FIELDBOOK OF ILLINOIS WILD FLOWERS 
Flowers pollinated by insects contrast sharply with those 
that are pollinated by wind. A majority of them are perfect 
lowers, and many have developed adaptations of form that 
oractically insure cross-fertilization. 
DIMORPHIC AND TRIMORPHIC FLOWERS 
Flowers of the same species which have in one form short 
stamens and long pistils, and in another form long stamens 
ind short pistils, are said to be dimorphic, meaning of two forms. 
[ntroduction of an intermediate stage between these two forms, 
naking another combination of stamens and pistils possible, 
sroduces trimorphic flowers, meaning of three forms. The 
ntermediate stage is the result of adding a second set of stamens 
hat alternate with and are never equal in length to the first 
et. Thus in trimorphic flowers we have: form z—a short 
vistil or pistils, one set of stamens of medium length and the 
second set long; form 2—the pistil of medium length, one set of 
stamens shorter and the other longer than the pistil; form 37— 
he pistil long and the stamens in two sets below it, one short 
ind the other medium. It is a general principle among flowers 
hat the lower the position of the anthers the smaller the pollen 
yrains; and, in trimorphic forms especially, the pollen will not 
rerminate well unless it is transferred to a stigma of the same 
elative position as the anther from which the pollen came. 
There are other notable characteristics of insect-pollinated 
lowers. Usually they are showy due to color, size, shape or 
irrangement, and frequently they have an odor. They com- 
nonly produce nectar, a sweetish secretion of glands at the base 
f the ovary or corolla. The pollen grains, instead of being dry 
ind smooth, are often rough and sticky. Flowers that are wide 
ypen and can be pollinated by nearly any kind of visiting insect 
often have numerous stamens and abundant pollen, but those 
vhich partly or wholly conceal the pollen in’tubular or closed 
orollas usually have few stamens and little pollen. 
INSECTS WHICH POLLINATE FLOWERS 
Honeybees and bumblebees are the most efficient among 
ollinating insects. First, they have a twofold interest in the 
lower, gathering pollen as well as nectar for food. Then they 
ire hardy and live longer than other insect visitors; also they 
ire stout fliers and visit a greater number of flowers over a 
vider area than do, let us say, butterflies and carrion flies. 
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