130 ANCIENT PLANTS 



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 Marattiaceae. 



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 im- 

 portant in Palaeozoic 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 Marattiacese are isolated from the present success- 

 ful types of modern ferns. From the Psaroniece 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 Palaeozoic 

 and to have slowly dwindled ever since. It has been 



