. Devonian floras; a study of the origin of Cormophyta. Paleobotany -- Devonian. VI] PTEROPSIDA 81. Several attempts have been recently made to determine whether Archaeopteris was a member of the Primofilices or a Pteridosperm, Kidston^ and others think the latter the more probable. We, however, agree with Johnson^ that there is absolutely no evidence that this very completely known type (at any rate in the case of A. hibernica) bore seeds. It is much more probably a Primofilix. The evidence of Rhacopteris, so far as it goes, agrees with this conclusion. On the other hand at least one Adiantit
. Devonian floras; a study of the origin of Cormophyta. Paleobotany -- Devonian. VI] PTEROPSIDA 81. Several attempts have been recently made to determine whether Archaeopteris was a member of the Primofilices or a Pteridosperm, Kidston^ and others think the latter the more probable. We, however, agree with Johnson^ that there is absolutely no evidence that this very completely known type (at any rate in the case of A. hibernica) bore seeds. It is much more probably a Primofilix. The evidence of Rhacopteris, so far as it goes, agrees with this conclusion. On the other hand at least one Adiantites (Fig. 43) was a seed-bearing plant, but here the seeds clearly arose by the metamor- phosis of a segment of the frond. No fructifications are yet known in the case of Cardiopteris. Another very common type of frond evolution is seen in Sphenojjteridium (Figs. 34, p. 61, 35, p. 62 and 44), beautifully fore- shadowed in the Psilophyton flora by Pseudo- sporochnus (Fig. 16, p. 34) and perhaps P/i7o- phyton (Fig. 13, p. 32), and fully developed in the Archaeopteris flora. Here the ends of large branches frequently divide, usually dichotomously, to form a tuft of very narrow forked, nerved segments^. This type of frond persisted long after the Devonian period. It is very common in Lower Carboniferous rocks, Sphenopteris qffinis (Fig. 45, p. 82) and S. bifida (Fig. 46, p. 82) among many others, and it is also met with in Upper Carboniferous times. The genus Eremopteris simply represents a somewhat peculiar modification of this tjq^e. Between Sphenopteridium and Sphenopteris it is not jiossible to draw any really satisfactory line.' The latter type possesses broader and more rounded segments as a rule, with a pinnate nervation. The term Sphenopteridiujn is in fact chiefly retained 1 Kidston (1906), p. 435. 2 Johnson (1911i). * A similar type of leaf also occurs where the division of an Archaeopteris or Rhacopteris type of pinnule is at its maximum. Fig. 44. Sphenopterid- ium m
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