Plants in Relation to Man 491 



adaptation to visiting insects. Not only flowers are provided 

 with such adaptive structures, but certain insects also have 

 organs that are peculiarly suited to the kinds of flowers they 

 frequent. Such mutual adaptation of insect and flower may 

 be noted in the case of the red clover and the bumblebee ; cer- 

 tain long-tube flowers and the butterfly; or night-blossoming 

 flowers and the moths. 1 



Colors of flowers. Colors and odors of flowers play an im- 

 portant r61e in securing cross-pollination by insects. Different 

 colors attract insects of one kind or another; the odors entice 

 the visiting insects to search within the chalice for the minute 

 drop of nectar which both color and odor advertise and which 

 the insects need for food. Observe how red clover attracts 

 the bumblebee by which alone it secures cross-pollination ; 

 how white clover and fruit tree blossoms generally attract the 

 honeybee ; many small, wide-open, yellow flowers, certain flies ; 

 red pinks and some flowers with long tubes, the butterfly ; and 

 how flowers blooming in the evening and night, which are 

 usually white and conspicuous, attract the moths which are 

 then flying. Colors are appropriate not only to the time of 

 day, but also to the season of the year. One may find many 

 instances of this and should note the visiting insects and other 

 conditions that seem to make such color adaptation necessary. 



The odor of flowers. Odor not only supplements, but some- 

 times takes precedence over or entirely replaces color as a 

 means of guiding insects to flowers. Petunias have the habit 

 of sending forth their fragrance only in the evening, when cer- 

 tain moths, by which they are cross-pollinated, are flying. 

 Those familiar with the woods will recall the heavy permeating 

 fragrance of certain wild flowers which without their odor would 

 escape notice, especially the small retiring kinds, the colors of 

 which would be inconspicuous in the shade of the trees. Then, 



1 Students will find most interesting accounts of cross-pollination and the 

 adaptive structure of flowers and insects in W. H. Gibson's "Blossom Hosts 

 and Insect Guests," and Darwin's "The Various Contrivances by which Orchids 

 are Fertilized by Insects." 



