AND HISTOLOGY OF PIPER DBETLE. 315 
inner one, which greatly overlap each other. The peripheral mucilage-canals 
are sometimes situated opposite the bundles constituting the outer ring. The 
shape of a bundle in transverse section is broadly triangular (РІ. 18. fig. 21). 
Its breadth may amount to 0*6 mm. and radial length to 07 mm. Each 
bundle has usually half a dozen large vessels. The outline of a vessel is 
circular. The diameter may measure 225 и; the minimum diameter observed 
was only 20 ш. The walls have sealariform markings surrounded by simple 
borders. The pits are very narrow and elongated. The height of a cell 
composing the vessel is 400 д. The scalariform vessels are surrounded by 
narrow pitted vessels or tracheids only 30 ш across. They are very abundant. 
The pits are simple and broadly oval. Besides these there are the primary 
annular, spiral, and annulo-spiral vessels. These are very varied. The rings 
of annular vessels may be close-set or sparse and circular or hexagonal. An 
annular vessel may be found to show irregularly spiral markings for a part 
of its course, or an annular vessel may be continued as a spiral one, thus 
constituting an annulo-spiral vessel. Of spiral vessels, there may be a single 
spiral or there may be two or more of them. When more than one, they 
may either run together or cross each other, Sometimes a single band is seen 
to split for a part of its course into two. The spiral band may be somewhat 
open or quite close; it may be thick or thin, The endings of the component 
cells are either gradually tapering or truncate. 
Other xylem elements of a bundle are wood-parenchyma and wood- 
prosenchyma ; both these are scanty. Wood-parenchyma is cylindrical 
in outline. The cells measure 30 ш to 60 ш by 30 ш; their walls bear 
numerous simple oval pits. The larger pits measure 7 p by 3 p; all of them 
invariably have their long axis horizontally directed. Wood-prosenchyma is 
septate, with thin transverse partitions of cellulose. А loculus of such a 
cell measures 200 p to 300 u by 15 u to 20 u. The end walls of а pros- 
enchyma-cell are either tapering or truncate. The side walls are marked 
with simple pits, which are mueh smaller and fewer than in the sclerosed 
parenchyma. The smaller of them measure only 1 micron, and look very 
much like the markings of the cuticle of an earthworm. The larger ones 
form obliquely-directed slits measuring 2 to 4 u by 1 ш. Sclerenchymatous 
fibres are also present, forming short ares tipping the bast and wood extre- 
mities of the bundles. They are from one to a few layers deep. The are at 
the xylem extremity is more extended, being almost semicircular. The com- 
ponent fibres are septate, like the prosenchyma, with thin transverse partitions 
of cellulose. The periphery of the partition is, however, thickened and 
lignified. A fibre measures about 1 mm. in length and 15 p in diameter. 
The length of a chamber is only about 250 u. The walls of a fibre towards 
its middle are 5 ш thick. Transitional forms between the sclerenchymatous 
fibres and wood-prosenchyma also occur. 
The bast is made up of the usual elements, viz., sieve-tubes, their companion 
2r2 
