Insect-Attractions in Flou'ers. 
167 
flies left the latter for the former, although the scentless flowers of 
D. plialaenopsis have much the colouring and form of those of D. 
superbum ; and also that partly opened flowers of the latter before 
they emitted any scent, but after the colour could be seen, were not 
noticed by the flies. Rough coloured representatives of this flower 
in paper were equally overlooked. 
The scents of these two orchids are quite different, but I have 
no doubt that the scent is the attraction and neither colour nor 
form in this case. Since writing the above I see that the flies have 
moved from the withered Dendrobium superbum to a flower of 
Plialaenopsis violacea which has a distinct though not very strong 
scent. 
In the matter of attraction by scent it may well be that insects 
can detect it more readily than we can. Fallen fruits such as those 
of Arenga saccliarifera and Elaeocarpus ganitrus, or Bananas, have 
to us little scent, yet they are very attractive to Lepidoptera, and 
some apparently almost scentless flowers seem to attract insects 
from considerable distances. 
In powerfully scented flowers it appears that the widely 
diffused scent attracts any insects which come within its area, but 
that then they are guided to the flower by its colouring or form. 
The scent is strongest usually in that part of the flower where the 
nectar lies hid, but this is not always the case. The orchid 
Renanthera moschifera is an example. The strong musky odour is 
produced from the back of the recurved tip of the upper sepal. The 
rest of the flower is scentless. The sepals and petals are green, 
with brown blotches, but the lip is white, and quite conspicuous for 
some distance. The flower is usually fertilized by Vespa cincta, but 
neither this insect nor any other have I ever seen to go for even a 
second to the scented sepal ; once attracted to the locality of the 
flowers even if fifty yards away, the insect seems to espy the white 
lip and fly straight to it. 
In conclusion I would suggest that scent alone is rarely suf¬ 
ficient for the fertilizer, with the sole exception here at least of the 
Muscidae, who seem to be unable clearly to distinguish colour, 
further, than dark and light, but that the form of the flower plays 
a conspicuous part in the attraction and that while bright colour, 
red, white and yellow is serviceable to attract wide-ranging diurnal 
insects, white will not attract nocturnal insects unless accompanied 
by a powerful scent. 
Singapore, May, 1904. H. N. RIDLEY. 
[Mr. Ridley’s very interesting observations on the whole confirm 
Andreae’s main conclusions very strikingly.—E d. New Phytologist. 
