In dealing with the structure of Palaeozoic plants, we shall be under constant obligation to the splendid series of memoirs from the pen of Prof. Williamson[34]. As the writer of a sympathetic obituary notice has well said: “In his fifty-fifth year he began the great series of memoirs which mark the culminating point of his scientific activity, and which will assure to him, for all time, in conjunction with Brongniart, the honourable title of a founder of modern Palaeobotany[35].” If we look back through a few decades, and peruse the pages of Lindley and Hutton’s classic work[36] on the Fossil flora of Great Britain, a book which is indispensable to fossil botanists, and read the description of such a genus as _Sigillaria_ or _Stigmaria_; or if we extend our retrospect to an earlier period and read Woodward’s description of an unusually good specimen of a _Lepidodendron_, and finally take stock of our present knowledge of such plants, we realise what enormous progress has been made in palaeobotanical studies. Lindley and Hutton, in the preface to the first volume of the Flora, claim to have demonstrated that both _Sigillaria_ and _Stigmaria_ were plants with “the highest degree of organization, such as _Cactaeae_, or _Euphorbiaceae_, or even _Asclepiadeae_”; Woodward describes his _Lepidodendron_ (Fig. 1) as “an ironstone, black and flat, and wrought over one surface very finely, with a strange cancellated work[37].” Thanks largely to the work of Binney, Carruthers, Hooker, Williamson, and to the labours of continental botanists, we are at present almost as familiar with _Lepidodendron_ and several other Coal-Measure genera as with the structure of a recent forest tree. While emphasizing the value of the microscopic methods of investigation, we are not disposed to take such a hopeless view of the possibilities of the determination of fossil forms, in which no internal structure is preserved, as some writers have expressed. The preservation of minute structure is to be greatly desired from the point of view of the modern palaeobotanist, but he must recognise the necessity of making such use as he can of the numberless examples of plants of all ages, which occur only in the form of structureless casts or impressions. [Illustration: FIG. 1. Four leaf-cushions of a _Lepidodendron_. Drawn from a specimen in the Woodward Collection, Cambridge. (Nat. size.)]