocarpus_ and other seeds that may fairly be assigned to Medullosan plants is in harmony with the conclusions based on vegetative characters with regard to a close affinity between the Medulloseae and Cycads.