358 MISS HILDA M. CUNNINGTON ON THE 
(y, y, y). When these reach the centre and fuse, a tetrarch-like appearance is produced 
(text-figs. 1, 2, 3, 4). This shows especially clearly near the apex. The exact arrange- 
ment of the inner bundles naturally varies with the level of the section. 
The root-bundles, after traversing the cortex, pass through the outer ring and join the 
central bundles. "They usually enter at points midway between the median and trans- 
verse planes from both above and below. 
The inner bundles do not run straight along the stem, but show an oblique or 
undulating course; hence, some transverse sections show an apparently irregular 
arrangement of parenchyma and pigment-cells. 
The bundles composing the outer ring all seem to be continuations of the smaller 
bundles of the leaf. Near the apex these bundles in the cortex are very small and 
difficult to see, and lower down they enter the stele at a very acute angle, but some 
of them can be seen fusing with the outer ring some distance below the point at which 
they enter the cortex. 
Structure of the Vascular Bundles. 
The outer vascular ring consists of a number of separate bundles containing both 
phloem and xylem elements. The xylem is usually inwards, so that the bundles are or 
tend to be collateral, but very often the phloem extends all round the xylem. 
The xylem (Pl. 36. fig. 3, x) in each bundle consists of 1-6 elements showing well-marked 
spiral or reticulate thickenings. They follow a sinuous longitudinal course, bending out 
of the plane of one longitudinal section into the next, but their continuity can be 
traced. The thickenings do not stain with aniline chloride, and only very slightly 
with phloroglucin, but they take up iodine-green well after previous treatment with 
Eau de Javelle. So they are very slightly lignified. 
The phloem (Pl. 36. fig. 3, p) consists of a few sieve-tubes with well-developed 
companion-cells which abut externally on the pericycle or endodermis. It may be 
radially outside or on both sides of the xylem. The phloem develops earlier than the 
xylem, so that near the apex phloem only can be seen. 
The Inner Vascular Bundles.—As the inner bundles approach the centre, their 
individuality becomes obscured, so that bundles of wood-vessels alone (Pl. 36. fig. 3, w) 
or wood-vessels accompanied by sieve-tubes lie irregularly arranged in a parenchy- 
matous matrix. In the centre the wood-vessels form a loose anastomosing network, so 
that many oblique vessels can be seen. In true longitudinal section a longitudinal line 
of vessels often seems to be interrupted by parenchyma or pigment-cells, the appearance 
being due to the wood-vessels bending out of the plane of the section. The main mass 
of intrastelar tissue is formed by the large pigment-cells (Pl. 36. fig. 2, p, fig. 3,7). These 
are elongated in the direction of the long axis of the stem, but they vary in shape. 
The apex of the stem is bent upwards slightly. Here the epidermis completely 
surrounds the stem and consists of cells of irregular size. The young leaves and 
intravaginal scales arise very near to the apex, and the leaf-bundles, at first consisting of 
phloem only, enter and pass into the centre. The endodermis is not developed in the 
younger parts of the stem, being visible only when the outer ring of bundles is fully 
developed. 
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