[L] Figs. 2, 3, and 4 are drawn from nature by Prof. Penhallow, of McGill College. From comparison of this singular wood, the structure of which is represented in Figs. 2, 3, 4, with the _débris_ of fossil taxine woods, mineralised after long maceration in water, I was inclined to regard _Prototaxites_, or, as I have more recently named it, _Nematophyton_, as a primeval gymnosperm allied to those trees which Unger had described from the Erian of Thuringia, under the name _Aporoxylon_.[M] Later examples of more lax tissues from branches or young stems, and the elaborate examinations kindly undertaken for me by Professor Penhallow and referred to in a note to this chapter, have induced me to modify this view, and to hold that the tissues of these singular trees, which seem to have existed from the beginning of the Silurian age and to have finally disappeared in the early Erian, are altogether distinct from any form of vegetation hitherto known, and are possibly survivors of that prototypal flora to which I have already referred. They are trees of large size, with a coaly bark and large spreading roots, having the surface of the stem smooth or irregularly ribbed, but with a nodose or jointed appearance. Internally, they show a tissue of long, cylindrical tubes, traversed by a complex network of horizontal tubes thinner walled and of smaller size. The tubes are arranged in concentric zones, which, if annual rings, would in some specimens indicate an age of one hundred and fifty years. There are also radiating spaces, which I was at first disposed to regard as true medullary rays, or which at least indicate a radiating arrangement of the tissue. They now seem to be spaces extending from the centre towards the circumference of the stem, and to have contained bundles of tubes gathered from the general tissue and extending outward perhaps to organs or appendages on the surface. Carruthers has suggested a resemblance to Algæ, and has even proposed to change the name to _Nematophycus_, or "thread-sea-weed"; but the resemblance is by no means clear, and it would be quite as reasonable to compare the tissue to that of some Fungi or Lichens, or even to suppose that a plant composed of cylindrical tubes has been penetrated by the mycelium or spawn of a dry-rot fungus. But the tissues are too constant and too manifestly connected with each other to justify this last supposition. That the plant grew on land I cannot doubt, from its mode of occurrence; that it was of durable and resisting character is shown by its state of preservation; and the structure of the seeds called _Pachytheca_, with their constant association with these trees, give countenance to the belief that they are the fruit of Nematophyton. Of the foliage or fronds of these strange plants we unfortunately know nothing. They seem, however, to realise the idea of arboreal plants having structures akin to those of thallophytes, but with seeds so large and complex that they