164 HISTORY OF BRITISH FERNS. 



the steins thus penetrating to a depth of fifteen feet. This 

 caudex is thickish, black-looking, and succulent, containing 

 a good deal of starch. Prom it are produced, at intervals, 

 the annual fronds, which generally make their appearance 

 about the latter end of May, when there is 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). 

 Now, 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 tripinnate, the pinnae standing opposite in pairs, 

 each pair in succession becoming fully developed, while the 

 main rachis is extending upwards, and the next pair is be- 

 ginning to unfold. The mature fronds are thus truly bi- or 

 tri-pinnate, with the pairs of pinna3 standing opposite. 

 When the fronds are much diminished in size by the sterility 

 of the soil which sustains them, they become almost trian- 

 gular, and then have somewhat the appearance of a three- 



