EQUISETUM. 
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Genus XXIV. EQUISETUM, or HORSETAIL. 
The jointed tubular siliceous stems, and the terminal 
cones of fructification consisting of spore-cases attached 
to peltate scales, are marks by which the Equisetums 
may always be readily distinguished from other plants. 
The species are, however, not so easily recognized among 
themselves, owing to the great sameness which occurs 
in 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 
strim 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 be at once 
known by means of those primd-facie appearances, which 
become associated with the plants in the mind of the 
attentive student. One peculiarity of the Equisetums is, 
that they have no leaves, these organs being represented 
by the tubular sheaths which are produced at every joint. 
