274 ADAPTATIONS AMONG ALPINE PLANTS 



Globe-flower (p. 207), only very small flies can reach 

 the honey. 



The diff'erent contrivances to be met with in 

 flowers adapted to particular insect visitors are 

 extremely numerous, but it will not be possible to 

 enter into this subject fully here. These remarks, 

 supplementary to the observations scattered through 

 the preceding chapters, may, however, serve to indicate 

 the chief points of interest of this nature to be met 

 with among Swiss Alpine plants. 



Before we leave the subject, we may explain how 

 insects recognise the flowers they visit. This subject 

 has been much discussed, and there is still a great 

 deal to be learnt in the matter, but certain facts seem 

 now clearly established. The eyes of insects are com- 

 pound, and fmther, they are immovable. The number 

 of "facets " in a single eye may vary from 4 to 25,000. 

 Despite this fact, insects are extremely short-sighted. 

 At one time it was thought that each facet reflected 

 the image of a flower, so that if 10,000 facets occur in 

 a single eye, the insect would receive 10,000 diS'erent 

 images of the flower from one eye alone. This 

 view, multiple vision as it was called, is now 

 abandoned, and it is believed that each facet only 

 receives the image of a small part of an object, the 

 whole object being seen by the total sum of the 

 images of each facet. This may perhaps explain the 

 short-sightedness of insects. At any rate, it appears 

 clear that though insects are attracted to a particular 

 flower from a considerable distance, it is by the sense 



