In summing up our information as to the structure of _Nematophycus_ we find there are certain points not definitely settled, and which are of considerable importance. The few recorded instances of spore-like bodies by Penhallow and Barber are not satisfactory; we are still ignorant of the nature of the reproductive organs. Such instances of lateral appendages as have been referred to do not throw much light on the habit of the plant. So far as we know at present the stem of _Nematophycus_ was not differentiated internally into a cortical and central region. It may be that the specimens have been only partially preserved, and the coaly layer which occasionally surrounds a stem may represent a carbonised cortex which has never been petrified. The large and loosely arranged tubes constitute the chief characteristic feature of the genus; in some cases (_N. Logani_) there is an accompanying plexus of smaller hyphae, in others (_N. Storriei_) there is no definite division of the tissue into two sets of tubes of uniform size, and in _N. Ortoni_ the tubular elements are all of the large type. Penhallow has recognised the branching of large tubes in _N. Logani_ and _N. crassus_ giving rise to the small hyphal elements. In most specimens, however, no such mode of origin of the smaller tubes can be detected. The spaces which interrupt the homogeneity of the tissues in some forms have been described as branching depots, on account of the frequent occurrence in these areas of much branched hyphae. The function of these spaces (fig. 39, D, and fig. 40) may be connected with aeration of the stem-tissues.