240 HISTORY OF BRITISH FERNS. 



Pilularia globulifera, Linnccus. 



The Pillwort or Pepper-grass. (Plate XVII. fig. 2.) 



Pepper-grass is a small creeping plant with grassy leaves 

 growing usually in the shallow margins of lakes and pools, 

 where it is occasionally overflowed ; but sometimes occur- 

 ring entirely submerged. The stem, or rhizome, is thread- 

 like, composed of several longitudinal rows of hollow cells, 

 rough externally on the younger portions with hair-like 

 scales, but otherwise smooth, occasionally branched, and 

 producing on the lower side, at intervals, small tufts of 

 fibrous roots, which descend almost perpendicularly into 

 the muddy soil in which they become fixed. On the 

 upper part of the stem, at the same points, occur tufts of 

 erect leaves, which are curled up in the incipient state, 

 like those of a Fern, but on unrolling assume the erect 

 position. These leaves are bristle-shaped, from one to 

 four inches long, bright green, smooth externally, hollow 

 within, but, unlike those of Isoetes, which are composed of 

 four lines of cylindrical tubes, the leaves of the Pillwort 

 are divided longitudinally into various cells, separated by 

 partitions radiating from the centre ; they are from one to 

 four inches long. 



