BRITISH FERNS. 



71 



The rachis is black, or dark purple, very smooth and shining 

 and for more than half its length, naked. 

 The normal form of the frond is tri- 

 angular and pinnate, the pinnae being 

 alternate, and also pinnate ; the pinnulae 

 are of varied form, but mostly some- 

 what triangular or lozenge-shaped ; 

 their exterior margin is generally 

 serrated. 



The veins radiate from the stalk to 

 the exterior margin of the pinnula, 

 and to these are attached the elongate 

 linear masses of thecae, two, three, 

 four, and even five on each pinnula; 

 these are at first covered by an elon- 

 gate, linear, white indusium, which is 

 pushed aside by the growing thecae, 

 turned back, and finally lost, the back 

 of the pinnula becoming eventually 

 covered by a dense brown mass of 

 thecae. 



A very remarkable form of this plant 

 has been found in several localities in 

 Germany, Hungary, and Scotland ; by 

 many botanists this has been considered 

 a species, under the name of Asplenium 

 germanicum, 'or A. alternifolium. A 

 representation of this plant, which I 

 would propose to name the alternate 

 type of A. ruta-muraria, is given at 

 )3j3 : the form of the frond is elongate 

 and pinnate ; the pinnae are distant, 

 small, linear, alternate, and generally 

 notched or divided at the apex. Above 

 the two singular plants )3j3 I have 

 figured a third, with three dissimilar 

 fronds ; this was gathered at Arthur's 

 Seat, near Edinburgh, in 1838. I have 

 introduced this, as forming a connect- 

 ing link between the normal type of the 

 plant represented above and the alternate type below ; and I think 



