i6o 



ONOCLEOID FERNS 



[CH. 



primitive Cyatheoid type into boreal and alpine climates. There additional 

 protection was a necessity, which has here been achieved partly by their firm 

 texture and by seasonal leaf-fall, partly by heterophylly, and partly by their 

 investure with broad protective scales. The two parallel series may be held 

 as outstanding colonists, in which the leaves more especially have been 

 modified so as to meet the conditions of the more exacting habitats to 

 which they have spread. They may in fact be regarded respectively as arctic 

 and xerophytic derivatives from the more primitive Cyatheoids. 



The anatomy of these Ferns accords with this view. The simple dictyostele 

 of J/, intermedia (Fig. 682) is only a slight advance on that of Lophosoria. 

 The leaf-trace of this Fern is divided in large leaves 

 into three straps, which unite upwards into a single 

 meristele. In Matteuccia, in accordance with its 

 smaller size, the trace divides only into two straps: 

 but these again fuse upwards into a single meristele 

 of essentially similar character to that of Lophosoria 

 (Fig. 685). This is the type of petiolar structure 

 described by Bertrand and Cornaille as the "Ono- 

 cleoid Trace" {^Structure des Filicinees actuelles, Lille, 

 1902, p. 91). Thus the vascular anatomy harmonises 

 with the view of the Onocleoids as being derivative 

 from an early Cyatheoid source. 



But the greatest interest naturally centres round 

 the sporophylls. The simply pinnate sporophyll with 

 narrow enrolled pinnae is a type that is not present 

 in the Cyatheoids. Among primitive Ferns it is seen 

 in Plagiogyria. Notwithstanding its markedly oblique 

 annulus, its dermal hairs, and as now known its mixed 

 sorus, Plagiogyria was long ranked as a section of 



the gen.us Lomaria (Hooker, Syn. Fil. 1883, p. 182). tV^petiokof J/a7^«^rrV«*5?/-«- 

 The heterophyllous condition alone does not justify t'jiopieris: C is near its base, 



. -^ A from a middle position, and 



that actual relationship, and for reasons given in ^ from a higher level. (After 

 Chapter XXXI Plagiogyria has been provisionally ^^''^'-and and Comaille.) 

 placed in relation to the Osmundaceae. With this exception heterophylly of 

 the Lomarioid type appears to be distinctive among Ferns where the sorus 

 is a separate entity. If the venation of the sporophylls and the disposition 

 of the sori upon them be examined, it is apparent that the Pecopterid open 

 type is common to the Cyatheoids and Onocleoids, while in the latter the 

 sterile and fertile leaves differ only in the sporophyll being narrower, and 

 the vein-branchings fewer. Further, the disposition of the sori upon them 

 follows the Cyatheoid type, where only one sorus appears on each vein, 

 inserted laterally upon it. The distance of insertion from the mid-rib may 



