on one's fingers, Schimper in his vegetable palæontology enumerates about eighty species of Carboniferous _Sigillariæ_; and while on the one hand many of these are so imperfectly known that they may be regarded as uncertain, on the other hand many species must yet remain to be discovered.[CA] Now, in so vast a number of species there must be a great range of organisation, and, indeed, it has already been attempted to subdivide them into several generic groups. The present state of the question appears to me to be this, that in these _Sigillariæ_ we have a group divisible into several forms, some of which will eventually be classed with the Lepidodendra as lycopods, while others will be found to be naked-seeded phænogams, allied to the pines and cycads, and to a remarkable group of trees known as _Cordaites_, which we must shortly notice. [CA] In a recent memoir (Berlin, 1887) Stur has raised the number of species in one subdivision of the _Sigillariæ_ (the _Favulariæ_) to forty-seven! [Illustration: Fig. 38.--_Stigmaria_ root, seen from above, showing its regular divisions. From "Acadian Geology".] [Illustration: Fig. 39.--Portion of bark of _Stigmaria_, showing scars of attachment of rootlets.] Before considering other forms of Carboniferous vegetation, let us glance at the accumulation of coal, and the agency of the forests of _Sigillariæ_ therein. Let us imagine, in the first instance, such trees as those represented in the figures, growing thickly together over vast swampy flats, with quantities of undergrowth of ferns and other plants beneath their shade, and accumulating from age to age in a moist soil and climate a vast thickness of vegetable mould and trunks of trees, and spores and spore-cases, and we have the conditions necessary for the growth of coal. Many years ago it was observed by Sir William Logan that in the coal-field of South Wales it was the rule with rare exceptions that, under every bed of coal, there is a bed of clay filled with roots of the _Stigmaria_, already referred to as the root of _Sigillaria_. This discovery has since been extended to all the coal-fields of Europe and America, and it is a perfectly conclusive fact as regards the origin of coal. Each of these "under-clays," as they are called, must, in fact, have been a soil on which grew, in the first instance, Sigillariæ and other trees having stigmaria-roots. Thus, the growth of a forest of _Sigillariæ_ was the first step toward the accumulation of a bed of coal. More than this, in some of the coarser and more impure coals, where there has been sufficient earthy matter to separate and preserve impressions of vegetable forms, we can see that the mass of the coal is made up of flattened _Sigillariæ_, mixed with vegetable _débris_ of all kinds, including sometimes vast quantities of lepidodendroid spores, and the microscopic study of the coal gives similar results (Fig. 40). Further, on the surfaces of many coals, and penetrating the shales or