The question as to the possible connection between the larger and smaller elements is one which is not as yet satisfactorily disposed of. Penhallow[378] regards the finer hyphal elements as branches of the larger tubes, but Barber[379], who has carefully examined good material of _Nematophycus Logani_, was unable to detect any organic connection between the two. My own observations are in accord with those of Barber. Further details and numerous figures of this species of _Nematophycus_ will be found in the memoirs of Carruthers, Penhallow and Barber. • • • • • Some specimens of silicified _Nematophycus_ stems afford particularly instructive examples of the state of preservation or method of mineralisation as a source of error in histological work. The sketches reproduced in fig. 39, D and E, were made from a section of a large specimen of _Nematophycus_ in the British Museum. In fig. D we have one of the radial spaces containing some indistinct small elements, the tissue surrounding the space appears to consist of polygonal cells suggesting ordinary parenchymatous tissue. In fig. E a few of these ‘cells’ are seen more clearly, they have black and ragged walls, and often contain very small and faint circles of which the precise nature is uncertain. The true interpretation of this form of structure was first supplied by Penhallow[380]. The black network simulating parenchymatous tissue consists of the substance of _Nematophycus_ tubes which has been completely redistributed during fossilisation and collected along fairly regular lines, as seen in figs. D and E. The original structure has been almost completely destroyed, and the material composing the walls of the large tubes has finally been rearranged as a network, interrupted here and there by the characteristic radial spaces which remain as evidence of the original _Nematophycus_ characters. It is possible in some cases to trace every gradation from sections exhibiting the normal structure through those having the appearance shown in figs. D and E to others in which the structure is completely lost. Penhallow describes this method of fossilisation in _N. crassus_ (Daws.); an examination of several specimens in the National Collection leads me to entirely confirm his general conclusions, and also to the opinion that _N. Logani_ shows exactly the same manner of mineralisation as _N. crassus_. The chief point of interest as regards this method of preservation lies in the fact that a fossil described by Dawson[381] as _Celluloxylon primaevum_, and referred to as a probable conifer, is undoubtedly a badly preserved _Nematophycus_. Penhallow examined Dawson’s specimens and obtained convincing evidence of their identity with certain forms of highly altered _Nematophycus_ stems. • • • • •