EQUISETUM. 251 



much similarity to the stem itself; it is the erect form of 

 the species, chiefly, which thus becomes branched. The 

 stems grow about a foot high, and, in what is taken as the 

 typical plant, their surface is very rough, and impressed 

 with from four to ten furrows, with alternating, rather pro- 

 minent ridges, each ridge margined on both sides, with a 

 line of minute siliceous points, which give it the appearance 

 of being grooved, and impart the peculiar roughness to the 

 steins. The sheaths are slightly enlarged towards their 

 margin, ribbed like the stem, green in the lower part, black 

 above, and terminating in a fringe of black teeth, equalling 

 the ribs in number ; in form ovate, with a broad white 

 membranous border, and tipped by a deciduous bristle. 

 Sometimes the contrast between the black ring and teeth, 

 and the white border to the latter, is very conspicuous. 



A certain number of the stems, usually the most vigorous, 

 terminate in a cone of fructification. This is small, elliptic, 

 crowned by a prominent point or apiculus. It is usually 

 black, and sessile in the uppermost sheath, but sometimes 

 elevated on a short stalk. All the stalked cones we have 

 seen have been much paler in colour than the sessile ones. 

 The scales are about twenty in number, and the spore-cases 

 are whitish. 



