126 ENGLISH BOTANY. 



Mr. Christie says that the stipes varies considerably in length. " In 

 the specimens sent, those in which it is long were taken out of chinks 

 in the rock, and therefore lengthened to bring the fronds towards the 

 light ; those in which the stipes is short were growing in an open 

 situation." 



The third subspecies admitted by Milde, " Onopteris," which 

 contains the var. " acutum" is frequent in the Mediterranean region, 

 Madeira, and the Canary Isles. I have not seen it in this country 

 except from the south of Ireland, and Mr. T. Moore also has seen 

 true examples of this variety only from Ireland, though it is closely 

 approached by English forms, and also by one which Mr. Moore 

 calls " oxypliyllum" gathered near Dunoon and near Stirling, but 

 which I have not seen. I am indebted to Mr. J. F. Duthie for 

 living plants of genuine acutum from the neighbourhood of Florence. 

 It differs conspicuously from the ordinary Adiantum-nigrum in the 

 texture of its fronds, which are not thick, cartilaginous and opaque, 

 as in the common form, and have a satiny, not a greasy lustre ; this 

 apparently arises from the epidermal cells being narrower in acutum 

 than in A. Adiantum-nigrum, at least this is the case with Mr. Duthie's 

 plants, but unfortunately this character is in a great measure lost in 

 dried specimens, which can be distinguished only by the longer stipes, 

 the deltoid-ovate outline of the more divided frond with narrow and 

 elongated ultimate segments. It appears to attain a larger size than 

 the other forms. The largest Irish specimen I possess has a stipes 

 8 inches long, and a lamina of 5^ by 3 inches at the broadest part ; 

 but a specimen from Naples has it 10^ inches long by 7 inches broad, 

 and Teneriffe specimens are quite as large. Mr. Moore has an Irish 

 specimen with the lamina of the frond 9 inches long and 7 inches 

 broad. 



Mr. Kinahan, of the Geological Survey of Ireland, has supplied 

 me with some notes on the Irish forms of Adiantum-nigrum. " In 

 north-west Gralway and south-west Mayo the A. Adiantum-nigrum 

 seems to grow as follows. It is always associated with more or 

 less calcareous rocks, which may be shales, limestones, dolomites, 

 serpentines, and the other associated pseudomorphic rocks. In 

 exposed sunny situations it is always diminutive (the obtusum of some 

 authors). This variety is not, however, very common. The most 

 usual form is like No. 1,* but the more shady the nook, and the more 

 northern the aspect, the more acute the form. The typical form of 

 acutum always grows in cliffs and caves facing the north and 

 north-east. The general character of its stipes is long, as when the 

 plant grows in a crevice the plant wants to get above the fissure, but 

 it depends altogether upon the situation. The best fronds usually 

 have a long stipes. I believe there is only one species that will 

 change according to the place it grows in. Acutum does not 



Typical Adiantum-nigruru. — Ed. 



