118 BRITISH FERNS. 



THE VARIEGATED ROUGH HORSETAIL. 



This species, the Equisetwn variegatum of botanists, is 

 found on the banks of rivers and lakes, and in sandy places 

 near the sea. It is one of the species whose stems are all simi- 

 lar, and almost quite unbranched. It extends by means of a 

 widely creeping underground stem, producing numerous 

 above-ground stems, often springing from joints in such close 

 proximity, that they appear in dense tufts. Though so nu- 

 merously branched just beneath or at the surface of the soil, 

 branches are seldom produced on the exposed part of the 

 stems ; but when this does occur, they spring singly from the 

 joints, and have much similarity to the stem itself. The 

 stem grows about a foot high ; its surface is very rough, and 

 impressed with from four to ten furrows, alternating with 

 rather prominent ridges, each ridge margined on both sides, 

 with a line of minute silicious points, which give it the 

 appearance of being grooved, and impart to it its peculiar 

 roughness. The sheaths are slightly enlarged towards their 

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

 above, and terminate in a fringe of black teeth, equalling the 

 ribs in number, with a broad white membranous border, in 

 form ovate, and tipped by a deciduous bristle. A certain 

 number of the stems, usually the most vigorouSj terminate 

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

 by a prominent point or apiculus. 



The section of the stem shows a small central cavity, an 

 exterior surface of rather prominent ridges, each channelled 

 so as to form two projecting angles, and a circle of moderate- 

 sized cavities occurring about the centre of the tissues. 



A variety of this, sometimes called E. arenarium, is smaller 

 and more slender, its stems always procumbent, and not 

 having more than six furrows. 



Another variety is the E. Wilsoni, which is a stouter and 

 taller plant, three feet high. < The section of its stem shows 

 the central cavity and the ring of cavities occurring in the 

 cylinder of the stem much larger than in the ordinary forms 

 of E^. variegatum. This plant grows in water at Mucruss, in 

 the immediate vicinity of the Lakes of Killarney. The stems 

 are tufted, generally simple, but sometimes sparingly 

 branched j they have about ten furrows, with broad inter- 

 mediate ridges, on which the silicious particles are less pro- 

 minent, so that the stems are not nearly so rough as in the 

 allied E. variegatum, Mackayi, etc. The sheaths are scarcely 

 larger than the stem, and are entirely green, except a 



