444 MR. W. C. WORSDELL ON THE 
just to the inside of the periderm, are found the cauline cortical 
strands which run perpendicularly through the stem. At this 
stage in the development of the stem they are of large size and 
are greatly extended in the tangential direction, but very narrow 
radially (Pl. 20. fig. 7). 
They have a distinctly concentric structure, though, owing to 
the compression which they have undergone through the growth 
of the stem, they appear rather to consist each of two mutually 
inversely orientated strands, of which fig. 8 represents only a 
small portion. In the central region of such a strand is a dense 
mass of tracheides, irregular and angular and mostly isodiametric 
in shape, and lying in every conceivable direction; many of 
them have beautiful reticulations on their walls, others bordered 
pits (fig. 9). Mettenius, in his description of these cauline 
strands, speaks of these tracheides as pertaining to the pith, 
which is a very natural inference from their position and very 
irregular arrangement. They belong, however, to the xylem, 
and are in reality the elements first formed by the cambium on 
the inner side of the latter. Subsequently, the cambium forms 
eight or ten layers of tracheides of the normal kind, which occur, 
as seen in transverse section, either in single rows or in groups 
of two or three rows, these strands being separated by wide rays 
of parenchyma. The phloem is of about the same thickness and 
contains great numbers of small fibres. As seen in longitudinal 
section, the tracheides have bordered or scalariform pits. The 
whole ofthe tissues composing these cauline strands are secondary j 
and the strands are situated immediately to the inside of the 
periderm, if not partially embedded therein, for the large M 
cells characteristic of the periderm occur in abundance 1m oh 
phloem of these strands, and appear to be in radial rows whic 
are continuous outward with those of the per iderm. These 
strands are not always perfectly vertical, but occasionally assum f 
for a short distance a horizontal course; at intervals the place o 
juncture with a leaf-trace bundle is observed. , ber 
The vascular zones, as above stated, are twelve in DU and 
The segments eomposing them are very irregular in position $ in 
the tracheides have the usual curved, bent course, as see " 
tangential section. The innermost zone of wood is very achy- 
subdivided in places into single rows of tracheides, the a the 
matous tissues being greatly developed. Remnants ° 
