Like Liverworts, Mosses have left very few traces of their existence in plant-bearing rocks. Without the aid of the characteristic moss-‘fruit’ or sporogonium it is almost impossible to recognise fossil moss-plant fragments. In species of the tropical genera _Spiridens_ and _Dawsonia_, e.g. _S. longifolius_[468] Lind. or _D. superba_[469] Grev. and _D. polytrichoides_[470] R. Br., the plant reaches a considerable length, and resembles twigs of plants higher in the scale than the Bryophytes. The finer branches of species of the extinct genus _Lepidodendron_ are extremely moss-like in appearance. Again, _Cyathophyllum bulbosum_ Muell[471], with its two kinds of leaves arranged in rows, is not at all unlike species of _Selaginella_ or the hepatic genus _Gottschea_. It is by no means improbable that some of the Palaeozoic specimens described as twigs of _Lycopodites_, _Selaginites_, or _Lepidodendron_, may be portions of mosses. The fertile branches of _Lycopodium phlegmaria_ in a fossil condition might be easily mistaken for fragments of a moss. In some conifers with small and crowded scale-leaves there is a certain resemblance to the stouter forms of moss stems. Such possible sources of error should be prominently kept in view when we are considering the value of negative evidence as regards the geological history of the Musci. A recent writer[472] on mosses has expressed the opinion that no doubt the Musci played an exceedingly important rôle in past time. Although we have no proof that this was so, yet it is far from improbable, and the absence of fossil mosses must no doubt be attributed in part to their failure to be preserved in a fossil state. In the numerous samples of Coal-Measure vegetation preserved in extraordinary perfection in the calcareous nodules of England, no certain trace of a moss has so far been discovered. The most delicate tissue in the larger Palaeozoic plants has often been preserved, and in view of such possibilities of petrifaction it might appear strange that if moss-like plants existed no fragments had been preserved. Their absence is, however, no proof of the non-existence of Palaeozoic mosses, but it is a fact which certainly tends towards the assumption that mosses were probably not very abundant in the Coal Period forests. Epiphytic mosses frequently occur on the stems and leaves of ferns and other plants in tropical forests. Such small and comparatively delicate plants would, however, be easily rubbed off or destroyed in the process of fossilisation, and it is extremely rare to find among petrified Palaeozoic plants the external features well preserved. It is probable that the forests extended over low lying and swampy regions, and that, in part, the trees were rooted in a submerged surface. Under such conditions of growth there would not be the same abundance of Bryophytes as in most of our modern forests.