PERNS OP GREAT BRITAIN. 163 



the sea-shore, and one which, if it occurs in any quan- 

 tity, proves valuable in binding down the loose sands. 

 Its underground stem creeps a long way just beneath 

 the surface of the soil, and its root is formed of numerous 

 whorls of fibres. It sometimes grows inland, on the 

 banks of lakes, rivers, and in ditches, and under such 

 circumstances becomes more luxuriant than on the sea- 

 sands. 



In this species the fertile and barren stems are alike ; 

 they are scarcely if at all branched, except at the base, 

 but they have numerous branches just at the surface 

 of the soil, or on the underground stem just below 

 it. Occasionally the erect stems have a branch, very 

 similar to the stem itself, arising from a joint here and 

 there. The stems, which are about a foot high, are 

 grooved, having from four to ten strong ridges. The 

 sheaths, which are ribbed like the stems, are green 

 below and black above, and their margins are fringed 

 with black teeth of the same number as the ridges on 

 the stem. These teeth have thin white edges and 

 bristle-points. 



The catkins are borne at the summit of some of these 

 stems, and are small, black, and pointed, sometimes 

 seated oa the uppermost sheath, sometimes elevated on 

 a short footstalk ; they have very few scales. 



One variety of this plant is by some writers con- 

 sidered a distinct species, and is called E. arendrium. 

 It is small, slender, and trailing, and the stem has about 

 six furrows. The JE. Wilsdni of some writers appears 

 to be but another form of E. variegdium -, it is much 

 stouter, taller, and more erect in habit, being sometimes 



