THE OTHER BRITISH FERNS 



for W. ilvensis and « = 82 for IV. alpina, and the maximum possible error is in both 

 species no more than one chromosome in the monoploid count. This uncertainty arises 

 from the presence of what appears to be a foreign body accidentally superimposed on 

 the cell of Fig. 108 a and indicated as such in the diagram. It gives, however, a super- 



a b 



Fig. 108. Meiosis in British pyoorfyfa, from permanent acetocarmine preparations, x 1000. For explana- 

 tory diagrams see Fig. 109. a. W. ilvensis (L.) R.Br. ^ = 41. b. W. alpina (Bolton) S. F. Gray. 

 n = 82. 



Woods la ilvensis n= 41 Woodsia alpina n - 82 ^ 



a b 



Fig. 109. Explanatory diagrams to Fig. 108. x 1500. 



ficial resemblance to an extra chromosome. As long as slight uncertainty affects the 

 monoploid count it would be unwise to depend on the higher number of the other species 

 (Fig. lo^b) for greater precision. These numbers should therefore for the moment be 

 accepted as probable, though not quite certain. The fact that in Woodsia we must for 

 the moment be content with less than the usual precision is due to the very delicate 



1 1 1 



