ILLINOIS NATURAL HISTORY SURVEY MANUAL 1 



They commonly attract insects that will pollinate the flower. 

 They may rise separately or be joined together for part or all 

 of their length. In any case, the variety of forms due to these 

 possibilities alone is so great we ought to consider it a little 

 more fully, and may by reading the descriptions of regular and 

 irregular flowers, page 15. 



The petals themselves have many shapes. A common one 

 is that of an ovate upper portion and a comparatively wide base; 

 less commonly the upper part is expanded and called the limb, 

 which tapers into a stalklike base called the clau;. Certain 

 modifications in the structure of petals, or appendages on them, 

 will be met in descriptions of Illinois wild flowers that follow. 

 Some are: the palate, a swollen projection into the throat of the 

 corolla on the lower half of such flowers as snapdragons; spurs, 

 as in wild columbine, which are hollow, pointed and backward 

 elongations of one or more petals; plaits, which are wrinkles or 

 slight lengthwise folds on the petals; and crowns, bractlike 

 outgrowths or fringe on the inner side at the junction ot claw 

 and limb. 



Sepals. — Finally, the outermost whorl consists also of 

 leaflike structures called sepals, fig. 4 III g. They comprise 

 the calyx, and like the petals may be separate or grown together. 

 The calyx is usually green and protects the flower in bud. In 

 certain cases where the corolla is lacking, and in some where it 

 is present, the calyx is white or colored and increases the 

 flower's attractiveness for insects. Calyx and corolla together 

 compose the perianth. 



Other structures. — Several additional structures may occur 

 on the lower parts of flowers, usually the sepals. Awns are stifiF 

 bristles which terminate some flower part. The hood is one or 

 more sepals or petals rolled up like a helmet or hood, covering 

 stamens or pistils or both. Within the hoods may be a glutinous 

 structure, called a horn, which curves over the stamens and pist- 

 ils, and assists pollination by forcing insects to brush against 

 anthers and stigmas. 



Perfect and imperfect flowers. — As we have said, a flower 

 that possesses all four sets of organs — pistils, stamens, petals and 

 sepals — is called complete; lacking one or more sets it is incom- 

 plete. In addition, the flower may be perfect or imperject. It a 

 flower has stamens and pistil, the organs directly concerned with 

 sexual reproduction, it is perfect, whether it has other parts or 



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