No roots of Orectanthe were available for study.
For each of the above species, serial longitudinal sections were prepared to
show the presence of vessels. All the species described above proved to have true
vessel elements with simple perforation plates. Vessels have been reported by
Solereder and Meyer (1929) in roots of Xyris laccra, X. lannia, and A", indica.
Likewise, Cheadle (1942) indicates vessels with simple perforation plates for
roots of Xyris fl.rxnosa and A'. smalliana.
The species of Abolboda described here offer no features not previously
mentioned by Solereder and Meyer for Abolboda, or Xyris. The possibility that endodermis-cell characteristics could be used as specific characteristics, suggested by Malme in 1925, appears to be valid. Malme shows very thick-walled
endodermal cells with centrally placed lumina for A. pulchella and A. vaginata.
He reports prominent thickenings on the inner wall, tapering sharply on the
radial walls, and absent on the outer walls, for endodermal cells in roots of
A. poeppigii, A. grandis, and A. macrostachyo. Malme's figure for A. macrostachya
is markedly different from the condition illustrated here for that species.
The endodermal cell thickenings Malme reports for A. poarchon and A. abbreviata
are like those illustrated in the present study for A. aeieularis.
Interestingly, Malme's figures all show an uninterrupted perieycle (A. vaginata,
A. macrostachya, A. poarchon). The species of Abolboda in the present
study in which uninterrupted perieycle was observed all belong to the group
termed "larger-stemmed abolbodas" in sections below. Malme's figures also
suggest a larger number (six or more) of xylem poles, a feature also characteristic
of the group just named. Thus as Malme (1925) claims, different types of
root anatomy in Abolboda appear to be characteristic of species or speciesgroups;
from the example of A. sprue ci described above, one may surmise that
such characters are not always limited to the stele, but may be found in the
cortical zone as well.
The several layers of cells between endodermis and outermost vessels, the
absence of central vessels, the presence of endodermis-like cells in their place,
and the distinctively staining endodermis thickenings are characteristics which,
taken together, would seem to give the roots of Achlyphila a generic differentiation
from the other three genera. In fact, some of these characteristics seem
new to Xijridaceae, althoug-h the sum of characteristics in this genus would not
exclude it from the family.
On the basis of the present study, one may conclude that the roots of
Abolboda offer no anatomical features (other than greater size, and therefore
more numerous vessels) which cannot also be found in Xyris roots, as the
account of Solereder and Meyer (1929) illustrates.
As the summary of Solereder and Meyer shows, remarkably little is known
about stem anatomy in Xyridaceae. The only facts that have been established
are that bundles are amphivasal, individual bundles may be sheathed with
sclerenchyma (incompletely in A". Janata), and that (in X. lanata) the bundles
may form concentric bands. As an additional generalization, the writer would
like to add the fact that in all taxa he examined, vascular bundles tend to be
more or less amphivasal except where they are demarcated as leaf traces, in
which case the structure of the bundles tends to be more nearly collateral.
The data given below are derived from study of mature portions of rosette
stems, except for Achlyphila, which has a rhizomatous habit. At and near the
base of a stem, especially in the smaller-stemmed species of Abolboda, departing
roots may be numerous in the cortex, and the vascular bundles may form a very
small group in the center of the stem. In A. americana, no part of the stem
(except the very youngest) was free from departing roots. The types of stem
anatomy observed in the Xijridaceae under study here fall into four main groups.