164 ELEMENTS OF BOTANT. 



Different kinds of insects are especially attracted by- 

 different colors. In general, dull yellow, 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.* 



203. 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 com- 

 monly lead toward the nectaries, and there is no doubt 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 perhaps leaves pollen on the 

 stigma and becomes dusted with new pollen which he carries 

 to another flower. 



204. Facilities for Insect Visits. — Eegular polypetalous 

 flowers have no special adaptations to make them singly 

 accessible to insects, but lie open to all comers. They do, 

 however, make themselves much more attractive and afford 

 especial inducements in the matter of saving time to flower- 

 frequenting insects by being grouped. This purpose is 

 undoubtedly served by dense flower-clusters, especially by 

 heads like those of the clovers and by the peculiar form of 

 head found in so-called compound flowers, like the sunflower 

 and the bachelor's button (Fig. 165). In many such clusters 

 the flowers are specialized, some as in Fig. 110, carrying a 

 showy strap-shaped corolla, to serve as an advertisement of 

 the nectar and pollen contained in the inconspicuous tubular 



1 See Lubbock's Flowers, Fruits, and Leaves, Chapter T. On the general subject 

 of colors and odors in relation to insects, see UuUer's Fertilization of Flowers, 

 Part IV. 



