HOW FLOWERS ATTRACT INSECTS 2II 
guests—are influenced in the choice of flowers, even more by food-value than by 
external appearance.’ 
4. The strong-smelling flowers of Ruta, Anethum, and the like, attract flies 
more particularly. The species of Prosopis, which themselves have a peculiar odour, 
display marked preference for strong-smelling flowers (Reseda, Lepidium, Ruta, 
Anethum, Achillea, Matricaria), Sweet aromatic odours (Thymus, Lavandula, Rosa, 
and others) strongly attract bees without excluding other insects. The odour—not 
strongly exhaled till towards evening—of many white flowers with long corolla- 
tubes (Lonicera Periclymenum and Caprifolium, Melandryum album, and the like), 
attracts hawk-moths (Sphingidae) and other crepuscular and nocturnal Lepidoptera. 
Flowers with the odour of carrion specially attract carrion-flies, and the urinous 
odour of Arum attracts moth-flies (Psychodidae). 
Numerous facts in Flower Pollination support the view that the corolla plays 
a prominent part in attracting insects. First let us ask ourselves why else does it 
exist, why are flowers provided with bright and varied colours if not for the 
purpose of alluring insects? Why, let us ask further, are the male flowers of 
diclinous plants larger than the female flowers if not to attract by their greater 
conspicuousness the earlier visits of insects, so that the female flowers may be 
pollinated? What can be the object of the remarkable change of colour in flowers 
that have been fertilized (e.g. Ribes sanguineum, R. aureum, Weigelia rosea, 
Melampyrum pratense, Aesculus Hippocastanum, and so forth) unless to render 
more conspicuous the entire inflorescence? And many more such questions might 
be propounded. 
Plateau’s experiments only show that the sense of smell perhaps guides insects 
to a greater extent than has hitherto been supposed. Apparently there is need of 
further experiment to decide questions as to the attraction of insects to flowers by 
means of the senses of smell and sight. Meanwhile the following law may be 
provisionally accepted.—A “traction from considerable distances is certainly effected for 
the most part by the odour of the flowers, which fills the air as with invisible clouds, and 
indicates the direction for flight: when the tnsects approach nearer (1-2 m.), the colours 
of flowers undertake the task of attracting them further, and whén they finally settle, the 
lines and potnts long since described by Sprengel under the name of ‘Saftmal’ (i.e. sap- 
mark) serve /o point out the way to the nectar. 
