Sf-
<ii
Prom these data Dr. Brewster concludes that the crystalline
portions of silex and other earths which are found in vegetable
films are not foreign substances of accidental occurrence,
but are integral parts of the plant itself, and probably
perform some important function in the processes of vegetable
life.”
Numerous stomates exist in the hollows of the fluted surface
of the stems, the depressed part of each channel having
two longitudinal series of these minute openings.
Beyond their employment in the arts, the Fquisetums are
of little importance in an economical point of view. They
are useless as fodder, and exploded as physic, though they
have had some reputed astringent virtues. The underground
stems, however, contain in winter, when the plants are inactive,
a considerable quantity of starch, and they may he
occasionally eaten by animals. In the cells of these underground
stems, during the month of October, the particles of
starch may he seen in active motion, passing up one side and
down the other, as is observed in the stems of Chara. Dr.
Lindley mentions having often noticed this phenomenon in
the stems of the great Water Horsetail.
The order of Horsetails consists of the . one genus Fquise-
ium, of which nine species are recognized as British.
Genus X X II. EQUISETUM, Linnæus.
The jointed tubular stems, and terminal cones of fructification,
are marks by which the Lquisetums may always be
readily distinguished from all other plants. The species are,
however, not so easily recognized among themselves, owing
to the great sameness which occurs among certain groups of
them. The chief features relied on for their discrimination,
are the similarity or otherwise of the fertile and barren stems,
the number of ridges or striæ which occur on the exterior
surface of these stems, and the structure of the sheaths
which surround the joints. By means of the peculiarities
which these parts present, the species may be certainly identified,
and after a little experience has been had, several of
them may he at once known by means of those pm n d facie
appearances, wdiich it is probable will become associated
with the plants, in the mind of the attentive student. One .
peculiarity of the Lquisetmns is, that they have no leaves,
these organs being represented by the tubular sheaths which
are produced at every joint.
The name Lquisetim is compounded from equus, a horse,
, and seta, a hair or bristle ; whence comes the English name
L