EQUISETUMS AND CALAMITES. 81 
h 
aerial branches are sent up yearly. The plants inhabit wet places, 
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thick. The small branches which are produced in whorls from the 
stem in some species are very peculiar. Hofmeister has shown that 
they arise from a single cell in the interior of the tissues at the base of 
the sheath-leaves, this endogenous formation of branches being peculiar 
isetums. These endogenous buds can be readily seen in a 
young branch of the rhizome of £. arvense taken late in autumn or 
early in spring by making a longitudinal section right ugh it. 
When fully formed the buds break through the base of the sheath- 
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leaf, or they may remain for a ime do buds 
should be s there are teeth on the sheath-leaves, and in 
_ @rvense and other species they form the narrow branches of the plant. 
The buds formed in the rhizomes may remain dormant e part 
becomes.exposed to light, when they may rapidly develope. On 
the underground stems the buds are not produced in complete 
verticils.. Two or three strong ones are formed which may either be 
marooned into new underground stems or form the. erect aerial 
ranch. . > 
The reots form in verticils, one immediately underneath each bud, 
but they are seldom alldeveloped. In structure they resemble much 
the roots of Ferns, and branch like them in a racemose (monopodial) 
numerous teeth on the sheath-leaves. The stem of the Equisetum 
consists of a series of generally hollow internodes, with a transverse 
diaphragm at the base and a sheath-leaf at the upper end. The 
diaphragms are absent in the cone-like fruit. The base of each inter- 
node is surrounded by the sheath-leaf of the internode next below. 
The outer surface of each internode presents a regular series of ridges 
* Sachs’ ‘* Lehrbuch ” (2 ed.), p. 357. + 
