Somewhat higher up in the Lower Silurian, in the Cincinnati group of America, Lesquereux finds objects which he refers to the genus _Sphenophyllum_, which is closely allied to _Annularia_ (Fig. 84, _a_), and also a plant which he terms _Protostigma_ (Fig. 84, _b_), and believes to be the stem of a tree allied to the club-mosses.[27] He also finds minute branching stems, which he refers to the genus _Psilophyton_, to be mentioned in the sequel; but as to these I have some doubts whether they may not be Zoophytes allied to the Graptolites, rather than plants of that genus. These discoveries tend to show the probable existence in the Siluro-Cambrian of plants representing two of the three leading families of the higher cryptogams or flowerless plants, namely, the Club-mosses and the Mare’s-tails. Thus land vegetation begins with the highest members of the lower of the two great series into which botanists divide the vegetable kingdom. [Illustration: FIG. 86.—Fragment of outer surface of _Glyptodendron_ of Claypole. A Silurian Tree.] If we now turn to the Silurian, further evidence of land vegetation presents itself. Near the base of this great series, the club-moss family is represented by a plant discovered by Claypole in the Clinton group, and referred to a new genus (_Glyptodendron_, Fig. 86). Plants of this family have also been noticed by Barrande in Bohemia, and by page in Scotland; and a humble but interesting member of the family, connecting it with the pillworts, _Psilophyton_ (Fig. 87), though more characteristic of the Devonian, has been found in the Upper Silurian both in Canada and the United States. No Ferns or Equiseta have as yet been found in the Silurian; but in 1870 I recognised in some fragments of wood from the Ludlow bone-bed, in the Museum of the Geological Survey of Great Britain, the structure of that curious prototypal tree, to which I have given the name _Nematophyton_, and which was first recognised in the Devonian of Gaspé. Since that time I have found in the Upper Silurian beds of Cape Bon Ami, in New Brunswick, similar fragments of fossil wood, associated with round seed-like bodies, having a central nucleus and a thick wall or test of radiating fibres. These bodies show a structure similar to that of those found in the Upper Ludlow of England, and described by Hooker under the name _Pachytheca_. In my judgment they are certainly true seeds.[28] Seeds of this kind have also been found by Hicks in the still older Denbighshire grits of North Wales, along with fragments of the wood of _Nematophyton_, and with remains of branching stems which have been described under the name _Berwynia_, though it is not unlikely that they represent the branches of _Nematophyton_. It is proper to add that these ancient vegetable fossils are regarded by some English botanists as gigantic algæ or sea-weeds, but I confess I am unable to adopt this view of their nature.