Johnson — Is Archceopteris a Pteridosperm ? 131 



knowledge, against the use of a term committing one to a preconceived idea. 

 We need a term which will stand for a group of primitive jplnuts which are no 

 longer purely aquatic, have begun to develop a vascular system, to show 

 differentiation into stem and leaf, and to reproduce themselves by sporangia. 

 Such a term is Archsegeophyta ; and, as an illustration of one member of 

 this group, I would mention a plant found in the Upper Devonian rocks of 

 Ireland, named by Baily " Sphenopteris sp.," and apparently identical with 

 Sphenopferi/s Devonica, linger, or as Nathorst thinks, with his Sphenopteridium 

 Keilliaui. The term " Primofilices " introduced by Arber to indicate the 

 primitive group from which the Filicinese arose, is unobjectionable if eon- 

 fined to Ferns. The term now proposed is more comprehensive, as it includes 

 the ancestral forms of the Ferns, and of the other groups mentioned. The 

 need of such a term is illustrated by the concluding paragraph of 

 M. P. Bertrand's " Etudes sur la fronde des Zygopteridese et Pterido- 

 spermes," where it is stated that the Zygopteridese and Pteridosperms are not 

 directly connected, but perhaps have their origin in a common stock, i.e. a 

 group of vascular Cryptogams in which the leaf or frond (appendage) had 

 ■ not yet attained to its fundamental feature of symmetry and branching. 

 Lignier adopts and employs in a wider sense Arber's term Primofilices, in 

 preference to his own of Propsilotaceee. 



Archseopteris seems capable, too, of throwing some light on the possible 

 paths of descent of the Spermophyta from the Pteridophyta. Thus in the 

 Aroidese we have a j^rimitive group of Monocotyledons so low in the scale 

 that it has, as has been said, no method of placentation of the ovule which 

 can be called the fixed, normal method. Every possible mode of placenta- 

 tion is represented in the Aroideae, as if the various ways were being tried 

 in the different genera. The spadix and spathe have a relationship to one 

 another roughly comparable to that of the " sporangiferous spike " to the 

 vegetative leaf in Ophioglossum.^ In both groups there are signs of the 

 same physiological division of labour. On the one cylindrical support are 

 borne a protective assimilating sterile expansion and a fertile part, on which 

 the reproductive organs are crowded together. In our specimen of Archse- 

 opteris, and in some Sphenophyllums, the same principle is illustrated in the 

 divided pinnules. In a discussion at Dresden a few years ago on the origin 

 of the Spermophyta, Wettstein, Porsch, and others traced a line of descent 

 of the Dicotyledons as represented by Casuariua from the Grnetaceee as 



' Anyone who has ohserved the leaves of Arum plants, as they break through the soil under the 

 hedgerow ia early spring, must have been struck by the similarity of their- appearance to that of 

 the unfolding fronds of an Adder's Tongue fern in a meadow. Is the resemblance of habit purely 

 supeiiicial, and not indicative of ancestral affinities ? 



u2 



