242 PRACTICAL COURSE IN BOTANY 



EXPERIMENT 82. DOES ODOR INFLUENCE INSECTS? Try the same 

 experiment with different odors, removing the bright colors and sprink- 

 ling some kind of perfume on each pane. Try also the effect of decay- 

 ing meat and other malodorous substances. Are any insects attracted by 

 these ? What kinds ? Does this account for the noisome smells of the 

 " carrion-flower " and skunk cabbage ? What kinds of insects are attracted 

 by sweet-smelling substances ? Do the greater number appear to be at- 

 tracted by these, or by foul odors? Are flowers of the sweet-smelling 

 or the foul-smelling kind more common in nature ? Do insects seem to 

 be more strongly influenced by colors or by odors ? 



276. The color of flowers, being an adaptation to changing 

 external conditions, is a very unstable quality, and varies 

 greatly within the limits of the same species. Even on the 

 same stem, flowers of different colors are often found, due, 

 probably, to hybridization. Yet, notwithstanding all this 

 apparently random intermingling of hues, the range of color 

 for each species is confined, approximately, within certain 

 limits. Nobody has ever seen a blue rose or a yellow aster; 

 and though the florist's art is constantly narrowing the ap- 

 plication of this law, it still remains true that in a state of 

 nature, certain colors seem to be associated together in the 

 floral art gamut. Yellow is considered the simplest and 

 most primitive color in flowers, and blue the latest and 

 most highly evolved. Yellow, white, and purple, in the 

 order named, are the commonest flower colors in nature ; 

 blue, the rarest. Do you see any relation between these facts 

 and the color preferences of insects? 



277. Advantages of insect pollination. It is evident that 

 this is a much more certain as well as a more economical 

 method of securing pollination than through the haphazard 

 agency of wind or water. In probing around for the nectar 

 or the pollen upon which they feed, these busy little creatures 

 get themselves dusted with the fertilizing powder, which they 

 unconsciously convey from the stamen of one flower to the 

 pistil of another. Insects usually confine themselves, as far 

 as possible, to the same species during their day's work, and 

 since less pollen is wasted in this way than would be done by 



