THE OTHER BRITISH FERNS— POLTSTICHUM, ATHTRIUM, CETERACH 

 (Fig. gja, b) has a very characteristic appearance which does not resemble closely 

 any other species, least of all those with which it is habitually found. Its hybrid nature 

 has, however, long been suspected both from its sporadic and sohtary occurrence, single 



Fig. 96. Two non-British species of Asplenium, from living leaves, grown in cultivation. Natural size. 

 a. A. Petrarchae DC. from southern France, b. A.fontamm (L.) Bernh. from Switzerland. 



Fig, 



a b a 



97. Asplenium germanicum auct. non Weiss and its supposed parents, from living fronds grown in 

 cultivation. Natural size. a. A. germanicum horn V^ ales. Cf. Fig. 98. b. The same from Runmaro, 

 Sweden, c. A. Trichomanes L. from southern France, a very depauperate specimen, but shown to 

 be tetraplold. Cf. Fig. 103 a. d. A. septentrionale (L.) Hoffm. from Arthur's Seat, Scotland. 



plants only but never populations of similar plants being found, and also from an 

 apparently invariable association with A. septentrionale (Fig. 97^) and A. Trichomanes 

 (Fig. 97c). From this circumstance, added to the fact that the spores are always com- 

 pletely or almost completely abortive, it is generally thought to be a hybrid between 



102 



