416 NATURAE, SCLENGCE, JuNE, 
presence known by their perfumes. They may be of that greenish white 
which is hardly distinguishable from the background of foliage, and 
yet be able to attract myriads of nocturnal insects. Pass by at 
any time in the day and not the faintest trace of perfume lingers 
upon them, but paddle along at night and you wonder whence comes 
the overpowering fragrance. 
Diurnal flowers and insects are comparatively scarce when 
contrasted with those of the night. The great tubular blossoms 
which glow in the sunlight are visited by humming-birds, butterflies, 
and bees, but the hum and whirr of insect life, so characteristic of 
night in the forest, is almost wanting. Where a few butterflies may 
be seen fluttering lazily from flower to flower at noon, after sunset 
moths are attracted in numbers by the great white blossoms, or the 
fragrance of thousands of smaller and less conspicuous flowers. 
How difficult it is to trace these perfumes. Sometimes it is 
quite impossible. Who recognises the odour of the morat flowers, or 
knows anything of the numerous scents that are wafted across the 
narrow rivers after nightfall? As certainly as we see a particular 
kind of whitisn flower, we can confidently state that it is odoriferous 
at night, but hardly a single species is known in this way. In passing 
along the creek, a perfume is suddenly wafted across, but where it 
comes from is a problem not easily solved. Even that common 
orchid, Epidendrum noctuynum, which derives its specific name from the 
fact that it distils its perfume after nightfall, is rarely known by this 
character. We have seen cases where these orchids have been kept 
for years without their owners knowing anything of their perfume, 
and when it was discovered, this came about by the accident of 
bringing a plant into the house for an evening. Other orchids are 
quite as peculiar in this respect; a most delicious odour may be 
perceived at one particular time, and not be appreciable at any other. 
Some flowers open for an hour or two, and then, whether 
fertilised or not, droop and wither; others are able to try again 
perhaps at the same time next morning or evening. Those which do 
not fall may still have their particular time for fertilisation, when it 
appears as if every effort is strained to attract the particular insect 
whose agency is so urgently required. It is surprising to find that so 
many are successful in these efforts. Even when their odour is not 
appreciable to us, the bees find them out. They may be hiddenaway 
under a tangle of bush-ropes, and not a single insect of the species 
required be visible in the neighbourhood, but somehow or other, as 
the flowers open, the bees or moths appear in considerable numbers. 
Flowers must be peculiarly sensitive at these times. Some, as 
1 A gigantic timber tree, belonging to the family Leguminosz, and forming 
extensive forests in British Guiana. It grows from 130 to 150 feet high, and pro- 
duces a very tough and close-grained wood, which is imported into this country in 
considerable quantities for ship-building, even rivalling oak in its non-liability to 
splinter. The bark is astringent, and useful for tanning.—Eb. 
