Holm . — Bartonia, Muehl. An Anatomical Study. 445 
Bartonia lanceolata, Small. 
The Roots. 
The roots are short and slender, sparingly branched and of a brownish 
colour ; no hairs were observed. Hyphae were found in epidermis, exoder- 
mis, and in all the cells of the cortex. Inside epidermis is a single layer of 
thick-walled cells representing an exodermis. The cortex consists of three 
strata of large, roundish cells with wide intercellular spaces. It borders on 
an endodermis, the cells of which are thin-walled and much smaller than 
those of the cortex proper ; the Casparyan spots were plainly visible. A 
thin-walled, continuous pericambium surrounds three small strands of lep- 
tome alternating with three rays of hadrome, the vessels of which are very 
narrow. Some other roots that were still thinner contained only two lep- 
tome-strands and two hadromatic rays. 
Although the majority of roots examined proved to be mycorhizae, 
we did observe a few in which no hyphae were to be traced. The structure 
of these roots agreed, however, with that of the others, but the epidermis 
showed here a tendency to develop low papillae, the exodermis was quite 
thin- walled, and the tissues showed a more regular structure and arrange- 
ment than observed in the mycorhizae. 
The Stem. 
One of the basal, cylindric internodes shows the structure as follows : 
A wrinkled cuticle covers the epidermis, the outer cell-walls of which are 
moderately thickened ; no stomata were observed, the internode being 
underground. No exodermis is differentiated, thus the cortex borders 
directly on epidermis ; the cortical parenchyma consists of seven layers in 
which the intercellular spaces are quite wide ; no chlorophyll or starch was 
noticed. There is, furthermore, an endodermis (Fig. 22), mostly thin- walled, 
or some of the cells showed a thickening all around, but only outside the 
leptome. A continuous ring of thick-walled cells separates the leptomatic 
strands from the hadrome, thus forming a protective sheath around the 
hadromatic cylinder. The cells of this sheath are, in longitudinal sections, 
longer than those of endodermis, and their cross-walls are straight and 
horizontal ; they are of a lighter colour than the vessels, and the walls are 
porous. Morphologically the elements of this protective sheath may be 
defined as representing thick-walled mestome-parenchyma rather than 
modified sclerenchyma. In regard to the leptome this tissue occurs as 
isolated strands, about ten in all, bordering directly on endodermis. The 
hadrome, on the other hand, forms a closed cylinder of vessels in several 
layers, wide reticulated and narrower scalariform. The central portion of 
the internode is occupied by a solid but thin-walled pith, in which no 
