40 COENOPTERIDACEAE [CH. 



It thus appears that while the material facts are still insufficient for any 

 trustworthy phyletic arrangement of the Coenopteridaceae among themselves, 

 they nevertheless provide, as any synthetic group of organisms may well do, 

 suggestions of value in relation to the principles used for that purpose. 

 Their early occurrence coupled with the small size and simple structure of 

 some of them; their dichotomous branching, the indeterminate distinction 

 of axis and leaf; their simple hairs, not scajes; and their primitive sporangia 

 with numerous homosporous spores, collectively mark them out as general- 

 ised types. They ran into several lines of complexity of leaf-construction 

 based upon dichotomy: they illustrate increasing vascular complexity in 

 stem and leaf accompanying greater size of those parts: also advances are 

 seen in the grouping and relations of sporangia. All of these being biologi- 

 cally probable advances may be recognised as valid, and probably true. 

 They appear however to have been carried out separately and in various 

 distinct types; and in some instances, such as the complex petiolar structure, 

 not perpetuated in any more recent line of Ferns. Much may thus be learned 

 that is of value in fern-morphology from these plants, which represent more 

 nearly than any other known organisms the source from which the Class of 

 the Filicales probably took its origin. It is significant that the genus Botryo- 

 pteris is not only relatively small among the Coenopterids, but also very 

 simple in construction, while the larger Zygopterids are more complex 

 anatomically. It would appear probable that the former approach more 

 nearly than the latter to some primitive stock. It has been suggested in 

 Chapter xvii (Vol. l) that an archetype for Ferns may not improbably have 

 shared the general characteristics of the Flora of the Rhynie Chert: and the 

 problematical plant Stauropteris affords perhaps the most valid basis for 

 comparison with those primitive fossils. 



BIBLIOGRAPHY FOR CHAPTER XVIII 



323. Seward. Fossil Plants. Vol. ii, p. 432. 1919. 



324. Scott. Studies in Fossil Botany. 3rd Edn. 1920, p. 337. 



325. Renault. Ann. d'. Sci. Nat. Ser. vi. Vol. i. 1875. 



326. Renault. Flore Foss. d'Autun et d'Epinac. Part ii, p. 33. 



327. Renault. Cours de ]3ot. Foss. Vol. iii. Chap. viii. 



328. Williamson. Plants of the Coal Measures. Part ix. Phil. Trans. 1878. 



329. Stenzel. Die Gattung Tiibicaulis Cotta. Cassel. 1889. 



330. Stopes. Tiibicaulis Siifciiffii. Mem. and Proc. Manchester Litt. and Phil. Soc. 

 Vol. i. 1906. 



331. Kidston. Trans. Roy. Soc. Edin. xlvi. Part ii. 1908. 



332. Scott. Sporangia attributed to Botfyopteris antiqita Kidston. Ann. of Bot. xxi\', 

 p. 819. 1910. 



333. Benson. Botryopteris aiiiiqua. Ann. of Bot. xxv, p. 1045. 1911. 



334. Chambers. Axillary strands of Trichomanes. Ann. of Bot. xxv, p. 1037. 



335. Bertrand. Tiibicaulis Berthieri. Mdm. de la Soc. d'Hist. Nat. d'Autun. xxiv. 1911. 



