OF THE DIPTEROCARPACEZ. 28 
been the guide of systematie botanists, until what is now called 
the anatomical method has been brought to his aid. In no case 
must the work of classification be based upon isolated characters, 
whether biological, anatomical, or external. 
Our knowledge of the organization of any order, genus, or 
species is as yet fragmentary in phenogamous plants; it is 
necessary to advance step by step; and hence it seemed right, in 
dealing with the anatomical characters of Dipterocarps on the 
present occasion, to limit my remarks to the leaf-traces and 
resin-ducts in a leaf-bearing internode, and to the internal struc- 
ture of the petiole. 
It will be readily admitted that those characters which are apt 
to be influenced by the surrounding medium, by soil and climate, 
are of comparatively little value for systematic arrangement ; 
and this is one reason why great caution must as a rule be 
used in employing characters taken from the internal structure 
of leaves for systematic purposes. However, as far as Diptero- 
carps are concerned, the external conditions under which they 
live in their native country are exceedingly uniform, compara- 
tively speaking. They inhabit a limited range of countries with 
a moist tropical climate and alternating dry and wet seasons, 
where the general climatic features are very much the same. 
Anatomical characters must be used with caution; but that 
holds good equally in the case of external morphological characters. 
Their study, however, in the order here under consideration has 
so far advanced, that without anatomical examination of inter- 
node and petiole no new genus of Dipterocarps can usefully be 
described. 
The treatment of genera and species in the following pages is 
somewhat unequal. My aim throughout has been to draw atten- 
tion to points which had not hitherto, in my opinion, received 
sufficient attention. As regards species, my intention was not 
to give complete lists of synonyms or of literary references, but 
reference has always been given to one standard work where the 
needful details can readily be found. With few exceptions, I 
have maintained the species as established by other authors. I 
am disposed to think that a critical examination of more abundant 
material will result in the disappearance of a number of species. 
However, my opinion is, that less confusion will arise by main- 
taining these doubtful species for the present than by uniting 
them on insufficient grounds. 
