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 I$. 
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 /imd, 
which tapers into a stalklike base called the claw. 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; p/aits, which are wrinkles or 
slight lengthwise folds on the petals; and crowns, bractlike 
outgrowths or fringe on the inner side at the junction of 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. 4was are stiff 
bristles which terminate some flower part. The ood 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 imcom- 
plete. In addition, the flower may be perfect or imperfect. If 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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