ig6 W or s dell. — On the Comparative Anatomy of 
There is a distinct endodermis present, which is clearly 
differentiated on treatment of the section with strong sul- 
phuric acid. It consists of a slightly sinuous layer of small, 
compactly-arranged cells immediately outside the cylinder. 
The pericycle is not so clearly distinguishable, and appears 
as if interrupted here and there by phloem-elements. It is 
one layer in thickness. There is considerable variation in 
different roots in the structure and general appearance of the 
central cylinder. In some roots the typical radial arrangement 
is very clear ; the small protoxylem elements lying at three, 
four, or five points on the periphery, entirely separating the 
phloem into as many groups (Fig. 4 b ) ; in others, however, 
the phloem-groups show a tendency to unite continuously to 
form a peripheral ring. The central part of the cylinder is 
usually occupied by a few xylem-elements and parenchyma ; 
in many roots, however, the entire central part consists of 
small, compactly-grouped stone-cells, which here, apparently, 
replace the xylem-elements, the latter having, in these plants, 
a very rudimentary development. In those roots which are 
destitute of the central strand of stone-cells, the xylem- 
elements are fairly numerous ; in those in which the stone- 
cells occur, they are fewer in number and greater in 
diameter, the phloem being also much more developed. 
Another form of root-structure in this plant is that in which 
the xylem-elements are considerably larger, more con- 
spicuous, and more numerous than in the ordinary type ; in 
such roots the phloem is developed to a remarkable degree, 
and occupies, not only the peripheral portion of the 
cylinder, but also the entire central region, where the pith 
would normally occur. This seems a strange occurrence, but 
the elements composing the central portion had an appearance 
identical with those of the periphery, consisting of sieve-tubes 
and companion-cells 1 . The phloem-elements are, like those of 
the xylem, much larger and more conspicuous than in the 
1 Cf. Scott and Brebner, Anatomy and Histogeny of Strychnos, Annals of Botany, 
Vol. iii., 1889. Also Scott and Sargant, On the Pitchers of Dischidia rafflesianca 
(Wall.), Annals of Botany, Vol. vii., 1893. 
