A more regular appearance is seen in Fig. D,
which is a section through the internode (b). In it we see the nuclear
sheath, varying in width from one to three cells, and inclosing a number
of crescent-shaped fibrovascular bundles, with their convexities toward
the center and their horns toward the nuclear sheath. There are also
from two to four or five free closed fibrovascular bundles in the
central pith.
These fibrovascular bundles consist mainly of dotted or reticulated
ducts (Fig. F), but all gradations from, this to the spiroids, or even
true spiral ducts (Fig. E). may be found, though the annular and spiral
ducts are quite rare. These ducts are often prismatically compressed
by each other. The fibrovascular bundles also contain soft-walled
prosenchyma cells. The peri-nuclear portion consists of soft-walled
parenchyma, smaller near the nuclear sheath and the epidermis, and
larger about midway between, and of the same character as the cells of
the pith. In longitudinal section they appear rectangular, similar to
the walls of the epidermis (G), but with thinner walls.
All parts of the plant have been used in medicine, either separately or
together, and according to some authorities the whole flowering plant is
the best form in which to use this drug.
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