XLix] COENOPTERIDACEAE 269 



robust as regards cellular construction, and traversed by conducting strands 

 with a solid xylem-core. The surface might be glabrous, or invested with 

 simple hairs. The solitary sporangia would be relatively large and distal in 

 position, with thick walls and a simple method of dehiscence: and each would 

 contain numerous homosporous spores. The archetype thus specified presents 

 a real similarity to plants which have actually lived and are now well known, 

 viz. the Psilophytales of the Devonian Period. From some such type of 

 vegetation we may conceive the true Ferns, as distinct from the Pteridosperms, 

 to have sprung. There need be no attempt to link any type of the F'ilicales 

 directly to any type of the Psilophytales as offspring or progenitor. What is 

 important is to bear in mind while studying the earliest Filical types that 

 one of the oldest terrestrial Floras included vascular plants such as those 

 which were found in the Rhynie Chert. 



The Coenopteridaceae may be regarded as the characteristic Ferns of 

 early Palaeozoic times. Of these Staiiropteris appears as the most archaic 

 type (Vol. II, p. 28). Though plentiful in the Coal Measures, it is suggestive 

 that no axis has yet been associated with the upward-growing, slightly 

 bifacial rachis, with its alternating pairs of appendages. These themselves 

 branch again, so as to form a feathery plexus of delicate terete branchlets. 

 Some of them bear terminal sporangia, which differ from typical fern- 

 sporangia in being radially constructed, and opening by a distal pore. The 

 anatomical structure suggests on the one hand the Psilophytales, on the 

 other a Zygopterid character. If there actually was no axis, nor yet roots, 

 the similarity to the Psilophytales would be impressive. But alternatively 

 the question might then be asked whether Stmiropteris could be adopted as 

 a true Fern. (For a full discussion see Scott, Fossil Plants, 3rd edn.. Part I, 

 pp. 329,413.) 



The relation of Stauropteris to the Zygopterideae is generally admitted: 

 in the latter the Filical characters are clearer, for there is a definite relation 

 of axis and leaf, while the plant is rooted in the soil: but here again the 

 leaves are strangely complicated, often bearing four rows of appendages 

 (Vol. II, Chapter XVIll). The sori command special interest, for they appear 

 as distal tassels of massive, dorsiventral, annulated sporangia, with lateral 

 dehiscence. In Etapteris these are all separate, each on its own vascular 

 stalk: but in Corynepteris they are closely grouped into radial sori marginally 

 seated upon the narrow leaf-segments. In these three Zygopterids we may 

 see three probable steps in the origin of the radiate uni-seriate sorus, which 

 plays so distinctive a part in later types of Ferns, viz. the solitary distal 

 sporangium with terminal pore; the pedicellate tassel, and the compact 

 sessile sorus ; both of these last have lateral dehiscence. 



The Botryopterideae were relatively small plants with upright or creeping 

 shoot, rooted in the soil. Here the structure of the elongated rhizome may 



