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INTRODUCTION. 
[CLASS. — These plants dift'er widely from all those hitherto described, and 
in some respects approach very much nearer to Flowering plants than the Ferns do. 
The structure of their spikes of fructification hears a strong resemblance to that of 
the male cones of some of the Conifers, but these produce, not pollen, but spores, 
the germination of which is essentially like that of the Ferns, resulting in the 
formation of prothallia hearing similar sexual organs. But the peculiar habit of 
Equisetum, which may be contrasted with the Ferns as consisting chiefly of stem, 
while the latter are almost all leaf, separates it clearly from them as a distinct 
arnily, while it differs still more importantly from the other Fern Allies. 
STRUCTURE (see woodcut illustrating the genus). — The erect stems, which 
arise from jointed rootstocks creeping beneath the surface of the ground, are, when 
young, filled with very loose ceUular tissue : the moisture of this soon drying up, 
they become hollow. They are set at intervals with joints, surrounded by toothed 
sheaths (l), are regularly channeled or striated, and either simple or furnished 
with whorls of branches at the joints, of similar character to the main stem (b). 
The teeth of the sheaths are rudimentary leaves. A transverse section of the 
hollow stem shows that between the outer and inner surfaces is a circle (and in 
Equisetum fiuviatile two circles, alternating with each other), of large air-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 (see woodcut, fig. j). 
Around these tubes, and especially towards the outside of the whole stem, and 
immediately under the epidermis, are the vessels of the plant, usually what 
are called annular or ringed vessels or ducts. The epidermis of these plants has 
a larger quantity of silex deposited on it, giving it great rigidity and a rough 
surface ; the inner surface of the stem is frequently more siliceous than the outer, 
forming 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 ; and in general the form of the epidermal cells and the stomates may be 
perceived in specimens from which the vegetable matter has been carefully burnt off, 
when these are submitted to the microscope. — A. U.] The stomates are arranged in 
longitudinal rows, a pair on each channel. M. John, of Berlin, states that the 
stems contain full 13 per cent, of silica. The following interesting particulars of 
the siliceous epidermis of Equisetum is given in Dr. Grcvillc’s excellent * Flora 
Edinensis,’ p. 214 : “ On subjecting a portion of the cuticle to the analysis of 
polarized light, under a high magnifying power, Dr. Brewster detected a beautiful 
arrangement of the siliceous particles, which are distributed in two lines parallel 
to the axis of the stem, and extending over the whole surface. The greater 
number of the particles form simple straight lines, but the rest arc grouped into 
oval forms, connected together like the jewels of a necklace, by a chain of particles 
forming a sort of curvilinear quadrangle ; these rows of oval combinations being 
arranged in pairs. (These are seemingly the stomates.) Many of those particles 
which form the straight lines do not exceed the 500th part of an inch in diameter. 
Dr. Brewster also observed the remarkable fact, that each particle has a regular 
