164 ELEMENTS OF BOTANY. 
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. — Regular polypetalous 
flowers have no special adaptations to make them singly 
accessible to insects, but he 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 I. On the general subject 
of colors and odors in relation to insects, see Miiller’s Fertilization of Flowers, 
Part LV. 
