INTRODUCTION. 
13 
STRUCTURE. — Tlic Stems, which are partly beneath and partly above the 
surface of the ground, arc, when young, fdled with very loose cellular tissue, 
and the moisture of this soon drying up, they become hollow. They are 
set at intervals with joints, covered with toothed sheaths, arc regularly chan- 
nelled or striated, rigid, and covered with fine particles of Silex, particularly 
at the ridges of the Stria;. The depressed part of each channel has two lon- 
gitudinal rows of minute holes or open pores, very different from the usual 
stomata;, and much resembling the pores which Dr. Mohl of Munich repre- 
sents as occurring in the woody tissue of the Conifera', now a well-known 
characteristic of that order, and which it will be recollected there, as here, are 
arranged in longitudinal lines. A transverse section of the stem shows that 
between the outer and inner cuticle is a circle (and in Equisetum fluviatile 
two circles, alternating with each other), of tubes, distinct from each other, but 
terminating at every joint of the stem, fresh tubes of a similar character being 
found at every other joint. These are evidently air tubes, the sap vessels 
being seated immediately under the cuticle, and around them are the real sap 
vessels of the plant, which appear to me to be perforated ducts, but Professor 
Lindlcy says, that these plants arc furnished with spirals, which spirals I pre- 
sume to be the ducts here alluded to. The inner surface of the stem is fre- 
quently more silicious than the outer, so as often to form a very beautiful 
object even to the naked eye. So abundant is this deposit in Equisetum 
Hyemale that after the vegetable matter has been removed by maceration, 
the Silex has been sufficiently abundant to retain the form of the plant. 
M. John, of Berlin states that they contain full 13 per cent, of Silica. 
REPRODUCTION. — The reproductive organs are borne in a terminal 
spike or catkin, composed of several sided shields ; from each of these depend 
hollow, scale-like follicles, opening inwardly, and emitting greenish, ovate 
spores, to each of which is attached four club-shaped filaments. These fila- 
ments have been considered anthers and the grains upon them pollen, but this 
is mere conjecture. When the spores are immature, the filaments are twisted 
tightly round them, but when ripe they become exceedingly elastic and hydro- 
metrical, so much so, that the irritability occasioned by a change of temperature 
or moisture causes the spores first to burst the thecae which bear them, and 
afterwards to scatter themselves to a considerable distance. 
GEOGRAPHY AND USES. — They are all found, and thrive best in 
damp situations, and when cultivated produce fruit constantly and abundantly. 
They arc harmless to, but refused by cattle on account of their husky, rigid 
texture. They arc useless as medicines, but valuable in the arts ; their silicious 
cuticle rendering them valuable as polishing substances for marble, wood, ivory, 
and even metals. 
