364 THE BIOLOGY OF FLOWERING PLANTS 



Honey Guides, — This gives a sound basis for work on 

 other insects, and for the investigation of the usefulness of 

 particular colours and colour arrangements. For the 

 possibilities of guidance by colour do not stop with the 

 production of a single colour. We have already mentioned 

 the first of the train of ideas which led Sprengel to his 

 discoveries ; the second step was the posing of the problem 



as to what was the use of the 

 yellow eye of Myosotis palustris. 

 Sprengel concluded that it 

 served to guide insects to the 

 entrance of the nectar-contain- 

 ing corolla tube, after they had 

 settled on the flower. Only then 

 did he see that the blue colour 

 of the corolla might guide the 

 insect, from a distance, to the 

 flower. His first idea concerned 

 the guiding of the already 

 alighted insect ; he termed the 

 yellow eye a honey guide (saft- 

 mal). By Sprengel, and by 

 many biologists since his day, 

 various markings on the general 

 ground colour of the corolla 

 have been described as such 



•"peas^^STi" Th^ honey guides. We need only 

 flower is pale blue-purple mention as familiar the dark 



with dark purple lines and 

 a cream-coloured eye . X 1 i . 



lines running towards the base 

 of the petals in the violets (Fig. 

 51) and eyebrights. The usefulness of such guides has 

 been the subject of a good deal of scepticism. A 

 general review of the types of guide has recently been 

 made by Kraepelin (1920) ; he concludes that they may 

 assist the insect to make its landing, but that thc'r 

 significance in helping to locate the nectar is small. 

 Von Frisch has given some attention to this subject. 

 He classified the colours of 94 European flowers with 



