459, C) in which the distal portion is on the point of being separated as a small annular strand. This, Bertrand considers, would gradually become converted into a _Clepsydropsis_ form of stele as it passed to the petiole. Bertrand’s drawings made from a section of _Cladoxylon taeniatum_ (Ung.) (fig. 459, G) illustrate successive stages in the departure of a leaf-trace from one of the plate-like steles of the stem (fig. 459, B). In fig. 459, G, 1, a piece of the stele is detached and near its extremity is a group of thin-walled cells with protoxylem: a later stage is seen in fig. 2, and in fig. 3 a small ring of xylem is being detached which, Bertrand assumes, would later in its course be converted into the Clepsydropsoid strand (fig. 4), which consists of primary tissue. The weak point in Bertrand’s contention[522] is the absence of any proof of a true Clepsydropsoid trace in connexion with a _Cladoxylon_ stem, and there is a strong probability that the leaf-trace of _Cladoxylon_ has the form shown in fig. 459, E. _Cladoxylon Kidstoni_ Solms-Laubach[523]. This species, founded on imperfectly preserved material in Dr Kidston’s collection from Lower Carboniferous rocks in Berwickshire, is referred to _Cladoxylon_ on evidence that cannot be regarded as convincing. The type-specimen consists of a small piece of stem about 3 cm. in breadth showing three complete oval steles and portions of two others which seem to be in their original position and probably formed part of a series of peripheral steles such as those shown in fig. 459, D. Each stele consists mainly of secondary xylem (fig. 460, A) with some crushed tissue, presumably phloem, on its outer face. The secondary xylem is narrower on the inner side of each stele where a wedge-shaped piece is partially detached. In the centre there is a narrow area parallel to the long axis of the stele containing crushed tissue which probably consists of parenchyma and primary xylem, but the preservation is very imperfect. The secondary xylem has a fairly compact structure and the rays are narrow, 1–10 cells in depth. The pits of the tracheids are described by Solms as scalariform with occasionally two rows of elliptical pits on the radial walls. A careful examination of the type-specimen leads me to describe the pits as uniseriate and transversely elongated, very like those of _Protopitys_, or biseriate and almost circular like those of Conifers, the pits of the two rows being alternate or sometimes opposite (fig. 460, C): in places three rows of bordered pits are present. There is a certain degree of resemblance between the steles of this species and those of the South African stem _Rhexoxylon_[524], but the data are inadequate for a satisfactory comparison. [Illustration: Fig. 460. A, C. A single stele and tracheids of _Cladoxylon Kidstoni_. (Kidston Coll. 630 B, 630 C.) B. _Cladoxylon mirabile_, part of a stele. (Museum of Practical Geology, 15872.)]