“The most interesting structural characteristic of _Osmundites Kolbei_ is not well seen in the figure owing to the compression of the xylem ring. This consists in the occurrence of tracheae in the pith. In fact, we have here a mixed pith, composed of parenchyma and true tracheae, a condition which connects the _Osmundaceae_ with a parenchymatous medulla with those possessing a solid xylem stele like _Zalesskya_ and _Thamnopteris_ and so completes the series of transitions extending from the older and solid-steled forms to the modern medullated members of the _Osmundaceae_.” _Osmundites skidegatensis_, Penhallow. This lower Cretaceous Canadian species, first described by Penhallow[791] and more recently by Kidston and Gwynne-Vaughan[792], is remarkable for the large size of the stem, the stele alone having a diameter of 2·4 cm. Penhallow figures a fragment of a leaf bearing a superficial resemblance to that of _Osmunda Claytoniana_, which may be the foliage borne by _Osmundites skidegatensis_. The xylem cylinder is broken by the exit of leaf-traces into 50 or more strands varying in size and shape, and it is noteworthy that the phloem is also interrupted as each leaf-trace is given off. In recent species the xylem cylinder is almost always interrupted, but the phloem retains its continuity. In the Canadian fossil an internal band of phloem occurs between the xylem and the pith, and this joins the external phloem at each leaf-gap. This internal phloem finds an interesting parallel in certain recent species[793], but in these the internal and external phloem do not meet at the foliar gaps as they do in the extinct type. In _Osmunda cinnamomea_ the internal phloem occurs only at the regions of branching of the stem stele; in the fossil it is always present. It is clear that _Osmundites skidegatensis_ represents the most complex type of stem so far recognised in the Osmundaceae; it illustrates a stage in elaboration of the primitive protostele in advance of that reached by any existing species. • • • • •