554 



BOTANY 



PART II 



and the insects that frequent them, no other department of biology 

 has been more actively studied than floral ecology. It is the more 

 remarkable that no one had put the question whether the colours seen 

 by our eyes were also perceived by the insects in the same way. It 

 was difficult to think of the display of colour in meadow or orchard 

 otherwise than as an apparatus of attraction for the visiting insects 

 seeking the food provided by the nectaries of the flowers. We owe 

 the opening up of this question to C. HESS ( 5 ). In the light of his 



exact demonstration that bees 

 are colour-blind the earlier 

 views require to be revised. 



HESS bases his argument on the 

 comparison of the behaviour of bees 

 with colour-blind human beings, 

 and shows that they, like all in- 

 vertebrate animals that have been 

 investigated, react quite similarly 

 to the stimuli of colour. Their 

 brightness -maximum lies in the 

 green-yellow region ; red appears 

 dark, and blue on the other hand 

 light. The attraction of flowers 

 for bees must accordingly depend 

 on the contrast effects of different 

 degrees of brightness. 



In this demonstration there 

 appears to be wanting the answer 

 to the question at what distances 

 the eyes of the bee are able to per- 

 ceive strong contrasts in bright- 

 ness. An orchard in flower, apart 

 from any colour-sense on the part 

 of bees, would be more readily seen 

 by them at a distance on account 

 of the bright flowers contrasting with the dark background of foliage. To this 

 would be added the tendency of bees, at least of the same colony, to collect 

 together, so that when one bee has found a source of food, a crowd of others will 

 follow. 



The facts regarding the pollination of flowers by insects which 

 SPRENGEL discovered still hold, although the particular question as to 

 how the apparatus rendering the flowers conspicuous affects the 

 eyes of insects, and how the conspicuousness has come about, is open 

 to reconsideration. It must be borne in mind that without any 

 relation to insect-pollination the Firs, Larch, and other Coniferae 

 exhibit intensely -coloured female cones, as do the male flowers of 

 the Pine when seen in mass. It would appear to be frequently of 

 importance to plants for their reproductive organs to have some colour- 

 other than green. The greater absorption of heat-rays may be con- 



FIG. 527. Anemophilous flower of Festuca elatior. 

 (After SCHENCK.) 



