ue, and potash should be used
to clear them. The fibro-vascular bundle is of the radial type,
there being two masses of xylem (_xy._) joined in the middle, and
separating the two phloem masses (_ph._), some of whose cells are
rather thicker walled than the others. The bundle sheath is not so
plain here as in the fern. The ground tissue is composed of
comparatively large cells with thickish, soft walls, that contain
much starch. The epidermis usually dies while the root is still
young. In the larger roots the early formation of the cambium ring,
and the irregular arrangement of the tissues derived from its
growth, soon obliterate all traces of the primitive arrangement of
the tissues. Making a thin cross-section of the stem, and magnifying
strongly, we find bounding the section a single row of epidermal
cells (Fig. 94, _A_, _ep._) whose walls, especially the outer ones,
are strongly thickened. Within these are several rows of thin-walled
ground-tissue cells containing numerous small, round chloroplasts.
The innermost row of these cells (_sh._) are larger and have but
little chlorophyll. This row of cells forms a sheath around the ring
of fibro-vascular bundles very much as is the case in the
horse-tail. The separate bundles are nearly triangular in outline,
the point turned inward, and are connected with each other by masses
of fibrous tissue (_f_), whose thickened walls have a peculiar,
silvery lustre. Just inside of the bundle sheath there is a row of
similar fibres marking the outer limit of the phloem (_ph._). The
rest of the phloem is composed of very small cells. The xylem is
composed of fibrous cells with yellowish walls and numerous large
vessels (_tr._). The central ground tissue (pith) has large,
thin-walled cells with numerous intercellular spaces, as in the stem
of _Erythronium_. Some of these cells contain a few scattered
chloroplasts in the very thin, protoplasmic layer lining their
walls, but the cells are almost completely filled with colorless
cell sap.

A longitudinal section shows that the epidermal cells are much
elongated, the cells of the ground tissue less so, and in both the
partition walls are straight. In the fibrous cells, both of the
fibro-vascular bundle and those lying between, the end walls are
strongly oblique. The tracheary tissue of the xylem is made up of
small, spirally-marked vessels, and larger ones with thick