OF THE DIPTEROCARPACEX. 47 
resin-duet occupies the centre of the pith, but in the main axis 
2 lateral leaf-traces, with a resin-duct in the pith of each, are on 
the point of separating from the central cylinder, that on the 
left side being in advance of the other. On fairly well preserved 
herbarium specimens the cortical leaf-traces can often be seen on 
the outside, aud this is the case in the internode represented in 
fig. 17. In the main axis two cortical leaf-traces enter the bark 
at the base of the internode, and continue in the bark through 
the entire length of it, until they enter the petiole. In the side 
branch the lateral leaf-traces separate from the central cylinder 
at a higher level. Higher up (fig. 2) the lateral leaf-traces have 
entirely separated from the central cylinder, and the main resin- 
duct in the pith has bifurcated. Before a resin-duct bifurcates, 
its diameter is always eularged in the direction of the bifurcation. 
Of the two branch-ducts, that towards the apex of the pith shows 
such an enlargement, and consequently, in fig. 3, it has sub- 
divided—one smaller branch-duct having entered the apical or 
median leaf-trace now in course of separation from the central 
cylinder. At the same time the duct in the opposite half 
of the pith is in the act of bifurcation, and fig. 4 shows that 
it has actually divided itself into 3 branches, but in a direction 
at right angles to the longer axis. Of the 7 ducts shown in that 
figure, those in the apical and in the two lateral leaf-traces enter 
the petiole, as shown in fig. 5—the one in the upper portion of 
the pith enters the axillary bud, while the 2 lateral ones in the 
lower portion are destined to enter the lateral leaf-traces of 
the petiole at the top of the next higher internode. In fig. 5 
these lateral resin-ducts have entered the wood, the medullary 
rays starting from that point having arranged themselves in a 
fan-shaped manner. This preparatory arrangement of the 
medullary rays can already be distinguished at a lower level, as 
indicated in fig. 4. Fig. 118 D (Engler) represents a section 
intermediate between figs. 2 and 3, while F shows a section 
intermediate between figs. 4 and 5. 
In fig. 5 the petiole is still attached to the branch, the vascular 
bundles of the three leaf-traces having arranged themselves in a 
complicated central vascular cylinder, and it will be noticed that 
while the apical resin-duct, which is on the underside of the 
petiole, remains undivided, the two lateral ones have each bifur- 
cated, so that the petiole at its base has 5 resin-ducts. Three 
of these are situated in the bands of pith, which run through 
