246 VITTARIOID FERNS [CH, 



Comparison 



The Vittarieae as now constituted are believed to be a coherent and 

 natural group of genera. But in their systematic history they have been 

 arbitrarily distributed on the ground of external characters, while other 

 Ferns which have now been placed elsewhere have been associated with them 

 on similar grounds. It is only as the internal details become available that 

 such sorting can be carried to a sound conclusion, and the Vittarieae offer 

 one of the best examples of a natural classification following on detailed 

 enquiry. The grounds for grouping together the five genera have been thus 

 summarised by Von Goebel (1924, p. 93): (i) the arrangement of the sori 

 along the veins: (2) the possession of a stomium of four cells: (3) the 

 presence of paraphyses: (4) spicular cells in the leaves: (5) the absence of 

 sclerenchyma in the rhizomes: (6) clathrate scales: (7) abnormal prothalli. 

 To these may be added the simple form of the leaves, a feature probably 

 related to the epiphytic habit; which is shared by other epiphytes. The 

 sum of these characters, together with the specialised stelar structure, the 

 frequent recurrence of reticulate venation, and the highly specialised type of 

 the sporangia, all point to an advanced place among the Leptosporangiate 

 Ferns. But as a first step, a grouping of the genera among themselves 

 would probably give substantial help in deciding what the place of the 

 family should be in relation to the larger groups. 



A key to some general view of the grouping of the Family has been 

 provided by Von Goebel in the suggestion that in Hecistopteris we see a 

 dwarfed state, in which propagation is imposed upon the plant early. All 

 its leaves are of the nature of juvenile leaves; they never get beyond that 

 state, but bear sori even upon an open venation. Such open venation is 

 found in the juvenile leaves oi Antroplijnnn, but it is only a phase quickly 

 passed over in the ontogeny (Fig. 746). If the leaf (Q oi Antrophywn be 

 compared with the leaf (/) of Hecistopteris, they are seen to coincide in 

 venation: but while a sorus is present in the latter, there is none in 

 Antrophyuvi. In its later leaves, however, the vascular loops are closed 

 (Z>, E) ; and it is upon these, in leaves still later in the ontogenetic series, 

 that the sori are borne. From a very wide comparison of Ferns it is held 

 that phyletically an open venation preceded a closed one. If that criterion 

 holds for the Vittarieae, then the sporophyll of Hecistopteris is nearer to an 

 original type than those of either Antrop/iyiun or Vittaria. Probably the 

 distal cutting, present in Hecistopteris but absent in all the other genera, is 

 also an ancestral character which they no longer retain. 



If this reasoning be sound, then Hecistopteris, with its linear sori, will more 

 nearly reflect a primitive state than the rest, notwithstanding the small size 

 and simple structure of the plant as a whole. Nearest to it sorally would be 



