PHOTORECEPTION 



185 



375 



Fig. 90. Tentative chromaticity diagram for the honeybee based on the 

 work of Daumer (1956). The behavioural experiments of Daumer led 

 to the prediction that any colour can be matched for bees by an appro- 

 priate mixture of three monochromatic reference stimuli, e.g., ultra- 

 violet (360 m[x), blue-violet (440 my.), and yellow (588 my.). Any light, 

 therefore, can be represented in Fig. 90 by a point; for example, 'W 

 is the white of the xenon emission spectrum. The proportions, in 

 fractions of the total energy - the chromaticity co-ordinates - of the 

 yellow and blue reference stimuli required for a colourimetric match 

 of the light represented by the point are given by the co-ordinates of 

 the point, 588 my. on the abscissa and 440 my. on the ordinate. Since 

 the sum of the three chromaticity co-ordinates is 1 , the fraction of the 

 energy at 360 my. can be calculated by difference. The locus of the 

 spectrum is given by the experimental points ; however, as is suggested 

 by the dashed line, it may actually lie somewhat outside the triangle, for 

 it is questionable whether this kind of experiment is sufficiently precise 

 to reveal the necessity for small negative values of one of the chroma- 

 ticity co-ordinates. The complementary to 360 my. is 490 my., for both 

 wavelengths lie on a straight line passing through the white point. 

 Similarly, the point 'p' is the 'bee-purple' complementary to 440 my. 

 and is composed of 79 per cent 588 my. and 21 per cent 360 ma. 

 (Redrawn from Goldsmith, 1961.) 



