I may here refer to the fact that the lower limit of the trees of this group coincides, in America, with the upper limit of those problematical trees which in the previous chapter I have named Protogens (_Nematophyton_, _Celluloxlyon_,[BM] _Nematoxylon_[BN]), though _Aporoxylon_ of Unger extends, in Thuringia, up to the Upper Devonian (Cypridina schists). [BM] "Journal of the Geological Society," May, 1881. [BN] _Ibid._, vol. xix, 1863. V.--Scottish Devonian Plants of Hugh Miller and others. (Edinburgh Geological Society, 1877.) Previously to the appearance of my descriptions of Devonian plants from North America, Hugh Miller had described forms from the Devonian of Scotland, similar to those for which I proposed the generic name _Psilophyton_; and I referred to these in this connection in my earliest description of that genus.[BO] He had also recognised what seemed to be plants allied to Lycopods and Conifers. Mr. Peach and Mr. Duncan had made additional discoveries of this kind, and Sir J. Hooker and Mr. Salter had described some of these remains. More recently Messrs. Peach, Carruthers, and McNab have worked in this field, and still later[BP] Messrs. Jack and Etheridge have summed up the facts and have added some that are new. [BO] "Journal of the Geological Society," London, 1859. [BP] _Ibid._, 1877. The first point to which I shall refer, and which will lead to the other matters to be discussed, is the relation of the characteristic _Lepidodendron_ of the Devonian of eastern America, _L. Gaspianum_, to _L. nothum_ of Unger and of Salter. At the time when I described this species I had not access to Scottish specimens of _Lepidodendron_ from the Devonian, but these had been well figured and described by Salter, and had been identified with _L. nothum_ of Unger, a species evidently distinct from mine, as was also that figured and described by Salter, whether identical or not with Unger's species. In 1870 I had for the first time an opportunity to study Scottish specimens in the collection of Mr. Peach; and on the evidence thus afforded I stated confidently that these specimens represented a species distinct from _L. Gaspianum_, perhaps even generically so.[BQ] It differs from _L. Gaspianum_ in its habit of growth by developing small lateral branches instead of bifurcating, and in its foliage by the absence or obsolete character of the leaf-bases and the closely placed and somewhat appressed leaves. If an appearance of swelling at the end of a lateral branch in one specimen indicates a strobile of fructification, then its fruit was not dissimilar from that of the Canadian species in its position and general form, though it may have differed in details. On these grounds I declined to identify the Scottish species with _L. Gaspianum_. The Lepidodendron from the Devonian of Belgium described and figured by Crepin,[BR] has a better claim to such identification, and would seem to prove that