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 ot 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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