Though these plants were so successful and so important in Palæozoic times, the group even then seems to have possessed little variety and little potentiality for advance in new directions. They stand apart from the other fossils, and the few forms which now compose the living Marattiaceæ are isolated from the present successful types of modern ferns. From the _Psaronieæ_ we can trace no development towards a modern series of plants, no connection with another important group in the past. They appear to have culminated in the later Palæozoic and to have slowly dwindled ever since. It has been suggested that the male fructifications of the Bennettiteæ and the Pteridosperms show some likeness to the Marattiaceæ, but there does not seem much to support any view of phylogenetic connection between them. [Illustration: Fig. 91.—Transverse Section of Stem of _Psaronius_ _v_, Numerous irregularly-shaped steles; _s_, irregular patches of sclerenchyma; _l_, leaf trace going out as a horseshoe-shaped stele; _c_, zone of cortex with numerous adventitious roots _r_ running through it; _sc_, sclerized cortical zone of roots; _w_, vascular strand of roots.] Before leaving the palæozoic ferns, mention should be made of the very numerous leaf impressions which seem to show true fern characters, though they have not been connected with material showing their internal structure. Among them it is rare to get impressions with the _sori_ or sporangia, but such are known and are in themselves enough to prove the contention that true ferns existed in the Palæozoic epoch. For it might be mentioned as a scientific curiosity, that after the discovery that so many of the leaf impressions which had always been supposed to be ferns, really belonged to the seed-bearing Pteridosperms, there was a period of panic among some botanists, who brought forward the startling idea that there were _no_ ferns at all in the Palæozoic periods, and that modern ferns were degenerated seed-bearing plants! [Illustration: Fig. 92.—Impression of Palæozoic Fern, showing _sori_ on the pinnules. (Photo.)]