198 BLECHNOID FERNS [CH. 



regarded rather as consequences of parallel condensation of leaf-structure 

 from a more diffuse and highly branched ancestry, than as signs of real 

 affinity. Most varied examples of such condensation and vascular fusion are 

 to be found illustrated by Bertrand and Cornaille {Struct, d. Filic. actuelles, 

 Lille, 1902, Figs. 51, 54, 59, 65, 78), while the same is now seen also in 

 Diellia (Fig. 596). Gwynne-Vaughan has also noted the caliper-wise fusion 

 of the paired vascular straps in the petiole of Ceropteris caloinelanos (L.) 

 Und. = Gymnogramme chrysophyllnm Klf (MS. research notes). A like state 

 appears also in the thin petiole oi Adiantiwt (Luerssen, Rab. Krypt. Fl. Ill, 

 p. 82). Such evidences of condensation may be held as cognate to that seen 

 in the petioles of climbing Ferns systematically quite distinct from one 

 another, such as Gleichenia, Lygodium and Odontosoria (Vol. i, p. 171, 

 Fig. 165). All of these may be held as resulting from homoplastic contraction 

 of the conducting system in the elongated leaf-stalk. Thus notwithstanding 

 this point of anatomical similarity the Asplenioids and Blechnoids may still 

 be held as consequences of convergent evolution rather than as nearly akin. 

 The ancestry of the one appears to have been relatively hygrophytic, with 

 elaboration of the individual sorus (Dryopteroids); of the other xerophytic 

 with a tendency to soral fusion to form coenosori (Onocleoids and Blech- 

 noids). Nevertheless the ultimate source from which these all took their 

 origin was probably that now represented by the Cyatheoid Ferns : in these, 

 as in all the Ferns here discussed, the sori are superficial in origin, as they 

 are also in their adult position. 



The Blechnoid Ferns may be grouped under four heads, according to the 

 characters disclosed in this chapter. They are disposed as follows in a 

 roughly phyletic sequence. 



I. Coenosori continuous, running parallel to the mid-rib of the fertile 

 pinna: with or without a photosynthetic "flange." 



(i) Blechmuii Linn., 1753 ... ... ... ... 138 species. 



(2) 5«(^/m« Kaulfuss, 1824 ... ... ... 4 species. 



II. Coenosori showing an Acrostichoid spread over the lower surface of 

 the pinna or of the flange. 



(3) StenocJdaena ].'^m\'^-\, 1841 ... ... ... 11 species. 



(4) Brainea]. Smith, 1856 i species. 



III. Coenosori secondarily interrupted, the parts forming two or more 

 rows parallel to the mid-rib. 



(5) Woodwardia Smith, 1793 ... ... ... 7 species. 



(6) Doodia R. Brown, 1810 ... ... ... 6 species. 



