230 HISTORY OF BRITISH FERNS. 



brown underground stems, which also produce whorls of 

 black fibrous roots. 



The stems are, though firmly ribbed, very smooth to the 

 touch, their furrows being very shallow ; their smoothness 

 no doubt arising from the presence of a very slight coating 

 of the siliceous particles, which, when more abundant, give 

 their peculiar harshness to some of the species ; probably, 

 also, the particles themselves are in this species much 

 finer and less prominent. Sometimes the stems are quite 

 unbranched ; sometimes furnished with irregular whorls of 

 branches along all their central portion ; and between these 

 two extremes there occurs every conceivable degree of 

 branching, from the single shoot produced here and there, 

 through every gradation of imperfect whorls up to whorls 

 of short branches almost complete. The branches, which 

 are simple, nearly erect, and never acquire much length, 

 are smooth like the stem. There is no material difference 

 between the barren and fertile stems, except the presence 

 of the fructification in the one case and not in the other ; 

 they are, therefore, said to be similar in structure. 



The surface of the stem is marked with from sixteen to 

 twenty very slight ridges, and the sheaths, which are short, 

 rather closely fitted to the stem, and of the same colour in 



