The members of the Palæozoic Marattiaceæ which have structure preserved generally go by the generic name Psaronius, in which there is a great number of species. They show considerable uniformity in their essential structure (in which they differ noticeably from the group of ferns just described), so that but one type will be considered.
In external appearance they probably resembled the “tree ferns” of the present day (though these belong to an entirely different family), with massive stumps, some of which reached a height of 60 ft. The large spreading leaves were arranged in various ways on the stem, some in a double row along it, as is seen by the impressions of the leaf scars, and others in complex spirals. On the leaves were the spore sacs, which were in groups, some completely fused like those of the modern members of the family, and others with independent sporangia massed in well-defined groups. In their microscopic structure also they appear to have been closely similar to those of the living Marattiaceæ.
The transverse section of a stem shows the most characteristic and best-known view of the plant. This is shown in [fig. 91], in somewhat diagrammatic form.
The mass of rootlets which entirely permeate and surround the outer tissues of the stem is a very striking and characteristic feature of all the species of Psaronius. Though such a mass of roots is not found in the living species, yet the microscopic structure of an individual fossil root is almost identical with that of a living Marattia.
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.
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!
