102 HISTORY or BRITISH FERNS. 



■R'liat is called bipinnate, though less decidedly so than 

 occurs in some other species, for here those pinnules only 

 which are nearest to the main rachis are quite separated 

 from each other. The pinnrc arc narrow and tapering", 

 with a few of the lowest pinnules distinct, the rest united 

 at the base. These pinnules are of an obtusely oblong 

 form, and sen'ated on the margin. The fructification 

 of this plant is generally A'ery copious, and is usually 

 confined to the lower half of the pinnules, where it is 

 crowded. 



Tliis is one of the best of the British species to study 

 vrith the view of understanding the fructification of Ferns ; 

 for here the indusium, a very important organ, is seen to 

 be remarkably prominent in fronds which have about 

 reached their full development. In that state the indu- 

 sium is as yet closed over the clusters of spore-cases, and 

 will be seen to consist of a lead-coloured, tumid, kidney- 

 shaped, conspicuous scale, which, at the proper time, 

 becomes elevated on one side, to allow the dispersion of 

 the spores. This may readily be noticed by watching the 

 progress of the fronds just as they reach their full growth. 

 If they are gathered in that state for preservation in 

 the herbarium, they burst open more or less, in the pro- 



