THE GENUS DRTOPTERIS IN BRITAIN 



The interest of finding an entirely new chromosome number in each of these two 

 species is enhanced by two further circumstances. It has aheady been seen that the 

 gametic number of 41 is fundamental to the D. Filix-mas complex, the D. spinulosa 

 complex, to D. aemula and D. rigida, but as will be shown in detail in the next chapter, 



irm 



^^^^ ^ 





Fig. 66. Meiosis in Dryopteris Oreopteris (Ehrh.) Max. Fig. 67. Meios'is in Dryopteris Thelypteris 



showing « = 34, permanent acetocarmine. x 1000. (L.) A. Gray showing « = 35, per- 



For explanatory diagram see Fig. 65. manent acetocarmine. x 1000. For 



explanatory diagram see Fig. 68. 







^£ht 



S^ 



D. Thelypteris n-35 



Fig. 68. Explanatory diagram to Fig. 67. x 1500. 



it is equally so to a number of other related genera, notably Polystichum, Cyrtomium and 

 perhaps Woodsia. It must therefore be an ancient character which may even antedate 

 the evolutionary separation of Dryopteris. It would, however, be a mistake to suppose 

 on this account that the numbers 34 and 35 are merely recent developments from 

 this. The inference should probably be that the generic boundaries have here been 

 wrongly drawn, and some very instructive comments suggesting this have been made 

 from time to time by taxonomists. Thus in 1920 Christensen wrote: 'As I have tried 



80 



