20 SIR DIETRICH BRANDIS—AN ENUMERATION 
blade. Plate I. figs. 18-15 represent sections through the 
petiole of Hopea cernua, T. et B., at different levels. At the 
base (fig. 18) are, apart from a central mass without resin-ducts, 
three distinct vascular bundles—xylem at the ends, pith in the 
centre, and phloém all round. Each of these has a resin-duct, 
no bifureation therefore has yet taken place. Near the top of 
the petiole, however (fig. 14), the lateral ducts have subdivided. 
At the base of the midrib (fig. 15) the 3 vascular bundles have 
united and now form a semicircle, with a bend below, consisting 
of xylem, phloém, with bast-fibres outside. The bast continues 
and forms a closed ring, at the top on the inside, with bands of 
xylem and phloém. It will be noticed that there is a central 
body of vascular bundles, which has gradually changed its shape, 
forming at the base of the midrib two horizontal bands—the lower 
xylem with phloém below; the upper a double band, xylem on 
both sides and phloém in the middle. "The midrib in this and all 
other cases gives off branches into the secondary nerves, each 
accompanied by a resin-duct. The consequence is, that the 
number of resin-ducts diminishes gradually from the base to the 
end of the midrib. In order to compare the structure of the 
petiole in different genera and species, it is necessary to examine 
them all at the same point, and the most useful point for this 
purpose is the top of the petiole just under the blade, or the base 
of the midrib. At this point we invariably find in the underside 
of the petiole an outer semicircle of vascular bundles, generally 
more or less halfmoon-shaped and more or less confluent, the 
phloém with a belt of bast-fibres outside, then the xylem, and at 
last the pith. Plate I. fig. 16 shows a section of the petiole of 
Hopea odorata, Roxb., below the blade, with a semicircle of 9, 
and fig. 18 a section of the midrib at base, of Vateria acuminata, 
Hayne, with 11 vascular bundles and the same number of resin- 
ducts in the outer semicircle. In both cases the vascular 
bundles are confluent and the outer ring is entirely closed. In 
V. acuminata the outer band of (white) bast-fibres is clearly 
shown, they are less distinct in JH. odorata. The central mass 
in both cases consists of two halfmoon-shaped vascular bundles, 
in Hopea without, in Vateria with 6 resin-ducts. 
These remarks will suffice to give a preliminary idea of the 
great variety in the internal structure of leaf-bearing internode 
and petiole. Under each genus I have endeavoured briefly to 
state what at present is known on this subject, and to these 
