"T 
AND HISTOLOGY OF PIPER BETLE. 363 
The Phyllotaxis.—It is always alternate. On the leader which bears only 
leaves and no sheaths the arrangement is distichous. The axis when young 
is distinctly but slightly flattened, and the two orthostichies run along either 
end of the long diameter. As regards the lateral branches we have to consider 
«ch sympodial unit by itself, for an apparently single straight branch is 
not a morphological unit in the case of a sympodium. The sympodial unit 
usually consists, as we have seen, of two nodes, the lower bearing a sheath 
and the upper a leaf. The angle of divergence between the sheath and the 
leaf is usually one of 45°, When the sympodial unit consists of more than 
two nodes, the lowest one bears a sheath as before and the others a leaf 
proper. The angle of divergence between the sheath and the first leaf is 
again one of 45°, but that between the leaves proper is usually one of 180? 
(text-fig. 1, p. 259, axis a to d). 
As regards the insertion of succeeding sympodial units, they are so 
arranged that, the branch being horizontal, the sheaths always come to be 
placed more or less upwards, while the bases of the leaves are generally on 
one or both flanks (РІ. 17. fig. 6). 
Leaves proper.—The base goes right round the stem. The mark left on 
the axis by a fallen leaf is crescentie. The horns of the crescent meet 
by a line round the stem, left by the fallen stipules. Hence we get a 
complete ring-mark on the stem. The base does not show any characteristic 
swelling, such as is found in leaves performing phototropic movements. 
The stipules (Pl. 17. fig. 1) are adnate to the axis as first stated; they are 
adnate to the petiole as well, and that almost: throughout their length. 
They are connate at the base as they meet each other round the stem on 
the side opposite the leaf-stalk; forming a short collar to the axis. This 
collar is pale green, membranous, and only about 1:5 mm. high. The 
stipules are connate again at their tips. The part adnate to the petiole is 
membranous, and measures about 2°5 em. in length : its breadth at the base, 
where it is greatest, is about 2 mm. ; at the apex it becomes reduced gradually 
toa point. As the stipules are functional only at an early stage, the function 
being that of protection of the bud, they drop off early and leave a scar along 
the lines of attachment to the axis and petiole. As the petiole elongates 
after this, often doubling its former length, the original continuous scar 
breaks up into a broad broken line. 
The petiole is generally plano-convex in transverse section, with a central 
groove along the plane upper surface. The groove at the base, where it 
is bounded by the diverging stipular ridges, is deep. Towards the middle 
of its length the petiole shows hardly any groove, while the upper one-third 
shows a distinct groove which deepens towards the apex. Variations from 
the above type freely occur ; the petiole may be fluted, for example. The 
length of the petiole varies greatly, the average may be put down at 6°25 em. 
Its surface looks like that of the leader-axis. 
