166 
H. N. Ridley. 
themum and visiting the tulip-like flowers, attempting to probe with 
their proboscides the conventionalised mouths of the flowers. Now 
there could be no doubt that here neither scent nor colour attracted 
the insects, but that the form, conventional as it was, of the 
painted flowers was what directed them in their pursuit of nectar. 
In the case of Diptera again I feel that we must distinguish 
between the groups. The pollen eating Syrphidae frequent Poraua, 
Rliodamnia and Eugenias, with white flowers, and certainly seem to 
go by colour, rather than scent. The Muscidae on the other hand 
seem to go exclusively by scent. The coarse-smelling green flowers 
of Kurrimia paniculata, Castanopsis, Quercus and Sindora are visited 
by myriads of a species of Musca, so that the roar of their wings 
can often be heard on a lofty Sindora, from the ground. The 
rapidity with which Muscidae discover a piece of carrion or other 
foul-smelling putrid matter even when covered up is I suppose well- 
known to all. In this connection the fertilization of the Amor- 
phophalli is very striking. These plants, A. Titanum, A.Prainianum 
and A. Rex, when the spathe is fully expanded, all give out a 
carrion, like odour, perceptible for twenty yards or more, for about 
twelve to twenty-four hours or less, and are then attractive to 
Muscidae. After this the smell quite ceases and though the spadix 
lasts for another two days otherwise unaltered, no flies are to be 
seen on it. These Amorphophalli are all differently coloured, but 
there is always a dark maroon-purple patch at the base of the 
spathe inside. This colouration also occurs at the entrance to the 
tube of Aristolochia gigas, and A. elegatis, and, I take it, may be 
classed as a large guiding mark for a class of insects whose power 
of vision is poor, and may be limited to distinguishing dark and light 
only. Another fly of a different group, but not identified, con¬ 
stantly visits the orchids Bulbophyllum macranthum (see Annals of 
Botany, Vol. IV., p. 327), Phalaenopsis violacea and Dendrobium 
superbum. I have never seen it on other flowers, and rarely on any 
other occasions, but when either of these plants is in bloom these 
flies appear in numbers. They fertilize the Bulbophyllum certainly, 
but I do not see that they fertilize the Dendrobium. They seem 
only to run about over the petal and sepals. The Bulbophyllum 
has a scent of cloves, and I attempted to attract the flies to pieces 
of paper scented with oil of cloves, but without success. However 
the scent of the oil is even to me different from that of the 
Bulbophyllum, and is probably more so to the flies. The Den¬ 
drobium smells strongly of rhubarb. I observed that though 
Dendrobium phalaenopsis was in flower close to the D. superbum, no 
