256 
HISTORY OF BRITISH FERNS. 
nearly smooth, and apparently without the siliceous coat- 
ing common to the stems of this race of plants. They 
are divided at intervals into joints of variable length, the 
number of joints being also variable — from six, on stems of 
about four inches in length, to eight, on those which 
measure eight inches, though sometimes specimens of equal 
length have but five or six joints. They are thus much 
more distant in certain cases than in others, a space of 
three-fourths of an inch being sometimes interposed be- 
tween the top of one sheath and the base of the next, 
while, on the other hand, they are sometimes so close as 
nearly to touch. The base of a sheath is, however, not 
covered by the sheath below it, except at the very lowest 
part of the stem, where they become much reduced in size, 
and are sometimes crowded. It is usual for each succeed- 
ing joint upwards to be somewhat more distant than the 
one beneath it. The sheaths are large and loose, widening 
upwards ; they are pale-coloured, somewhat yellowish at 
the base, and are divided above into about ten dark-brown 
teeth, which often adhere together in twos and threes/ 
The teeth are very narrowly lance-shaped and sharp-pointed, 
and are the terminations of the ribs, about ten in number, 
by which the sheaths are marked These stems are ter- 
