358 FOUNDATIONS OF BOTANY 



brownish, or dark purple flowers, especially if small, seem 

 to depend largely on the visits of flies. Red, violet, and 

 blue are the colors by which bees and butterflies are most 

 readily enticed. The power of bees to distinguish colors 

 has been shown by a most interesting set of experiments 

 in which daubs of honey were put on slips of glass laid on 

 separate pieces of paper, each of a different color, and 

 exposed where bees would find them.^ 



It is certain, however, that colors are less important 

 means of attraction than odors from the fact that insects 

 are extremely near-sighted. Butterflies and moths cannot 

 see distinctly at a distance of more than about five feet, 

 bees and wasps at more than two feet, and flies at more 

 than two and a fourth feet. Probably no insects can make 

 out objects clearly more than six feet away.^ Yet it is 

 quite possible that their attention is attracted by colors at 

 distances greater than those mentioned. 



430. Nectar Guides. —In a large number of cases the 

 petals of flowers show decided stripes or rows of spots, of 

 a color different from that of most of the petal. These 

 commonly lead toward the nectaries, and it is possible that 

 such markings point out to insect visitors the way to the 

 nectaries. Following this course, the insect not only 

 secures the nectar which he seeks, but probably leaves 

 poUen on the stigma and becomes dusted with new pollen, 

 which he carries to another flower. 



431. Facilities for Insect Visits Regular polj^etalous 



flowers have no special adaptations to make them singly 



. } See Lubbock's Flowers, Fruits, and Leaves, Chapter I. On the. general 

 subject of colors and odors In relation to Insects, see Muller's Fertilization of 

 Flowers, Part IV. 



" See Packard's Text-Book of Entomology, p. 260. 



