18 HISTORY OF BRITISH TELMS. 



racliis, whicli is, as it were, quite bared of the contiguous 

 leafy expausion ; and when this occurs, tlie frond is said to 

 be pinnate ; in this case, each of the distinct leaf-like- 

 divisions is called a pinna. When these pinnn3 are 

 divided again upon precisely the same plan, the frond 

 becomes hipinnate, or tAvice pinnate ; but if the pinnae 

 are only deeply lobed, they are, like the frond Avhen simi- 

 larly divided, said to be pinnatifid. 



When the fronds are thrice pinnate, they are called 

 tripinnate ; and in all other more intricate forms they are 

 called decompound ; but this seldom occurs in any of the 

 native kinds, the neiirest approach to it being in very 

 vigorous plants of the common Bracken, and in some of 

 the Lastreas, when very largely developed. 



The young fronds of the ferns, before being developed, 

 are arranged in a very curious manner, the rachis being 

 rolled inwards volutely from the point to the base. In 

 the compound sorts, the divisions are each again rolled up 

 in a similar wav. This arran2;ement is what is called 

 circinate. All the British species, uith two exceptions, 

 are folded up in this way, so that their development 

 consists of an unrolling of the parts of the fronds. The 

 exceptions mentioned are the Moonwort and the Adders- 



