376 MR. H. M. CHIBBER ON THE MORPHOLOGY 
cells, aud bast-parenchyma. But the last is freely interspersed with secretory 
cells. These are, unlike those in the rest of the plant, greatly elongated in 
the vertical direction. They may measure 45 u by 15 ш. The sieve-tubes 
carry the sieve-plates only on the transverse walls. They may be quite 
horizontal or more or less obliquely directed. The apertures are very fine 
and uniformly distributed. Several sieve-plates, sometimes as many as 
iwenty, may be seen in one transverse section of a bundle. This is due 
to the sieve-tubes, whieh are of about the same length, possessing a tier-like 
arrangement. — The length of each tier of tubes is generally found to 
be 520 u. The diameter of the tube measures 45 pat the most, while that 
of the companion cells is only 6 p. 
A strip of eambium is interposed between the xylem and phloem sections 
of the bundles. Typical cambium celis measure 9 pw radially and 21 ш 
tangentially. 
Peripheral ring of Bundles.—The number of bundles in this ring, in an 
old piece about 9 mm. diameter, may be as great as fifty. They lie strictly 
in a single circle. Their orientation is always normal. They are, in a 
transverse section, oval in outline (РІ. 18. fig. 28) ; their longer diameter may 
amount to 1 mm. ; the breadth in that ease is usually a third of the length. 
The smaller bundles are somewhat circular in outline, and measure only a 
fourth of a millimetre across. The number of sealariform vessels in a bundle 
varies from one to twelve. Their lumina are narrower than those of the 
medullary bundles. The larger of them average about 100 ш. The sieve- 
tubes of these bundles are also narrower than those of the other or medullary 
set (30 u across) and fewer in number. These bundles otherwise agree with 
those of the medullary ring. 
Towards the pith, this peripheral ring of bundles rests on an undulating 
sclerenchymatous zone. This zone is thickest opposite the larger bundles, 
where it also dips inwards towards the pith. The thickest part is some 
twelve cells broad, while to the thinnest part there go only two to three 
cells. It is continuous and homogeneous. The fibres composing it are 
chambered with transverse partitions of cellulose. Their diameter varies 
from 10 y to 25 д. | 
Тһе bundles are separated by broad medullary rays. The breadth of the 
rays measures from 100 ш to 500 д. The cells are typically lignified ; the 
walls have simple oval pits, like the sclerosed parenchyma of the pith. The 
outlines of the cells are rectangular, and the intercellular spaces are also 
regular rectangles extending along the entire radius of a ray. The height of 
the cells is very uniform, aud all the cells in one plane are often precisely in 
one level. In other words, they are arranged in regular tiers ; and longitudinal 
sections along a ray reveal horizontal straight lines passing throughout the 
ray. The tangential dimensions have also the same characters ; so that in а 
transverse section we see radial rows of cells between any two bundles. The 
