THE GENUS DRTOPTERIS IN BRITAIN 

 widely different sources and to owe their present resemblance to parallel evolution. 

 Within the curtailed genus Dryopteris polyploidy and hybridization are rife; the other 

 three genera are still too few in analysed species for conclusions to be drawn. Apogamy 

 has arisen repeatedly, both in the restricted genus Dryopteris and in the relatively un- 

 related Beech Fern, thereby adding a very clear example of the polyphyletic origin 

 of a fairly complicated set of characters. 



V 



Oak Fern (Gt/mnocarpium) n = 80 



Fig. 73. Explanatory diagram to Fig. 72 c. x 1500. 



SUMMARY 



Since the above statement recapitulates most of the points of general interest raised in 

 the chapter a formal summary may perhaps be replaced by a simple hst in which the 

 cytological facts of this chapter and the last are assembled. The specific and generic 

 subdivisions follow the conclusions given in the text of both chapters, but special 

 attention should perhaps be drawn to the newly discovered diploid forms of D. dilatata, 

 PP- 75-785 ^^^ ^- Villarsii [D. rigida), p. 65, both of which deserve further study. 



86 



