THE ANCIENT FERNS 



fixed in cultivation in April of the following year. The chromosomes are fairly large 

 and very distinct (Figs. 268-269). Their number is ^ = 45. This number has not so far 

 been found elsewhere in the ferns, a fact which is of no special importance. Further 

 comment must, however, await the study of a greater number of species. 



Turning now to the Hymenophyllaceae we have three British species to consider. 

 The Killarney Fern, our only species of Trichomanes, is almost confined to the very moist 

 conditions of the west of Ireland from whence it derives its name. The two species of 

 Hymenophyllum, the Filmy Ferns of our mountains and of a few lowland localities such as 

 the Common at Tunbridge Wells from which H. tunbridgense has long since disappeared, 



♦r * * + * 



♦ -* ♦ . ^ 







% * 





f 





fi 



^i 



Fig. 268. Meiosis in Botrychium lunaria 

 (L.) Sw., permanent acetocarmine. 

 X 1000. For explanatory diagram 

 see Fig. 269. ^ = 45. 



Bof-rychium n = 45 



Fig. 269. Explanatory diagram to 

 Fig. 268. X 1500. 



are widespread and not difficult to find, though H. unilaterale is the more abundant of the 

 two in most parts of England. Both rank among our smallest vascular plants though 

 they may each cover extensive surfaces with a dense mat of saturated, translucent 

 foliage on suitable shaded rocks or even, at the extreme west of our islands, on the bare 

 ground. 



Considering the very delicate nature of their leaves all British members of the 

 Hymenophyllaceae are surprisingly hardy in cultivation though they are not always fer- 

 tile under these conditions, and fixations should therefore, if possible, be made in their 

 native haunts. I was unable to do this with Trichomanes, but I was fortunate in receiving 

 some very fertile leaves of Irish origin from the Botanic Garden at Glasnevin in Dublin, 

 one of which is represented in Fig. 270. The chromosomes of this species appear in 

 Figs. 271 and 272. They are fairly large and their number is n = 72. The longevity of 

 this leaf was so astonishing, it being remembered that the lamina is only two cells thick, 

 that the facts are worthy of mention. It remained shut up in a tin box for four weeks in 

 total darkness after the fixings had been taken, at the end of which time it was still fresh 

 and green and the sori had increased considerably in size by comparison with the other 

 specimen which had been pressed at once. 



270 



