C, are in oblique longitudinal section and are probably being detached to form a leaf-trace. This type of stele may be compared with the steles of _Medullosa Solmsi_ (fig. 416, L) but those of _Rhexoxylon_ differ in the lack of continuity of the secondary xylem round the narrow band of crushed primary xylem. The other steles of the inner ring exhibit the same dual nature though with local modifications. In the stele seen in fig. 438, B, there is a close approach to a continuous cylinder of secondary xylem especially on the right-hand side. External to the inner series are several portions of normally orientated secondary xylem-groups (fig. 437): these probably represent a second series of steles separated from the inner series by a narrow crushed arc of tissue on which the protoxylem strands of the outer groups abut. The xylem of the outer steles agrees in its normal orientation with the outer and smaller part of the inner steles and, as there is no accompanying group of inversely orientated xylem corresponding to the larger mass of secondary xylem of the inner series, the outer strands are designated partial steles. The central stele consists of two curved irregular bands composed of vertically and obliquely running tracheids: the central part of this stele consists of crushed tissue that probably represents primary xylem like that between the two parts of each of the peripheral steles. [Illustration: Fig. 438. _Rhexoxylon africanum_. A, radial wall of tracheid; B, C, peripheral steles; _a_, primary portion of stele; _b_, lateral strand. (After Bancroft.)] _Rhexoxylon_ differs from the usual Medullosan type in the structure of the secondary xylem which is composed of tracheids with an Araucarian form of pitting: there are usually two alternate rows of contiguous pits (fig. 438, A) and occasionally one or three rows. The medullary rays are uniseriate and 3 to 15 cells in depth, a feature characteristic of coniferous wood and not of the wood of the Medulloseae. In the absence of more complete information as to the anatomical structure of this stem and of all information as to the leaves or reproductive organs it is impossible to fix with precision the systematic position of the genus. It is, however, clear that _Rhexoxylon_ is closely connected with _Medullosa_ in certain features though in the structure of the wood it exhibits important peculiarities. The imperfectly known stem _Cladoxylon Kidstoni_[408] shows a fairly close agreement with the African plant in the form of the steles (fig. 460) but the pitting is scalariform. =SUTCLIFFIA.= Scott. _Sutcliffia insignis_ Scott.