ILLINOIS NATURAL HISTORY SURVEY MANUAL 1 
They work continuously from beginning to end of the flowering 
season and they are good botanists, often confining their visits 
on any one collecting trip to one species of flower, and so do not 
mix different kinds of pollen. Their hairy legs and bodies are 
well fitted for carrying pollen and their elongated mouthparts 
enable them to obtain nectar from almost any sort of flower. 
Butterflies are frequent visitors of showy and fragrant flowers, 
especially those with long corolla tubes. These insects feed on 
nectar only and are apt to visit several species within a short 
time. Thus they may cross-pollinate flowers of different species, 
and that pollen may or may not germinate on the foreign 
stigma, depending on certain other factors. 
Moths are closely related to butterflies, but are night flyers 
instead of day-flying insects, and are thus important as polli- 
nators of some fragrant light-colored flowers which open in the 
evening. 
In the southern hemisphere birds are nearly as common 
pollinating agents as are insects, but in Illinois the single species 
of hummingbird which occurs is the only one of importance. 
FERTILIZATION 
Pollination is followed after a suitable interval by fertiliza- 
tion, an event which takes place within each ovule in the ovary. 
A pollen grain must germinate on the stigma and send out a 
pollen tube, a fine microscopic thread which grows from a pollen 
grain down through the pistil until it reaches one of the ovules 
within the ovary. Each ovule must receive the contents of the 
end of the pollen tube before it can develop into a seed, and 
unless fertilization occurs, no seeds will develop. Many flowers 
fail to develop into fruits because of failure of fertilization, and 
the number of seeds in the fruit may be few or many depending 
not only upon the number of ovules in the flower, but also upon 
the number of these which were successfully fertilized. 
THE FRUIT 
To the botanist, the fruit does not necessarily refer to an 
edible part accompanying or bearing the seeds. The fruit 
is usually that part of the flower which matures along with the 
seeds, and often the fruit appears as nothing more than an 
extra layer or two surrounding the seed coat. A seed is the unit 
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