240 
HISTORY OF BRITISH FERNS. 
Pilularia globulifera, Linnams. 
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. 
