1G8 HISTORY OF BRITISH FERNS. 



little risk of frosts, for the least frost would destroy them, 

 and, indeed, it is not uncommon for the earlier growth to 

 be destroyed in exposed places by the very slight frosts 

 which occur at that season of the year. 



The fronds themselves have been variously described, 

 and often erroneously, for they are not unfrequently said 

 to be three-branched, a form which really occurs in one of 

 the smaller Polypodies (P. Dryopteris). They are not 

 properly three-branched, and except when very much 

 starved and stunted, do not approach that form very nearly. 

 They are, in reality, bipinnate, or, when very luxuriant, tri- 

 pinnate, the pinnse standing opposite in pairs, each pair in 

 succession becoming fully developed, while the main rachis 

 is extending upwards, and the next pair is beginning to un- 

 fold. The mature fronds are thus truly bi- or tri-pinnate, 

 with the pairs of pinnse standing opposite. When the fronds 

 are much diminished in size by the sterility of the soil 

 which sustains them, they become almost triangular, and 

 then have somewhat the appearance of a three-branched 

 frond, the development of the lower pair of branches not 

 leaving the plant energy enough to carry up its rachis, 

 and produce the other pairs of pinnaB which it would 

 normally possess. That this is the true habit of the 



