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its spore-cases enveloped by the dilated bases of its hollow
leavTEs ; some of the spore-cases containing large, and some
much smaller pollen-like sporules. It may also be known
by its hollow leaves being composed of four rows of elongated
cells, which give it a bluntly quadrangular section ;
but this peculiar construction of the stems is not always
to be observed, except in fresh specimens, the pressure to
which they are subjected in the process of drying breaking
up the partitions of the cells, so that the stem appears to
be composed of one series of large elongated ceUs. There
is but one species, the I. lacustris, a stemless quill-leaved
submerged plant, which gives the appearance of a green
turf to the bottom of the water where it occurs.
I soetes l a cu str is , Linnæus.—The European Quillwort,
or Merlin’s Grass. (Plate XIX. fig. 1.)
This is a very curious plant, growing at the bottom of
our mountain lakes, and having, as has been remarked,
the appearance of a submerged grass, so that the unexperienced
eye would probably pass it by unnoticed. It has a
fleshy tuber, of a nearly globular form, white, and of compact
texture internally, but spongy and of a dark brown colour
externally. In the centre is a small nearly pellucid part,
which appears to be the growing point, since it is from this
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