54 MORPHOLOGY OF GYMNOSPERMS 



The general conclusion is that " ferns with marattiaceous affinities 

 formed an important constituent of the permo-carboniferous flora, 

 especially toward the close of that period" (82). 



Primofilices. — Only one family of Primofilices has been distin- 

 guished clearly, and that is the peculiar group Botryopterideae, 

 brought to light by Scott (24), and probably extensively displayed 

 during the Paleozoic. The structure of all the important organs of 

 two of the genera (Zygopteris and Botryopteris) is fairly well known. 

 The stems are monostelic; those of Botryopteris being endarch pro- 

 tostelic and the vascular cylinder circular in section; while those of 

 Zygopteris are exarch protostelic and the vascular cylinder has a 

 lobed (five-rayed) section. In the latter genus the stele is differen- 

 tiated into a peripheral region of large tracheids, and a central region 

 (once thought to be pith) of small tracheids; and there is both internal 

 and external protoxylem. Among Botryopterideae, therefore, there 

 is both exarch and endarch protostely (79), and these conditions 

 vary in a single group. For example, one of the two groups of the 

 family contains Botryopteris, which is endarch; Tubicaulis, all or 

 nearly all of whose xylem is centripetal; and Grammatopteris, which 

 is exarch. The exarch protostele of Tubicaulis and Grammatopteris 

 has been regarded as the most primitive type of vascular strand found 

 in the axis of a vascular plant (75). The range of vascular struc- 

 ture displayed by the Botryopterideae is said (65, 75) to be sufficient 

 to serve as a starting point for the modern groups of ferns and for 

 Cycadofilicales. 



The sporangia of Zygopteris and Botryopteris are elongated sacs, 

 with walls at least two layers of cells thick, each with a short pedicel, 

 and borne in terminal tufts (3-8) on a common peduncle (fig. 52) from 

 a branching rachis of a dimorphic leaf (la). In Zygopteris there is a 

 vertical annulus band, several cells wide (multiseriate), on each side 

 of the sporangium (figs. 53 and 54) ; while in Botryopteris there is 

 such a band only on one side. That these sporangia are those of 

 ferns is further indicated by the fact that in Stauropteris, whose 

 affinities are probably with the Botryopterideae, germinating spores 

 of undoubted fern character have been found (70). 



The conclusion is (82) that in habit, anatomy, and sporangia, 

 the Botryopterideae show that they are ferns, which in all probability 



