OF THE DIPTEROCARPACEÆ. 19 
exceedingly. The number is largest in Dipterocarpus, up to 100 
having been observed, sometimes arranged in several concentric 
circles. This genus is, moreover, distinguished by the large 
number of stipular traces which enter the bark a little above the 
lateral leaf-traces, each with a resin-duct in the pith. In most 
species there are also large mucilage-cavities in pith and cortex. 
What has been stated will make it clear that the genus Dipte- 
rocarpus, Dryobalanops, and Stemonoporus can always be readily 
recognized by the arrangement of leaf-traces and stipular traces, 
and by the number and arrangement of the resin-ducts. Vateria 
and Monoporandra probably agree with Stemonoporus, but on this 
question my researches have not yet been concluded. All other 
genera, so far as known, have the normal arrangement, that is 
the lateral leaf-traces separate from the central cylinder at vary- 
ing levels, while the apical leaf-trace leaves it at the node, all 
three entering the petiole, stipular traces, if any, branching off 
from the central cylinder or from the lateral traces. In the 
circumference of the pith there is a circle of resin-ducts varying 
in number from 3 to 30. Doona is distinguished by mucilage- 
cavities in pith and cortex. 
The vascular bundles in the petiole of Dipterocarps originate 
in the leaf-traces. As a rule, therefore, three vascular bundles, 
each with a resin-duct in the pith, enter the petiole. In most 
cases these original vascular bundles, and the resin-ducts which 
accompany them, ramify, and the result is a very intricate mass 
of xylem and phloém with a considerable number of resin-ducts. 
Those cases where the petiole in its entire length has only three 
resin-ducts are rare; Vatica obscura, Trimen, is one of the few 
species known to me. Dryobalanops has 5 ducts in the petiole 
from base to insertion of the blade. Plate I. fig. 5 shows the 
petiole still attached to a branch of D. lanceolata, Burck, and 
fig. 6 represents a section a little higher up. Here the duct of 
the apical leaf-trace (cf. fig. 4) occupies the underside of the 
petiole and has not divided. The two lateral ducts, however, 
which in fig. 4 are in the lateral cortical leaf-traces, have each 
bifurcated, the branches on the underside being outside the mass 
of vascular bundles, a feature peculiar to all species of the genus. 
Here, therefore, the petiole at the base has 5 resin-ducts, and 
these 5 ducts continue throughout its length to the blade. 
In most species the internal structure of the petiole changes 
considerably in its progress from the base to the insertion of the 
c2 
