The sporophylls consist of a short axis terminating in two small divergent forks and bearing on its adaxial surface a trilocular or in rare cases a bilocular synangium (fig. 118, A and B). The walls of the loculi are composed of several layers of cells and dehiscence takes place along three lines radiating from the centre of the synangium. Professor Thomas[41] has recorded “fairly numerous instances in _Psilotum_ of a second dichotomy of one branch of the first fork, or, less frequently, of both branches”: instead of one synangium subtended by the two slender leaflets of the forked sporophyll-axis, there may be two synangia and three leaf-lobes or three synangia and four leaf-lobes. The occurrence of both these abnormalities in _Psilotum_ and _Tmesipteris_ shows a decided tendency in the Psilotales to a repeated dichotomy of the sporophylls[42]. A single stele[43] with a fluted surface occupies the axis of an aerial shoot (fig. 119, A); the axial region is occupied by a core of elongated mechanical elements (_s_), which may occasionally extend to the periphery of the xylem and break the continuity of the band of scalariform tracheae (fig. 119, A, _a_). The tracheae form the arms of an irregularly stellate stele and each arm is terminated by protoxylem elements (fig. 119, B, _px_). The rays of the xylem cylinder, which may be as many as six or eight in the upper part of the aerial shoots, become reduced in number as the rhizome is approached, assuming a diarch structure near the junction. In the rhizome the xylem forms an approximately triangular group of tracheae without any core of mechanical elements. Three to four layers of parenchyma succeeded externally by an ill-defined phloem (fig. 119, A, _p_) surround the xylem and a fairly distinct endodermis (fig. 119, A and B, _e_) encloses the whole. To Mr Boodle[44] is due the interesting discovery that in some parts of the rhizome the parenchymatous zone surrounding the scalariform tracheae may become the seat of meristematic activity which results in the production of secondary tracheae often characterised by a sinuous longitudinal course. There is no definite cambium, but the radially disposed tracheae and the adjacent parenchymatous elements clearly demonstrate the secondary nature of the tissue immediately external to the group of primary xylem. Fig. 119, C, drawn from a section kindly supplied by Mr Boodle, shows the secondary xylem elements at _x_² associated with radially disposed thin-walled cells abutting on the primary xylem, _x_¹. It is probable that this added tissue may be a remnant of a more extensive secondary thickening characteristic of the ancestors of the recent species. In their manner of occurrence and sinuous course these secondary tracheids bear a resemblance to the secondary xylem of _Lepidodendron fuliginosum_[45]. The stele of the aerial shoot bears a fairly close resemblance to the vascular axis of _Cheirostrobus_, and its three-rayed form in the lower