THE OTHER BRITISH YERNS—POLTSTICHUM, ATHYRIUM, CETERACH 



Cumberland; it is absent from Scotland. The remaining species, A. ruta-muraria L., 

 A. Trichomanes L. and A. Adiantum-nigrum L., are fairly generally distributed and often 

 rich in individuals, the first two at least being familiar occupants of the cracks in masonry 

 in all our moister districts. 



Athyrium flexile n = 40 



Fig. 88. Explanatory diagram to Fig. 82 c. 

 X 1500. 



a h 



Fig. 89. Two diploid British species of 



Asplenium. Natural size. a. A. mari- 



«MmL. from a dried wild frond. b.A. 



viride Huds.from a living wild frond. 





Fig. 90. Meiosis in Asplenium viride 

 Huds., permanent acetocarmine. 

 X 1000. ?z = 36. 



A . marinum n -36 



Fig. 9 1 . Explanatory diagram to 



Fig. 93 c. X 2000. 



The easiest species to investigate cytologically, though not perhaps the simplest to 

 collect, are A. viride and A. marinum (Fig. 89). In their chromosomes these two resemble 

 each other very closely, and both possess a haploid chromosome number of 36 with 

 no uncertainty. The clearest demonstration of this number is contained in Fig. 90, 

 which represents a squash preparation oi A. viride, the root of which is represented by 

 Figs. 93 a and 94. A section of A. marinum is represented in Figs. 91 and 931;. 



99 



7-2 



