EQUISETUM. 253 



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 

 spreading 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 termi- 

 nate 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 



