CONSPICUOUSJVESS OF FLOWERS 87 



land the flowers of Omphalodes verna can be seen a hundred yards off over the pale 

 yellow, faded grasses and foliage of the edge of the wood ; while at the same distance 

 against a green background they would stand out much less clearly. The same 

 thing is true of many Boragineae, which grow in similar places {Pulmonaria angusti- 

 folia, officinalis, stiriaca, Lithospervium purpureo-coeruleum), of the lesser Periwinkle 

 ( Vinca minor), of the Squill {Scilla bifolid), and of many others. . . . Above the 

 dark mould of the forest-floor a pale colour, such as that of the Bird's Nest {Neottia), 

 of Monotropa, and of the Toothwort {Lathraea), and other saprophytic and 

 parasitic plants, is plainly visible from a distance. These plants would hardly 

 be noticed in a green meadow.' 



I may mention here an investigation which renders it not improbable that 

 there are floral colours which are easily perceived by insects, though the human 

 eye cannot see them. I observed (Bot. Centralbl., xlviii, 1891, pp. 161 et seq.), 

 that the inconspicuous greenish-white flowers of Sicyos angulata Z. were visited 

 by a very large number of species of bees and flies, although the blossoms present 

 but little contrast to the green foliage leaves and tendrils of the plant. By comparing 

 the action of different floral tints on photographic plates, I showed that Sicyos 

 angulata L. is probably of an ultra-violet colour. This would be an analogue to 

 the capacity supposed by Landois to exist in many insects of being able to hear 

 higher tones than the human ear can perceive. In a later publication (op. cit., 

 pp. 314-18) I have demonstrated that in numerous cases where I determined the 

 brightness of the flowers of Sicyos (and Bryonia dioica) they never equalled three- 

 quarters of the intensity of white, but acted on a photographic plate much more 

 strongly than a rotating disk, which was three-quarters white and a quarter black. 

 This fact can only be explained as due to ultra-violet rays, which are chemically 

 very effective. Perhaps the powerful influence of flowers of Sicyos and Bryonia on 

 photographic plates is also to be explained by supposing that the numberless smaller 

 glands which cover them act as so many mirrors or lenses receiving and reflecting 

 light, so that their glitter strongly aff'ects gelatine sensitized by silver bromide, and 

 also the optic nerves of insects. At any rate, it seems to be established that the 

 flowers named possess a means of attraction to which the human eye is less sensitive 

 than the eye of insects. Haberlandt (' Eine botanische Tropenreise,' 1893, p. 289) 

 was struck by the innumerable bright yellow flowers of desert plants, which are 

 scarcely to be distinguished from the equally yellow sands of their habitat : ' With 

 regard to the visits of insects, one would expect for the sake of contrast a pre- 

 dominance of blue and violet floral colours.' ' Perhaps we may suppose that ultra- 

 violet floral colours are possessed by desert plants. Their flowers would then appear 

 yellowish only to our eyes, and therefore be barely distinguishable from their sur- 

 roundings ' (op. cit., p. 295, note 33). 



It may here be remarked that Kerner also has investigated the means of 

 attraction of Bryonia dioica, and he explains the almost exclusive visits of a small 

 bee (Andrena florea) by supposing that its flowers possess an odour which is 

 perceptible neither to man nor to most insects, but only to the bee in question 

 (' Nat. Hist. PI.,' Eng. Ed. i, II, p. 206). 



The following note by Fritz Muller (Kosmos, iii, 1878, p. 495) may also find 

 fitting place here: — 'There is now blooming in this place (South Brazil) one of the 



