XLix] GENERAL CONCLUSION 283 



a suspensor to those with none — all of these as well as others are essentially 

 independent steps, though the}' commonly march together. So usual is this 

 that when a discrepancy occurs the attention of the observer is at once drawn 

 to it. On the other hand, the discrepancies show that some degree of inde- 

 pendence of the several criteria actually exists. For instance, in Ophioglosswn 

 and in Christcnsenia stelar disintegration is associated with a massive Euspo- 

 rangiate structure; in Cheiropleuria a protostele, an undivided leaf-trace, and 

 dermal hairs are associated with an Acrostichoid sporophyll. Such examples 

 show that parallel progressions in respect of the several criteria, though 

 usual, are not obligatory. Nevertheless the conclusion that follows is that, 

 subject to exceptions, the organisation of a Fern has evolved as a whole, its 

 general progress being expressed in a plurality of characters which appear 

 distinct from one another, and may be subjected to separate comparative 

 treatment. There is in fact a general drift of organisation of the individual, 

 affecting as a rule all its parts. The organism behaves in its evolution as an 

 integer, or whole. 



Further, the progressions in respect of the several criteria are not restricted 

 to any single phylum: they are exhibited with a high degree of uniformity 

 in a plurality of phyla, which palaeontology shows to have been broadly 

 distinct from one another in descent from very early periods. The chief 

 lines of descent of Ferns are already suggested by Palaeozoic Fossils, but 

 they became for the most part clearh^ defined in the early Mesozoic Rocks. 

 From that time onwards, since the several phyla have maintained their 

 characteristic features, their evolution must have been independent and 

 homoplastic, however similar the steps of advance in the several phyla may 

 appear to be. Moreover, the progress in respect of these has not been 

 merely parallel, but at times actually convergent. It is this fact which has 

 led so frequently to those systematic difficulties which have found expression 

 in a wide synonymy. Its results centre round the old genera Polypodhmi, 

 Acrostic/mm, and Gyvinograminc. In their old extended sense none of these 

 represented of necessity any real kinship: the genera comprised Ferns that 

 show conditions or states of the sori now known to have been acquired b}- 

 types of quite distinct affinity. In fact these are not genera at all in the 

 phyletic sense. For instance, it is now recognised that the Acrostichoid 

 state has been arrived at along fully half a dozen different phyletic lines. 

 After the representatives of these have been severally allocated to their 

 natural places, the old genus in the strict systematic sense retains onl}' three 

 species, which are themselves advanced Pteroid derivatives. 



The fact is that advances shown in characters such as those above 

 enumerated have not been restricted to the individual, the species, the 

 genus, or even to the family. They have been liable to affect a plurality 

 of Families, or even the whole Class. The most striking instance of all 



