PRESIDENTIAL ADDRESS, 15 
and commercial progress must be advantaged when proper 
value is attached to the results of chemical work, if this is 
able to supply the evidence required. Morphological 
characters are not always sufficiently distinctive to enable 
important differences to be determined, and with certain 
genera discrimination is difficult between species the 
botanical features of which have very much in common. 
For instance, one species may yield in quantity a substance 
which has, or may have, considerable economic importance, 
while another species, thought perhaps by some to be 
identical with it, has no economic possibilities in a similar 
direction. If these distinctive peculiarities are eventually 
found to be definite throughout the whole extent of the 
distribution of the species, then such a constancy of specific 
character, in this direction, is shown, that it becomes 
desirable to investigate more deeply the morphological and 
other features, so that these may be arranged in agreement 
with the combined botanical and chemical evidence. When 
examined under such a suggestion it may be expected that 
differences which originally appeared not to be particularly 
worthy of notice for specific purposes, would become well 
defined characteristics, and thus allow discrimination 
between them to be easily made. Such has been our 
experiences during the investigations, so far undertaken 
with the Melaleucas, the Callitris and the EKucalypts. 
Melaleuca genistifolia and its allied species will furnish 
one illustration in support. M. genistifolia was first 
described by Dr. Smith in 1776. In 1858 Baron von Mueller 
named a species M. bracteata, which tree has botanical 
characters somewhat closely resembling M. genistifolia. 
Bentham certainly thought so, because in the Flora Aus- 
traliensis he there synonymised them. The chemical 
evidence is conclusive that the two trees are quite distinct, 
so much so, that all doubts are now set at rest, and the 
