POLLINATION AND FERTILIZATION 125 



\ 7 irginia creeper (Psedera), the Dutchnian's-pipe, the blueber- 

 ries, and many others are so inconspicuous that apparently 

 their numerous insect visitors must be attracted by an odor 

 which is almost or quite imperceptible to us. 



It seems certain that the odors of flowers have been devel- 

 oped with reference to the sense of smell in animals (usually 

 insects), and that these odors serve as a most efficient means 

 of insuring insect visits. 



It is a most interesting fact that many flowers give off their 

 scent mainly at the time of day when the insects which polli- 

 nate them are most active. Thus some catchflies, the petu- 

 nias, some kinds of tobacco, and several honeysuckles have 

 little odor by day, but are very fragrant at night when the 

 moths which pollinate them are on the wing. On the other 

 hand, many plants of the Pea family, which are pollinated by 

 day-flying bees and butterflies, give off their scent mostly by 

 day, and especially in strong sunshine. 



119. Colors of flowers as attractions to insects. There has 

 been much discussion among botanists as to how far insects are 

 led to visit flowers by displays of color. It appears to be fairly 

 certain that no insects can make out the forms and sizes of 

 objects at a distance of more than six feet, and that many are 

 unable to see clearly even two feet. 1 In spite of this, however, 

 it seems probable that the colors of flowers are an important 

 means of attraction for many flower-frequenting insects. 2 



The commonest method of color display is that in which the 

 color (other than green) is mainly found in the corolla, as in 

 the flowers of the poppy, rose, sweet pea, and morning-glory. 

 Sometimes the calyx also is bright-colored, or, as in the Hepat- 

 ica, the Anemone, and the Clematis, the corolla is wanting and 

 the showy calyx looks like a corolla. Not infrequently the 



1 See Packard, Text-Book of Entomology. The Macmillan Company, 

 New York. 



2 See Kerner-Oliver, Natural History of Plants, Vol. II. Henry Holt and 

 Company, New York. Also Knuth-Davis, Handbook of Flower Pollination, 

 Vol. I ; and Andreae, Inwief ern werden Insekten durch Farbe und Duft der 

 Blumen angezogen, Beiheft, Bot. Centralblatt, 15, 1903, pp. 427-470. 



