PROLOGUE TO VOLUME II 



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Euripides, Suppliants 653-4. 

 " On a far-looking tower I stood to watch, 

 And three tribes I beheld, of war-bands three." 



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In offering this Second Volume on the Ferns, the author may fitly quote 

 these words of the messenger in the Greek Play. By establishment of the 

 twelve criteria of comparison detailed in the first Volume we have taken 

 our place upon a tower of vision. Thence we may now witness the phyletic 

 advance. As the armies in the play were seen to be formed in three distinct 

 columns, each moving independently, so also the three main phyla of Ferns, 

 which our comparative study will disclose, may be held to have progressed 

 independently in their evolutionary march, their separate movements being 

 discernible by the observer from his point of vantage. It is immaterial that 

 on both sides of our comparison the number is three. Later writers on Ferns 

 may recognise some different number. The point is that each phylum takes 

 its own course : in fact the evolutionary movements are polyphyletic. 



An impressive feature that will emerge from further phases of this study 

 of Ferns is that the lines of development, previously distinct, converged in 

 character as their evolution progressed. Their constituent genera and species 

 thus assumed features so similar that it may often baffle the student to trace 

 their phyletic origin. As in the battle, graphically described by the messenger 

 in the play, the several columns finally merged in an inextricable melee, so 

 in the later phases of the evolution of Ferns it becomes difficult or even im- 

 possible to segregate completely the several phyla of descent according to 

 their detailed features. But this problem of convergent evolution will be 

 reserved for later treatment : the present Volume deals with the evolutionary 

 progressions of earlier geological time. 



The author desires to acknowledge with gratitude the continued assistance 

 given by the Carnegie Trustees, in the form of a grant towards the cost of 

 illustration of this Volume. By such means they promote the advancement 

 of science in a most practical way. 



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