In the diagrammatic section shown in fig. 158 the outer cortex of the main stem is represented by _oc_ 1; this consists of secondary tissue. The corresponding tissue in the branch is seen at _oc_ 2. The stele of the stem is shown at Tr. St. and that of the branch at Br. St.; _lt_, _lt_, mark the position of the leaf-traces. If we assume the branch to be detached along the line LS, the depression would show numerous spirally arranged dots representing the points of exit of leaf-traces and the vascular axis would be exposed in the umbilicus. This explanation appears to me to be in harmony with the surface-features of Ulodendron scars on both Bothrodendron and Lepidodendron stems. The occasional occurrence of leaf-cushions on a portion of a Ulodendron scar is a difficulty on the cladoptosis hypothesis. Assuming that true leaf-cushions occur, their presence may, as Watson suggests, be due to the folding back of a piece of the outer cortex of the branch which has been “crushed down on to the area of the scar[301].” Since this account was written a note has been published by M. Renier[302] in which he describes a specimen of _Bothrodendron_ from Liège, one face of which shows a projecting Ulodendroid scar with an excentric umbilicus. On the other face is a dichotomously branched shoot with surface-features corresponding to those on the scar; the evidence that the scar represents the base of the branch is described as indisputable. Stur[303] held the view that the depressions on Ulodendron stems represent the places of attachment of special shoots comparable with the bulbils of _Lycopodium Selago_, or, it may be added, with the short branches occasionally produced on _Cycas_ stems. If the depressions were formed by the pressure of the bases of cones, it is clear that the size of the cavity must be an index of the diameter of the cone. The larger Ulodendron scars exceed in diameter the base of any known lepidodendroid strobilus. Another obvious difficulty, which has not been overlooked by Kidston who holds that the scars were produced by sessile cones, is that in _Lepidodendron Veltheimianum_ strobili were borne at the tips of slender branches; the same difficulty is presented by _Bothrodendron_ (Fig. 213). It is unlikely that two types of strobili were produced on the same plant, particularly as the cone of _L. Veltheimianum_ was heterosporous.