A FERN FORMING A NEW GENUS — ETHERIDGE. 145 



to belong to Sphenopteris elegans, the cortex of which displayed 

 an exactly similar series of thickened horizontal parallel bands. 

 Still more recently, he received from ray friend Professor Von 

 Weiss, of Berlin, and forwarded to me, a beautiful specimen of an 

 exactly identical stem, attached to which are the unquestionable 

 pinnules of Sphe7iopteris elegans. As far as these internally 

 structureless specimens affect the question, they suggest the 

 possibility that both the species of Heterangium may also prove 

 to be Ferns." Again, speaking of the two genera already referred 

 to, Prof. Williamson remarked* — "One thing is certain, viz., 

 that in their internal organisation they present combinations of 

 tissues that find no representatives amongst living plants. Possibly 

 they are the generalised ancestors of both Ferns and Cycads, 

 which transmitted their external contours to the former, and their 

 exogenous modes of growth to the latter types. In considering 

 this possibility, we must not forget that in Stra.ngeria we have a 

 still living plant in which the stem of a Cycad bears fronds, the 

 leaflets of which retain the dichotomous nervation of a true Fern. 

 The Strangeria has retained, not only the primitive exogenous 

 stem of some ancestral type, in common with its other Cycadean 

 relatives, but also the peculiar Fern-like leaflets, which may also 

 have come down to it from Palaeozoic times. Hence we have 

 here a combination of Fern-like features and of an exogenous 

 mode of growth. Such being the case, it need not startle us if 

 we have to conclude that a similar cambination existed during the 

 Carboniferous age." On this subject Messrs. Williamson and 

 Scott remark conjointly! — ''In all cases where the petioles can be 

 determined as belonging to Rachopteris aspera, we now know that 

 we have to do with the foliage of Lyginodendron" thus confirm- 

 ing previous conclusions, " namely, that the leaf would fall under 

 the form-genus Sphenopteris of Brongniart, as shown by the finely 

 cut foliage and the acute angles between the veins. . . The 

 mere fact that the foliage of Lyginodendron resembled that of 

 certain Ferns is in itself no proof of affinity with Filices. The 

 classical case of Strangaria is a sufficient warning against any 

 such hasty inference. It must, however, be remembered that in 

 the foliage of Lyginodendron we have not only fern-like yor?/i and 

 venation, but also fern-like structure, whereas in the case of 

 Strangeria, a single transverse section of the petiole would be 

 sufficient to prove that the plant is no Fern but a Cycad." 



The form of the leaf in the present fossil is certainly that of a 

 fern, but unfortunately the structure is not in a sufficiently good 

 state of preservation to warrant any definite generalisations. 

 There is certainly no evidence of the existence of palisade paren- 

 chyma ; on the other hand the presence of a bifacial structure 



* Phil. Trans. (B) for 1887, clxxviii., p. 299. 

 t Phil. Trans. (B) for 1895, clxxxvi., p. 727. 



