POLLINATION AND FERTILIZATION 151 
An idea of the number of insect visits made to some flowers 
may be gathered from the fact that in a single locality one 
hundred kinds of insects have been seen to frequent dandelion 
flowers. The statistics in regard to visitors to the flowers of 
yarrow, Canada thistle, and the willows are fully as remarkable. 
142, Odors of flowers as attractions to insects. It is evident 
from familiar facts that many insects have an acute sense of 
smell. The way in which flies are attracted by decaying meat 
or fish, and bees and wasps by a cider press at work or by 
fruit-preserving operations, is a matter of common observation. 
A single cluster of carrion-scented flowers has been known to 
attract carrion flies and dung beetles from a distance of hun- 
dreds of yards. Some flowers, such as those of the Virginia 
creeper (Psedera), the Dutchman’s-pipe, the blueberries, and 
many others, are so inconspicuous that apparently their numer- 
ous 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 securing 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 petunias, 
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. 
143. 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. In spite of this, however, 
