FIELDBOOK OF ILLINOIS WILD FLOWERS 
not. If either the pistil or stamens are missing the flower is 
imperfect. The flower may be incomplete by absence of stamens 
or pistils and therefore be imperfect, or it may be incomplete 
by absence of calyx or corolla or both, and remain a perfect 
flower. A complete flower is necessarily perfect. 
A flower without pistils (incomplete and imperfect), and 
having stamens, is called a staminate flower; likewise a flower 
without stamens and having pistils (also incomplete and im- 
perfect), is called a pistillate flower. A plant which bears the 
two forms of flowers 1s monoecious; plants that bear only pistillate 
or only staminate flowers are dicoecious. 
Regular and irregular flowers——The majority of flowers 
are star shaped, having petals nearly alike in size and shape 
radiating from the center of the flower. Usually the remaining 
parts of star-shaped flowers are similarly arranged, and where 
the members of each set or whorl are alike, the flower is regular 
or radial. Unlike sepals or petals make the flower irregular or 
bilateral. 
Five principal types of irregularity will be met among 
Illinois wild flowers. Perhaps the simplest is that form in 
which a petal or sepal is deformed, modified or enlarged out 
of likeness to the others. Orchids, for example, have the lowest 
petal inflated into a sac and sometimes prolonged backward 
into a spur. A second form is that of the violets, wherein the 
two upper petals are alike, the two side petals resemble each 
other, and the lowest is unequal, swollen or spurred. A third 
and very pronounced type is illustrated by the pea and bean, 
whose flowers are butterfly shaped. In them one petal is broad 
and conspicuous, and in the bud is folded about the others; 
this is the standard. Two narrower petals, one on either side, are 
called wings; the two lower and usually smallest petals are loosely 
united to form the kee/, enclosing stamens and pistil. Five- 
parted flowers in which the two upper petals unite nearly or 
entirely their length, the three lower uniting similarly and the 
two groups thus formed joining below or partly up the sides 
are called two-lipped, labiate or bilabiate flowers. The snap- 
dragon is a good example. The fifth type of irregularity is that 
of the strap-shaped ray flowers of the Composites. Here the 
petals are united into a tube upward a slight distance from the 
base, and the rest of the way the tube is as though split open, 
and the corolla lies flat like a strap. 
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