48 HISTORY OF BRITISH FERNS. 



about twenty from twelve to twenty in number, equalling 

 the ribs on the sheath. These fertile stems are very slightly 

 striated. 



The barren stems grow erect to the height of eighteen 

 inches or more, and have their surface disposed in about 

 twenty sharp ridges, with corresponding furrows, the ridges 

 being coated with prominent siliceous warty particles, so 

 that the stems become very rough. The few lower joints 

 are without branches, but in all the upper part of the stem 

 they produce whorls of from ten to sixteen branches, which 

 are simple, and at first drooping, but eventually take a spread- 

 ing or slightly ascending direction. The sheaths of these 

 barren stems are much smaller than those of the fertile, less 

 funnel-shaped, and more closely set to the stem, and their 

 teeth are also fewer, shorter, and blunter ; but in respect of 

 colour they do not materially differ. The branches, which are 

 slender, and about four inches long, are three- or four-ribbed, 

 and have loose sheaths, which terminate in three or four short, 

 acute, membranous- edged, faintly brown-tipped teeth; the 

 ribs of the stem extend upwards into the teeth, one entering 

 each, but they do not quite reach the apex. 



The fructification forms a moderate-sized, terminal, oval, 

 cone-like head; at first sessile in the uppermost sheath, but 



