io8 WorsdelL — On the Comparative Anatomy of 
perhaps, be expected from the reduced nature of this tissue, 
the vertical rows of xylem-elements are frequently interrupted 
and cut off by parenchyma, the continuity of the series 
being maintained by an oblique connexion with other elements 
of a different vertical row — the perforation between the two 
connecting elements being thus often in their lateral walls. 
The terminal walls of these elements, usually seen in section, 
appeared to show in nearly every case evidence of one or 
more perforations. With the exception of the protoxylem, 
all the elements are reticulately thickened. 
The stone-cells , occupying the centre of some roots, are 
narrow, much elongated elements ; being so conspicuously 
developed here, I may suggest for them a function, which 
consists in resisting longitudinal tension-strains set up by the 
separation, on maturing of the flowering-stems, into distinct 
plants of the subterranean root-system. 
The apex of the root (Fig. ix, C. subacaulis , Gardn.) shows 
a differentiation into three layers, viz. plerome, periblem, and 
a common layer for the dermatogen and root-cap. The apices 
of some roots examined showed no distinguishable root-cap 
whatsoever. 
Lateral roots arise from the central cylinder, and most 
probably from the pericycle, though their exact origin from 
this layer was not ascertained. The youngest stage observed 
was where the young organ was about two or three layers of 
cells distant from the cylinder. As the young root gets older 
its origin becomes more obscure, as its cortical cells, though 
mostly traceable in radial rows back to the central cylinder, 
appear at the same time not sharply defined against those of 
the parent-root ; the sharp line of demarcation between the 
young root and the ground-tissue of its parent extends only 
a short distance from its tip (Fig. 19) on either side; this 
gives rise to an appearance as though the lateral root had 
a cortical origin, instead of a pericyclic one as is probably the 
case. Fig. 19 shows a section of a lateral root at the stage 
where it is about to burst through the external layer ; it is 
seen to possess a well-marked root-cap (re) of a single layer of 
