APOGAMOUS FERNS. EVOLUTION OF THE SEPARATE SPECIES 



Other there is the unmodified natural wild species to which reference has already been 

 made in Chapter 5, with its range of polyploid chromosome numbers. Taking the 

 monstrosities first, the polydactylas need not detain us long. Evidence has already been 

 presented, both by Dopp and in Figs. 45-7 of Chapter 4, that these two forms follow 

 the normal story common to apogamous ferns in general, and it was already known to 



Fig. 194. Meiosis in Dryopteris remota A.Br, in balsam after acetocarmine. x 1000. a. From an eight- 

 celled sporangium with regular pairing, b. From a sixteen-celled sporangium with virtually no 

 pairing. 



Fig. 195. One pinna oi Dryopteris Borreri var. polydactyla Dadds, Natural size. 



Compare with var. Wills on p. 58. 



Farmer and Digby (1907) that two different chromosome numbers are represented. 

 It is not surprising that Farmer and Digby 's actual counts are incorrect, considering 

 the early date of their investigation, and it is perhaps sufficient to emend their statement 

 by the demonstration already given (Fig. 45) that var. polydactyla Wills is a diploid 

 with 82 chromosomes in both generations, whilst var. polydactyla Dadds (Fig. 196) is 

 approximately triploid. Further, as Fig. 196^ illustrates, there is complete failure of 

 pairing in the sixteen-celled sporangia, at least in the latter variety. 



Of far greater importance than the monstrosities which, at most, have a historic 

 interest, is the study of the naturally occurring wild species. Here we have evidence 

 from Britain, Switzerland, Germany, and more recently Norway. Fig. 197 indicates 



187 



