14 The Irish Naturalist. February 



So that acutum is distinguished from Adiantum-nigrum 

 by having fronds twice as large, tripinnate throughout (not 

 bipinnate, or in the lower part tripinnate), with the apex 

 of the frond and of the pinnae extremely drawn out, the 

 pinnules " pinnatiiid-incised,"-^ and the lobes " acutely 

 subbidcntate " at the apex. The important characters here 

 are the fully tripinnate division and the caudate tips of the 

 frond and pinnae. 



As we trace this fern onward through botanical literature, 

 and as illustrations begin to be added to descriptions, a want 

 of uniformity of definition becomes apparent. 



Sadler^ says, " Frons . . . inf erius perfecte tripinnata, . . . 

 in medio bipinnata . . . Laciniae omnes lanceolatae, acutae, 

 acutissime et profonde inciso-dentatae,'' and emphasizes the 

 acuminate character of the tips of the frond and pinnae. 

 He thus does away with the essentially tripinnate character 

 on which the original description lays special emphasis. In 

 his subsequent work on the Ferns of Hungary,^ he says, 

 " laciniis lanceolatis, approximatis, acute et profunde inciso- 

 dentatis." 



Mackay* writes, " I found in 1805, on the limestone rocks 

 at Mucruss, a beautiful and delicate variety with fronds 

 tripinnate throughout, or with pinnules deeply and finely 

 laciniated " — again a description somewhat modified in 

 comparison with Bory's as regards the subdivision of the 

 frond. 



Newman^ (who follows Bory, Sadler, Sprengel® and 

 Presl^ in considering the plant a distinct species) says, 

 " Stipes very much longer than the frond, glabrous, black 



1 There is a slight contradiction here, since, if the pinnules are only 

 pinnatifid, the frond is only sub-tripinnate, not fully tripinnate. The 

 emphasis laid on the tripinnate character justifies the acceptance of this 

 as a criterion as between the type and the variety. 



2 " Adumbratio Epiphyllospermarum Hungariae," 28, 1820. 



3 " De Filicibus veris Hungariae," 31, 1830. 

 * " Flora Hibernica," 342, 1836. 



^ " History of British Ferns," ed. 3, 230, 1854. 



" " Linnaei Systema vegetabilium," 4 (pars i), 90, 1827. 



' " Tentamen Pteridographiae," 107, 1836. 



